bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐732: The Effects of Calcification Modeling for Monte Carlo Dose Calculations of Low Dose Rate Prostate Brachytherapy
Authors: Sutherland J , Miksys N , Soubiran P , Cygler J , Thomson R 
Published: June 2015

Purpose:Retrospective Monte Carlo calculations recently revealed that tissue calcifications cause significant dose perturbations in low dose rate prostate brachytherapy patients. This work investigates dose differences due to calcification modeling schemes of varying complexity for MC dose calculations.Methods:A prostate cancer patient with a large prostatic calcification (∼2.3 cm3) treated with 125I seeds was studied. MC calculations were performed using the EGSnrc user‐code BrachyDose with dose scored to medium in medium. Computational phantoms were generated from CT images acquired one month post‐implant. Tissues were assigned to voxels within structure contours based on CT number: prostate and calcification within the target, air and muscle within the rectum, urinary bladder within the bladder, and ICRU 46 soft tissue and bone in remaining voxels. Target models included: water only (TG‐43), prostate tissue with CT‐derived mass densities except for higher calcification densities over¬ridden with prostate nominal density, only prostate with unmodified CT‐derived densities, prostate and 100% calcification with CT‐derived densities (PC), and prostate and incremental mixtures of prostate and calcification with CT‐derived densities (PCmix).Results:Local dose differences of up to a factor of 3 or more were found between the various models including significant dose differences between PC and PCmix inside and adjacent to the calcification. Dose metrics differ between the models with the minimum dose that 90% of the target received (D90) differing by 4% between PC and PCmix. Adjacent to calcification, doses for calcification models were approximately 50% less than those calculated by TG‐43. D90 for calcification models was approximately 80–90% the value of that calculated by TG‐43.Conclusions:Considerable dose differences were found between calculations using various calcification modeling schemes for a low dose rate prostate brachytherapy patient with prostatic calcifications, highlighting the importance of detailed and accurate calcification modeling for MC dose calculations of these treatments.
SU‐E‐T‐737: The Impact of the Size of Custom Lead Shields On the Dosimetry of Electron Beam Therapy
Authors: Georgiev G , Jacobs K , Zuro D , Kim Y 
Published: June 2015

Purpose:Often the management of deeply penetrated skin cancer (>1cm) involves a standard open election field that is blocked with lead shields at patient's surface to shield adjacent organs at risk. This may Result in change of the known dose distribution inherent to the respective standard electron cone size. The purpose of this study is to investigate the impact of such shield on the depth dose and profile and to provide more accurate dose distribution.Methods:Gafchromic EBT2 film was used to measure the doses and dose profiles in solid water for 6 MeV and 9 MeV electron beams. The film was calibrated up to 300 cGy. Each film was scanned 24 hours after irradiation. The doses at central axes were measure at 3 different depths (dmax, 90% and 80% isodose lines (IDL)) for two standard circular sizes (5 cm and 8 cm diameters). Each field was either open or partially blocked at the surface of the solid water by 1, 2 and/or 3 cm wide and 5mm thick lead strips from two opposite edges of the light field.Results:For the majority of the cases the dose to the central axes decreases with increase of the blocked area of the field. This difference is more pronounced for smaller field size and higher energy. Compared to the depth of 80% and 90% IDL, the dose at d max is less influenced by increasing of the blocked area.Conclusion:This work accentuates on the important aspect of the use of custom shields in clinical electron radiation therapy. Particularly when smaller field sizes are used, the dose difference at the prescription depth could be as high as 60%.
SU‐E‐T‐741: The Resources and Cost to Operate An Intraoperative Radiation Therapy Program for Accelerated Partial Breast Irradiation Using a Low‐Energy X‐Ray Source
Authors: Morales‐Paliza M , Ding G 
Published: June 2015

Purpose:To report our experience regarding resource requirements and cost to operate an intraoperative‐radiation therapy (IORT) since 2011, for accelerated‐partial‐breast irradiation (APBI) using the Axxent controller (Xoft Inc.).Methods:To start an IORT program for APBI utilizing the Axxent controller with 50‐keV x‐ray source, the required resources include acquisition of the Axxent controller and a set of quality assurance (QA) tools, the training of involved professionals‐surgeons, oncologists, nurses, and physicists‐to use and operate the system, state license, storage room for the equipment, full‐time availability of the operating personnel on the procedure day, a survey meter, an ultrasound unit, sparing for x‐ray source (at least, two) and cooling‐tubing system, shielding equipment, etc. In each treatment day, QA procedures are required to test the controller performance before patient irradiation in the operation room (OR).Results:During 40 months, 76 procedures were performed. Six surgeons, two oncologists, three nurses and three physicists were trained for the procedure. Irradiation times ranged 7.4–28.6 (mean=11.7) minutes. Eight different x‐ray sources were utilized with usage times ranging 33.4–166.8 (mean=108.7) minutes. Sixteen different combinations of spherical‐balloon applicators and volumes were employed, with 40‐cc (22%) and 30‐cc (20%) volumes of the 3–4‐cm applicator being the most used. Replacement of the x‐ray sources due to arcing during patient irradiation and leak of the cooling‐water system in the OR occurred twice and once, respectively. A defective brand‐new x‐ray source (arcing) happened once.Conclusion:To start and maintain a successful IORT program, for APBI using a low‐energy x‐ray source, institutional commitment‐in addition to the resource requirements that are specific to the program‐is necessary. Based on our over‐3‐year experience, the cost of the x‐ray sources and equipment services along with vendor contract averaged US$1,000–2,000 per treatment, without considering manpower and any other resource expenses.
SU‐E‐T‐742: The Risk of Secondary Malignancies as An Evaluation Factor in the Comparison of Prostate Cancer Intensity Modulated Radiotherapy (IMRT) and Conformal Radiotherapy (CRT) Treatment Plans
Authors: Komisopoulos G , Buckey C , Stathakis S , Sakellaropoulos G , Kardamakis D , Nikoforidis G , Papanikolaou N , Mavroidis P 
Published: June 2015

Purpose:To examine the clinical efficacy of both MLC‐based IMRT, and 3D‐Conformal Radiation Therapy modalities (CRT) to treat prostate cancer using radiobiological measures. Furthermore, to investigate the risk for developing secondary malignancies in bladder and rectum due to radiotherapy from the corresponding modalities.Methods:Treatment plans for prostate cancer were developed using IMRT and CRT for ten patients. For the IMRT plans, two different treatment protocols were used (RTOG and FCCC). For the evaluation of these plans, the complication‐free tumor control probability, the total probability of injury, the total probability of control/benefit, and the biologically effective uniform dose were employed. Furthermore, based on the dosimetric data of IMRT and CRT, the risk for secondary malignancies was calculated for bladder and rectum.Results:The average risk for secondary malignancy was lower for the bladder (0.37%) compared to the rectum (0.81%) based on all the treatment plans of the ten prostate cancer patients. The highest average risk for secondary malignancy for bladder and rectum was for the 6X 3D modality (0.46% and 1.12%, respectively) and the lowest was for the 18X IMRT RTOG modality (0.33% and 0.56%, respectively). The response probability was lower for the bladder than for the rectum in all the plans. For the bladder the highest value was for the 18X IMRT FCCC (0.03%) and the lowest was for the 18X 3D modality (0.0%). For the rectum, the highest value was for the 6X IMRT RTOG (3.52%) and the lowest was for the 18X IMRT FCCC modality (0.41%).Conclusion:By using radiobiological measures it is shown that the IMRT FCCC plans had the lowest risks for normal tissue complications, whereas the IMRT RTOG had the highest. Regarding the risk for secondary malignancies, the CRT plans showed the highest values both in bladder and rectum.
SU‐E‐T‐743: The Simple Monitor Unit Calculation for Irregular Field in Passive Proton Beam
Authors: Yamakawa T , Hayashi N , Hamano H , Yasui K , Kato H 
Published: June 2015

Purpose:We try to apply the monitor unit (MU) calculation procedure for passively proton beam therapy. For estimation of field size factor (FSF) in the process, we used root A method for conversion from irregular field to equivalent field so far. In this time, we changed the conversion from root A method to Clarkson method. The purpose of this study is to ensure the calculation accuracy by comparative evaluation between root A and Clarkson methods.Methods:As fundamental study, we measured absolute dose with several circular field. Then we performed experimental fitting of conversion curve. With this method, the conversion from the equivalent circular field to equivalent square field is available by the assumed equation. As clinical study, we compared the measured MU with the calculated MU (root A and Clarkson method) in 28 prostate patients (76 fields) for the purpose of evaluating the feasibility of our procedure. To simplify the comparison of the calculation procedure, we built the dedicated MU calculation software.Results:As the Result of fundamental study, the assumed equation for conversion from circular field to square field was estimated. As the Result of clinical study, the differences between the measured MU and the calculated MU were within 2% in all cases. All calculated MU were calculated by our software. The differences of MU calculation between measurement MU and calculation MU (root A and Clarkson) were less than 2% for all cases. The average difference and standard deviation of MU calculation between the root A and Clarkson was 0.05±0.05%. However, the calculation accuracy of Clarkson method should be verified in the complicated cases.Conclusion:The MU calculation by use of Clarkson method was supposed and verified in this study. For prostate cases, the Clarkson method is feasible for MU calculation procedure.
SU‐E‐T‐756: Tissue Inhomogeneity Corrections in Intra‐Operative Radiotherapy
Authors: Sethi A , Chinsky B , Gros S , Diak A , Roeske J , Emami B , Small W 
Published: June 2015

Purpose:Investigate the impact of tissue inhomogeneities on dose distributions produced by low‐energy X‐rays in intra‐operative radiotherapy (IORT).Methods:A 50‐kV INTRABEAM X‐ray device with superficial (Flat and Surface) applicators was commissioned at our institution. For each applicator, percent depth‐dose (PDD), dose‐profiles (DP) and output factors (OF) were obtained. Calibrated GaFchromic (EBT3) films were used to measure dose distributions in solid water phantom at various depths (2, 5, 10, and 15 mm). All recommended precautions for film‐handling, film‐exposure and scanning were observed. The effects of tissue inhomogeneities on dose distributions were examined by placing air‐cavities and bone and tissue equivalent materials of different density (ρ), atomic number (Z), and thickness (t = 0–4mm) between applicator and film detector. All inhomogeneities were modeled as a cylindrical cavity (diameter 25 mm). Treatment times were calculated to deliver 1Gy dose at 5mm depth. Film results were verified by repeat measurements with a thin‐window parallel plate ion‐chamber (PTW 34013A) in a water tank.Results:For a Flat‐4cm applicator, the measured dose rate at 5mm depth in solid water was 0.35 Gy/min. Introduction of a cylindrical air‐cavity resulted in an increased dose past the inhomogeneity. Compared to tissue equivalent medium, dose enhancement due to 1mm, 2mm, 3mm and 4mm air cavities was 10%, 16%, 24%, and 35% respectively. X‐ray attenuation by 2mm thick cortical bone resulted in a significantly large (58%) dose decrease.Conclusion:IORT dose calculations assume homogeneous tissue equivalent medium. However, soft X‐rays are easily affected by non‐tissue equivalent materials. The results of this study may be used to estimate and correct IORT dose delivered in the presence of tissue inhomogeneities.
SU‐E‐T‐757: TMRs Calculated From PDDs Versus the Direct Measurements for Small Field SRS Cones
Authors: Li H , Zhong H , Song K , Qin Y , Snyder K , Gordon J , Chetty I , Wen N 
Published: June 2015

Purpose:To investigate the variation of TMR for SRS cones obtained by TMR scanning, calculation from PDDs, and point measurements. The obtained TMRs were also compared to the representative data from the vendor.Methods:TMRs for conical cones of 4, 5, 7.5, 10, 12.5, 15, and 17.5 mm diameter (jaws set to 5×5 cm) were obtained for 6X FFF and 10X FFF energies on a Varian Edge linac. TMR scanning was performed with a Sun Nuclear 3D scanner and Edge detector at 100 cm SDD. TMR point measurements were measured with a Wellhofer tank and Edge detector, at multiple depths from 0.5 to 20 cm and 100 cm SDD. PDDs for converting to TMR were scanned with a Wellhofer system and SFD detector. The formalism of converting PDD to TMR, given in Khan's book (4th Edition, p.161) was applied. Sp values at dmax were obtained by measuring Scp and Sc of the cones (jaws set to 5×5 cm) using the Edge detector, and normalized to the 10×10 cm field.Results:Along the central axis beyond dmax, the RMS and maximum percent difference of TMRs obtained with different methods were as follows: (a) 1.3% (max=3.5%) for the calculated TMRs from PDDs versus direct scanning; (b) 1.2% (max=3.3%) for direct scanning versus point measurement; (c) 1.8% (max=5.1%) for the calculated versus point measurements; (d) 1.0% (max=3.6%) for direct scanning versus vendor data; (e) 1.6% (max=7.2%) for the calculated versus vendor data.Conclusion:The overall accuracy of TMRs calculated from PDDs was comparable with that of direct scanning. However, the uncertainty at depths greater than 20 cm, increased up to 5% when compared to point measurements. This issue must be considered when developing a beam model for small field SRS planning using cones.
SU‐E‐T‐758: To Determine the Source Dwell Positions of HDR Brachytherapy Using 2D 729 Ion Chamber Array
Authors: Kumar Syam , Sitha  
Published: June 2015

Purpose:Determination of source dwell positions of HDR brachytherapy using 2D 729 ion chamber arrayMethods:Nucletron microselectron HDR and PTW 2D array were used for the study. Different dwell positions were assigned in the HDR machine. Rigid interstitial needles and vaginal applicator were positioned on the 2D array. The 2D array was exposed for this programmed dwell positions. The positional accuracy of the source was analyzed after the irradiation of the 2D array. This was repeated for different dwell positions. Different test plans were transferred from the Oncentra planning system and irradiated with the same applicator position on the 2D array. The results were analyzed using the in house developed excel program.Results:Assigned dwell positions versus corresponding detector response were analyzed. The results show very good agreement with the film measurements. No significant variation found between the planned and measured dwell positions. Average dose response with 2D array between the planned and nearby dwell positions was found to be 0.0804 Gy for vaginal cylinder applicator and 0.1234 Gy for interstitial rigid needles. Standard deviation between the doses for all the measured dwell positions for interstitial rigid needle for 1 cm spaced positions were found to be 0.33 and 0.37 for 2cm spaced dwell positions. For intracavitory vaginal applicator this was found to be 0.21 for 1 cm spaced dwell positions and 0.06 for 2cm spaced dwell positions. Intracavitory test plans reproduced on the 2D array with the same applicator positions shows the ideal dose distribution with the TPS planned.Conclusion:2D array is a good tool for determining the dwell position of HDR brachytherapy. With the in‐house developed program in excel it is easy and accurate. The traditional way with film analysis can be replaced by this method, as the films will be more costly.
SU‐E‐T‐759: To Replan Or Not To Replan for Each Fraction Using Inverse Optimization for Multichannel Vaginal Cylinder
Authors: Balik M , Rybak M , Andrews M , Strongosky M , Blair H , Obi B , Vermont C 
Published: June 2015

Purpose:This study investigates whether replanning each fraction for vaginal cuff HDR therapy using a multichannel cylinder (MC) and brachytherapy inverse optimization (BIO) provides dosimetric benefits to organs‐at‐risk (OAR). The goal was to appropriately cover the target and limit dose to OAR, as well as evaluate dosimetric changes for each fraction, while doing this in a timely and cost effective manner.Methods:From an initial selection of 57 patients that were treated with 3 fractions using a MC and BIO, a subset of n=12 patients was selected based on the criterion that one plan was used for all 3 fractions. A simulation CT was acquired prior to each fraction. CT scans for fractions 2 and 3 were fused to the initial CT. Contours for the bladder and rectum were manually drawn on CTs for all 3 fractions, and the clinical treatment volume (PTVeval) was defined. Cylinders were reconstructed using applicator modeling library, influencing time and cost effectiveness. Planning objectives were at least 95% prescription dose to 95% (D95%) of target volume and limiting high dose to OAR. Dose to 2 cm3 (D2cc) for each OAR was analyzed using a t‐test.Results:This study concentrated on comparing 2cm3 of highest dose to OAR (D2cc), for each fraction for the plans that were used to treat all 3 fraction. Based on statistical analysis, using the initial plan for fractions 2 and 3 resulted in approximately 6% change to the highest D2cc of the bladder (p=0.03).Conclusion:Performing CT fusion and contours of each OAR on each fraction allows objective plan evaluation and supports decision making on the necessity of replanning based on improved dose sparing for OAR. Future studies will investigate the effects of replanning on maximum dose (D0.1cc) using the same physician‐drawn OAR contours to avoid subjectivity.
SU‐E‐T‐761: TOMOMC, A Monte Carlo‐Based Planning VerificationTool for Helical Tomotherapy
Authors: Chibani O , Ma C 
Published: June 2015

Purpose:Present a new Monte Carlo code (TOMOMC) to calculate 3D dose distributions for patients undergoing helical tomotherapy treatments. TOMOMC performs CT‐based dose calculations using the actual dynamic variables of the machine (couch motion, gantry rotation, and MLC sequences).Methods:TOMOMC is based on the GEPTS (Gama Electron and Positron Transport System) general‐purpose Monte Carlo system (Chibani and Li, Med. Phys. 29, 2002, 835). First, beam models for the Hi‐Art Tomotherpy machine were developed for the different beam widths (1, 2.5 and 5 cm). The beam model accounts for the exact geometry and composition of the different components of the linac head (target, primary collimator, jaws and MLCs). The beams models were benchmarked by comparing calculated Pdds and lateral/transversal dose profiles with ionization chamber measurements in water. See figures 1–3. The MLC model was tuned in such a way that tongue and groove effect, inter‐leaf and intra‐leaf transmission are modeled correctly. See figure 4.Results:By simulating the exact patient anatomy and the actual treatment delivery conditions (couch motion, gantry rotation and MLC sinogram), TOMOMC is able to calculate the 3D patient dose distribution which is in principal more accurate than the one from the treatment planning system (TPS) since it relies on the Monte Carlo method (gold standard). Dose volume parameters based on the Monte Carlo dose distribution can also be compared to those produced by the TPS. Attached figures show isodose lines for a H&N patient calculated by TOMOMC (transverse and sagittal views). Analysis of differences between TOMOMC and TPS is an ongoing work for different anatomic sites.Conclusion:A new Monte Carlo code (TOMOMC) was developed for Tomotherapy patient‐specific QA. The next step in this project is implementing GPU computing to speed up Monte Carlo simulation and make Monte Carlo‐based treatment verification a practical solution.
SU‐E‐T‐762: Toward Volume‐Based Independent Dose Verification as Secondary Check
Authors: Tachibana H , Tachibana R 
Published: June 2015

Purpose:Lung SBRT plan has been shifted to volume prescription technique. However, point dose agreement is still verified using independent dose verification at the secondary check. The volume dose verification is more affected by inhomogeneous correction rather than point dose verification currently used as the check. A feasibility study for volume dose verification was conducted in lung SBRT plan.Methods:Six SBRT plans were collected in our institute. Two dose distributions with / without inhomogeneous correction were generated using Adaptive Convolve (AC) in Pinnacle3. Simple MU Analysis (SMU, Triangle Product, Ishikawa, JP) was used as the independent dose verification software program, in which a modified Clarkson‐based algorithm was implemented and radiological path length was computed using CT images independently to the treatment planning system. The agreement in point dose and mean dose between the AC with / without the correction and the SMU were assessed.Results:In the point dose evaluation for the center of the GTV, the difference shows the systematic shift (4.5% ± 1.9 %) in comparison of the AC with the inhomogeneous correction, on the other hands, there was good agreement of 0.2 ± 0.9% between the SMU and the AC without the correction. In the volume evaluation, there were significant differences in mean dose for not only PTV (14.2 ± 5.1 %) but also GTV (8.0 ± 5.1 %) compared to the AC with the correction. Without the correction, the SMU showed good agreement for GTV (1.5 ± 0.9%) as well as PTV (0.9% ± 1.0%).Conclusion:The volume evaluation for secondary check may be possible in homogenous region. However, the volume including the inhomogeneous media would make larger discrepancy. Dose calculation algorithm for independent verification needs to be modified to take into account the inhomogeneous correction.