bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐201: Comparison Between Two Immobilization Systems for Cranial Stereotactic Radiosurgery Using The ExacTrac Image‐Guidance System
Authors: Nedialkova L , Ostenson J , Sabbas A , Kulidzhanov F , Wernicke G , Trichter S
Published: June 2015

Purpose:

The ExacTrac Image‐Guidance system enables frameless stereotactic radiosurgeries with real‐time image guidance that allows repositioning on a sub‐millimetric scale. In order for such treatments to be effective, the patient's head has to be immobilized using a custom mask created to conform to the patient's anatomy. There are two cranial immobilization systems used in our institution: masks manufactured by Brainlab and Civco. For both systems, it is not evident what the achievable level of intrafraction immobilization is for each system in our patient population. The ExacTrac system makes it possible to quantitatively assess the immobilization the two mask systems offer.

Methods:

The ExacTrac imaging system was used to assess intrafraction geometric displacement in the three Cartesian directions for each of these masks multiple times during Stereotactic Radiosurgery, SRS or hypofractionated treatment. Intrafraction motions were considered uncorrelated random movements away from isocenter. The displacement from isocenter, excluding initial correction, was calculated in over 100 instances for each mask system. The distances from isocenter were compared with histograms, average, median, and by percentile.

Results:

It was found that the Brainlab mask had mean distance from isocenter of 0.5 mm (SD 0.45 mm, median 0.37 mm) compared to 1.0 mm (SD 1.25, median 0.61 mm) for Civco. The distributions were compared with a Mann‐Whitney U test and were found to be significantly different (P < 0.001). The 75th and 95th percentile of displacements were 1.2 and >3 mm and 0.6 mm and <1.5 mm, for the Civco and Brainlab systems respectively. As a rule of thumb, the averages, medians, and percentiles for the Civco system were approximately twice that of the Brainlab system.

Conclusion:

Given the results, the Brainlab mask system should be used to minimize risk of geometric error in delivery of SRS or high dose gradient techniques.
SU‐E‐T‐207: Comparison of Integrated Tissue Air Ratio (ITAR) to Traditional TAR for Kilovoltage Pencil‐Beams
Authors: Hanlon J , Koruga I , Chell E , Pintaske R
Published: June 2015

Purpose:

Clinically viable depth dose determination in kilovoltage pencil‐beams is a great challenge that resulted in a published dosimetry method called ITAR, which involves measurement of air kerma and attenuation with a detector in a low scatter environment coupled with MCNP scatter calculations. The objective of this work is to compare ITAR to traditional TAR using inherently water‐proof microchambers that have only recently become commercially available.

Methods:

An Exradin A26 microchamber was centered 150 mm from a 100 kVp x‐ray source with 2 mm aluminum HVL. Depth dose in water from 16 to 24 mm in 2 mm increments was determined by: (1) placing blocks of Plastic Water LR near the source to minimize scatter and using previously published conversion coefficients [ITAR method] and (2) submerging the detector in a water tank with 2 mm thick Plastic Water LR walls and jogging the tank with motor controllers while keeping the detector position fixed [traditional TAR method]. Each method was repeated four to five times. For each repetition, dose was measured free in‐air to normalize the data for exponential regression.

Results:

Traditional TAR indicated higher depth dose than ITAR; differences ranged from 2.1% at 24 mm depth to 2.5% at 16 mm depth. However, the results of traditional TAR did not include a correction for Pq,cham because it is unknown for this detector type in these conditions. It is estimated that the component of Pq,cham due to the effect of water displacement alone is ∼0.94, but Pq,cham is likely several percent larger than 0.94 due to the energy dependency of the microchamber in the presence of low energy scatter that is not present during in‐air calibration.

Conclusion:

The ITAR method remains preferable for clinical depth dose determination in kilovoltage pencil‐beams due to Pq,cham being unknown for suitable detectors in relevant conditions.

All four of the authors are either current full time employees, which include stock option grants, or consultants of Oraya Therapeutics Inc.
SU‐E‐T‐208: Comparison of MR Image Quality of Various Brachytherapy Applicators for Cervical Cancer
Authors: Soliman A , Elzibak A , Fatemi A , Safigholi H , Han D , Leung E , Ravi A , Song W
Published: June 2015

Purpose:

To compare the quality of Magnetic Resonance (MR) images of a recently‐proposed novel direction‐modulated brachytherapy (DMBT) tandem applicator against two conventional clinical applicators, using the current MRI clinical protocol.

Methods:

Three tandem applicators were compared: (1) tungsten‐based DMBT applicator, (2) conventional plastic applicator and (3) conventional stainless steel applicator. Physical dimensions were 5.4, 3.8 and 3.2 for tandems (1), (2) and (3), respectively. Each applicator was placed in the same water‐phantom and independently scanned using the same parameters and coil settings on a 1.5 T 450w GE scanner. Images were acquired using T2‐weighted turbo‐spin‐echo (TSE) with 8‐channel body coil. Acquisition parameters were TR/TE =7000/108 ms; acquisition matrix = 320 × 256; 30 slices with 4 mm thickness and 0.5 gap; pixel bandwidth = 122 Hz and voxel size = 0.5 × 0.625 mm2 and number of excitations (NEX) = 4. Multiple acquisitions were obtained in para‐sagittal and para‐axial views (with respect to the tandem axis) for each applicator. Diameters of the tandem were measured at multiple angles and multiple locations and compared to the physical dimensions of the corresponding tandems.

Results:

Minimal susceptibility artifact was observed with the DMBT and the plastic tandems. The stainless steel tandem produced significantly larger artifact than the first two tandems. The average diameter of the DMBT applicator measured 5.94 ± 0.3 mm. The average diameter of the plastic tandem measured 3.9 ± 0.1 mm. The maximum extent of artifact was 1.5 mm and 0.7 mm for DMBT and plastic tandems, respectively. The susceptibility artifact induced by the stainless steel tandem prevented the measurement of its diameter, and the edges of the tandem could not be identified in any acquisition.

Conclusion:

This work demonstrated that the plastic and the tungsten‐based DMBT tandem applicators are both suitable for MRI‐guided brachytherapy of cervical cancer.
SU‐E‐T‐210: Comparison of Proton with Electron Boost in Breast Cancer Treatment
Authors: Zheng Y , Liu Y , Chang A
Published: June 2015

Purpose:

Electron beams are commonly used for boost radiation following whole breast irradiation (WBI) to improve the in‐breast local control. Proton beams have a finite range and a sharper distal dose falloff compared to electron beams, thus potentially sparing more heart and lung in breast treatment. The purpose of the study is to compare protons with electrons for boost breast treatment in terms of target coverage and normal tissue sparing.

Methods:

Six breast cancer patients were included in this study. All women received WBI to 45–50 Gy, followed by a 10–16.2 Gy boost with standard fractionation. If proton beams were used for the boost treatment, an electron plan was retrospectively generated for comparison using the same CT set and structures, and vice versa if electron beams were used for treatment. Proton plans were generated using the treatment planning system (TPS) with two to three uniform scanning proton beams. Electron plans were generated using the Pinnacle TPS with one single en face beam. Dose‐volume histograms (DVH) were calculated and compared between proton and electron boost plans.

Results:

Proton plans show a similar boost target coverage, similar skin dose, and much better heart and lung sparing. For an example patient, V95% for PTV was 99.98% and skin (5 mm shell) received a max dose close to the prescription dose for both protons and electrons; however, V2 and V5 for the ipsilateral lung and heart were 37.5%, 17.9% and 19.9%, 4.9% respectively for electrons, but were essentially 0 for protons.

Conclusions:

This dosimetric comparison demonstrates that while both proton therapy and electron therapy provided similar coverage and skin dose, proton therapy could largely reduce the dose to lung and heart, thus leading to potential less side effects.
SU‐E‐T‐211: Comparison of Seven New TrueBeam Linacs with Enhanced Beam Data Conformance Using a Beam Comparison Software Tool
Authors: Grzetic S , Hessler J , Gupta N , Woollard J , DiCostanzo D , Ayan A , Carlson M
Published: June 2015

Purpose:

To develop an independent software tool to assist in commissioning linacs with enhanced beam conformance, as well as perform ongoing QA for dosimetrically equivalent linacs.

Methods:

Linac manufacturers offer enhanced beam conformance as an option to allow for clinics to complete commissioning efficiently, as well as implement dosimetrically equivalent linacs. The specification for enhanced conformance includes PDD as well as profiles within 80% FWHM. Recently, we commissioned seven Varian TrueBeam linacs with enhanced beam conformance. We developed a software tool in Visual Basic to allow us to load the reference beam data and compare our beam data during commissioning to evaluate enhanced beam conformance. This tool also allowed us to upload our beam data used for commissioning our dosimetrically equivalent beam models to compare and tweak each of our linac beams to match our modelled data in Varian's Eclipse TPS. This tool will also be used during annual QA of the linacs to compare our beam data to our baseline data, as required by TG‐142.

Results:

Our software tool was used to check beam conformance for seven TrueBeam linacs that we commissioned in the past six months. Using our tool we found that the factory conformed linacs showed up to 3.82% difference in their beam profile data upon installation. Using our beam comparison tool, we were able to adjust the energy and profiles of our beams to accomplish a better than 1.00% point by point data conformance.

Conclusion:

The availability of quantitative comparison tools is essential to accept and commission linacs with enhanced beam conformance, as well as to beam match multiple linacs. We further intend to use the same tool to ensure our beam data conforms to the commissioning beam data during our annual QA in keeping with the requirements of TG‐142.
SU‐E‐T‐214: Comparison of Treatment Techniques for Dupuytren's Contracture and Risk Assessment of Normal Tissue Complications
Authors: Arentsen L , Lopater Z , Dusenbery K , Gerbi B
Published: June 2015

Purpose:

Duputren's contracture (DC) is a benign disease characterized by abnormal thickening of the fascial surfaces of the hands or feet causing curling of the surface, functional impairment, weakness, and pain. The purpose of the investigation is to describe the radiation treatment approaches, compare these techniques, and discuss the potential side effects and complications of these techniques.

Methods:

Early stage DC has been treated with 120 kVp X rays but also with high‐energy electrons or photons. High‐energy electrons have been the radiation of choice but severe contracture of the hand makes it difficult to produce a plan with acceptable dose uniformity. High‐energy photons can overcome this difficulty either by directing a beam onto the palmer or back of the surface of the hand, including bolus to maximize the surface dose. We calculated the dose to the bone for the 120 kVp treatment using published %DD data and mass energy absorption coefficients for bone and muscle.

Results:

The dose to underlying bone from megavoltage photons and electrons is essentially the same, but dose to the bone for using 120 kVp can be 4–5 times greater due to the photoelectric effect. For the 30 Gy dose deliver using this technique, the dose to the bone could be 84–105 Gy after taking the penetration of the beam into account. After radiotherapy, there is often decreased osteoblastic activity and vascular fibrosis that leads to osteitis, atrophy, and decreased metabolic bone activity. Incidence of fractures occurs routinely above 60 Gy with higher doses potentially leading to higher incidences of bone complications.

Conclusion:

Radiation therapy for DC using low‐energy X rays can deliver a prohibitively high dose to the underlying bone potentially leading to severe bone complications.
SU‐E‐T‐217: Comprehensive Dosimetric Evaluation On 3D‐CRT, IMRT and Non‐Coplanar Arc Treatment for Prone Accelerated Partial Breast Irradiation (APBI)
Authors: Chiu T , Yan Y , Ramirez E , Lee P , Jiang S , Gu X
Published: June 2015

Purpose:

Accelerated partial breast irradiation (APBI) is an effective treatment for early stage breast‐cancer. Irradiation in a prone position can mitigate breast motion and spare heart and lung. In this study, a comprehensive study is performed to evaluate various treatment techniques for prone APBI treatment including: 3D‐CRT, IMRT, co‐planar and non‐coplanar partial arcs treatment.

Methods:

In this treatment planning study, a left breast patient treated in prone position in our clinic was imported into Varian Eclipse TPS. Six beams tangential to chest wall were used in both 3D‐CRT and IMRT plans. These six beams were coplanar in a transactional plane achieved by both gantry and couch rotation. A 60‐beam IMRT plan was also created to explore the maximum benefit of co‐planar IMRT. Within deliverable couch rotation range (±30°), partial arc treatment plans with one and up to ten couch positions were generated for comparison. For each plan, 30Gy in 6 fractions was prescribed to 95% PTV volume. Critical dosimetric parameters, such as conformity index, mean, maximum, and volume dose of organ at risk, are evaluated.

Results:

The conformity indexes (CI) are 3.53, 3.17, 2.21 and 1.08 respectively to 3D‐CRT, 6‐beam IMRT, 60‐beam IMRT, and two‐partial‐arcs coplanar plans. However, arc plans increase heart dose. CI for non‐coplanar arc plans decreases from 1.19 to 1.10 when increases couch positions. Maximum dose in ipsilateral lung (1.98 to 1.13 Gy), and heart (0.62 to 0.43 Gy) are steadily decreased with the increased number of non‐coplanar arcs.

Conclusions:

The dosimetric evaluation results show that partial arc plans have improved CIs compared to conventional 3D‐CRT and IMRT plans. Increasing number of partial arcs decreases lung and heart dose. The dosimetric benefit obtained from non‐coplanar arcs should be considered with treatment delivery time.
SU‐E‐T‐225: Correction Matrix for PinPoint Ionization Chamber for Dosimetric Measurements in the Newly Released Incise™ Multileaf Collimator Shaped Small Field for CyberKnife M6™ Machine
Authors: Zhang Y , Li T , Heron D , Huq M
Published: June 2015

Purpose:

For small field dosimetry, such as measurements of output factors for cones or MLC‐shaped irregular small fields, ion chambers often Result in an underestimation of the dose, due to both the volume averaging effect and the lack of lateral charged particle equilibrium. This work presents a mathematical model for correction matrix for a PTW PinPoint ionization chamber for dosimetric measurements made in the newly released Incise™ Multileaf collimator fields of the CyberKnife M6™ machine.

Methods:

A correction matrix for a PTW 0.015cc PinPoint ionization chamber was developed by modeling its 3D dose response in twelve cone‐shaped circular fields created using the 5mm, 7.5mm, 10mm, 12.5mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 50mm, 60mm cones in a CyberKnife M6™ machine. For each field size, hundreds of readings were recorded for every 2mm chamber shift in the horizontal plane. The contribution of each dose pixel to a measurement point depended on the radial distance and the angle to the chamber axis. These readings were then compared with the theoretical dose as obtained with Monte Carlo calculation. A penalized least‐square optimization algorithm was developed to generate the correction matrix. After the parameter fitting, the mathematical model was validated for MLC‐shaped irregular fields.

Results:

The optimization algorithm used for parameter fitting was stable and the resulted response factors were smooth in spatial domain. After correction with the mathematical model, the chamber reading matched with the calculation for all the tested fields to within 2%.

Conclusion:

A novel mathematical model has been developed for PinPoint chamber for dosimetric measurements in small MLC‐shaped irregular fields. The correction matrix is dependent on detector, treatment unit and the geometry of setup. The model can be applied to non‐standard composite fields and provides an access to IMRT point dose validation.
SU‐E‐T‐226: Correction of a Standard Model‐Based Dose Calculator Using Measurement Data
Authors: Chen M , Jiang S , Lu W
Published: June 2015

Purpose:

To propose a hybrid method that combines advantages of the model‐based and measurement‐based method for independent dose calculation. Modeled‐based dose calculation, such as collapsed‐cone‐convolution/superposition (CCCS) or the Monte‐Carlo method, models dose deposition in the patient body accurately; however, due to lack of detail knowledge about the linear accelerator (LINAC) head, commissioning for an arbitrary machine is tedious and challenging in case of hardware changes. On the contrary, the measurement‐based method characterizes the beam property accurately but lacks the capability of dose disposition modeling in heterogeneous media.

Methods:

We used a standard CCCS calculator, which is commissioned by published data, as the standard model calculator. For a given machine, water phantom measurements were acquired. A set of dose distributions were also calculated using the CCCS for the same setup. The difference between the measurements and the CCCS results were tabulated and used as the commissioning data for a measurement based calculator. Here we used a direct‐ray‐tracing calculator (ΔDRT). The proposed independent dose calculation consists of the following steps: 1. calculate D_model using CCCS. 2. calculate D_ΔDRT using ΔDRT. 3. combine

Results:

D=D_model+D_ΔDRT.

Results:

The hybrid dose calculation was tested on digital phantoms and patient CT data for standard fields and IMRT plan. The results were compared to dose calculated by the treatment planning system (TPS). The agreement of the hybrid and the TPS was within 3%, 3 mm for over 98% of the volume for phantom studies and lung patients.

Conclusion:

The proposed hybrid method uses the same commissioning data as those for the measurement‐based method and can be easily extended to any non‐standard LINAC. The results met the accuracy, independence, and simple commissioning criteria for an independent dose calculator.
SU‐E‐T‐227: Could the Alpha/Beta Ratio Change in a Strong Magnetic Field?
Authors: Pang G
Published: June 2015

Purpose:

Magnetic resonance imaging (MRI) is being integrated into radiotherapy delivery for MRI‐guided radiotherapy. The presence of a strong magnetic field from a MRI machine during radiotherapy delivery presents a new challenge since the trajectories of electrons liberated by ionizing radiation in patients are strongly dependent on the applied magnetic field. The purpose of this work is to explore the potential effect of a strong magnetic field on the α/β ratio, an important radiobiological parameter in radiotherapy.

Methods:

Based on the theory of dual radiation action, the α/β ratio can be expressed by an integral of the product of two microdosimetry quantities γ(x) and t(x), where γ(x) is the probability that two energy transfers, a distance × apart, results in a lesion, and t(x) is the proximity function, which is the energy‐weighted point‐pair distribution of distances between energy transfer points in a track. The quantity t(x) depends on the applied magnetic field. An analytical approach has been used to derive a formula that can be used to calculate the α/β ratio in an extremely strong magnetic field.

Results:

The α/β ratio has been evaluated in the special case when the applied magnetic field approaches infinity, which gives the upper limit of the potential change of the α/β ratio due to the presence of a strong magnetic field. For V79 Chinese hamster cells it has been shown that the α/β ratio could be increased by 2.90 times for Pd‐103, 2.97 times for I‐125 and about 2.3 times for Co‐60 sources when the applied magnetic field approaches infinity.

Conclusion:

It has been shown theoretically that the α/β ratio can change in a strong magnetic field, and there could be up to a nearly three‐fold increase in the α/β ratio, depending on the strength of the applied magnetic field, the cell type and the radiation used.
SU‐E‐T‐231: Cross‐Validation of 3D Gamma Comparison Tools
Authors: Alexander KM , Jechel C , Pinter C , Salomons G , Lasso A , Fichtinger G , Schreiner LJ
Published: June 2015

Purpose:

Moving the computational analysis for 3D gel dosimetry into the 3D Slicer (www.slicer.org) environment has made gel dosimetry more clinically accessible. To ensure accuracy, we cross‐validate the 3D gamma comparison module in 3D Slicer with an independently developed algorithm using simulated and measured dose distributions.

Methods:

Two reference dose distributions were generated using the Varian Eclipse treatment planning system. The first distribution consisted of a four‐field box irradiation delivered to a plastic water phantom and the second, a VMAT plan delivered to a gel dosimeter phantom. The first reference distribution was modified within Eclipse to create an evaluated dose distribution by spatially shifting one field by 3mm, increasing the monitor units of the second field, applying a dynamic wedge for the third field, and leaving the fourth field unchanged. The VMAT plan was delivered to a gel dosimeter and the evaluated dose in the gel was calculated from optical CT measurements. Results from the gamma comparison tool built into the SlicerRT toolbox were compared to results from our in‐house gamma algorithm implemented in Matlab (via MatlabBridge in 3D Slicer). The effects of noise, resolution and the exchange of reference and evaluated designations on the gamma comparison were also examined.

Results:

Perfect agreement was found between the gamma results obtained using the SlicerRT tool and our Matlab implementation for both the four‐field box and gel datasets. The behaviour of the SlicerRT comparison with respect to changes in noise, resolution and the role of the reference and evaluated dose distributions was consistent with previous findings.

Conclusion:

Two independently developed gamma comparison tools have been cross‐validated and found to be identical. As we transition our gel dosimetry analysis from Matlab to 3D Slicer, this validation serves as an important test towards ensuring the consistency of dose comparisons using the 3D Slicer environment.
SU‐E‐T‐232: Custom High‐Dose‐Rate Brachytherapy Surface Mold Applicators: The Importance Source to Skin Distance
Authors: Park S , Demanes J , Kamrava M
Published: June 2015

Purpose:

Surface mold applicators can be customized to fit irregular skin surfaces that are difficult to treat with other radiation therapy techniques. Optimal design of customized HDR skin brachytherapy is not well‐established. We evaluated the impact of applicator thickness (source to skin distance) on target dosimetry.

Methods:

27 patients had 34 treated sites: scalp 4, face 13, extremity 13, and torso 4. Custom applicators were constructed from 5–15 mm thick thermoplastic bolus molded over the skin lesion. A planar array of plastic brachytherapy catheters spaced 5–10 mm apart was affixed to the bolus. CT simulation was used to contour the target volume and to determine the prescription depth. Inverse planning simulated annealing followed by graphical optimization was used to plan and deliver 40–56 Gy in 8–16 fractions. Target coverage parameters (D90, Dmean, and V100) and dose uniformity (V110–200, D0.1cc, D1cc, and D2cc) were studied according to target depth (<5mm vs. ≥5mm) and applicator thickness (5–10mm vs. ≥10mm).

Results:

The average prescription depth was 4.2±1.5mm. The average bolus thickness was 9.2±2.4mm. The median CTV volume was 10.0 cc (0.2–212.4 cc). Similar target coverage was achieved with prescription depths of <5mm and ≥5mm (Dmean = 113.8% vs. 112.4% and D90 = 100.2% vs. 98.3%). The <5mm prescription depth plans were more uniform (D0.1cc = 131.8% vs. 151.8%). Bolus thickness <10mm vs. ≥10mm plans also had similar target coverage (Dmean = 118.2% vs. 110.7% and D90 = 100.1% vs. 99.0%). Applicators ≥10mm thick, however, provide more uniform target dosimetry (D0.1cc = 146.9% vs. 139.5%).

Conclusion:

Prescription depth is based upon the thickness of the lesion and upon the clinical needs of the patient. Applicators ≥10mm thick provide more dose uniformity than 5–10mm thick applicators. Applicator thickness is an important variable that should be considered during treatment planning to achieve optimal dose uniformity.
SU‐E‐T‐233: Cyberknife Versus Linac IMRT for Dose Comparision in Hypofractionated Hemi Larynx Irradiation of Early Stage True Vocal Cord Cancer: A Dosimetric Study
Authors: Ding C , Lee P , Jiang S
Published: June 2015

Purpose:

To compare dosimetric data of patients treated for early‐stage larynx cancer on Cyberknife and Linac IMRT.

Methods:

Nine patients were treated with Cyberknife to a dose of 45 Gy in 10 fractions of the involved hemilarynx. The prescription dose provided at least 95% of PTV coverage. After Cyberknife treatment, the CT images and contours were sent to Pinnacle treatment planning system for IMRT planning on a regular SBRT linac with same dose prescription and constrains. Dose to target and normal tissue, including the arytenoids, cord, carotid arteries, thyroid, and skin, were analyzed using dose volume histograms.

Results:

For Cyberknife plan, the conformity indices are within 1.11–1.33. The average dose to the contralateral arytenoids for Cyberknife plans was 28.9±6.5Gy), which is lower than the same mean dose for IMRT plans (34.0±5.2 Gy). The average maximum dose to the ipsilateral and contralateral carotid artery were 20.6 ±9.1 Gy and 10.2±6.0 Gy respectively for Cybeknife comparing with 22.1±8.0 Gy and 12.0±5.1 Gy for IMRT. The mean dose to the thyroid was 3.6±2.2 Gy for Cyberknife and 3.4±2.4 Gy for IMRT. As shown in DVH, the Cyberknife can deliver less dose to the normal tissue which is close to target area comparing with IMRT Plans. However, IMRT plan's can give more sparing for the critical organs which is far away from the target area.

Conclusion:

We have compared the dosimetric parameters of Cyberknife and linac IMRT plans for patients with early‐stage larynx cancer. Both Cyberknife and IMRT plans can achieve conformal dose distribution to the target area. Cyberknife was able to reduce normal tissue dose in high doses region while IMRT plans can reduce the dose of the normal tissue at the low dose region. These dosimetric parameters can be used to guide future prospective protocols using SBRT for larynx cancer.
SU‐E‐T‐237: Deformable Image Registration and Deformed Dose Composite for Volumetric Evaluation of Multimodal Gynecological Cancer Treatments
Authors: Albani D , Cantley J , Sherertz T , Ellis R , Herrmann K , Podder T
Published: June 2015

Purpose:

Radiotherapy plans for patients with cervical cancer treated with EBRT followed by HDR brachytherapy are optimized by constraining dose to organs at risk (OARs). Risk of treatment related toxicities is estimated based on the dose received to the hottest 2cc (D2cc) of the bladder, bowel, rectum, and sigmoid. To account for intrafractional variation in OAR volume and positioning, a dose deformation method is proposed for more accurate evaluation of dose distribution for these patients.

Methods:

Radiotherapy plans from five patients who received 50.4Gy pelvic EBRT followed by 30Gy in five fractions of HDR brachytherapy, using split‐ring and tandem applicators, were retrospectively evaluated using MIM Software version 6.0. Dose accumulation workflows were used for initial deformation of EBRT and HDR planning CTs onto a common HDR planning CT. The Reg Refine tool was applied with user‐specified local alignments to refine the deformation. Doses from the deformed images were transferred to the common planning CT. Deformed doses were scaled to the EQD2, following the linear‐quadratic BED model (considered α/β ratio for tumor as 10, and 3 for rest of the tissues), and then combined to create the dose composite. MIM composite doses were compared to the clinically‐reported plan assessments based upon the American Brachytherapy Society (ABS) guidelines for cervical HDR brachytherapy treatment.

Results:

Bladder D2cc exhibited significant reduction (−11.4%±3.85%, p< 0.02) when evaluated using MIM deformable dose composition. Differences observed for bowel, rectum, and sigmoid D2cc were not significant (−0.58±7.37%, −4.13%±13.7%, and 8.58%±4.71%, respectively and p>0.05 for all) relative to the calculated values used clinically.

Conclusion:

Application of deformable dose composite techniques may lead to more accurate total dose reporting and can allow for elevated dose to target structures with the assurance of not exceeding dose to OARs. Further study into deformable dose composition and correlation with clinical outcomes is warranted.
SU‐E‐T‐238: Deriving Electron Contamination Spectra From Pure and Clinical Photon Beams
Authors: Smit C , du Plessis F
Published: June 2015

Purpose:

To extract the electron contamination energy spectra for an Elekta Precise Linac, based on pure photon and measured clinical beam percentage depth dose data. And to include this as an additional source in isource 4 in DOSXYZnrc.

Methods:

A pure photon beam was simulated for the Linac using isource 4 in the DOSXYZnrc Monte Carlo (MC) code. Percentage depth dose (PDD) data were extracted afterwards for a range of field sizes (FS). These simulated dose data were compared to actual measured dose PDD data, with the data normalized at 10 cm depth. The resulting PDD data resembled the electron contamination depth dose. Since the dose fall‐off is a strictly decreasing function, a method was adopted to derive the contamination electron spectrum. Afterwards this spectrum was used in a DOSXYZnrc MC simulation run to verify that the original electron depth dose could be replicated.

Results:

Various square aperture FS's for 6, 8 and 15 megavolt (MV) photon beams were modeled, simulated and compared to their respective actual measured PDD data. As FS increased, simulated pure photon depth‐dose profiles shifted deeper, thus requiring electron contamination to increase the surface dose. The percentage of electron weight increased with increase in FS. For a FS of 15×15 cm2, the percentage electron weight is 0.1%, 0.2% and 0.4% for 6, 8 and 15 MV beams respectively.

Conclusion:

From the PDD results obtained, an additional electron contamination source was added to the photon source model so that simulation and measured PDD data could match within 2 % / 2 mm gamma‐index criteria. The improved source model could assure more accurate simulations of surface doses.

This research project was funded by the South African Medical Research Council (MRC) with funds from National Treasury under its Economic Competitiveness and Support package.
SU‐E‐T‐240: Design and Implement of An Electronic Records Function for Treatment Plan Checked Meeting
Authors: Wu Q
Published: June 2015

Purpose:

To replace the paper records, we designed an electronic records function for plan checked meeting in our in‐house developed radiotherapy information management system(RTIMS).

Methods:

Since 2007, the RTIMS has been developed on a database and web service of Apache+PHP+MySQL, and almost all computers and smartphones could access the RTIMS through IE browser, to input, search, count, and print the data. In 2012, we also established an radiation therapy case conference multi‐media system(RTCCMMS) based on Windows Remote Desktop feature. Since 2013, we have carried out the treatment plan checked meeting of the physics division in every afternoon for about half an hour. In 2014, we designed an electronic records function, which includes a meeting information record and a checked plan record. And the meeting record includes the following items: meeting date, name, place, length, status, attendee, content, etc. The plan record includes the followings: meeting date, meeting name, patient ID, gender, age, patient name, course, plan, purpose, position, technique, CTsim type, plan type, primary doctor, other doctor, primary physicist, other physicist, difficulty, quality, score, opinion, status, note, etc.

Results:

In the past year, the electronic meeting records function has been successfully developed and implemented in the division, and it could be accessed from an smartphone. Almost all items have the corresponding pull‐down menu selection, and each option would try to intelligently inherit default value from the former record or other form. According to the items, we could do big data mining to the input data. It also has both Chinese and English two versions.

Conclusion:

It was demonstrated to be user‐friendly and was proven to significantly improve the clinical efficiency and quality of treatment plan. Since the RTIMS is an in‐house developed system, more functions can be added or modified to further enhance its potentials in research and clinical practice.

Project supported by the National Natural Science Foundation of China (Grant No.81101694).
SU‐E‐T‐242: Design of a Novel Afterloader Clearance QA Device for Biliary HDR Therapy
Authors: Mullins JP , Deufel CL
Published: June 2015

Purpose:

Bile duct cancer affects 2–3 thousand people annually in the United States. Radiation therapy has been shown to double median survival, with combined external beam and intraluminal high dose‐rate (HDR) brachytherapy being most effective. Endoscopic retrograde cholangiopancreatography (ERCP) biliary HDR, a less‐invasive alternative to trans‐hepatic brachytherapy, is delivered through a catheter that travels a tortuous path from nose to bile duct, requiring wire drive force and dexterity beyond typical afterloader performance specifications. Thus, specific afterloader quality assurance(QA) is recommended for this procedure. Our aim was to create a device and process for Varisource afterloader clearance QA with objectives that it be quantitative and can monitor afterloader performance over time, compare performance between two distinct afterloaders and potentially Result in a predictive nomogram for patient‐specific clearance.

Methods:

Based on retrospective reconstruction of 20 ERCP patient anatomies, we designed a phantom to test afterloader ability to drive the source wire along an intended treatment path. The ability of the afterloader to fully extend the intended treatment path is a function of number and diameters of turns. We have determined experimentally that relative position of the turns does not impact performance.

Results:

Both patient and QA paths involve three common turns/loops: a large turn representing the stomach(10.8cm±2.0cm), an elliptical loop representing the duodenum(7.3cm±1.5cmx4.8cm±0.7cm), and a final turn at the end of the bile duct that may be tight for some patient‐specific anatomies and absent in others(3.7cm±0.7cm, where present). Our phantom design uses anatomical average turn diameters for the stomach and duodenum then terminates in a turn of quantitatively selectable diameter. The smallest final turn diameter that an afterloader can pass is recorded as the QA parameter.

Conclusion:

With this device and QA process, we have the ability to quantitatively evaluate and track our afterloader performance for a technically challenging ERCP brachytherapy procedure.
SU‐E‐T‐243: Design of a Novel Testing Port for Radiation Protection and Shielding Measurements
Authors: Tanny S , Harrell D , Chopra M , Noller J , Parsai E
Published: June 2015

Purpose:

The majority of radiation shielding research utilizes Monte Carlo simulation because of the difficulty in eliminating secondary radiations from measurements. We have designed a test port into a primary barrier of our newest vault to allow for shielding measurements while ensuring adequate protection to the public and staff during normal machine operation. This port allows for measurement of attenuation values of shielding materials, differential dose albedos, and radiation scatter fractions.

Methods:

The vault design utilized the maze as part of a compound primary barrier. The test port is contained within the maze and is centered along isocenter. The inner 30 cm has a 20×20 cm2 opening, while the remaining length has a 30×30 cm2 opening. The block that contains the port has a density of 200 pcf to minimize internal scatter. The 30×30 cm2 opening is occupied by removable 215 pcf concrete blocks. The innermost and outermost blocks activate an interlock wired into the beam‐enable loop. This disallows beam‐on in treatment mode if the interlock isn't closed. The interlock can be overridden in service mode, or by‐passed via an override switch in case of circuit failure.

Results:

The test port was installed in August. The beam is disabled when the interlock is tripped. Measurements taken when the primary beam is not incident on the port are indistinguishable from background. Ambient dose levels surrounding the vault with the designed shielding blocks in place are all within allowable limits for occupational workers.

Conclusions:

We have designed and installed a unique testing port for radiation protection and shielding measurements. This port is appropriately interlocked and designed to mitigate any risks of incidental exposure to staff or members of the public. The test port design allows measurements with “good geometry” and efficient removal of contaminating sources of radiation present in many shielding measurements.

Daniel Harrell and Jim Noller are employees of Shielding Construction Solutions, Inc, the shielding construction company that built the vault discussed in this abstract. Manjit Chopra is an employee of Universal Minerals International, Inc, the company that provided the aggregates for the high density concretes used in the vault construction.
SU‐E‐T‐246: Detector Selection for Small Field Measurements, a Comparative Study
Authors: Sigler M , Pavord D , Irwin J , Kriminski S
Published: June 2015

Purpose:

To compare commercially available detectors for small field dosimetry.

Methods:

PTW (Freiburg, Germany) diode E, PTW microDiamond, and SunNuclear (Melbourne, FL) Edge detector were used to measure output factors, PDD, and profiles on a Varian iX linear accelerator (Varian Medical Systems, Palo Alto, CA) using 6MV and 18MV photon beams. The water tank was set to 100cm SSD. Centering profiles at 5cm and 20cm depth confirmed an offset <0.1mm. High resolution PDD (0.1mm) aligned the collecting volume at water surface. For setup and linearity verification, PDD and profiles were matched to annual measurements, which were performed with an A1SL ion chamber.Scans were taken for 6X and 18X, for 10cmx10cm, 10cmx2cm, 10cmx1cm, and 10cmx0.5cm fields. Profiles were measured at Dmax (6X=1.5cm, 18X=3.5cm), 5cm, 10cm, and 20cm depths. All fields used 10cmx10cm jaws with the MLC defining the field in the X‐direction. PDDs used 2mm step size and 0.2s discrete collecting time. Profiles used 1mm step size and a 0.4s discrete collecting time.

Results:

The PTW diode E and Edge detector exhibit centering stability, but all detectors require vertical shifts from Vendor defined vertical alignment. Output factor measurements reveal good agreement between detectors. The Edge detector demonstrates the sharpest penumbra and the closest consistent match to ion chamber measurements in the out of field regions for 6MV (3.2%). Each detector provides comparable curve quality for PDDs, with a maximum difference across detectors giving a standard deviation of 0.6% at 30cm depth, 18X, and 10cmx0.5cm. Profiles match closely across all detectors, depths, energies, and field sizes. The microDiamond detector produces the largest penumbra width, largest deviation from ion chamber dose in the tail region for 6MV, and exhibits centering instability.

Conclusion:

Based on our findings, the Edge detector was chosen for stereotactic measurements. The PTW diode E is an acceptable alternative.
SU‐E‐T‐247: Determinations of the Optimal Phase for Respiratory Gated Radiotherapy From Statistical Analysis Using a Visible Guidance System
Authors: Oh S , Yea J , Kang M , Lee H , Kim S
Published: June 2015

Purpose:

Respiratory gated radiation therapy (RGRT) is used to minimize the radiation dose to normal tissue in lung cancer patients. Determination of the optimal point in the respiratory phase of a patient is important in RGRT but it is not easy. The goal of the present study was to see if a visible guidance system is helpful in determining the optimal phase in respiratory gated therapy.

Methods:

The breathing signals of 23 lung cancer patients were recorded with a Real‐time Position Management (RPM) respiratory gating system (Varian, USA). The patients underwent breathing training with our visible guidance system, after which their breathing signals were recorded during 5 min of free breathing and 5 min of guided breathing. The breathing signals recorded between 3 and 5 min before and after training were compared. We performed statistical analysis of the breathing signals to find the optimal duty cycle in guided breathing for RGRT.

Results:

The breathing signals aided by the visible guidance system had more regular cycles over time and smaller variations in the positions of the marker block than the free breathing signals. Of the 23 lung cancer patients, 19 showed statistically significant differences by time when the values obtained before and after breathing were compared (p < 0.05); 30% and 40% of the duty cycle, respectively, was determined to be the most effective, and the corresponding phases were 30 60% (duty cycle, 30%; p < 0.05) and 30 70% (duty cycle, 40%; p < 0.05).

Conclusion:

Respiratory regularity was significantly improved with the use of the RPM with our visible guiding system; therefore, it would help improve the accuracy and efficiency of RGRT.
SU‐E‐T‐314: Dosimetric Effect of Smooth Drilling On Proton Compensators in Prostate Patients
Authors: Reyhan M , Yue N , Zou J
Published: June 2015

Purpose:

To evaluate the dosimetric effect of smooth drilling of proton compensators in proton prostate plans when compared to typical plunge drilling settings.

Methods:

Twelve prostate patients were planned in Eclipse treatment planning system using three different drill settings Smooth, Plunge drill A, and Plunge drill B. The differences between A and B were: spacing X[cm]: 0.4(A), 0.1(B), spacing Y[cm]: 0.35(A), 0.1(B), row offset [cm]: 0.2(A), 0(B). Planning parameters were kept consistent between the different plans, which utilized two opposed lateral beams arrangement. Mean differences absolute dosimetry in OAR constraints are presented.

Results:

The smooth drilled compensator based plans yielded equivalent target coverage to the plans generated with drill settings A and B. Overall, the smooth compensators reduced dose to the majority of organs at risk compared to settings A and B. Constraints were reduced for the following OAR: Rectal V75 by 2.12 and 2.48%, V70 by 2.45 and 2.91%, V65 by 2.85 and 3.37%, V50 by 2.3 and 5.1%, Bladder V65 by 4.49 and 3.67%, Penial Bulb mean by 3.7 and 4.2Gy, and the maximum plan dose 5.3 and 7.4Gy for option A vs smooth and option B vs smooth respectively. The femoral head constraint (V50<5%) was met by all plans, but it was not consistently lower for the smooth drilling plan.

Conclusion:

Smooth drilled compensators provide equivalent target coverage and overall slightly cooler plans to the majority of organs at risk; it also minimizes the potential dosimetric impacts caused by patient positioning uncertainty.
SU‐E‐T‐317: Dosimetric Evaluation of Acuros XB Advanced Dose Calculation Algorithm in Head and Neck Patients
Authors: Faught A , Wu Q
Published: June 2015

Purpose:

The Acuros XB photon dose calculation algorithm is a newly implemented calculation technique within the Eclipse treatment planning system using deterministic solutions to the linear Boltzmann transport equations. The goal of this study is to assess the clinical impact of dose differences arising from a retrospective comparison of calculations performed using the Analytical Anisotropic Algorithm (AAA) and Acuros XB on patients.

Methods:

Ten head and neck patients receiving intensity modulated radiation therapy were selected as a pilot study. Initial evaluation was based on the percentage of the planning target volume (PTV) covered by the prescription dose, minimum dose within the PTV, and dose differences in critical structures. For patients receiving boost plans, dosimetric evaluations were performed on the plan sum of the primary and boost plans.

Results:

Among the ten patients there were a total of 21 PTVs corresponding to primary and boost volumes. Using the same normalization within Eclipse, the average percentage of the PTVs receiving the prescription dose were 95.6% for AAA and Acuros XB. The average minimum doses within the PTVs, expressed as a percentage of the prescription to the volume, were 82.3% and 83.6% for AAA and Acuros XB respectively. Neither comparison showed differences with statistical significance when subjected to a paired t‐test. Statistical significance was found in the average difference of the maximum dose for the mandible (242.5cGy, p=0.0005) and cord with a 5mm radial expansion (105.0cGy, p=0.0005) and in the median dose for the left parotid (25.0cGy, p=0.0423) and oral cavity (36.3cGy, p=0.002).

Conclusion:

The Acuros XB dose calculation algorithm did not exhibit significant differences in PTV coverage when compared to the AAA algorithm. Significant differences in critical structures are likely attributed to the structures proximity to high atomic number materials or air cavities, regions of known difficulty for the AAA algorithm.
SU‐E‐T‐319: Dosimetric Evaluation of IMRT with Mix‐Energy Beam for Deep Seated Targets
Authors: Sharma S , Manigandan D , Gandhi A , Sharma D , Subramani V , Chander S , Julkha P , Rath G
Published: June 2015

Purpose:

IMRT is preferred in the range of 6–10MV X‐rays. Partially adding high energy (>10MV) treatment fields, may provide advantage of both higher and lower energies. To study IMRT dose distribution obtained from treatment plans with single (6MV) and mixed‐energy (6MV and 15MV) for deep seated targets (separation more than 30cm).

Methods:

Five patients of carcinoma of cervix were studied using eclipse planning system. Two different dynamic IMRT plans were generated for Varian CL2300C/D linear accelerator; one is by using 6MV X‐ray with seven equally spaced coplanar beams. In second plan, 2 lateral oblique fields (gantry angle 102°, 255°) beam energy was modified to 15MV by keeping all other parameters and dose volume constraints constant. Dose prescription for the planning target volume (PTV) was (5040cGy/28f). For plan comparison, dose volume histogram (DVH) was used and PTV coverage index (CI=Target volume covered by prescription dose/Target volume), heterogeneity index (D5/D95), mean dose to organ at risk (OAR) and normal tissue integral dose (NTID, liter‐Gray) was also noted. Total monitor unit (MU) required to deliver a plan was also noted.

Results:

Mixed‐energy plan showed a better conformity and CI values were 0.942±0.032 and 0.960±0.040 for single‐energy and mixed‐energy plan, respectively. In addition, HI value of mixed energy beam is comparable to that of single energy and the values were within 1.084±0.034 and 1.082±0.032 for single energy and mixed‐energy plan, respectively. Variation in mean dose to bladder, rectum and bowel were within 1.05%, 0.87% and 0.90%. NTID was lesser for mixed‐energy beam due to use of two high‐energy fields. NTID were 1573.40±214.60 and 1510.20±249.80 litre‐Gray for single energy and mixed‐energy plan. MU needed to deliver a plan was similar in both plans and MUs were 238±45 and 237±47.

Conclusion:

Partial use of 15MV treatment fields in IMRT plan for deep seated targets showed dosimetric advantage over 6MV plan.