bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐F‐T‐22: Clinical Implications When Using TG‐186 (ACE) Heterogeneity Software
Authors: Likhacheva A , Grade E , Sadeghi A , Sokolowski T
Published: July 2016

Purpose:

The purpose of this study is to compare dosimetric calculations using traditional TG‐43 formalism and Oncentra Brachy Advanced Collapsed cone Engine (ACE) TG‐186 calculation algorithm in clinical setting.

Methods:

We analyzed dosimetry of four patients treated with accelerated partial breast irradiation using a multi‐channel intracavitary device (SAVI). All patients were treated to 34 Gy in 10 fractions using a high‐dose‐rate (192) Ir source. The plans were designed and treated using the TG‐43 model. ACE was used to assess the effect heterogeneity correction on various dosimetric parameters. Mass density was estimated using Hounsfield units.

Results:

Compared to TG‐43 formalism, ACE estimated lower doses to targets and organs at risk. The mean difference was 19.8% (range 15.3–24.1%) for PTV_eval V200, 12.0% (range 9.7–17.7%) for PTV_eval V150, 4.3% (range 3.3–6.5%) for PTV_eval D95, 3.3% (range 1.4–5.4%) for PTV_eval D90, 5.4% (range 2.9–9.9%) for maximum rib dose, and 5.7% (2.4–7.4%) for maximum skin dose. There was no correlation between the magnitude of the difference and the PTV_eval volume, air volume, or tissue‐applicator conformance.

Conclusion:

Based on our preliminary study, the TG‐43 algorithm appears to overestimate the dose to targets and organs at risk when compared to the ACE TG‐186 software. We hypothesize that air adjacent to the SAVI struts contributes to lack of scatter thereby contributing a significant difference in dose calculation when using ACE. We believe that ACE calculation provides a more realistic isodose distribution than TG‐43. We plan to further investigate the impact of heterogeneity correction on brachytherapy planning for a wide variety of clinical scenarios, include skin, cervix/uterus, prostate, and lung
SU‐F‐T‐29: The Important of Each Fraction Image‐Guided Planning for Postoperative HDR‐Brachytherapy in Endometrial Carcinoma
Authors: Piriyasang D , Pattaranutaporn P , Manokhoon K
Published: July 2016

Purpose:

Cylindrical applicators are often used for postoperative HDRbrachytherapy in endometrial carcinoma. It has been considered that dosimetric variation between fractions for this treatment is minimal and might not be necessary to perform treatment planning for every fractions. At our institute, it is traditional to perform treatment planning with CT simulation on the first fraction and uses this plan for the rest of treatment. This study was aim to evaluate the errors of critical structure doses between the fractions when simulation and planning were done for first fraction only.

Methods:

Treatment plans of 10 endometrial carcinoma patients who received postoperative HDR‐brachytherapy and underwent CT‐simulation for every HDR‐fractions at our department were retrospectively reviewed. All of these patients were treated with cylindrical applicator and prescribed dose 15Gy in 3 fractions to 0.5cm from vaginal surface. The treatment plan from the first fraction was used to simulate in second and third CT‐simulation. Radiation dose for critical structures in term of Dose‐to‐2cc (D2cc) were evaluated and compared between planning CT.

Results:

The D2cc for bladder and rectum were evaluated. For bladder, the mean error of D2cc estimation for second and third fractions was 7.6% (0.1–20.1%, SD=5.7). And the mean error for D2cc of rectum was 8.5% (0.1–29.4%, SD=8.5).

Conclusion:

The critical structure doses could be significant difference between fractions which may affects treatment outcomes or toxicities. From our data, image‐guided brachytherapy at least with CT‐Simulation should be done for every treatment fractions.
SU‐F‐T‐39: Comparing Nomograms for Ordering of Palladium‐103 Seeds for Dynamic Intraoperative Prostate Seed Implantation
Authors: Taylor P , Wang L , Riegel A
Published: July 2016

Purpose:

Several nomograms exist for the purpose of ordering palladium‐ 103 seeds for permanent prostate seed implants. Excess seeds pose additional radiation safety risks and increase the cost of care. This study compared three seed ordering nomograms with seed counts from dynamic intra‐operative PSI to determine (1) the cause of excess seeds and (2) the optimal nomogram for our institution.

Methods:

Pre‐operative and intra‐operative clinical data were collected for 100 Gy (n=151) and 125 Gy (n=224) prostate seed implants. The number of implanted seeds which would have given D90=100% was normalized to that criteria and seed strength of 2U. This was plotted against intra‐operative prostate volume and compared to two previously published nomograms and an in‐house nomogram. A linear fit was produced and confidence intervals were calculated. The causes of excess seeds were assessed by comparing pre‐ and intra‐operative prostate volumes, variability of D90 around 100%, and variance of seed strength from 2U.

Results:

Of the 375 total cases, 97.6% had excess seeds. On average, 27.17±12.91% of ordered seeds were wasted. Of this percentage, 6.98±5.47% of excess seeds were due to overestimation of pre‐operative prostate volume, 1.10±0.88% were due to D90<100%, 1.17±0.67% were due to seed strength over 2U, and 17.36±7.79% could not be directly attributed to a specific reason. The latter percentage may be due to overestimation of the in‐house nomogram. Two of three nomograms substantially overestimated the number of seeds required. The third nomogram underestimated the required seed number for smaller prostate treatment volume. A linear fit to the clinical data was derived and 99.9% confidence intervals were calculated.

Conclusion:

Over 85% of clinical cases wasted over 15% of ordered seeds. Two of three nomograms overestimated the required number of seeds. The upper 99.9% C.I. of the clinical data may provide a more reasonable nomogram for Pd‐103 seed ordering.
SU‐F‐T‐41: 3D MTP‐TRUS for Prostate Implant
Authors: Yan P
Published: July 2016

Purpose:

Prostate brachytherapy is an effective treatment for early prostate cancer. The current prostate implant is limited to using 2D transrectal ultrassound (TRUS) or machenical motor driven 2D array either in the end or on the side. Real‐time 3D images can improve the accuracy of the guidance of prostate implant. The concept of our system is to allow realtime full visualization of the entire prostate with the multiple transverse scan.

Methods:

The prototype of 3D Multiple‐Transverse‐Plane Transrectal Ultrasound probe (MTP‐TRUS) has been designed by us and manufactured by Blatek inc. It has 7 convex linear arrays and each array has 96 elements. It is connected to cQuest Fire bird research system (Cephasonics inc.) which is a flexible and configurable ultrasound‐development platform. The size of cQuest Firebird system is compact and supports the real‐time wireless image transferring. A relay based mux board is designed for the cQuest Firebird system to be able to connect 672 elements.

Results:

The center frequency of probe is 6MHz±10%. The diameter of probe is 3cm and the length is 20cm. The element pitch is 0.205 mm. Array focus is 30mm and spacing 1.6cm. The beam data for each array was measured and met our expectation. The interface board of MTP‐TURS is made and able to connect to cQuest Firebird system. The image display interface is still under the development. Our real‐time needle tracking algorithm will be implemented too.

Conclusion:

Our MTP‐TRUS system for prostate implant will be able to acquire real‐time 3D images of prostate and do the real‐time needle segmentation and tracking. The system is compact and have wireless function.
SU‐F‐T‐47: MRI T2 Exclusive Based Planning Using the Endocavitary/interstitial Gynecological Benidorm Applicator: A Proposed TPS Library and Preplan Efficient Methodology
Authors: Richart J , Otal A , Rodriguez S , Santos M , Perez‐Calatayud J
Published: July 2016

Purpose:

ABS and GEC‐ESTRO have recommended MRI T2 for image guided brachytherapy. Recently, a new applicator (Benidorm Template, TB) has been developed in our Department (Rodriguez et al 2015). TB is fully MRI compatible because the Titanium needles and it allows the use of intrauterine tandem. Currently, TPS applicators library are not currently available for non‐rigid applicators in case of interstitial component as the TB.The purpose of this work is to present the development of a library for the TB, together with its use on a pre‐planning technique. Both new goals allow a very efficient and exclusive T2 MRI based planning clinical TB implementation.

Methods:

The developed library has been implemented in Oncentra Brachytherapy TPS, version 4.3.0 (Elekta) and now is being implemented on Sagiplan v 2.0 TPS (Eckert&Ziegler BEBIG). To model the TB, free and open software named FreeCAD and MeshLab have been used. The reconstruction process is based on three inserted A‐vitamin pellets together with the data provided by the free length. The implemented preplanning procedure is as follow: 1) A MRI T2 acquisition is performed with the template in place just with the vaginal cylinder (no uterine tube nor needles). 2) The CTV is drawn and the required needles are selected using a developed Java based application and 3) A post‐implant MRI T2 is performed.

Results:

This library procedure has been successfully applied by now in 25 patients. In this work the use of the developed library will be illustrated with clinical examples. The preplanning procedure has been applied by now in 6 patients, having significant advantages: needle depth estimation, needle positions and number are optimized a priori, time saving, etc

Conclusion:

TB library and pre‐plan techniques are feasible and very efficient and their use will be illustrated in this work.
SU‐F‐T‐49: Dosimetry Parameters and TPS Commissioning for the CivaSheet Directional Pd‐103 Brachytherapy Source
Authors: Rivard MJ
Published: July 2016

Purpose:

The CivaSheet is a new LDR Pd‐103 brachytherapy device offering directional‐radiation for preferentially irradiating malignancies with healthy‐tissue sparing. Observations are presented on dosimetric characterization, TPS commissioning, and evaluation of the dosesuperposition‐ principle for summing individual elements comprising a planar CivaSheet

Methods:

The CivaSheet comprises individual sources (CivaDots, 0.05cm thick and 0.25cm diam.) inside a flexible bioabsorbable substrate with a 0.8cm center‐to‐center rectangular array. All non‐radioactive components were measured to ensure accuracy of manufacturer‐provided dimensional information. The Pd spatial distribution was gleaned from radioactive and inert samples, then modeled with the MCNP6 radiation‐transport‐code. A 6×6 array CivaSheet was modeled to evaluate the dose superposition principle for treatment planning. Air‐kerma‐strength was estimated using the NIST WAFAC geometry. Absorbed dose was estimated in water with polar sampling covering 0.05≤r≤15cm in 0.05cm increments and 0°≤θ≤180° in 1° increments. These data were entered into VariSeed9.0 and tested for the dose‐superposition‐principle.

Results:

The dose‐rate‐constant was 0.579 cGy/h/U with g(r) determined along the rotational‐axis of symmetry (0°) instead of 90°. gP(r) values at 0.1, 0.5, 2, 5, and 10cm were 1.884, 1.344, 0.558, 0.088, and 0.0046. F(r,θ) decreased between 0° and 180° by factors of 270, 23, and 5.1 at 0.1, 1, and 10cm. The highest dose‐gradient was at 92°, changing by a factor of 3 within 1° due to Au‐foil shielding. TPS commissioning from 0.1≤r≤11cm and 0°≤θ≤180° demonstrated 2% reproducibility of input data except at the high‐dose‐gradient where interpolations caused 3% differences. Dose superposition of CivaDots replicated a multi‐source CivaSheet array within 2% except where another CivaDot was present. Following implantation, the device is not perfectly planar. TPS accuracy utilizing the dose‐superposition‐principle through geometric repositioning of CivaDots supersedes TPS limitations of intersource shielding effects

Conclusion:

Dosimetric characterization, source commissioning, and evaluation of the dose‐superposition‐principle with VariSeed9.0 permits treatment planning for the CivaSheet brachytherapy device.

Research supported in part by CivaTech Oncology, Inc.
SU‐F‐T‐64: An Alternative Approach to Determining the Reference Air‐Kerma Rate from Extrapolation Chamber Measurements
Authors: Schneider T
Published: July 2016

Purpose:

Since 2008 the Physikalisch‐Technische Bundesanstalt (PTB) has been offering the calibration of 125I‐brachytherapy sources in terms of the reference air‐kerma rate (RAKR). The primary standard is a large air‐filled parallel‐plate extrapolation chamber. The measurement principle is based on the fact that the air‐kerma rate is proportional to the increment of ionization per increment of chamber volume at chamber depths greater than the range of secondary electrons originating from the electrode x0.

Methods:

Two methods for deriving the RAKR from the measured ionization charges are: (1) to determine the RAKR from the slope of the linear fit to the so‐called 'extrapolation curve’, the measured ionization charges Q vs. plate separations x or (2) to differentiate Q(x) and to derive the RAKR by a linear extrapolation towards zero plate separation. For both methods, correcting the measured data for all known influencing effects before the evaluation method is applied is a precondition. However, the discrepancy of their results is larger than the uncertainty given for the determination of the RAKR with both methods.

Results:

A new approach to derive the RAKR from the measurements is investigated as an alternative. The method was developed from the ground up, based on radiation transport theory. A conversion factor C(x1, x2) is applied to the difference of charges measured at the two plate separations x1 and x2. This factor is composed of quotients of three air‐kerma values calculated for different plate separations in the chamber: the air kerma Ka(0) for plate separation zero, and the mean air kermas at the plate separations x1 and x2, respectively. The RAKR determined with method (1) yields 4.877 µGy/h, and with method (2) 4.596 µGy/h. The application of the alternative approach results in 4.810 µGy/h.

Conclusion:

The alternative method shall be established in the future.
SU‐F‐T‐66: Characteristics of Electron Beams From Varian Trubeam
Authors: Dimofte A , Kennedy C , Zhu T
Published: July 2016

Purpose:

The purpose of this study was to compare the electron beam data between Truebeam and 2300ix Varian accelerators for percent depth dose for broad beam and small circular cutouts, cone factors, head scatter factor as a function of cone size and SSD, phantom scatter factor, blocking factor, distance factor and virtual source position.

Methods:

Measurements were performed for Truebeam and 2300ix Varian accelerators. The main energies used were: 6, 9, 12, 16 and 20 MeV. PDD was measured at SSD = 100 cm for open beam and small circular cutouts (r = 0.5, 1.0, 1.5, 2.0, 3.0, 4.0 and 6.6cm) for different energies. Measurements to determine the head scatter factor (H) were done as a function of radius for six representative energies and five cone sizes (6, 10, 15, 20 and 25cm2). The phantom scatter factor (PSF) is defined as the ratio of blocking factor in water at reference depth and head scatter factor in air. PSF was measured as a function of radius and electron energy. Distance factor was measured for all energies and cones for three SSD's (100, 110 and 120cm).

Results:

The percent depth dose (PDD) was measured for small cutouts of radius r = 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0 and 5.6cm. Blocking factor (BF) was measured for Truebeam and 2300ix accelerators, for different circular cutouts and energies for a 10×10 cone. Cone factors were compared between the two accelerators for different energies and applicator sizes.

Conclusion:

Cone factors measured for the two accelerator types differ by up to 5% for the largest applicator size. Blocking factors differs by up to 3%, with the largest variation for the smallest field size (0.5cm). Distance factor for different SSD's differ by up to 4.5%.
SU‐F‐T‐67: Correction Factors for Monitor Unit Verification of Clinical Electron Beams
Authors: Haywood J
Published: July 2016

Purpose:

Monitor units calculated by electron Monte Carlo treatment planning systems are often higher than TG‐71 hand calculations for a majority of patients. Here I've calculated tables of geometry and heterogeneity correction factors for correcting electron hand calculations.

Method:

A flat water phantom with spherical volumes having radii ranging from 3 to 15 cm was created. The spheres were centered with respect to the flat water phantom, and all shapes shared a surface at 100 cm SSD. Dmax dose at 100 cm SSD was calculated for each cone and energy on the flat phantom and for the spherical volumes in the absence of the flat phantom. The ratio of dose in the sphere to dose in the flat phantom defined the geometrical correction factor. The heterogeneity factors were then calculated from the unrestricted collisional stopping power for tissues encountered in electron beam treatments. These factors were then used in patient second check calculations. Patient curvature was estimated by the largest sphere that aligns to the patient contour, and appropriate tissue density was read from the physical properties provided by the CT. The resulting MU were compared to those calculated by the treatment planning system and TG‐71 hand calculations.

Results:

The geometry and heterogeneity correction factors range from ∼(0.8–1.0) and ∼(0.9–1.01) respectively for the energies and cones presented. Percent differences for TG‐71 hand calculations drop from ∼(3–14)% to ∼(0–2)%.

Conclusion:

Monitor units calculated with the correction factors typically decrease the percent difference to under actionable levels, < 5%. While these correction factors work for a majority of patients, there are some patient anatomies that do not fit the assumptions made. Using these factors in hand calculations is a first step in bringing the verification monitor units into agreement with the treatment planning system MU.
SU‐F‐T‐73: Experimental Determination of the Effective Point of Measurement in Electron Beams Using a Commercial Scintillation Detector
Authors: Simiele E , Smith B , Culberson W
Published: July 2016

Purpose:

The aim of this work was to determine experimentally the effective point of measurement (EPOM) in clinical electron beams for three cylindrical ionization chambers using a commercial scintillation detector as a reference detector.

Methods:

Percent depth dose (PDD) curves were measured using an Exradin W1 scintillation detector and were used as a representative PDD to water. Depth dose curves were measured with the Exradin A18, A1SL, and A28 ionization chambers. The raw ionization chamber curve data were corrected by the chamber fluence perturbation correction factor and restricted mass collisional stopping power ratio at each depth to obtain a percent depth dose curve to the gas volume (PDDGV) of the detector. Ratios of the W1 PDD to the ion chamber PDDGV were calculated for each measurement depth. The W1 PDD curve was shifted by small depth increments, Δz, until the ratio of the W1 PDD to the ion chamber PDDGV was depth‐independent (optimal Δz). A MATLAB routine was developed to determine the optimal Δz value.

Results:

The optimal Δz shift was used as an estimate of the EPOM for each chamber. The average calculated EPOM shifts (expressed as a fraction of the chamber cavity radius) for the A18, A1SL, and A28 ionization chambers were 0.21 ± 0.04, 0.10 ± 0.05, and 0.22 ± 0.03, respectively.

Conclusion:

The experimentally determined EPOM values for the A18 and A1SL in this work agreed with the simulated values of Muir and Rogers (MedPhys 2014). The results also indicate that the Exradin W1 scintillator is water equivalent for electron energies of 6 MeV, 9 MeV, 12 MeV, and 16 MeV. In addition, we confirmed that the AAPM TG51 recommended EPOM shift of 0.5 times the cavity radius is not accurate for the A18 and A1SL chambers.
SU‐F‐T‐76: Total Skin Electron Therapy: An‐End‐To‐End Examination of the Absolute Dosimetry with a Rando Phantom
Authors: Cui G , Ha J , Zhou S , Cui J , Shiu A
Published: July 2016

Purpose:

To examine and validate the absolute dose for total skin electron therapy (TSET) through an end‐to‐end test with a Rando phantom using optically stimulated luminescent dosimeters (OSLDs) and EBT3 radiochromic films.

Methods:

A Varian Trilogy linear accelerator equipped with the special procedure 6 MeV HDTSe‐ was used to perform TSET irradiations using a modified Stanford 6‐dual‐field technique. The absolute dose was calibrated using a Markus ion chamber at a reference depth of 1.3cm at 100 cm SSD with a field size of 36 × 36 cm at the isocenter in solid water slabs. The absolute dose was cross validated by a farmer ion chamber. Then the dose rate in the unit of cGy/Mu was calibrated using the Markus chamber at the treatment position. OSLDs were used to independently verify the dose using the calibrated dose rate. Finally, a patient treatment plan (200 cGy/cycle) was delivered in the QA mode to a Rando phantom, which had 16 pairs of OSLDs and EBT3 films taped onto its surface at different anatomical positions. The doses recorded were read out to validate the absolute dosimetry for TSET.

Results:

The OSLD measurements were within 7% agreement with the planned dose except the shoulder areas, where the doses recorded were 23% lower on average than those of the planned. The EBT3 film measurements were within 10% agreement with the planned dose except the shoulder and the scalp vertex areas, where the respective doses recorded were 18% and 14% lower on average than those of the planned. The OSLDs gave more consistent dose measurements than those of the EBT3 films.

Conclusion:

The absolute dosimetry for TSET was validated by an end‐to‐end test with a Rando phantom using the OSLDs and EBT3 films. The beam calibration and monitor unit calculations were confirmed.
SU‐F‐T‐80: A Mobile Application for Intra‐Operative Electron Radiotherapy Treatment Planning
Authors: Williams C , Crowley E , Wolfgang J
Published: July 2016

Purpose:

Intraoperative electron radiotherapy (IORT) poses a unique set of challenges for treatment planning. Planning must be performed in a busy operating room environment over a short timeframe often with little advance knowledge of the treatment depth or applicator size. Furthermore, IORT accelerators can have a large number of possible applicators, requiring extensive databooks that must be searched for the appropriate dosimetric parameters. The goal of this work is to develop a software tool to assist in the planning process that is suited to the challenges faced in the IORT environment.

Methods:

We developed a mobile application using HTML5 and Javascript that can be deployed to tablet devices suitable for use in the operating room. The user selects the desired treatment parameters cone diameter, bevel angle, and energy (a total of 141 datasets) and desired bolus. The application generates an interactive display that allows the user to dynamically select points on the depth‐dose curve and to visualize the shape of the corresponding isodose contours. The user can indicate a prescription isodose line or depth. The software performs a monitor unit calculation and generates a PDF report.

Results:

We present our application, which is now used routinely in our IORT practice. It has been employed successfully in over 23 cases. The interactivity of the isodose distributions was found to be of particular use to physicians who are less‐frequent IORT users, as well as for the education of residents and trainees.

Conclusion:

This software has served as a useful tool in IORT planning, and demonstrates the need for treatment planning tools that are designed for the specialized challenges encountered in IORT. This software is the subject of a license agreement with the IntraOp Medical Corporation.

This software is the subject of a license agreement between Massachusetts General Hospital / Partners Healthcare and the IntraOp Medical Corporation. CLW is consulting on software development with the IntraOp Medical Corporation.
SU‐F‐T‐81: Treating Nose Skin Using Energy and Intensity Modulated Electron Beams with Monte Carlo Based Dose Calculation
Authors: Jin L , Fan J , Eldib A , Price R , Ma C
Published: July 2016

Purpose:

Treating nose skin with an electron beam is of a substantial challenge due to uneven nose surfaces and tissue heterogeneity, and consequently could have a great uncertainty of dose accuracy on the target. This work explored the method using Monte Carlo (MC)‐based energy and intensity modulated electron radiotherapy (MERT), which would be delivered with a photon MLC in a standard medical linac (Artiste).

Methods:

The traditional treatment on the nose skin involves the usage of a bolus, often with a single energy electron beam. This work avoided using the bolus, and utilized mixed energies of electron beams. An in‐house developed Monte Carlo (MC)‐based dose calculation/optimization planning system was employed for treatment planning. Phase space data (6, 9, 12 and 15 MeV) were used as an input source for MC dose calculations for the linac. To reduce the scatter‐caused penumbra, a short SSD (61 cm) was used. A clinical case of the nose skin, which was previously treated with a single 9 MeV electron beam, was replanned with the MERT method. The resultant dose distributions were compared with the plan previously clinically used. The dose volume histogram of the MERT plan is calculated to examine the coverage of the planning target volume (PTV) and critical structure doses.

Results:

The target coverage and conformality in the MERT plan are improved as compared to the conventional plan. The MERT can provide more sufficient target coverage and less normal tissue dose underneath the nose skin.

Conclusion:

Compared to the conventional treatment technique, using MERT for the nose skin treatment has shown the dosimetric advantages in the PTV coverage and conformality. In addition, this technique eliminates the necessity of the cutout and bolus, which makes the treatment more efficient and accurate.
SU‐F‐T‐86: Electron Dosimetric Effects of Bolus and Lens Shielding in Treating Superficial Eye Lesions
Authors: Young L , Wootton L , Gopan O , Liao J
Published: July 2016

Purpose:

Electron therapy for the treatment of ocular lymphomas requires the lens to be shielded to prevent secondary cataracts. This work evaluates the dosimetry under a suspended eyeshield with and without bolus for low energy electron fields.

Methods:

Film (GafChromic EBT3) dosimetry and relative output factors were measured for 6, 8, and 10 MeV electron energies. A customized 5 cm diameter circle electron orbital cutout was constructed for a 6×6 cm applicator with a lens shield, 1 cm diameter Cerrobend cylinder with 2.2 cm length, suspended from an XV film covering the open field. Relative output factors were measured using a Scanditronix electron diode in a solid water phantom. Depth dose profiles were collected for bolus thicknesses of 0, 3, and 5 mm in solid water at a source to surface distance (SSD) of 100 cm. These measurements were repeated in a Rando phantom.

Results:

At 5 mm, the approximate distance of the lens from the surface of the cornea, the estimated dose in solid water under the suspended lens shield was reduced to 16%, 14%, and 13% of the unblocked dose at the same depth, for electron energies of 6, 8, and 10 MeV, respectively. Applying bolus increased estimated doses under the block to 22% for 3‐mm and 32% for 5‐mm thicknesses for a 6 MeV incident electron beam. This effect is reduced for higher energies where the corresponding values were 15.5% and 18% for 3‐mm and 5‐mm for an 8 MeV electron beam.

Conclusion:

The application of bolus to treat superficial eye lesions of the conjunctiva increases lens dose at a depth of 5‐mm under the shielding block with decreasing electron energy. Careful selection of electron energy is needed to account for electron scatter under the lens shield with the application of bolus in order to prevent cataracts.
SU‐F‐T‐90: Patterns of Electron IORT Treatments in the U.S., Europe and Asia
Authors: Adamczyk S , Goer D , Ash R
Published: July 2016

Purpose:

We analyzed data collected from worldwide centers active in electron IORT with a focus on the technical variables of the treatment. Particular attention was given to the dominant tumor sites.

Methods:

54 Mobetron users from 14 countries in clinical operation prior to December 31, 2014, were invited to participate in this study. 29 centers contributed to this survey in sufficient detail to be included in this report. 6,035 patients were treated since 1997. Parameters were analyzed separately for each treatment site. However, special attention was given to the breast cancer, which turned out to be dominant tumor site.

Results:

The average number of patients treated per year in each center was 41 and exceeded 100 patients/year in 3 centers. For data received, 70% of patients worldwide were treated for breast cancer (93% in Europe, 14% in the U.S. and 21% in Asia). In 31% of cases electron IORT was the only breast irradiation. In breast patients, 9 MeV was used in 50% cases; 4MeV, 6MeV and 12MeV in 2%, 25% and 23% of cases respectively. 85% of patients were treated with field sizes between 4 and 6 cm and 35% of them were treated with 1/2 cm sized applicators. Beveled applicators (0°, 15° and 30° tips) were used in 51%, 33% and 16% of cases respectively. In 55% cases bolus was required with 5mm bolus used twice as often as 10mm. Chest‐wall protectors were used in 53% of treatment procedures. For Non‐breast data, main sites were: colorectal tumors (31%), pancreatic cancers (20%), extremity sarcomas (13%) and retroperitoneal sarcomas (5%).

Conclusion:

A large variety of tumors have been treated with IORT, with breast, colorectal, pancreas and sarcomas being the most frequently treated sites. This survey shows the most common applicators and energies used to treat each tumor site.
SU‐F‐T‐103: Analysis of Hepatitis B Virus Reactivation After Conformal Radiotherapy in Patients with Hepatocellular Carcinoma Using the Lyman NTCP Model
Authors: Li Z , Huang W , Li H , Li B
Published: July 2016

Purpose:

The aim of this research was to investigate the feasibility of Lyman‐Kutcher‐Burman (LKB) normal tissue complication probability (NTCP) model in analyzing hepatitis B virus (HBV) reactivation in patients receiving conformal radiotherapy for patients with hepatocellular carcinoma (HCC).

Methods:

Between June 2009 and June 2012, 108 HBV‐related HCC patients (90 were specifically selected and 18 patients were excluded) treated with conformal RT at three centers were enrolled in this retrospective study. They were all diagnosed as HCC by pathology or cytology. All 90 patients were followed up to September 2013 with a median follow‐up time of 25.2 months. The parameters (TD50 (1), n, and m) of the modified LKB NTCP model were derived using maximum likelihood estimation. Bootstrap and leave‐one‐out were employed to test the generalizability of the results for use in a general population.

Results:

The incidences of complications in the study population were as follows: radiation‐induced liver diseases (RILD) were 17.6%, HBV reactivation was 24.8%, and HBV reactivation‐induced hepatitis was 22.7%, respectively. In multivariate analysis, the NTCP (p<0.001), and V20 were associated with HBV reactivation. TD50 (1), m and n were 42.9Gy (95% CI) (38.2–46.8), 0.14 (0.12–0.15) and 0.30 (0.2–0.33), respectively, for HBV reactivation. Bootstrap and leave‐one‐out results showed that the HBV parameter fits were extremely robust.

Conclusion:

A modified LKB NTCP model has been established to predict HBV reactivation for patients with HCC receiving conformal RT. The finding derives parameters set to predict potential endpoints of HBV reactivation.
SU‐F‐T‐106: A Dosimetric Study of Intensity Modulated Radiation Therapy to Decrease Radiation Dose to the Thoracic Vertebral Bodies in Patients Receiving Concurrent Chemoradiation for Lung Cancer
Authors: DiCostanzo Dominic , Barney Christian L. , Bazan Jose G.
Published: July 2016

Purpose:

Recent clinical studies have shown a correlation between radiation dose to the thoracic vertebral bodies (TVB) and the development of hematologic toxicity (HT) in patients receiving chemoradiation (CRT) for lung cancer (LuCa). The feasibility of a bone‐marrow sparing (BMS) approach in this group of patients is unknown. We hypothesized that radiation dose to the TVB can be reduced with an intensity modulated radiation therapy(IMRT)/volumetric modulated arc radiotherapy(VMAT) without affecting plan quality.

Methods:

We identified LuCa cases treated with curative intent CRT using IMRT/VMAT from 4/2009 to 2/2015. The TVBs from T1–T10 were retrospectively contoured. No constraints were placed on the TVB structure initially. A subset were re‐planned with BMS‐IMRT/VMAT with an objective or reducing the mean TVB dose to <23 Gy. The following data were collected on the initial and BMS plans: mean dose to planning target volume (PTV), lungs‐PTV, esophagus, heart; lung V20; cord max dose. Pairwise comparisons were performed using the signed rank test.

Results:

94 cases received CRT with IMRT/VMAT. We selected 11 cases (7 IMRT, 4 VMAT) with a range of initial mean TVB doses (median 35.7 Gy, range 18.9–41.4 Gy). Median prescription dose was 60 Gy. BMS‐IMRT/VMAT significantly reduced the mean TVB dose by a median of 10.2 Gy (range, 1.0–16.7 Gy, p=0.001) and reduced the cord max dose by 2.9 Gy (p=0.014). BMS‐IMRT/VMAT had no impact on lung mean (median +17 cGy, p=0.700), lung V20 (median +0.5%, p=0.898), esophagus mean (median +13 cGy, p=1.000) or heart mean (median +16 cGy, p=0.365). PTV‐mean dose was not affected by BMS‐IMRT/VMAT (median +13 cGy, p=0.653).

Conclusion:

BMS‐IMRT/VMAT was able to significantly reduce radiation dose to the TVB without compromising plan quality. Prospective evaluation of BMS‐IMRT/VMAT in patients receiving CRT for LuCa is warranted to determine if this approach results in clinically significant reductions in HT.
SU‐F‐T‐110: LKB Modeling of Acute Hematologic Toxicity in Rectal Cancer
Authors: Deng H , Cheng K , Wan X
Published: July 2016

Purpose:

To investigate dosimetric parameters correlated with acute hematologic toxicity (HT) in patients with rectal cancer treated with IMRT and concurrent chemotherapy.

Methods:

We analyzed 127 rectal cancer patients receiving IMRT and concurrent chemotherapy. Whole pelvic bone marrow (PBM) was contoured for each patient including lumbosacral spine (LSSP), ilium and lower pelvic (LP). The equivalent uniform dose (EUD) of each region and the PBM were calculated. Endpoints for HT is grade ≥3 (HT3+) leukopenia, neutropenia or thrombocytopenia. Normal tissue complication probability (NTCP) was evaluated with the Lyman‐Kutcher‐Burman (LKB) model. On the basis of our NTCP modeling, we get the value of TD5, TD10, TD50 and other predictors of hematologic toxicity.

Results:

Twenty six patients experienced HT3+. Constrained optimization of the LKB model for HT3+ yielded the parameters m=0.583, n=1, and TD50=59.6Gy. With this model, mean PBM doses of 1.5Gy, 15Gy, 30.5Gy, 42Gy and 51Gy result in a 5%, 10%, 20%, 30% and 40% risk of HT3+, respectively. Our model suggested chemotherapy alone induced a HT3+ complication rate of about 4.6%.

Conclusion:

LKB modeling indicates that PBM acts like a parallel organ, implying that the mean dose to the organ is a useful predictor for toxicity. Compared with a Stanford study about anal cancer patients, the patients of anal cancer received chemotherapy with MMC and 5‐FU which can cause much more severe HT than 5‐FU or FOLFOX in our rectal cancer study. Therefore, the incidence of HT3+ is much higher in anal cancer and resulted in a much lower TD50 than our study.
SU‐F‐T‐112: Long‐Term Follow‐Up of NSCLC Patients Treated with Lung SBRT Using the Modified Conformal Arc (MDCA) Planning Technique
Authors: Ku E , Desai A , Fang D , Lawrence C , Iannuzzi C , Shi C
Published: July 2016

Purpose:

To assess long‐term toxicity and primary tumor changes for Stage I/II non‐small cell lung carcinoma (NSCLC) patients after treatment with lung SBRT using the modified dynamic conformal arc (MDCA) planning technique.

Methods:

Clinical and radiograph data from electronic health records of 15 NSCLC patients treated with lung SBRT utilizing the MDCA technique between October 2011 and July 2014 were retrospectively reviewed. MDCA uses a coplanar beam arrangement, patient body center for the beam isocenter, and six partial rotation conformal arcs to target the tumor. Radiation Therapy Oncology Group (RTOG) guidelines for treatment parameters were followed. Most patients received 5 radiation fractions (Range: 3 to 7 fractions) with 48 hours between each fraction. Median total dose was 60 Gy (range: 45 to 70 Gy).

Results:

Median follow‐up was 18 months (range: 6–51 months). Median age was 72.5 years (range: 48–90 years). Post‐treatment findings included fatigue (n = 5) and chronic chest wall pain (n=1). Seven patients reported respiratory symptoms, which included: cough (n = 4), dyspnea (n = 5), and hemoptysis (n = 1). No patients deaths or grade ≥4 toxicity were recorded. Radiographic scarring was seen on computed tomography (CT) imaging in 6 patients. Local control rate was 93.3% (n = 14) and 1 patient had local recurrence.

Conclusion:

Our results were very similar to RTOG 0236 findings reported by Timmerman et al. – our local control rate was 93.3% compared to their 3‐year primary tumor control rate of 97.6%. Toxicity rates were also similar – RTOG 0236 constitutional symptoms and pulmonary/upper respiratory symptoms rates were 36.4% and 60.0%, respectively, while ours were 33.3% and 46.7%, respectively. We were limited by a small sample size and relatively short follow‐up but our findings support the use of the MDCA technique for lung SBRT treatment of Stage I/II NSCLC.
SU‐F‐T‐126: Microdosimetic Evaluation of Proton Energy Distributions in the Vicinity of Metal Implants
Authors: Heczko S , McAuley GA , Slater JM , Wroe A
Published: July 2016

Purpose:

To evaluate the impact of titanium and surgical stainless steel implants on the microscopic dose distribution in proton treatment plans

Methods:

Geant4 Monte Carlo simulations were used to analyze the microdosimetric distribution of proton radiation in the vicinity of 3.1 mm thick CP Grade 4 titanium (Ti) or 316 stainless steel (SS316) plates in a water phantom. Additional simulations were performed using either water, or water with a density equivalent to the respective metals (Tiwater, SS316water) (to reflect common practice in treatment planning). Implants were placed at the COM of SOBPs of 157 MeV (range of ∼15 cm in water) protons with 30 or 60 mm modulation. Primary and secondary particle dose and fluence, frequency‐weighted and dose‐weighted average lineal energy, average radiation quality factor, dose equivalent and energy deposition histograms in the plate vicinity were compared.

Results:

Preliminary results show frequency‐weighted (yf) and dose‐weighted lineal energy (yd) was increased downstream of the Ti plate (yf = 3.1 keV/µm; yd = 5.5 keV/µm) and Tiwater (yf = 4.1 keV/µm; yd = 6.8 keV/µm) compared to that of water (ie, the absence of a plate) (yf = 2.5 keV/µm; yd = 4.5 keV/µm). In addition, downstream proton dose deposition was also elevated due to the presence of the Ti plate or Tiwater. The additional dose deposited at higher lineal energy implies that tissues downstream of the plate will receive a higher dose equivalent. Detailed analyses of the Ti, Tiwater, SS316, and SS316 water simulations will be presented.

Conclusion:

The presence of high‐density materials introduces changes in the spatial distribution of radiation in the vicinity of an implant. Further work quantifying these effects could be incorporated into future treatment planning systems resulting in more accurate treatment plans.

This project was sponsored with funding from the Department of Defense (DOD # W81XWH‐10‐2‐0192).
SU‐F‐T‐132: Variable RBE Models Predict Possible Underestimation of Vaginal Dose for Anal Cancer Patients Treated Using Single‐Field Proton Treatments
Authors: McNamara A , Underwood T , Wo J , Paganetti H
Published: July 2016

Purpose:

Anal cancer patients treated using a posterior proton beam may be at risk of vaginal wall injury due to the increased linear energy transfer (LET) and relative biological effectiveness (RBE) at the beam distal edge. We investigate the vaginal dose received.

Methods:

Five patients treated for anal cancer with proton pencil beam scanning were considered, all treated to a prescription dose of 54 Gy(RBE) over 28–30 fractions. Dose and LET distributions were calculated using the Monte Carlo simulation toolkit TOPAS. In addition to the standard assumption of a fixed RBE of 1.1, variable RBE was considered via the application of published models. Dose volume histograms (DVHs) were extracted for the planning treatment volume (PTV) and vagina, the latter being used to calculate the vaginal normal tissue complication probability (NTCP).

Results:

Compared to the assumption of a fixed RBE of 1.1, the variable RBE model predicts a dose increase of approximately 3.3 ± 1.7 Gy at the end of beam range. NTCP parameters for the vagina are incomplete in the current literature, however, inferring value ranges from the existing data we use D50 = 50 Gy and LKB model parameters a=1–2 and m=0.2–0.4. We estimate the NTCP for the vagina to be 37–48% and 42–47% for the fixed and variable RBE cases, respectively. Additionally, a difference in the dose distribution was observed between the analytical calculation and Monte Carlo methods. We find that the target dose is overestimated on average by approximately 1–2%.

Conclusion:

For patients treated with posterior beams, the vaginal wall may coincide with the distal end of the proton beam and may receive a substantial increase in dose if variable RBE models are applied compared to using the current clinical standard of RBE equal to 1.1. This could potentially lead to underestimating toxicities when treating with protons.
SU‐F‐T‐141: Proton Dose Validation in a Phantom Beyond TRUFILL N‐BCA Embolization Glue
Authors: Mandapaka A , Ghebremedhin A , Patyal B , Linda Loma
Published: July 2016

Purpose:

To validate the treatment planning system predicted proton dose beyond a heterogeneity (n‐BCA glue) by making a measurement in a custom acrylic phantom.

Methods:

A custom cubic acrylic phantom was designed for this experiment. A container was designed to fit in the phantom. This container was filled with TRUFILL™ n‐Butyl Cyanoacrylate(n‐BCA) glue. When the container was placed in the phantom, its center was at a distance of 7.4cm from the entrance. This depth allows us to make measurements around the center of modulation of a 126 MeV proton beam with a 3cm spread‐out‐Bragg peak. To make measurements at other beam energies, additional acrylic can be added in front of the phantom, to adjust the depth of the heterogeneity. A diamond detector was cross calibrated against a standard cylindrical ion chamber in a 126MeV beam. The diamond detector was then used to make dose measurements beyond the inhomogeneity. The measurement was repeated with the container filled with water. Several measurements were made at each setup, to check reproducibility of measurements.

Results:

For the same number of Tic3R1 counts, the dose measured with the diamond detector beyond n‐BCA glue was 1.053 times the dose measured beyond the water filled container. This result is in agreement with the measured stopping power of glue (1.06). These measurements were in agreement with the dose predicted by the treatment planning system when the electron density of the heterogeneity was replaced with 1.06 before the dose calculation.

Conclusion:

Our initial measurements validate the dose predicted by our treatment plan in the presence of heterogeneity in a phantom. The material tested (n‐BCA glue) is commonly used in the treatment of AVM's prior to an SRS treatment. An error in dose predicted by the treatment plan in the presence of the glue can be detrimental in a single fraction high dose SRS treatment

I received the n‐BCA liquid embolic system samples from Codman and Shurtleff, Inc.
SU‐F‐T‐149: Development of the Monte Carlo Simulation Platform Using Geant4 for Designing Heavy Ion Therapy Beam Nozzle
Authors: Shin Jae‐ik , Yoo SeungHoon , Cho Sungho , Ho Kim Eun , Song Yongkeun , Jung Won‐Gyun
Published: July 2016

Purpose:

The significant issue of particle therapy such as proton and carbon ion was a accurate dose delivery from beam line to patient. For designing the complex delivery system, Monte Carlo simulation can be used for the simulation of various physical interaction in scatters and filters. In this report, we present the development of Monte Carlo simulation platform to help design the prototype of particle therapy nozzle and performed the Monte Carlo simulation using Geant4. Also we show the prototype design of particle therapy beam nozzle for Korea Heavy Ion Medical Accelerator (KHIMA) project in Korea Institute of Radiological and Medical Science(KIRAMS) at Republic of Korea.

Methods:

We developed a simulation platform for particle therapy beam nozzle using Geant4. In this platform, the prototype nozzle design of Scanning system for carbon was simply designed. For comparison with theoretic beam optics, the beam profile on lateral distribution at isocenter is compared with Mont Carlo simulation result. From the result of this analysis, we can expected the beam spot property of KHIMA system and implement the spot size optimization for our spot scanning system.

Results:

For characteristics study of scanning system, various combination of the spot size from accerlator with ridge filter and beam monitor was tested as simple design for KHIMA dose delivery system.

Conclusion:

In this report, we presented the part of simulation platform and the characteristics study. This study is now on‐going in order to develop the simulation platform including the beam nozzle and the dose verification tool with treatment planning system. This will be presented as soon as it is become available.
SU‐F‐T‐151: Measurement Evaluation of Skin Dose in Scanning Proton Beam Therapy for Breast Cancer
Authors: Yu J , Nichols E , Strauss D , Chung H , Langner U , Langen K
Published: July 2016

Purpose:

To measure the skin dose and compare it with the calculated dose from a treatment planning system (TPS) for breast cancer treatment using scanning proton beam therapy (SPBT).

Methods:

A single en‐face‐beam SPBT plan was generated by a commercial TPS for two breast cancer patients. The treatment volumes were the entire breasts (218 cc and 1500 cc) prescribed to 50.4 Gy (RBE) in 28 fractions. A range shifter of 5 cm water equivalent thickness was used. The organ at risk (skin) was defined to be 5 mm thick from the surface. The skin doses were measured in water with an ADCL calibrated parallel plate (PP) chamber. The measured data were compared with the values calculated in the TPS. Skin dose calculations can be subject to uncertainties created by the definition of the external contour and the limitations of the correction based algorithms, such as proton convolution superposition. Hence, the external contours were expanded by 0, 3 mm and 1 cm to include additional pixels for dose calculation. In addition, to examine the effects of the cloth gown on the skin dose, the skin dose measurements were conducted with and without gown.

Results:

On average the measured skin dose was 4% higher than the calculated values. At deeper depths, the measured and calculated doses were in better agreement (< 2%). Large discrepancy occur for the dose calculated without external expansion due to volume averaging. The addition of the gown only increased the measured skin dose by 0.4%.

Conclusion:

The implemented TPS underestimated the skin dose for breast treatments. Superficial dose calculation without external expansion would result in large errors for SPBT for breast cancer.