bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐373: Evaluation and Reduction of Contralateral Skin /subcutaneous Dose for Tangential Breast Irradiation
Authors: Butson M , Carroll S , Whitaker M , Odgers D , Martin D , Hinds S , Kader J , Ho K , Amos S , Toohey J 
Published: June 2015

Purpose:Tangential breast irradiation is a standard treatment technique for breast cancer therapy. One aspect of dose delivery includes dose delivered to the skin caused by electron contamination. This effect is especially important for highly oblique beams used on the medical tangent where the electron contamination deposits dose on the contralateral breast side. This work aims to investigate and predict as well as define a method to reduce this dose during tangential breast radiotherapy.Methods:Analysis and calculation of breast skin and subcutaneous dose is performed using a Varian Eclipse planning system, AAA algorithm for 6MV x‐ray treatments. Measurements were made using EBT3 Gafchromic film to verify the accuracy of planning data. Various materials were tested to assess their ability to remove electron contamination on the contralateral breast.Results:Results showed that the Varian Eclipse AAA algorithm could accurately estimate contralateral breast dose in the build‐up region at depths of 2mm or deeper. Surface dose was underestimated by the AAA algorithm. Doses up to 12% of applied dose were seen on the contralateral breast surface and up to 9 % at 2mm depth. Due to the nature of this radiation, being mainly low energy electron contamination, a bolus material could be used to reduce this dose to less than 3%. This is accomplished by 10 mm of superflab bolus or by 1 mm of lead.Conclusion:Contralateral breast skin and subcutaneous dose is present for tangential breast treatment and has been measured to be up to 12% of applied dose from the medial tangent beam. This dose is deposited at shallow depths and is accurately calculated by the Eclipse AAA algorithm at depths of 2mm or greater. Bolus material placed over the contralateral can be used to effectively reduce this skin dose.
SU‐E‐T‐376: Evaluation of a New Stereotactic Diode for Small Field Dosimetry
Authors: Kralik J , Kosterin P , Mooij R , Solberg T 
Published: June 2015

Purpose:To evaluate the performance of a new stereotactic diode for dosimetry of small photon fields.Methods:A new stereotactic diode, consisting of an unshielded p‐type silicon chip, and with improved radiation hardness energy dependence was recently developed (IBA Dosimetry, Schwarzenbruch, Germany). The diode has an active volume of 0.6 mm dia. × 0.02 mm thick. Two new diodes were evaluated, one which was pre‐irradiated to 100kGy with 10 MeV electrons and another which received no prior irradiation. Sensitivity, stability, reproducibility, and linearity as a function of dose were assessed. Beam profiles and small field output factors were measured on a CyberKnife (CK) and compared with measurements using two commercially available diodes.Results:The new diodes exhibit linear behavior (within 0.6%) over a dose range 0.02 – 50 Gy; a commercially available device exhibits excursions of up to 4% over the same range. The sensitivity is 4.1 and 3.8 nC/Gy for the un‐irradiated and pre‐irradiated diodes, respectively. When irradiated with 150 Gy in dose increments of 5, 20 and 35 Gy, both new diodes provide a stable response within 0.5%. Output factors measured with the two new diodes are identical and compare favorably with other commercially available diodes and published data. Similarly, no differences in measured field size or penumbra were observed among the devices tested.Conclusion:The new diodes show excellent stability and sensitivity. The beam characterization in terms of output factors and beam profiles is consistent with that obtained with commercially available diodes.
SU‐E‐T‐378: Evaluation of An Analytical Model for the Inter‐Seed Attenuation Effect in 103‐Pd Multi‐Seed Implant Brachytherapy
Authors: Safigholi H , Meigooni A Soleimani , Han D , Soliman A , Song W 
Published: June 2015

Purpose:Brachytherapy treatment planning systems based on TG‐43 protocol calculate the dose in water and neglects the heterogeneity effect of seeds in multi‐seed implant brachytherapy. In this research, the accuracy of a novel analytical model that we propose for the inter‐seed attenuation effect (ISA) for 103‐Pd seed model is evaluated.Methods:In the analytical model, dose perturbation due to the ISA effect for each seed in an LDR multi‐seed implant for 103‐Pd is calculated by assuming that the seed of interest is active and the other surrounding seeds are inactive. The cumulative dosimetric effect of all seeds is then summed using the superposition principle. The model is based on pre Monte Carlo (MC) simulated 3D kernels of the dose perturbations caused by the ISA effect. The cumulative ISA effect due to multiple surrounding seeds is obtained by a simple multiplication of the individual ISA effect by each seed, the effect of which is determined by the distance from the seed of interest. This novel algorithm is then compared with full MC water‐based simulations (FMCW).Results:The results show that the dose perturbation model we propose is in excellent agreement with the FMCW values for a case with three seeds separated by 1 cm. The average difference of the model and the FMCW simulations was less than 8%±2%.Conclusion:Using the proposed novel analytical ISA effect model, one could expedite the corrections due to the ISA dose perturbation effects during permanent seed 103‐Pd brachytherapy planning with minimal increase in time since the model is based on multiplications and superposition. This model can be applied, in principle, to any other brachytherapy seeds. Further work is necessary to validate this model on a more complicated geometry as well.
SU‐E‐T‐380: Evaluation of BEBIG HDR 60Co System for AccuBoost Therapy
Authors: Zehtabian M , Sina S , Rivard M , Meigooni A Soleimani 
Published: June 2015

Purpose:In this project, the possibility of utilizing the BEBIG 60Co HDR system for AccuBoostTM treatment has been evaluated.Methods:Dose distributions in various breast sizes have been calculated for both Co‐60 and Ir‐192 sources using the MCNP5 code. These calculations were performed in breast tissues with thicknesses of 4cm, 6cm, and 8cm. The initial calculations were performed with the same applicator dimensions as the existing applicators used with the HDR Ir‐192 system. The activity of the Co‐60 source was selected such that the dose at the breast center was the same as the values from 192Ir. Then, the applicator thicknesses were increased to twice of those used with HDR Ir‐192 system, for reducing skin and chest doses by Co‐60 system. Dose to breast skin and chest wall were compared for both applicators types, with and without inclusion of a focusing cone at the applicator center.Results:The results showed that loading HDR Co‐60 source inside the thin applicators impose higher doses to breast skin and chest wall compared to the 192Ir source. The area of the chest wall covered by 10Gy when treated by Co‐60 with the thin and thick applicators, or treated by Ir‐192 with thin applicator are 79cm2, 39cm2, and 3.8cm2, respectively. These values are reduced to 34cm2, 0cm2, and 0cm2 by using the focusing cone. It is worth noting that the breast skin areas covered by the 60Gy isodose line are 9.9cm2 and 7.8cm2 for Co‐60 with the thin and thick applicators, respectively, while it is 20cm2 for Ir‐192 when no focusing cone is present. These values are 0cm2, 0cm2, and 11cm2 in the presence of the focusing cone.Conclusion:The results indicate that using Co‐60 with the thicker applicators is beneficial because of the higher half‐life of Co‐60, and the reduced maximum skin dose when compared with Ir‐192.
SU‐E‐T‐381: Evaluation of Calculated Dose Accuracy for Organs‐At‐Risk Located at Out‐Of‐Field in a Commercial Treatment Planning System for High Energy Photon Beams Produced From TrueBeam Accelerators
Authors: Wang L , Ding G 
Published: June 2015

Purpose:Dose calculation accuracy for the out‐of‐field dose is important for predicting the dose to the organs‐at‐risk when they are located outside primary beams. The investigations on evaluating the calculation accuracy of treatment planning systems (TPS) on out‐of‐field dose in existing publications have focused on low energy (6MV) photon. This study evaluates out‐of‐field dose calculation accuracy of AAA algorithm for 15MV high energy photon beams.Methods:We used the EGSnrc Monte Carlo (MC) codes to evaluate the AAA algorithm in Varian Eclipse TPS (v.11). The incident beams start with validated Varian phase‐space sources for a TrueBeam linac equipped with Millennium 120 MLC. Dose comparisons between using AAA and MC for CT based realistic patient treatment plans using VMAT techniques for prostate and lung were performed and uncertainties of organ dose predicted by AAA at out‐of‐field location were evaluated.Results:The results show that AAA calculations under‐estimate doses at the dose level of 1% (or less) of prescribed dose for CT based patient treatment plans using VMAT techniques. In regions where dose is only 1% of prescribed dose, although AAA under‐estimates the out‐of‐field dose by 30% relative to the local dose, it is only about 0.3% of prescribed dose. For example, the uncertainties of calculated organ dose to liver or kidney that is located out‐of‐field is <0.3% of prescribed dose.Conclusion:For 15MV high energy photon beams, very good agreements (<1%) in calculating dose distributions were obtained between AAA and MC. The uncertainty of out‐of‐field dose calculations predicted by the AAA algorithm for realistic patient VMAT plans is <0.3% of prescribed dose in regions where the dose relative to the prescribed dose is <1%, although the uncertainties can be much larger relative to local doses. For organs‐at‐risk located at out‐of‐field, the error of dose predicted by Eclipse using AAA is negligible.This work was conducted in part using the resources of Varian research grant VUMC40590‐R.
SU‐E‐T‐383: Evaluation of Deep Inspiration Breath‐Hold Technique for Post‐Mastectomy Proton Pencil Beam Scanning Therapy
Authors: Depauw N , Patel S , MacDonald S , Lu H 
Published: June 2015

Purpose:Deep inspiration breath‐hold techniques (DIBH) have been shown to carry significant dosimetric advantages in conventional radiotherapy of left‐sided breast cancer. The purpose of this study is to evaluate the use of DIBH techniques for post‐mastectomy radiation therapy (PMRT) using proton pencil beam scanning (PBS).Method:Ten PMRT patients, with or without breast implant, underwent two helical CT scans: one with free breathing and the other with deep inspiration breath‐hold. A prescription of 50.4 Gy(RBE) to the whole chest wall and lymphatics (axillary, supraclavicular, and intramammary nodes) was considered. PBS plans were generated for each patient's CT scan using Astroid, an in‐house treatment planning system, with the institution conventional clinical PMRT parameters; that is, using a single en‐face field with a spot size varying from 8 mm to 14 mm as a function of energy. Similar optimization parameters were used in both plans in order to ensure appropriate comparison.Results:Regardless of the technique (free breathing or DIBH), the generated plans were well within clinical acceptability. DIBH allowed for higher target coverage with better sparing of the cardiac structures. The lung doses were also slightly improved. While the use of DIBH techniques might be of interest, it is technically challenging as it would require a fast PBS delivery, as well as the synchronization of the beam delivery with a gating system, both of which are not currently available at the institution.Conclusion:DIBH techniques display some dosimetric advantages over free breathing treatment for PBS PMRT patients, which warrants further investigation. Plans will also be generated with smaller spot sizes (2.5 mm to 5.5 mm and 5 mm to 9 mm), corresponding to new generation machines, in order to further quantify the dosimetric advantages of DIBH as a function of spot size.
SU‐E‐T‐387: Evaluation of Effective Treatment Depth in Skin Cancer Treatments with Xoft Electronic Brachytherapy
Authors: Dragojevic I , Hoisak J 
Published: June 2015

Purpose:To evaluate changes in the percent depth dose (PDD) and effective depth of treatment based on exerted force by applicator on the skin during treatments of skin cancer with Xoft Electronic Brachytherapy.Methods:To simulate compressible tissue, 5mm tissue‐equivalent bolus was used. An ion chamber (Soft X‐ray Chamber, PTW) and electrometer (Max 4000, Standard Imaging) were used for output measurements. Measurements were done for all available Xoft surface applicators (10, 20, 35, and 50mm cones) with plastic endcap. Fig1 shows the experimental setup. The PDD was measured first with no or minimal pressure of the applicator on the bolus, followed by increasing uniform pressure on the applicator applied with custom cerrobend weights. The measurements were used to calculate the effective PDD and effective depth.Results:Force applied with the applicator was plotted against the change in PDD relative to the PDD when no force is applied. For the 10mm cone, moderate force of 5N can change the PDD by more than 20%, (Fig2). The effect is also pronounced for the 20mm cone, while it is minimal for the 35 and 50mm cones. Even when only moderate force is applied, the effective prescription depth can be changed by a several millimeters, which is on the order of the typical prescription depth (Fig3).Conclusion:Based on the results of this simulation, excessive pressure applied on the patient's skin by the applicator cone can drastically alter the PDD and effective treatment depth. The effect is most pronounced for the 10mm cone, and to a lesser extent, 20mm, which is significant as these cones tend to be used most frequently in the clinic. Applicator placement therefore may Result in significant consequences such as excessive dose to target, severe skin reaction, permanent discoloration, skin indentation, and poor overall cosmesis upon completion of treatment.
SU‐E‐T‐399: Evaluation of Selection Criteria for Computational Human Phantoms for Use in Out‐Of‐Field Organ Dosimetry for Radiotherapy Patients
Authors: Pelletier C , Jung J , Lee C , Pyakuryal A , Kim J , Lee C 
Published: June 2015

Purpose:To quantify the dosimetric uncertainty due to organ position errors when using height and weight as phantom selection criteria in the UF/NCI Hybrid Phantom Library for the purpose of out‐of‐field organ dose reconstruction.Methods:Four diagnostic patient CT images were used to create 7‐field IMRT plans. For each patient, dose to the liver, right lung, and left lung were calculated using the XVMC Monte Carlo code. These doses were taken to be the ground truth. For each patient, the phantom with the most closely matching height and weight was selected from the body size dependent phantom library. The patient plans were then transferred to the computational phantoms and organ doses were recalculated. Each plan was also run on 4 additional phantoms with reference heights and or weights. Maximum and mean doses for the three organs were computed, and the DVHs were extracted and compared. One sample t‐tests were performed to compare the accuracy of the height and weight matched phantoms against the additional phantoms in regards to both maximum and mean dose.Results:For one of the patients, the height and weight matched phantom yielded the most accurate results across all three organs for both maximum and mean doses. For two additional patients, the matched phantom yielded the best match for one organ only. In 13 of the 24 cases, the matched phantom yielded better results than the average of the other four phantoms, though the results were only statistically significant at the .05 level for three cases.Conclusion:Using height and weight matched phantoms does yield better results in regards to out‐of‐field dosimetry than using average phantoms. Height and weight appear to be moderately good selection criteria, though this selection criteria failed to yield any better results for one patient.
SU‐E‐T‐400: Evaluation of Shielding and Activation at Two Pencil Beam Scanning Proton Facilities
Authors: Remmes N , Mundy D , Stoker J , Classic K , Nelson K , Beltran C , Bues M , Kruse J , Herman M 
Published: June 2015

Purpose:To verify acceptably low dose levels around two newly constructed identical pencil beam scanning proton therapy facilities and to evaluate accuracy of pre‐construction shielding calculations.Methods:Dose measurements were taken at select points of interest using a WENDI‐2 style wide‐energy neutron detector. Measurements were compared to pre‐construction shielding calculations. Radiation badges with neutron dose measurement capabilities were worn by personnel and also placed at points throughout the facilities. Seven neutron and gamma detectors were permanently installed throughout the facility, continuously logging data. Potential activation hazards have also been investigated. Dose rates near water tanks immediately after prolonged irradiation have been measured. Equipment inside the treatment room and accelerator vault has been surveyed and/or wipe tested. Air filters from air handling units, sticky mats placed outside of the accelerator vault, and water samples from the magnet cooling water loops have also been tested.Results:All radiation badges have been returned with readings below the reporting minimum. Measurements of mats, air filters, cooling water, wipe tests and surveys of equipment that has not been placed in the beam have all come back at background levels. All survey measurements show the analytical shielding calculations to be conservative by at least a factor of 2. No anomalous events have been identified by the building radiation monitoring system. Measurements of dose rates close to scanning water tanks have shown dose rates of approximately 10 mrem/hr with a half‐life less than 5 minutes. Measurements around the accelerator show some areas with dose rates slightly higher than 10 mrem/hr.Conclusion:The shielding design is shown to be adequate. Measured dose rates are below those predicted by shielding calculations. Activation hazards are minimal except in certain very well defined areas within the accelerator vault and for objects placed directly in the path of the beam.
SU‐E‐T‐402: Evaluation of the Accuracy of a Novel Open Mask System for Immobilization of Cranial Stereotactic Radiosurgery Patients
Authors: Song K , Wen N , Qin Y , Kim J , Li H , Snyder K , Gordon J , Chetty I , Siddiqui S 
Published: June 2015

Purpose:To evaluate the accuracy of a novel open mask for intracranial SRS and to investigate the capability of monitoring intrafraction motion of the patient within this mask using the optical surface monitoring system (OSMS) on a linac‐based platform.Methods:Efficiency was evaluated by measuring mask fabrication time during CT simulation and setup time in the treatment room. Mask shrinkage was assessed by comparing shim settings during treatment to simulation and also by measuring the distance between anterior and posterior sections of the mask on CBCT and Sim CT. Mask comfort was evaluated qualitatively post‐treatment by surveying patients. Intrafraction motion was examined using 2D‐3D autofusion of orthogonal kV images at mid‐treatment. The intrafraction motion accuracy of the OSMS was analyzed by measuring the surface area of mask opening in Eclipse and pictures from the OSMS cameras.Results:The average preparation time for mask setup during simulation and treatment was 12.7 ± 2.3 min and 1.8 ± 0.9 min, respectively. Shims needed to be increased on average 0.8 mm, 0.8 mm, and 0.6 mm for right, left, and superior positions, respectively. CBCT measurements showed mask shrinkage, 0.8 mm both anteriorly and posteriorly. Greatest discomfort was reported on forehead followed by neck and chin. Intrafraction motion was less than 1 mm/1°. Accuracy of OSMS monitoring depended on the selected ROI. The OSMS monitored motion within 1 mm and 1° when the open surface area measured in Eclipse and captured by the camera > 147 cm2 and 33 cm2, respectively. When such conditions were not met, the accuracy somewhat degraded, an issue which can be mitigated by increasing the superior area or by angling the mask to expose greater surface to the camera.Conclusion:The new mask system rigidly immobilizes with sub‐mm accuracy during treatment according to optical camera (OSMS) measurements.Research supported in part by a grant from QFix (Avondale, PA) and Varian Medical System (Palo Alto, CA)
SU‐E‐T‐403: Evaluation of the Beam Performance of a Varian TrueBeam Linear Accelerator Under External Device‐Based Gated Delivery Conditions
Authors: Kobulnicky K , Pawlak D , Purwar A 
Published: June 2015

Purpose:To examine the beam performance of a Varian TrueBeam linear accelerator under external device‐based gated delivery conditions.Methods:Six gating cycles were used to evaluate the gating performance of a standard production TrueBeam system that was not specially tuned in any way. The system was equipped with a factory installed external gating interface (EXGI). An in‐house EXGI tester box was used to simulate the input gating signals. The gating cycles were selected based on long beam‐on and short beam‐off times, short beam‐on and long beam‐off times, or equal beam on and off times to check linac performance. The beam latencies were measured as the time difference between the logic high gating signal and the first or last target pulses with an oscilloscope. Tissue‐Phantom Ratio, beam flatness, and dose distributions from 5 different plans were measured using the 6 different gating durations and the un‐gated irradiation. A PTW 729 2‐D array was used to compare 5 plans versus the un‐gated delivery with a 1%/1mm gamma index passing criteria.Results:The beam latencies of the linac were based off of 20 samples for beam‐on and beam‐off, for each gating cycle. The average beam‐on delays were measured to be between 57 and 66msec, with a maximum of 88 msec. The beam off latencies averaged between 19 and 26msec, with a maximum of 48 msec. TPR20,10 measurements showed beam energy stability within 0.5% of the un‐gated delivery. Beam flatness was better than 2.5% for all gated cycles. All but two deliveries, the open field with 4 seconds on, 1 second off, and a five field IMRT plan with 0.5 seconds on, 2.5 seconds off, had >90% passing rate.Conclusion:TrueBeam demonstrates excellent beam stability with minimal beam latencies under external device‐based gated operations. Dosimetric measurements show minimal variation in beam energy, flatness, and plan delivery.Authors are employees of Varian Medical Systems, Inc.