bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐288: Skin Dose Measurement of Whole Brain with GAFCHROMIC EBT2 Films
Authors: Jia Y , Costlow H , Akino Y , Peng Y , Desrosiers C , Zhang H
Published: June 2012

Purpose: To measure skin dose of whole brain irradiation of a humanoid unsliced phantom treated by standard lateral fields with GAFCHROMIC EBT2 films. Methods: The head and neck of the whole body phantom was scanned at the slice thickness of 2mm. A whole brain plan using 6MV beam was created with standard parallel opposed lateral fields. The isocenter was placed at the outer canthus to avoid divergence to orbital structures. The plan was normalized to the calculation point and with = 95% of brain volume covered by = 95% of prescription dose. The EBT2 films were carefully cut and labeled with same orientation in the film calibration and skin dose measurement. EBT2 film was calibrated in the reference condition with various dose (0–10Gy). After the phantom was positioned for treatment and correct setup was verified by kV‐kV imaging and CBCT, the films were placed at various sites and irradiated. An Epson flatbed color scanner was utilized and the scanner response from the red channel of the RGB image was used as the density value for the estimation of dose. The comparison was made between the measured dose and the planned dose for different head locations. Results:Our preliminary results indicated that the measured skin dose agrees with the planned dose within 10% for the sites centered in the treatment fields such as mid right/left sphenoid bones. For the sites outside or near the edge of the treatment fields, such as the right/left orbits and low chin, the measured dose is significantly different from the planned dose (>15%). Conclusions: Skin dose of whole brain irradiation could be measured by GAFCHROMIC EBT2 films. The difference between the measured dose and the planned dose varies significantly depending on the location of interest relative to the treatment field. Further investigation is needed.
SU‐E‐T‐289: On the Use of a Diode Array for the Commissioning of Dynamically‐Wedged Asymmetric Fields Generated by Varian EDW's in the Pinnacle Treatment Planning System
Authors: Ahmad M , Liu W , Deng J , Nguyen K , Wu D , Chen Z , Moran M , Nath R
Published: June 2012

Purpose: To present a validation study of enhanced dynamic wedges (EDWs) implemented into Pinnacle3 treatment planning system (TPS) using a diode array, Monte Carlo (MC) simulation, and measurements. Method and Materials: Modeling of EDW dose distribution in the Pinnacle3 TPS is based on a combination of open‐field beam data and the Varian ‘Golden Segmented Treatment Table’ (GSTT) unique to each photon beam. To validate the EDW models, dose profiles of 6‐ and 10‐MV photon beams from a Clinac 2100C/D were measured in virtual water at depths from near‐ surface to 30 cm for a wide range of asymmetric field sizes and wedge angles using the Profiler‐2 diode array system. The EDW output factors for asymmetric fields were measured in solid water using a small‐volume cylindrical ionization chamber placed at a depth of 10 cm on the central axis. In addition, absolute doses on central axis at depths of 5, 10, 15 and 20 cm were measured in virtual water using a small‐volume cylindrical chamber for comparison with the collapsed‐cone convolution (CCC) calculations. The 6‐ and 10‐MV photon beams emerging from the treatment head of the Clinac 2100C/D were fully simulated using the Monte Carlo code BEAMnrc and DOSXYZnrc. This code was used to calculate the central‐axis percentage depth doses and dose profiles for the open and dynamically‐wedged fields in a water phantom. Results:The off‐axis dose profiles of various EDWs computed with the CCC dose model and MC simulations agreed with measured EDW dose distributions to an accuracy of better than 2%/2 mm. Measured EDW output factors used for MU calculations in Pinnacle3 TPS agreed with MC predictions within 1–2%. Conclusions: The utility of Profiler‐2 diode array system to measure dose profiles for commissioning of EDWs into the Pinnacle3 TPS has been demonstrated to have acceptable accuracy for clinical implementation.
SU‐E‐T‐298: Evaluation of the CNAO Spot Scanning Technique Based on the First Clinical Deliveries
Authors: Hosseini MA , Donetti M , Garella MA , Giordanengo S , Lavagno M , Capasso L , Cirio R , Marchetto F , Peroni C , Sacchi R
Published: June 2012

Purpose: The first Italian hospital‐based facility for hadrontherapy is the Centro Nazionale di Adroterapia Oncologica (CNAO) which started the clinical activity on September 2011 with protons beams. The control of the treatment is performed online by the Dose Delivery (DD) system which guides the whole treatment by measuring beam characteristics as number of delivered particles and beam position. The author will present the comparison between the required and delivered quantities. Methods: The CNAO facility is based on a synchrotron designed to accelerate and deliver proton and carbon ion beams in the clinical ranges. Unlike most of the proton‐therapy centres, the delivery technique adopted at CNAO is the “quasi‐discrete” active scanning where dedicated magnets are used to drive a pencil beam through the target and the beam is normally not switched off during the transition between adjacent spots. These operations are performed by the DD system which, based on the treatment planning and the online analysis of dedicated beam monitor chambers, drives the scanning magnets. Spot by spot the DD records data which allow the comparison between the measured number of particles and position and the prescription. Results: The data collected by the dose delivery during the treatments were analyzed in detail, each treatment consisting in more than 30 identical fractions. This allows checking the stability and the accuracy of the CNAO delivery over identical spot sequences. The comparison between the measured number of particles, the measured position of each spot, and the corresponding prescribed quantities will be presented in detail. Critical points will be discussed together with the proposed improvement of the system. Conclusions: The results confirm the good performance of the CNAO beam delivery obtained during the commissioning phase.
SU‐E‐T‐300: Monte Carlo Simulation of Single‐Plane Magnetically Focused Narrow Proton Beams
Authors: McAuley G , Barnes S , Wroe A , Slater J
Published: June 2012

Purpose To investigate narrow, elongated magnetically focused proton beams and compare their properties with passively collimated beams using Monte Carlo simulation. Methods: We performed Geant4 Monte Carlo simulations involving a single quadrapole focusing magnet, thereby creating a flattened beam with an elongated elliptical cross section. The parameters of the magnet were chosen to mimic k=3 (quadrapole) Halbach cylinders that are available commercially as assemblies of rare earth permanent magnetic materials. For comparison, simulations were also performed with the same beam line components and passively collimated beams (using an elliptically shaped collimator). To facilitate fair comparison, efforts were made to closely match the planned treatment volumes (PTV) for each simulation case in dose, volume, and major and minor diameters of the elliptically shaped PTV at Bragg depth. Results: Magnetic focusing delivered significantly better dose localization to the target over collimated beams which are the current beam delivery modality. Compared to collimated beams, the magnetically focused beams showed a 31% smaller therapeutic ratio, a 31% smaller integrated dose, a 34% smaller entrance dose, a 30% larger peak‐to‐entrance central depth dose ratio, a 37% smaller penumbra volume, and were 35% more efficient in dose delivery (based on proton number). Conclusions: The clinically relevant advantages of the magnetically focused beams compared to the collimated beams (the current standard of care) can be attributed to the preferential directional acceleration of protons due to the magnetic field. Our simulations suggest such magnets can be used to deliver tissue sparing doses to normal and at‐risk tissue, and enhanced dose to elongated, narrow targets. Future work to characterize and test prototype magnets is in progress. Such beams my find application in novel proton treatments including application to the spinal cord.
SU‐E‐T‐305: Limitations of Using DICOM Data for BrachyVision Treatment Plan Evaluation
Authors: Sun B , Kavanaugh J , Yang D , Garcia‐Ramirez J , Mutic S , Grigsby P , Richardson S
Published: June 2012

Purpose: To evaluate the accuracy of a real‐time automated method of performing dosimetric quality assurance using Eclipse DICOM files for patients receiving HDR‐brachytherapy and IMRT. Methods: GYN patients are treated with concurrent high‐dose rate brachtherapy and IMRT. The dosimetric parameters were obtained through an in‐house QA program developed using Matlab. The DICOM files containing DVH data for organsat‐risk (OAR) were analyzed Dosimetric data for 7 patients (total 42 fractions) were collected for bladder, rectum and sigmoid. The accuracy of the dosimetric parameters was estimated by comparing the parameters obtained from the DICOM based QA program and those in BrachyVision. Results: The maximal dose values (Dmax) for the OARs obtained using the DICOM‐based program are significantly smaller than those valued reported in BrachyVision by 36.2%–48.3%. The mean dose has a deviation from 1% – 2.4%. The dose for the volume of 2cc (D2cc) has a difference up to 7.6% for structures with the volume larger than 200 cc. The average difference of D2cc is 0.5% for structures less than 200 cc. We found that Eclipse BrachyVision only exports DVH data down to a volume equivalent to 1% of the maximum volume for a given structure. Therefore, the reported maximal dose values obtained from DICOM RT dose file do not accurately reflect the maximum dose in a treatment plan. This will also slightly affect the mean dose calculation and D2cc when the structure volume is larger than 200cc. Conclusions: The automatic QA tool based on DICOM files provides a quick retrieval of dose to organs‐at‐risk and coverage of targets. However, maximal dose to structures is not accurate due to the truncationof the DVH information contained in DICOM files.
SU‐E‐T‐308: Dosimetry of a New Minimally Invasive Episcleral Brachytherapy Device
Authors: Hamilton R , Cetas T , Gordon J , Lutz W , Marsteller L
Published: June 2012

Purpose: Describe the dosimetry of an episcleral brachytherapy device. Methods: The SMD‐I device is designed to treat exudative age‐related macular degeneration (AMD) and employs a Sr‐90/Y‐90 source encapsulated in a stainless steel cylinder. The source is welded to a flexible wire allowing it to travel from a shielded vault in the SMD‐I handle to the distal end of a curved cannula to deliver a therapeutic dose of radiation through the sclera to the neovascular target in the subchoroidal space. The SMD‐I handle and vault are comprised of Ultem, a lightweight radiation tolerant plastic, which shields the surgeon. Dose calculations were performed using the MCNPX radiation transport code. The absolute dose rate was determined using radiochromic film (GAFChromatic© MD‐55) at a point in solid water 2.0mm from the source center perpendicular to the cannula. Dose rates at several depths were measured using Kodak EDR2 film in water equivalent phantoms to compare with the absolute dose rate measurement and MCNPX calculations. The surgeon's hand dose received while manipulating the device with the source in the vault was measured using standard TL (thermoluminescence) finger ring dosimeters, TL ChipstratesTM, and calculated with MCNPX. Results: The absolute dose rate 2.0mm from the source center is 0.45 Gy/min/mCi. The EDR2 film results agree with the absolute dose measurement and the MCNPX calculations. The dose rate decreases rapidly with depth so that the dose at the target depth (3mm) is approximately 8 times less than at 1mm depth (sclera). The dose distribution is sensitive to the angle between the cannula and the neovascular plane. Both TL methods yield a maximum dose rate of 6 μSv/min mCi to the surgeon's fingers consistent with the MCNPX calculation. Conclusions: The SMD‐I device permits accurate delivery of a therapeutic radiation dose for the treatment of exudative AMD. Russell J. Hamilton is a founder and currently serves on the Scientific Advisory Board of Salutaris Medical Devices, Inc. Wendell Lutz and Thomas Cetas serve on the Scientific Advisory Board of Salutaris Medical Devices, Inc. All authors have received financial support from Salutaris Medical Devices, Inc.
SU‐E‐T‐317: Dynamic Modulated Brachytherapy (DMBT): Robotic Applicator Design
Authors: Han Dae Yup , Webster Matthew J. , Devic Slobodan , Vuong Te , Scanderbeg Dan , Song William Y.
Published: June 2012

Purpose: To investigate the hardware necessary for implementing our Dynamic Modulated Brachytherapy (DMBT) treatment concept for rectal cancer. Methods: The DMBT robot has three major parts: 1) shield and shield delivery module, 2) controlling module, and 3) DMBT controlling and monitoring software. The shield is a tungsten alloy cylinder (r=0.95cm, l=4.5cm) with a 5.5mm rectangular‐shaped opening. The shield is controlled by an aluminum pipe with gear set (1:3) and linear actuator (2mm/turn). An Ir‐192 radiation source will be placed through the aluminum pipe. The power source is a Nema‐17 stepping motor with EvoDrive ST‐17 (EVA Robotics, Queensland, Australia) and USB‐6009 DAQ (National Instrument, Austin, TX). With our in‐house operating program through LabView (National Instrument, Austin, TX), we can make and load plans for treatment as well as testing. Checking the shield position is also possible through the operating program. For safety, a lexan sheath tube and emergency buttons are built‐in. Results: The DMBT robot has 2 degrees of freedom, which are linear translation and rotation. With our power delivery system, the spatial resolutions are 0.0125mm (linear stage) and 0.012Ëš (rotation). In 0.5s, motors achieve the desired position with the maximum speeds 450 step/s (1Ëš), 7,500 step/s (30Ëš), and 12,000 step/s (5mm). Four registers are triggered with USB‐6009 DAQ signals. The operating program includes gages for checking shield position, loading treatment plans, and safety buttons. Conclusions: In all, we have designed the hardware components of the DMBT system for rectal cancer. For treatment, the system needs more elements to support the DMBT robot; lexan sheath tube holder, DMBT robot security joint, and a system for reducing friction between the tube and shield. We will also refine our system to be more compact by using DC servomotors instead of the larger Nema‐17 stepping motors.
SU‐E‐T‐318: Source Position Localization for ICBT Tandem & Ovoid Applicators Utilizing Oncentra Brachy Applicator Modeling
Authors: Kemp J , Price M
Published: June 2012

Purpose: Nucletron's Oncentra Brachy Applicator Modeling plugin (AMp) may facilitate HDR cervical brachytherapy treatment planning when image artifact inhibits dwell position localization. The AMp utilizes a 3D CAD rendering of the corresponding applicator to define possible source dwell positions. This study compares the equivalence of source localization within a CT/MR Fletcher‐type tandem and ovoid applicator utilizing clinical practice and Oncentra's AMp in a water phantom containing OAR surrogate structures. Methods: KVCT image sets were acquired of a water phantom containing bladder and rectum surrogates as well as an assembled Nucletron Fletcher CT/MR applicator with various ovoid sizes (20, 25, 30mm) and a 30° tandem. Using Oncentra's Brachy TPS, OAR‐surrogates were segmented and catheters were reconstructed using (1) clinical protocols (i.e. using source dwell position markers) and (2) using the AMp. Treatment plans were generated following clinical protocol, ensuring 600cGy to the ICRU 38‐defined Point A. The center coordinates of each active dwell position were spatially compared. The dosimetric impact of these differences was quantified by determining D0. 1cc, D1cc and D2cc for the surrogate OARs. Results: Preliminary results obtained for the 25mm ovoid / 30° tandem applicator show 80% of dwell positions defined by clinical protocol and the AMp agree within 1mm with a maximum deviation of 1.17mm. Differences in source positions resulted in an increase of 2.9%, 0.48% and 0.3% and 0.66%, 0.87%, and 0.59% for D0.1cc, D1cc and D2cc for the bladder‐ and rectum‐surrogates, respectively, when utilizing the AMp rather than clinical protocol for source position localization. Conclusions: Preliminary results indicate that source dwell position localization utilizing Nucletron's Applicator Modeling plugin and our clinical protocol results in equivalent dosimetry for the simple, water phantom geometry investigated. Currently we are investigating the validity of this conclusion utilizing ovoids of different sizes as well as a CT/MR‐compatible vaginal cylinder.
SU‐E‐T‐319: Monte Carlo Characterization of a New Directional Pd‐103 High Dose Rate Source for Brachytherapy Application
Authors: Heredia A , Robinson A , Henderson D , Thomadsen B
Published: June 2012

Purpose: Standard brachytherapy sources emit radiation in a non‐preferential direction away from the source. Though treatment outcomes are good, this can lead to late skin and subcutaneous toxicities in sensitive structures. Proposed low dose rate directional sources for interstitial brachytherapy, showed to have an improvement in the dose uniformity within the subcutaneous volume, reduction in skin dose, and reduction in volume receiving dose outside the target. The objective of this work is to demonstrate the potential use of a new Pd‐103 directional seed for application in high dose rate brachytherapy treatments. Methods: Monte Carlo simulations were performed using the MCNP5 F6 energy deposition tallies as well as the MCNP5 F4 flux density tallies placed around a partially shielded Pd‐103 source at angles(deg): 0, 45, 90, 135, 180, 225, 270, 315 as well as radial distances (cm): 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10. The source that modeled was a Pd‐103 core using TG‐43U recommended nuclear data, with a diameter = 1.4 mm, active length = 1.0 cm. In addition osmium metal with .03 mm thickness was used as shielding material to cover half of the cylindrical surface of the Pd‐103 volume. The seed was encapsulated using .05 mm thick titanium. Results: MCNP models show that the dose to the radial distances, corresponding to the osmium shielded side, are dramatically reduced to less than 4% of the total dose. Conclusions: The potential of a Pd‐103 directional brachytherapy source has been studied. The results show that a seed with a partially shielded volume can be exploited to reduce side effects associated with radiation therapy to sensitive structures surrounding target volumes.
SU‐E‐T‐320: A New Verification Phantom for GYN Brachytherapy Applicators Using GafChromic ‐ Films
Authors: Gholami S , Meigooni AS , Mahdavi SR Mehdi , Mirzaei H
Published: June 2012

Purpose: Brachytherapy plays an important role in radiation therapy a wide range of tumor sits such as vaginal, cervical and endometrial cancers. The purpose of this project was to design, fabricate and verify a new phantom for dosimetric verification at small distances from GYN applicators used with GZP6 cobalt‐60 HDR system. Methods: A new phantom has been designed and fabricated from 90 slabs of 18×16×0.2 cm3 Perspex to accommodate one tandem and two ovoids. The thin layer of the slabs was chosen to place GafChromic films in between the slabs for dosimetry with GZP6 cobalt‐60 HDR system. For verification of this device, an assembly composed of a large ovoid size (3cm diameter) and tandem #1 with the least curvature was selected in this study. With this assembly, GafChromic films were exposed using a plan with 500 cGy dose delivery to point “A”. The irradiated films were scanned. The responses of the films were converted to dose by calibrating samples of these films using a cobalt‐60 teletherapy system in the range of 25 to 800 cGy dose. The measured isodose curves with the films were compared to calculated isodose lines by the treatment planning software. Results: The Result of these investigations indicated differences of up to ± 23 % between the planning and measured dosimetry at different points in GYN implant with cobalt‐60 HDR source of GZP6 system. Therefore, this phantom enabled us to confirm the accuracy of radiation delivery to the GYN patients with cobalt‐60 HDR source of GZP6 system. Conclusions: The new phantom design could be utilized for the QA procedure of the GZP6 cobalt‐60 HDR system as well as the Ir‐192 HDR system to confirmation the accuracy of dose distribution in GYN implants, especially in non‐traditional implants. The Radiotherapy Department of Shahid Beheshti University at Shohada hospital sponsored the purchase of the phantom materials and films used in the investigations.
SU‐E‐T‐321: Dynamic Modulated Brachytherapy
Authors: Webster MJ , Devic S , Vuong T , Scanderbeg D , Song WY
Published: June 2012

Purpose: We introduced the concept of Dynamic Modulated Brachytherapy (DMBT) for rectal cancer, last year. To continue our work, we studied different shield designs and investigated the system's tolerance against systematic setup errors. Methods: As previously presented, our system uses a cylindrical tungsten shield to create a directional radiation profile, which is modulated through translation and rotation using a specialized robotic arm. We used Monte Carlo simulations and an in‐house gradient projection optimization algorithm to look at key design parameters. First, we used ideal phantoms to study treatment quality from shield radii ranging 0.5–1.5 cm in 0.25 cm increments. Second, using 36 patient plans, the dependence on radial source position within the shield was studied. We also analyzed the tolerance of the system to systematic setup errors by simulating dose distributions from possible inaccuracies. These included translational and rotational errors as well as possible Ir‐192 source misplacements by the afterloading system. Results: Changes in shield radius followed steady patterns. Increasing the radius showed a consistent increase in dose conformality to the tumor volume and better sparing to surrounding tissues. However, there was also a linear increase in total dwell time. There was a trade off to changing the radial position of the source. As the source is brought away from the center, there is a decrease in conformality to the tumor volume, but sparing to healthy tissues was increased and there is a decrease in total dwell time. We found that any potential setup errors for our system, within anticipated margins, had negligible effects on the dose distributions (< 3% deviation). Conclusion: Various parameters for shield designs must be balanced for an effective DMBT application. It was found that the system is highly robust against systematic setup uncertainties.
SU‐E‐T‐325: Clinical Implementation Experiences of Low KV Intraoperative Radiation Therapy (IORT) Intrabeam System for Low Risk Breast Cancer Patients
Authors: Pokhre D , David J , Small W , Hayes J , Strauss J , Bethke K , Sathiaseelan V
Published: June 2012

Purpose: Clinical implementation of the IORT (Intrabeam X‐ray) system for low risk breast cancer patients in terms of quality assurance, reproducibility, treatment time, and operating room ambient radiation exposures. Methods and materials: We have clinically implemented a new treatment system (Intrabeam) for early stage low risk breast cancer patients using 50kV X‐rays. Pretreatment QA is performed in four major steps: probe straightening, dynamic offsets check, photo‐diode‐array check, and X‐ray output check. Treatment time is verified by dose‐rate measurement. An intraoperative ultrasound is performed to determine distance of the applicator surface to the skin. Ambient radiation levels were measured at different locations in the OR during treatment. Results: We have treated in excess of 35 patients in the past 11 months, using spherical applicators from 3 to 5 cm in diameter, with a boost dose of 20Gy in a single fraction. The mean probe straightening, dynamic offset, and photo‐diode‐array source checks were within tolerances of 0.1mm, 0.7mm and ±1.5%, respectively. Pretreatment daily X‐ray output checks agreed within to ±2.0% of baseline values and calculated treatment times within ±1% of given values. Radiation surveys of the OR during IORT showed that when ∼1mm of soft lead sheet covered the breast under treatment, exposures to the Physicist and Anesthesiologist were =2mR/hr. Summary and Discussion: With the IORT Intrabeam system, it is feasible to deliver a single high dose fraction to the breast immediately following tumor resection in the OR, providing the patient a convenient, waiting time free treatment, with no geographic miss. The nearly 1/r3 dose fall off minimizes dose to the distal breast and healthy tissues, with relatively fewer side effects compared to EBRT. Daily QA showed very small output variations. Radiation exposure in the OR was reduced nearly 12 folds when using a thin lead shield on the patient.
SU‐E‐T‐329: Measurement of I‐125 Brachytherapy Dose in Lung
Authors: Gayou O , Kim Y , Johnson M , Colonias A , Werts ED
Published: June 2012

Purpose: Sublobar resection and intraoperative placement of I‐125 seeds along the staple line is an accepted treatment for patients with high risk stage I non‐small cell lung cancer. The dosimetry standard for such an implant is to follow the TG43U1 protocol, which assigns water as the universal medium for dose calculation. This may not be appropriate for lung tissue. The purpose of this study is to characterize the dose distribution in lung relative to water using radiochromic film. Methods: Seven Amersham 6711 I‐125 seeds were sandwiched between slabs of Solid Water® on one side and lung‐equivalent material on the other side. A sheet of Gafchromic EBT2 film was inserted parallel to the sources axes at the depth of measurement in the water and the lung simultaneously. Separate measurements were performed for three depths of 0.5, 1.0 and 1.5 cm. The seeds were far enough apart from each other so as not to influence the measurement from the neighboring seeds. The exposures lasted 2 hours, 5.5 hours and 15 hours for 0.5 cm, 1.0 cm and 1.5 cm, respectively. The total dose in water for these exposure times was 52 cGy, 35 cGy and 39 cGy, respectively. The ratios of lung over Solid Water® doses were averaged over the 7 seeds. Results: The lung to Solid Water® dose ratio was 1.071±0.062, 1.205±0.090 and 1.259±0.053 for the depths of 0.5, 1.0 and 1.5 cm, respectively. Conclusions: The dose in lung is quite similar to the dose in water at the depth of 0.5 cm, which is the prescription depth for a typical lung low dose rate brachytherapy implant. However, the attenuation in lung is smaller than in water, leading to an underestimation of lung dose at 1.5 cm by approximately 25% when TG43 parameters are used.
SU‐E‐T‐335: Fetal Dose Estimates for Radiotherapy Using IMRT and VMAT
Authors: Bannon E , Lo Y , Urie M
Published: June 2012

Purpose: 4000 pregnant women are irradiated every year. Research has reported the dose to the fetus for static fields, but not for dynamic fields. Dose to the fetus was measured for a series of sites for IMRT and VMAT. Methods: It was assumed that a woman would be treated during the first and second trimester only. A RANDO® phantom was used as is to simulate the first trimester. A prosthetic abdomen was attached to simulate the second trimester. Kodak PPL‐2® film was placed in an axial plane of RANDO®, representing the uterine fundus, moving superiorly for the second trimester. A full course, i.e., typical prescription dose, was delivered for each site. IMRT was planned for esophagus, left breast, head & neck and right upper lung/mediastinum. VMAT was planned for esophagus, left upper lung SRT and brain. OmniPro‐I'mRT® was used to scan and analyze the films. A calibration curve was created with a film of known dose deposition. Results: Dose to the fundus ranged from 0.01%–0.10% of the prescription dose (0.6cGy–4.6cGy) in the first trimester and 0.3%–0.16% (1.2cGy–8.8cGy) in the second trimester. Treatment of the breast and lung (IMRT) resulted in the highest absolute dose as well as the highest percentage of total dose in both trimesters. Absolute dose and percent of total dose delivered was greater in the second trimester. Conclusions: Fetal dose with IMRT and VMAT as a percentage of total dose is similar to previously reported results for static fields. TG‐36 suggests that reducing the dose to the fetus to a value below 5cGy substantially reduces the risks associated with irradiating a fetus. In most of the treatment sites, the dose to the fetus fell below this value. In terms of fetal dose, there appears to be no significant detriment to using either IMRT or VMAT.
SU‐E‐T‐343: Respiratory‐Gated Volumetric Modulated Arc Therapy for Lung SBRT with an Elekta Digital Accelerator: A Pre‐Clinical Evaluation
Authors: Cui Guoqiang , Housley David , Chen Fan , Mehta Vivek , Shepard David
Published: June 2012

Purpose: To evaluate the machine‐delivery capabilities and dosimetric accuracy of respiratory‐gated VMAT delivered with an Elekta digital accelerator. Method and Materials: Three lung patients previously treated with SBRT using un‐gated 6 MV VMAT were used for this evaluation. The treatment plans were created in Monaco treatment planning system (ver. 3.0). For each case, one un‐gated and two gated deliveries were delivered to a static ion‐chamber‐array phantom. Surface motion was used as a surrogate for breathing motion and was simulated using a moving chest plate driven by a motor with a constant amplitude range of +/− 3 mm and a period of 4 seconds using a cos6ωt waveform. Two gating windows (GWs), 77% and 66% around the end of exhalation were used for the gated deliveries. An ion chamber array was used and comparisons were made between the measured and the planned coronal dose distributions. The dosimetric accuracy of gated VMAT plans was determined using gamma‐index analyses (3 mm/3% passing rate criteria). Results: There were insignificant differences between the two gated deliveries and the un‐gated delivery. For the planar dose comparisons between the measured and the planned, the gamma passing rates were all higher than 99.0%. For the two gated deliveries, the true duty cycles were calculated as 57% and 39%, as against the corresponding GWs 77% and 66%. This was mainly due to the beam‐on latencies, which were estimated as 0.25 second and 0.40 second for GWs 77% and 66%, respectively. Conclusions: Respiratory‐gated VMAT was demonstrated for the first time using an Elekta digital accelerator with a pre‐clinical gating interface provided by Elekta and a novel surface imaging system as a respiratory input. High dosimetric accuracy was demonstrated in three SBRT lung cases for as many as 213 beam interruptions during a single 360°‐arc delivery. This work is sponsored by a research grant from Elekta AB.
SU‐E‐T‐347: Evaluation of DQA Results Using a Super‐Sampling Dose Calculation in Helical Tomotherapy
Authors: Rupolo R , Wang S , Xu Z , Deschesne K , Chang S , Lian J
Published: June 2012

Purpose: The aim of this work is to evaluate the impact of a new supersampling dose calculation method on delivery quality assurance (DQA) results for helical tomotherapy patient plans. Methods: Accuray's Tomotherapy treatment planning system performs its dose calculation by approximating the continuous beam of a full gantry rotation into 51 discrete beam projections, with one dose calculation per projection (TomoHD version 1.0). In a recent software release, TomoHD version 1.1, Accuray enhanced this technique by employing three dose calculation samples per projection. This ‘super‐sampling’ methodology is meant to improve agreement between measured and calculated dose. For this study, we compare the results of the 24 patient DQA plans calculated in our clinic with the newer version of dose calculation with the previous 24 patient plans which were calculated with the older method. The plans were delivered to a SunNuclear ArcCHECK cylindrical detector array, and data were compared using a γ evaluation, with criteria of 3%/3mm. To quantify the results, the percentage of points with γ<l (Pγ<l) was calculated within the 10% isodose line for each plan. We used a pass/fail criteria of (Pγ 95%. Results: 21 of 24 DQA plans (87%) calculated with the older TomoHD 1.0 algorithm passed our (Pγ 95% criteria, while all 24 DQA Plans (100%) generated with the TomoHD 1.1 super‐sampling dose calculation passed. The average values for (Pγ<l) was 97.9% and 98.9% for the original and super‐sampling calculation, respectively. The standard deviation for the older software was 2.1, versus 1.5 for the newer super‐sampling method. Conclusions: The increased number of samples per projection angle employed in the new TomoHD Version 1.1 software leads to a reduction in the dose discrepancies seen in patient DQA plan results. This can improve the agreement between the calculated dose and delivered dose to patients.
SU‐E‐T‐349: Variation in VMAT QA Pass Rate Caused by Detector Setup Errors
Authors: Liu T , Rajaguru P , Dieck G , Edwards J , He R , Huang Z , Vijayakumar S , Yang C
Published: June 2012

Purpose: To test the sensitivity of pass rates of Gamma Index to the detector setup errors in six degrees of freedom. Methods: VMAT (Volumetric Modulated Arc Therapy) treatment technique is used in our clinic on an Elekta Beam Modulator with a HexaPOD couch. The HexaPOD system is a robotic patient positioning platform with six degrees of freedom. ScandiDos Delta4 system is used for our VMAT patient QAs. Delta4 is a pseudo 3D diode detector array which is capable of calculating 3D Gamma Index. Seven prostate and four H&N VMAT treatment plans were delivered. The measurements were compared with the Pinnacle TPS calculations and the pass rates of Gamma Index were calculated. Then the HexPod couch was shifted or rotated either by 1 mm or 1 degree in any of the six degrees of freedom to simulate the setup errors, and the pass rates were re‐measured and re‐calculated. The criterion used for Gamma Index calculation was 3% and 3mm. A detector point is considered pass if the calculated Gamma Index is smaller than 1. Pass rates of Gamma Index with different detector setup errors in the six degrees of freedom were compared. Results: Regarding the rotational setup error of different directions, the changes of pass rates of Gamma Index are significantly different (p < 0.001). While one degree change in Roll angle causes the least change of the pass rates of Gamma Index, one degree change in Pitch angle causes the biggest change. Regarding the translational setup error of different directions, the changes of pass rates of Gamma Index are insignificant (p > 0.1). Conclusions: Although 1 mm or 1 degree machine‐type tolerance was recommended by AAPM TG reports, they don't translate to the same amount of changes in pass rates of Gamma Index for VMAT QA.
SU‐E‐T‐352: Commissioning and Quality Assurance of the First Commercial Hybrid MRI‐IMRT System
Authors: Green O Pechenaya , Goddu S , Mutic S
Published: June 2012

Purpose: To describe the commissioning process for the first installed commercial MRI‐guided IMRT system (ViewRay, Village of Oakwood, OH) and outline quality assurance methods for this novel treatment modality. Methods: The ViewRay™ System (510(k) pending) consists of a 0.35‐T double‐doughnut MRI coupled with a gantry that houses three Co‐60 sources,each with an activity up to 15,000 Ci (120° apart). IMRT delivery is enabled by doubly‐focused MLCs that serve as the only beam‐shaping collimators for each head, allowing a maximum field size of 27.3 cm2 at the 105‐cm isocenter. MRI imaging is used prior to and during delivery for setup evaluation, adaptive radiotherapy, and gating. The challenges in commissioning as well as periodic and patient‐specific QA arise due to the presence of the magnetic field, unique geometry of this device which is not compatible with many of conventional RT QA devices and techniques, and the penumbra of a 2‐cm wide Co‐60 source. The following devices were used for commissioning and quality assurance tests: radiochromic and radiographic film, ionization chambers (Exradin A12 & A16), Sun Nuclear's IC Profiler (Melbourne, FL), and a water tank. Tests were conducted to evaluate the beam profiles, penumbra, and PDDs. Also, tests to check MLC accuracy and reproducibility were evaluated. Results: Tests were developed to validate geometric performance of the device including a comprehensive set of MLC tests. Due to the low strength of the magnetic field, the mean free path of electrons in the ionization chamber volume is too long to have a noticeable curvature; therefore the magnetic field is not expected to have a noticeable effect on dose measurement. Conclusions: While the presence of the magnetic field limited the choice of QA devices, it was found that satisfactory methods for MRI‐IMRT machine QA exist and can be successfully employed. Drs. Green, Goddu, and Mutic served as scientific consultants for ViewRay, Inc. Dr. Mutic is on the clinical focus group for ViewRay, Inc., and his spouse holds shares in ViewRay, Inc.
SU‐E‐T‐358: Penumbral Dose with Limited Scatter in Photon Beams with and Without Flattening Filter
Authors: Srivastava S , Akino Y , Cheng C , Das I
Published: June 2012

Purpose: Dose outside the active radiation beam plays an important role in estimation of critical organs complications and also an important contributing factor in IMRT plan optimization. In this study, we investigated the effect of scattering material and characteristics of penumbral dose between conventional accelerator and machine with flattening free filter (FFF). Methods: A Varian True Beam was used that has FFF option for low energy beam. Penumbral dose was measured in a water phantom for all energies (6, 10, and 15 MV) with and without the flattening filter. Beam profiles were collected using a 0.125 cm3 ion chamber at various depths, from dmax‐15cm for a set of field sizes. To study the effect of limited scatter in the penumbra, the water tank was shifted to reduce the scattering distance from the tank and field edge systematically from 5–20 cm including tank wall. The measured data were also compared with the Eclipse treatment planning data. Results: For all beams with the flattening filter, penumbral dose vary from 5% to 12% from 5 cm to 15 cm depth. The variation is larger for lower energies and is a linear function of depth for all energies. It increases with depth linearly and decreases with beam energy. For FFF beam the slope is greater than that of a regular beam. The penumbral dose varies by <1% with scattering condition. For the same depth, the penumbra is significantly larger for FFF. There is significant difference between TPS FFF data compared to the measured values. Conclusion: Penumbral dose is dependent on scattering distance, depth, beam energy and flattening filter. FFF provides relatively higher dose which is not properly modeled in treatment planning system. For high degree of precision, data should be collected with large scattering condition and beam modeling for FFF should be adequately performed.
SU‐E‐T‐361: Evaluation of a New Commercially Device for Patient Specific IMRT QA
Authors: Stathakis S , Myers P , Esquivel C , Gutierrez A , Mavroidis P , Papanikolaou N
Published: June 2012

Purpose: To evaluate the performance of a new system for patient specific IMRT QA. Methods: The new Octavius 4D system and its accompanying software (Verisoft) by PTW were used to compare calculated and measured dose distributions for ten (n=10) patients' plans. Five IMRT and five SmartArc plans were used for the comparison. All plans were optimized using the Pinnacle treatment planning system and the plans and their respective verification plans were calculated using collapsed cone convolution superposition dose calculation algorithm. The verification plans were evaluated using the gamma index and also by visually inspecting the dose profiles and isodose distributions. The Verisoft IMRT QA is able to reconstruct the 3D dose from individual planar measurements and hence provide comparison for transverse, sagittal, and coronal planes. Results: The gamma index values varied from 92.1 to 99.2% when the coronal plan was only evaluated. Because of the ability of the system to compose thedose distribution from the individual measurements, comparison of the sagittal, transverse planes as well as 3d dose distributions were available. The gamma index values varied from 88.3 to 99.5% for different planes while the 3D gamma index values ranged from 85.0 to 99.5%. Conclusions: The new phantom for patient specific IMRT QA in this study can effectively be used for clinical use. The ability of the software to compute 3D dose distribution from all measurements taken is powerful tool that aids the physicist to evaluate the verification plan by providing 3D information not available from other commercial systems. Further investigation of the system's dose reconstruction algorithm is necessary to determine its accuracy. This work was partially funded with an educational grant from PTW.
SU‐E‐T‐363: Sensitivity of ArcCheck to Delivery Errors in IMRT/VMAT Treatment
Authors: Yang W , Wallace R , Huang K , Cook R , Fraass B
Published: June 2012

Purpose: There is an increasing trend to perform IMRT QA measurements using ion chamber or diode arrays in place of film. This change has improved QA efficiency but raises questions about the system's sensitivity to machine mechanical accuracies due to their coarse resolution. This work uses intentional set up and mechanical errors to test the sensitivity of a cylindrical IMRT QA detector array to operator and machine errors. Methods: A cylindrical phantom (Sun Nuclear ArcCheck) with a 3D array of 1385 diodes, arranged in a spiral pattern with 10 mm detector spacing, was studied. Translational, rotational (via collimator rotation) and multi‐leaf collimator positioning errors were deliberately induced and applied. Translational shifts of 2–10 mm were applied on a VMAT plan. Collimator rotations up to 5o were applied to a 10 cm open anterior‐posterior field. 1–3mm systemic shifts were applied to all MLC leaves in the same bank in an IMRT plan. Gamma analysis of varying thresholds was used to analyze the results. Results: ArcCheck is sensitive to <1 mm translational shifts in all major axes, resulting in a 20% to 60% drop in passing rates for 2% tolerance, with much higher sensitivity to longitudinal shifts. Collimator rotation of 1o is detectable in the static 10 cm open field test. The systemic MLC positioning errors could be detected in gamma tests with tolerances ranging from 1%/1mm to 3%/3mm. Conclusions: Despite the 1 cm detector spacing, ArcCheck is sensitive to small set‐up and systematic MLC shifts on the order of 1 mm. It is also sensitive to small (1 degree) rotational errors in the setup field. The spiral placement geometry and large number of the detectors statistically helps compensate for the relatively coarse resolution of the detectors. The study shows that it is possible to tighten the criteria in IMRT/VMAT patient QA.
SU‐E‐T‐365: IMRT Monte Carlo Dose Calculations for a Novalis TX LINAC Equipped with HD‐120 MLC
Authors: Quino L Vazquez , Stathakis S , Gutierrez A , Esquivel C , Papanikolaou N
Published: June 2012

Purpose: To investigate the accuracy of a Monte Carlo dose calculation engine for IMRT using a Novalis Tx LINAC with the HD‐120 MLC. Methods: PDD and beam profiles ranging from 1×1 to 20×20 cm2 were calculated and compared against measured data in water to commission the LINAC built on the BEAMNRC platform. An in‐house, MATLAB‐based software was used to extract the parameters needed for the MC simulation from the DICOM‐RT plan and create input files for the MCSim egs4 Monte Carlo code. MCSim egs4 software was used to simulate the IMRT treatment plans in a cylindrical solid‐water phantom and ultimately used to compute the dose. In‐house software using a MATLAB platform was utilized to convert the 3D dose file obtained from the Monte Carlo simulation to a universal file which can be read on the RIT Software platform. Within RIT, the MC and treatment planning system (TPS) dose calculations could be compared. Results: 5 IMRT plan simulations were performed and good agreement results were achieved for TPS and MC dose comparison. Gamma analysis with a 3% dose and 3 mm DTA criteria shows a mean gamma index value of 92% for the cases studied. Conclusions: Based on our preliminary results, the Monte Carlo based Novalis Tx linear accelerator and the MCSim simulations of the IMRT treatments on a cylindrical phantom demonstrate good accuracy with regards to the treatment planning dose calculation.
SU‐E‐T‐370: A Dynamic 3‐D Dosimetry Phantom for Commissioning and QA of Gated RapidArc Radiotherapy Treatment
Authors: Cheung K , Lam W , Geng H , Leung T , Wu P , Yu S
Published: June 2012

Purpose: To develop a dynamic dosimetry phantom suitable for commissioning and QA of gated RapidArc radiotherapy of moving targets. Methods: A high precision dynamic dosimetry phantom was developed for commissioning and dosimetric verification of gated RapidArc radiotherapy treatments. The phantom consisted of two main parts (a) a high precision 3‐D dosimetry phantom and (b) a two‐dimensional motion driving mechanism. The 3‐D dosimetry phantom, which was made of acrylic, consisted of a cylindrical main body with a several replaceable inserts to facilitate point dose measurement using an ionization chamber and dose distribution measurement in the sagittal and coronal planes using radiochromic films. The dosimetry inserts could be replaced by a geometry verification insert which had a 3mm stainless steel ball located (within 0.05mm) at the effective measurement point of the ion chamber or the centre of the radiochromic films. The 2‐D motion of the dosimetry phantom was achieved by means of a driving mechanism that utilized three sets of stepping motor‐actuators, i.e. one for generating motion in the superior‐posterior axis and two for producing the anterior‐posterior motion. The pattern, frequency and amplitude of the 2‐D motion could be programmed through a motion controller to simulate different breathing patterns of patients. The phantom was tested for positioning reproducibility before being used to commission the gated RapidArc treatment of a Varian TrueBeam linear accelerator. Results: The phantom motion had a positioning reproducibility of better than 1 mm. It was successfully used for verification of gated RapidArc treatment of a moving C‐shaped target. The dose and dose distribution as measured in different treatment fractions given in different days withdifferent target motion patterns were highly consistent and reproducible. Conclusions: The dynamic 3‐D dosimetry phantom developed is useful for commissioning and regular QA of gated RapidArc treatment of moving targets.