bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐J‐174: Volume Rendered Cardiac Segmentation and Analysis for Breast Radiotherapy
Authors: Wolfgang J , Lee J , Sharp G , Chen G
Published: April 2010

Purpose: Development of a non‐rigid deformable template algorithm for the segmentation of cardiac anatomy allowing for quantification of dose delivered to the heart during breast irradiation. Method and Materials: A high resolution, contrast enhanced, cardiac CT scan was used for manual delineation of cardiac? anatomy. This reference scan consisted of 163 slices, 0.75 mm thick. In‐plane reconstruction voxel dimension of the scan was 0.373×0.373×0.75mm. Manual contours were generated to delineate cardiac anatomy, describing in detail position of relevant anatomy such as the left anterior descending coronary artery (LAD). This set of segmented structures, along with the corresponding cardiac CT image, define a reference set of cardiac data, to be used to match corresponding structures in our patient population. Plastimatch, a b‐spline, non‐rigid registration algorithm, was employed to determine the vector fields necessary to deform the reference CT image to match the designated patient volume. Using this vector field, the segmented model may then be deformed and registered to the new patient anatomy. Using the Fovia High Definition® Volume Rendering platform, the segmented volume may be analyzed volumetrically, visualizing anatomy, segmented volumes and delivered dose in near real‐time. Results: Retrospective application of this algorithm upon a selection of previously irradiated free breathing and breath hold left breast patients shows good agreement with expected geometry. However, alignment issues persist where significant thoracic and pulmonary motion obscures the registration image of the patients heart, resulting in poor registration of the treated anatomy with the cardiac template. Conclusion: Risk of late cardiopulmonary toxicity from left breast irradiation has motivated new treatment techniques to reduce cardiac exposure during radiotherapy. Implementation of a deformable segmentation model imaged volumetrically allows for careful analysis of delivered cardiac dose.
SU‐FF‐T‐05: A Monte Carlo Based Dose Calculation and Evaluation Toolkit for Electronic Brachytherapy: Feasibility of IMBT
Authors: Guo B , Cheng C , Director B , Rusch T , Esquivel C , Stathakis S , Shi C , Papanikolaou N
Published: April 2010

Purpose: To develop a Monte Carlo based dose calculation and evaluation toolkit for electronic brachytherapy sources, capable of simulating Intensity Modulated Brachytherapy (IMBT). Material and methods: This toolkit used Monte Carlo code EGS4 to calculate the dose distribution for a treatment in a realistic virtual human phantom converted from the patient's CT images and contours. An in‐house Matlab program was developed to analyze the dose distribution and generate DVHs and isodoses. Results: The system was benchmarked by comparing the calculated radial dose functions (in water) with experimental data published. Difference was within 3%. A typical intracavitary accelerated partial breast irradiation (APBI) treatment plan using Xoft Axxent electronic brachytherapy source was simulated using this toolkit. DVHs and isodoses revealed that the dose to the ribs were high in this plan due to proximity of balloon to the chest wall and the high absorption coefficient of bone to low energy X‐rays. A simple IMBT plan using partial block could conform the isodose distribution to the target, reduce the dose to ribs and chest wall without compromising the dose homogeneity to the target or increasing the dose to other critical structures. Conclusion: A Monte Carlo based dose calculation and evaluation system was developed for electronic brachytherapy sources. Benchmarked through published data, this system is capable of producing reliable and detailed dose distributions for both isotropic and intensity modulated sources. The feasibility of intensity modulation in improving the plan quality was proved.
SU‐FF‐T‐07: Treatment Planning Considerations and the Effect of Tissue Heterogeneities On the Absorbed Dose Distribution From the Xoft Axxent 50 KVp Electronic Brachytherapy Source
Authors: DeMarco J , Fahimian B , Iwamoto K , Holt R
Published: April 2010

Purpose: Tissue heterogeneity on low‐energy photon emitters can be significant due to the dependence of the photoelectric effect on atomic number and photon energy. This study evaluates the effect of tissue heterogeneities on the absorbed dose distribution from the Xoft Axxent 50 kVp electronic brachytherapy source. Materials and Methods: The MCNPX Monte Carlo code was used to simulate various tissue configurations surrounding a 50 kVp electronic brachytherapy source. The absorbed dose distribution was simulated from a single source position at the middle of a 5.0 cm diameter water filled balloon. The dependence on surrounding tissue type was studied by inserting the balloon in three different tissue regions; water, breast, and muscle. The dose enhancement from a bone region was also studied based upon a composite bone layer that included outer and inner layers of cortical bone sandwiched between a region of spongiosa bone. Results: The absorbed dose decreased by 12% in breast tissue immediately adjacent to the water balloon. At 1.0cm from the balloon edge the dose difference was approximately 5% for breast tissue. The absorbed dose difference between muscle and water was negligible. The composite bone layer produced an absolute dose enhancement of approximately 4.5 relative to water at the outer edge of the bone layer. This dose enhancement is dependent upon the distance from the source point to the bone layer. Conclusions: We present simulation results for the effect of idealized tissue heterogeneities on the absorbed dose difference from a 50 kVp electronic brachytherapy source. In general breast tissue produces a lower absorbed dose relative to water based upon the increased percentage of carbon and the resulting reduction in the effective atomic number and photoelectric effect. Cortical bone will create a significant dose enhancement due to the higher percentage of photoelectric interactions.
SU‐FF‐T‐20: Near Source Dosimetry of HDR Base of Tongue Treatments Using BrachyVision TPS & GrafChromic HD‐810 Film
Authors: Luckstead M , Lamba M , Kassing W , Elson H
Published: April 2010

Purpose: To determine the accuracy of the BrachyVision HDR treatment planning computer at predicting near source doses in the presence and absence of bone scatter in base of tongue treatments. Materials & Methods: A HDR treatment plan was developed to deliver a uniform planer dose at a depth of 1cm from a custom made planer geometry applicator with 5 catheters separated by 1cm. Plan dwell times were scaled to deliver doses of 10, 20, 50, 75, and 150Gy for a dose calibration curve for GrafChromic HD‐810 film. Dose measurements were performed at distances of 0mm, 1mm, 2mm, 3mm, 5mm, 7mm, & 10mm from the surface of the catheters. Three prescription doses were used for these measurements depending on distance from the catheters; 10Gy (0mm), 15Gy (1mm), & 25Gy (2, 5, 7, 10mm). Measurements were performed in solid water and in solid water directly against and 1mm away from a bone equivalent backscatter (Schedule 80 PVC). Doses were compared using 35 point doses (7 along each of 5 catheters) at 1cm increments. Results: Analysis of the films showed average percent differences of; 24±13%, ∼0±6%, 4±4%, 2±6%, 2±6%, & 4±3% (0, 1, 2, 5, 7, 10mm respectively) for solid water, 31%, 5%, 9%, 11%, 16%, & 14% (0, 1, 2, 5, 7, 10mm respectively) with similar standard deviations to solid water, for directly against the PVC. Conclusions: For this planar geometry are within a standard deviation of predicted doses for a homogeneous media except directly against the catheter. At a plane 5mm from the catheter the presence of high‐z back scatter produced an average increase in dose of 5%.
SU‐FF‐T‐21: The Optimal Number of Lumens for Multi‐Lumen Devices Used in Partial Breast Irradiation
Authors: Liu B , Jiang H , Kampp T , Astrahan M
Published: April 2010

Purpose: To compare the dosimetry of single‐lumen MammoSite device to multi‐lumen devices and to find the optimal number of lumens Methods and Materials: Four designs of multi‐lumen devices are studied: a central lumen with two, three, four, or six off‐set lumens which are 180°, 120°, 90° and 60° rotationally symmetric around the central lumen. All lumens are straight and parallel to the central lumen. Patients of three different clinical conditions are simulated: (1) skin and chest wall spacing from balloon are larger than 10 mm, (2) smaller than 5 mm and (3) between 5 mm and 10 mm. 10 mm extension from the balloon is defined as planning target volume (PTV). In clinical conditions (2) and (3), where the spacing of skin and/or the spacing of chest wall are less than 10 mm, PTV are shaped to avoid skin and chest wall. The region of PTV excluding balloon is defined as PTV_EVAL, which is used for DVH constraints and dosimetric comparison. Results: For clinic condition (1), where the PTV is symmetric, single‐lumen MammoSite and multi‐lumen devices provide similar dosimetric results, whereas in clinic condition (2) and (3), the PTV is asymmetric, the multi‐lumen devices provide good coverage to PTV_EVAL with V95 > 90%, and the multi‐lumen devices deliver significantly less incidental dose to skin and chest wall: three‐lumen device reduce the dose to skin/chest wall by 10%, while four‐ five‐ and six‐lumen device provide similar results, reducing the skin/chest wall dose to be less than 120% of the prescription dose, a 25% drop. Conclusion: Compared with single‐lumen MammoSite device, Multi‐lumen device have better dosimetric results in partial breast irradiation where the PTV spacing is less than 10 mm. Devices with more than four lumens provide similar results to four lumen device.

Research sponsored by Hologic
SU‐FF‐T‐22: Treatment Planning Changes to Reduce Side Effects From Prostate Cancer Brachytherapy with Cs‐131
Authors: Lasher D , Shah A , Wojcicka J , Kassas B , Bagan E
Published: April 2010

Purpose: To reduce gastrointestinal (GI) and genitourinary (GU) side effects in patients receiving Cesium‐131 prostate brachytherapy by modifying the treatment planning technique. Methods and Materials: 15 patients were pre‐planned with Cs‐131 according to the modified peripheral loading technique. For the next 15 patients, the planning technique was modified to increase seed placement around the periphery of the gland, reduce the prostate V150, and decrease dose to the rectum. All implants were conducted with pre‐loaded needles and stranded seeds. Dose volume statistics were analyzed according to a 2‐sided T‐test with 95% confidence interval. The follow‐up range was 6 to 19 months. Maximum GI and GU toxicity scored according to the Common Terminology Criteria for Adverse Events (NCI, version 3.0) were reported for all patients. Minimum PSA value in the 6–11 month follow‐up period was reported. Results: The number of seeds and total activity implanted decreased 22.0%(p<0.0001) and 14.9%(p<0.005), respectively. The prostate V150 decreased 19.2%(p<0.02), the rectum D10 and V100 decreased 24.8%(p<0.0002) and 73.3%(p<0.04), respectively. The prostate V100, V90, D90 and urethra UV150 were unchanged. Before the planning change, 40% (6 out of 15) of patients reported higher grade (Levels 2 and 3) GI toxicity and 53.3% (8 out of 15) of patients reported higher grade GU toxicity. After the planning change, these values reduced to 13% (2 out of 15) GI and 40% GU (6 out of 15). 4 patients in the first group and 1 in the second group experienced urinary retention. The mean PSA follow‐up was 8.93 and 8.5 months for the first and second groups, respectively. The minimum PSA reported was unchanged (1.00 in the first group, 0.98 in the second group,p=0.95). Conclusion: Implementing these treatment planning changes reduced the severity of GI and GU side effects without compromising dosimetric coverage of the prostate or initial PSA response.
SU‐FF‐T‐24: A Monte Carlo Phantom Study for Brachytherapy Dose Perturbation in Henschke Type GYN Applicator
Authors: Yu P , Chao T , Lee C , Tung C
Published: April 2010

Purpose: The commercial brachytherapy planning system does not evaluate the dose perturbation of the rectal shielding material near the Iridium source. Because the electron equilibrium can't exist around the Iridium source, the dose measurement near the source will be very difficult. In this study, Monte Carlo simulation has been used to estimate the dose perturbation near the source. In order to realize the volume dose of normal tissue, phantom study is need. According to this study, the dose of rectum by brachytherapy will be assessed more accurately. Materials and Methods: The first Monte Carlo simulation result of the Iridium source in water is based on the brachytherapy planning result. This first step is used to verify the simulation parameter. Another simulation condition included with rectal shielding material will be compare to the first condition. The dose difference between these two simulation conditions will suggest the extent of influence rectal shielding material. In the co‐operative hospital, physician used Henksche applicator to treat GYN patient, so the three source positions will be put into three individual tandems to cover the mucosa layer of treatment area. Results: When the Henksche applicator is used for the treatment of GYN patient, the rectal shielding material which is made by tungsten alloy will reduce the tissue dose around the Iridium source. So the brachytherapy planning system will overestimate the rectum point dose. Through this study, the dose of rectum can be defined more precisely. Because the limited dose of rectum can be assessed, the physicist will adjust the dose distribution to achieve the optimization dose distribution more reasonable. Conclusions: The influence of rectal shielding material can be assessed more precisely by this study. By adding simulation results to the volume rectum dose of external beam treatment can give the physician a comprehensive assessment.
SU‐FF‐T‐25: Cervix Brachytherapy Dosimetry: Observed Improvement in Data Submitted to Clinical Trials
Authors: Lowenstein J , Roll J , Ibbott G
Published: April 2010

Purpose: For over 40 years, the Radiological Physics Center (RPC) has reviewed the completeness, consistency with protocols, and the dosimetric accuracy of data submitted for cervix patients treated with brachytherapy on national clinical trials. In 2005 the RPC presented data which showed that 65% of cervix patients placed on study had one or more dosimetry errors in at least one of their implants. This study was conducted to determine if brachytherapy dosimetry has improved in the last 4 years. Methods & Materials: In the last 4 years the RPC has reviewed 695 HDR and LDR implants. Independent dose calculations were performed at points A, B, vaginal surface, bladder and rectum as defined by the protocol in accordance with ICRU‐38. The vaginal surface dose was defined as a point lateral to the center of the source (s) at 0.5cm from the surface of the ovoid. RPC doses were compared to the institution's reported doses. Results: From 2005 to 2009 the RPC has determined that dosimetry errors have decreased by 50%. Most remaining errors result from incorrectly defining calculation points. However the use of CT has created some new issues due to the manipulation of the CT images when visualizing the tandem. Conclusion: The decrease in dosimetry errors is due to several different aspects: increase in rapid reviews, more timely reviews of patients and better communication with an institution when discrepancies are discovered.

This work was supported by PHS grant CA 10953 awarded by NCI, DHHS
SU‐FF‐T‐26: Correlation Between Radiation Post‐Survey and Planning Parameters in Permanent Prostate Brachytherapy
Authors: Li Texin , Tong Shidong , Gong Jason , Fountain Betty , Duffy Edward
Published: April 2010

Purpose: To establish correlation between radiation post‐survey and planning dosimetric parameters in permanent prostate brachytherapy. Combined with patient separation, it is possible to calculate the dose rate at patient surface and exposure rate 1 meter away from the patient. Materials /Methods: The transrectal ultrasonography (TRUS) images are obtained using the B&K unit (Analogic Corporation) in 5 mm steps. Planning goals are: for prostate V100 95%, D90 100%, and for prostatic urethra D10 150%. Dose calculations are performed using VariSeed (Varian Medical System) planning system. The dose rate is obtained by dividing the absolute dose by 1.44T1/2, where T1/2 is the half ‐life of implanted isotope. The center of the prostate is determined by locating a point on the D column in the ultrasound template at the midline and the mid‐section of the prostate. The distance from the center of the prostate to patient surface is about half of the patient separation. The dose rate is also calculated using AAPM TG‐43 point source model, g(r)/r2, using the same dosimetric parameters for planning. Comparisons are made between point source and VariSeed (discrete multiple sources) results. Results: For distances larger than 8.0 cm from the center of the prostate, the dose rate by discrete multiple sources can be accurately approximated by AAPM TG‐43 point source model calculation within 5.0% for I‐125 and Pd‐103, for Cs‐131 within 10.0%. In addition, depending on patient separation, dose rate for Cs‐131 can be more than 30 times higher than that for Pd‐103, 10 times higher than that for I‐125. Conclusion: Planning dosimetric parameters along with patient separation can be used to calculate the post‐survey results at the patient surface using AAPM TG‐43 point source model. The exposure rate 1 meter away from the patient can be obtained by applying the inverse square factor.
SU‐FF‐T‐34: Dosimetric Evaluation of Gammamed High Dose Rate Intraluminal Brachytherapy Applicators
Authors: Chandraraj V , Supe S , Manickam R
Published: April 2010

Purpose: The aim of this study was to dosimetrically evaluate various intraluminal brachytherapy applicators for the Gammamed high dose rate afterloading system. Materials and methods: Dosimetric evaluation was carried out for 8 mm, 10 mm, 12 mm and 14 mm diameter intraluminal applicators available with the Gammamed high dose rate afterloading system. Treatment planning for these applicators was carried out with abacus treatment planning system for active source length and 8 cm, 10 cm and 12 cm. All evaluations were carried out for prescription dose of 5 Gy at the reference point of 1cm from source axis. Reference volume length (RVL), Treated volume (TV), Hyper dose sleeve radius (HSR) were noted down from the isodose plans. Iterative, geometric and equal times optimization routines were carried out for all evaluations with step size of 0.5cm. Results: The isodose curves showed tapering pattern towards the distal and proximal regions. The reference volume lengths were larger than active source lengths for 8mm and 10mm diameter applicators. Reference volume lengths were smaller than active source length for 12mm and 14mm diameter applicators hyper dose sleeve radius decreases with increase in diameter of the applicator. For 14mm diameter applicators, the hyper dose sleeve radius was smaller than the radius of the reference isodose. Iterative optimization routine gave better average in terms of reference volume length few are four diameter applicators.

Conclusions: We evaluated the dosimetric parameters for various intraluminal applicators available with the Gamma med high dose rate remote after loading system. The values of RVL and HSR were within acceptable limits for the four applicators considered in this study.
SU‐FF‐T‐35: A Monte Carlo Study for Evaluation of Tissue Heterogeneity Effect of Inversely Optimized Intracavitary High Dose Rate Brachytherapy Plan
Authors: Cheong K , Lee M , Kang S , Park S , Kim K , Hwang T , Bae H , Oh D , Suh T
Published: April 2010

Purpose: To investigate tissue heterogeneity effect of an intracavitary high dose rate brachytherapy plan which is optimized by the inverse planning option. Method and Materials: A CT and VOI based brachytherapy plan for an intra‐uterine and cervix cancer treatment was made using inverse planning simulated‐annealing (IPSA) module provided by Plato TPS. The microSelectron‐HDR Ir‐192 afterloader and 3 catheters (2 ovoids and 1 tandem) were used for the treatment. For a verification of the plan result, EGSnrc based dosxyznrc Monte Carlo code was employed. Patient CT data was converted to egsphant data by the ctcreate code and each source position and weight from the plan data was used for a Monte Carlo simulation as well. Ir‐192 source was approximately modeled by 3.6 mm length and 0.6 mm diameter and it was assumed to be located at the center of the catheters, while parallel to the z‐axis at each position because of restricted freedom of source modeling. The microSelectron‐HDR Ir‐192 spectrum data could be obtained from the EGSnrc code, however, number of history was determined empirically based on known air‐kerma and dose rate value. Conventional point A and B doses and DVHs of PTV, bladder and rectum were evaluated for a quantitative comparison. Results: Significant decrease of dose at point A and B more than 10% was observed in the Monte Carlo simulation. PTV coverage by 100% isodose surface was degraded while rectum and bladder mean dose was reduced up to 15%. Resultant dose rate decrease was also observed. Conclusion: Conventional brachytherapy dose calculation method could not appropriately consider tissue heterogeneity effect and inverse planning optimization could invoke serious erroneous result. Therefore inverse planning optimization should be carefully implemented for a HDR brachytherapy planning.
SU‐FF‐T‐40: Brachytherapy TPS QA Using EBT Model GafChromic Film
Authors: Devic S , Tomic N , DeBlois F
Published: April 2010

Purpose: We describe a method for quality assurance (QA) test that assesses all steps of conformal CT‐based high dose rate (HDR) brachytherapy. A procedure was developed to compare dose distribution generated by the treatment planning system and measured by the EBT model GAFCHROMIC™ film within a dedicated brachytherapy QA phantom. Method and Materials: A phantom consists of 3 catheters embedded in a surface plane of 2 cm thick slab of solid water (SW) mimicking the Fletcher GYN applicator set. Additional slabs of solid water were added above and below this slab to provide full scattering conditions. A single sheet of EBT model GAFCHROMIC™ film was placed 2 cm below the plane containing the catheters. Dose distribution, mimicking the GYN treatment, was calculated in OnCentra Brachy treatment planning software and dose distribution within the film plane was exported in DICOM format. Same plan was delivered to the phantom containing the film, and dose distribution was measured using our novel extended range radiochromic film dosimetry protocol, which employs all three channels of the film absorption spectrum and can measure dose in the range from 0.02 to 100 Gy. Calculated and measured dose distributions were compared within FilmQA software in terms of gamma function. Comparison was made over region of interest (ROI), defined by region containing isodose ⩾ 5% of prescription dose. Results: Based on recommendations given in the commissioning of brachytherapy treatment planning systems section from IAEA TRS‐430 report, we have established a 5% dose/2 mm distance criterion for gamma function. We found that 95% of points within ROI were passing this criterion. Conclusions: QA method described provides a comprehensive verification of all the steps involved in CT‐based HDR brachytherapy. We recommend the method to be used during commissioning process and once a year as a part of brachytherapy QA program.
SU‐FF‐T‐44: Dosimetric Analysis of the Effect of Edema in 131Cs Prostate Permanent Seed Implants
Authors: Kehwar TS , Jones HA , Huq MS , Beriwal S , Benoit RM , Smith RP
Published: April 2010

Purpose: To investigate the effect of edema on different dosimetric parameters in prostate permanent seed implants. Materials and Methods: Transrectal ultrasound (US) and computer tomography (CT) images were used to determine pre‐ and post‐needle implant volumes, and post‐implant prostate volumes in 31 patients who had received implant. Dose volume histograms(DVH) were generated to determine the prostate volumes that received 100%, 150% and 200% of prescribed dose to calculate quality indices(QIs) and fractional D90(FD90) for each set of volumes for all patients. Results: No statistical differences were found between post‐needle and post‐implant(day 0) volumes obtained by US and CT images(p=0.56). The half life of the edema was found to be 9.72days.

The change in mean values of coverage index(CI), dose non‐uniformity ratio(DNR), overdose index(ODI), relative dose‐homogeneity index(DHI) and FD90 can be described by (1) (2) (3) (4) and (5) differential equations. The values of correlation coefficients and time constants obtained from least square fit of these equations were found to be 0.9867 & 0.0316 for CI, 0.9988 & 0.0148 for DNR, 0.9958 & 0.00148 for ODI, and 0.9983 & 0.0125 for DHI, respectively. Conclusions: CI, DHI and FD90 decreased, while DNR and ODI increased from pre‐implant plans to post‐implant plans at day 0 due to edema formation. CI, DNR, ODI and FD90 increased and DHI decreased with increasing post‐implant time and attained optimal values in 4 weeks. During this period 85% dose is delivered due to short half life of seeds. Therefore, it is important to account for the effect of edema at the time of implant while defining seed positions. Implants performed based on pre‐implant volume study only result in poor dosimetric results in implants.
SU‐FF‐T‐48: Dosimetric Feasibility of Using Low Energy Sources in Multi‐Lumen Device for Partial Breast Brachytherapy
Authors: Liu H , Fu L , Xiao Y , Yu Y
Published: April 2010

Purpose: To evaluate the dosimetric feasibility of using low energy sources (Cs‐131, I‐125, Pd‐103) in the multi‐lumen device for partial breast brachytherapy. The sources are placed into the device for multiple days until the desired dose is achieved, then withdrawn with the device. This outpatient procedure only requires two visits, one for source placement and another for device withdrawal. Method: A 10‐1 SAVI device was fully expanded, CT‐scanned and imported into VariSeed. Cavity, PTV (cavity + 1cm margin) and PTV_eval (PTV − cavity) were created. The same type and activity of seeds were added into the multi‐lumen device to cover the PTV_eval and seed activity was adjusted to achieve a nominal dose (50Gy in one half‐life of source). Different seed types and distributions were tested. Oncentra Brachy and IPSA optimization was used to generate a HDR plan for comparison. Dosimetric parameters (D90, V100, V150, and V200 of PTV_eval) and skin dose were compared. Results: D90, V100, V150, and V200 of PTV_eval of HDR plan are 107%, 97%, 52cc, and 24cc. The most comparable LDR plan is from a non‐uniform distributed 90 3.2U Cs‐131 source, which gives 102%, 92%, 52cc, and 26cc. Skin dose is lower than the HDR plan by ∼10% of the prescription dose from 0.5 ∼ 5 cm away from the PTV edge. With the comparable coverage, I‐125 gives slightly higher V150 and V200 (56cc and 30cc, respectively), while Pd‐103 gives much higher V150 and V200 (66cc and 46cc respectively). Conclusion: Cs‐131 is the best choice among the 3 commercially available low energy sources. It can provide adequate target coverage and similar dose homogeneity compared to HDR dosimetry in reasonable days (10 days). The faster dose fall‐off of the low energy sources give it advantage of less dose to the surrounding healthy tissues including skin, heart, and lung.
SU‐FF‐T‐58: Dosimetric Study of a New Surface Applicator for the Xoft Axxent System
Authors: Axelrod S , Kelley L , Walawalkar A , Yao S , Rusch T
Published: April 2010

Purpose: To determine the dosimetric properties of a new surface applicator designed for the Xoft 50 kVp x‐ray system Method and Materials: A 35mm conical stainless steel applicator with Al flattening filter interfaces to the Xoft 50 kVp x‐ray source to provide therapeutic radiation to surfaces such as skin. Measurements of the dose profile at the surface and at depths to 20 mm were performed using a PTW ionization chamber in a water phantom. The chamber was controlled by a stepper motor and linear stage, and data was read into a controlling computer. In addition, film data was taken both parallel and perpendicular to the surface. Results: Nominal dose profiles and depth dose characteristics were determined from an average of ten sources. Dose profiles across at least 80% of the applicator width were flat to within ± 10% for all sources, and to within 5% on average. Depth dose characteristics are very similar to those published for HDR based surface applicators, with the percent depth dose at 5 and 10 mm at 58% and 36%. Such data can be used for treatment planning purposes. The variation seen among sources determines an error band representative of what will be experienced in clinical use. Conclusion: The FDA approved surface applicator delivers a dose profile that is flat to within ± 10% over a span of 80% of the defined width of the device. It can be used for treatment of skin lesions in lightly shielded rooms due to the low energies employed. There are also intriguing possibilities for use intra‐operatively, since the system can be used in an operating room.

Conflict of Interest: Research supported by Xoft, Inc.
SU‐FF‐T‐59: Experimental Verification of Dosimetric Parameters for a New I‐125 Interstitial Brachytherapy Source
Authors: Kennedy R , Davis S , Micka J
Published: April 2010

Purpose: This investigation experimentally determined the dosimetric parameters of a new brachytherapy source from GE Healthcare, henceforth referred to as model 9011. This new source is designed to be used with smaller gauge needles and may reduce trauma to the patient during the implant procedure. The results of the experiments performed in this work were compared to published values for the model 9011 and the model 6711. Methods and Materials: The AAPM TG‐43U1 document details the dosimetric parameters that must be determined for any new low‐energy interstitial brachytherapy source. Thermoluminescent microcube dosimeters were used to experimentally determine the radial dose function, dose rate constant and anisotropy functions. Two PMMA phantoms were machined in‐house with tolerances of 0.001″. The atomic composition of the acrylic was verified by Colombia Analytical Laboratories (Tucson, AZ). Two 9011 seeds were studied as well as the standard 6711 conventional model. Each parameter was also determined computationally using MCNP5 for both the 9011 and 6711. These and other published values were compared to the experimental results. Results: Initial measurements of the 9011 indicate good agreement in the dose rate constant and radial dose function as compared to the Monte Carlo calculated values and to the published values. Additionally, as expected, the 9011 dose rate constant and radial dose function values are similar to those of the 6711. Initial measurements of the 2D anisotropy function show good agreement with published values as well. Conclusions: The 9011 seed may provide an advantage to the patient without compromising the dosimetric qualities of the seed. Although the model 6711 and model 9011 are quite similar, their TG‐43 parameters are not identical and should be entered into a treatment planning system separately. Conflict of Interest: Funding for this project was funded in part by GE Healthcare.
SU‐FF‐T‐64: Characterization of MOSFET Dosimetry System for Source Position Verification in HDR Brachytherapy
Authors: Ivanova T , Gilbert L , Lazos D , Todor D
Published: April 2010

Purpose: To test the Metal‐Oxide‐Semiconductor Field Effect Transistor (MOSFET)‐based method for HDR Brachytherapy source tracking and to assess how accuracy and precision of the method changes with the MOSFET reading fluctuations and the number of dosimeters. Methods and Materials: Three standard MOSFET dosimeters connected to a high sensitivity bias supply were placed at fixed positions, 3 to 7 cm from the Ir‐192 source, driven by a Remote Afterloader (VariSource iX, Varian Medical Systems Inc.), within a solid water phantom. Six source dwell positions were planned. MOSFETs calibration was performed at a distance of 3 cm from source. MOSFET characteristics, including energy and angular dependence, dose linearity and reading variation in time, were established. A Matlab optimization code, based on the minimizing the sum of the normalized squared differences between the measured and analytically calculated dose values, was developed for source position calculation. Randomly generated measurement errors 1 to 8% were added to MOSFET readings to assess the method accuracy and precision degradation. The effect of the MOSFETs number on the system performance was also studied. Results: Measurements with three MOSFETs result in 0.2 to 1.9 mm deviations between calculated and actual source positions, with average of 0.8 mm. If fluctuations added to the MOSFET readings are of 1% of the reading value, accuracy of (0.7±0.3) mm is achieved, while fluctuations of 8% result in (5.2±2.6) mm accuracy. Increase in the number of MOSFETs until 12 results in improved accuracy of (0.3±0.2) mm and (2.9±1.5) mm for 1% and 8% high fluctuations, correspondingly. Conclusions: The study showed the potential of the method to verify the position the HDR Ir‐192 and to improve the quality control in HRD Brachytherapy. Increasing the number of MOSFET detectors improves the accuracy of the method even for higher MOSFET reading uncertainties.
SU‐FF‐T‐67: Implementation of the TG‐128 Recommendations for Quality Assurance of Prostate Brachytherapy Ultrasound Systems
Authors: Sutlief S
Published: April 2010

Purpose: The purpose of this work is to assess several aspects of the implementation of the recommended TG‐128 quality assurance tests, including the time to perform the tests, the general range of parameters for several ultrasound systems, and correlation of QA components with treatment technique. Method and Materials: The TG‐128 tests were performed on a selection of ultrasound units and biplane transducers commonly used in prostate brachytherapy. The author used the following ancillary equipment to conduct the tests: the CIRS Model‐45 Prostate Brachytherapy Phantom, a container of distilled water, brachytherapy needles, a needle template, a stepper/stabilizer for the probe, and a computerized treatment planning system. Each test was independently timed and notes were made of any deviations in terms of equipment limitations and expected results. Results: The typical time to complete all required tests was approximately ninety minutes. Once the user establishes baseline data and develops a system for conducting the tests, this duration can readily be shortened to one hour. The measurements generally fell well within the tolerances recommended in TG‐128 with the exception of needle template/electronic grid alignment (Test 7), where discrepancies approached the action level of 3 mm and the tissue/water correction factor was important. Care must be exercised in performing the volume measurements, as it can be difficult (a) to get acoustic coupling across the angle subtended by the target to be measured, and (b) to move the probe longitudinally without losing coupling. Based on the experience gained performing these tests, a standard form has been developed for recording the results. Conclusion: The quality assurance tests recommended by TG‐128 for prostate brachytherapy ultrasound systems can be completed in a reasonable amount of time. Consideration must be given by the user as to how these tests relate to the overall quality assurance of the prostate brachytherapy program.
SU‐FF‐T‐70: In‐Phantom Calibration of High Dose Rate Ir‐192 Brachytherapy Source — A Feasibility Study
Authors: Mandiram Kuppuswamy , Senthil G , Sundaram Visalatchi , Muthulingam S , Karthik S
Published: April 2010

Purpose: The purpose of this study is to develop the independent method of calibration of the brachytherapy source using the modified Radiotherapy Treatment Planning System (RTPS) Phantom and compare the results with the well chamber measurement or system activity. Method and Materials: Nucletron (HDR) unit with Ir‐192 source, modified solid cylindrical PMMA RTPS phantom with 12 inserts and 0.6cc Farmer chamber(FC) are used for this study. Out of these twelve inserts, any one insert can hold the source and rest eleven insert positions can be used as a measuring point with the 0.6cc FC. Phantom scatter factors are derived for various distances against the well chamber measurement activity and system activity values and made as a standard for reference. Measurements for activity calculation were taken at a distance varying from 4.4 to 15.69 cm between the source and the chamber and at a distance of 1m from the floor to minimize the room scattering. Maximum response position of the chamber was taken for each position. Results: The variation between the measured activity and system activity by in‐phantom method was −0.02% to 1.28%. and is mainly depends upon the phantom scatter factor for various distances. The percentage of variation (−0.02 to 1.28) is directly proportional to the distance (4.40–15.69cm) between source and the chamber because of phantom scatter contribution. So the percentage of variation increases with source to chamber distance but using RTPS the percentage of variation is within the tolerance limits. Conclusion: The mechanical rigidity and reproducibility of a solid phantom is superior to in‐air calibration jig however in chamber measurement chamber technique found to be reproducible and to agree within ±1.5%, as long as the appropriate corrections are applied. This method of calibration is being verified against well chamber & jig calibration.The results are within the tolerance limit.
SU‐FF‐T‐83: An Image‐Guided Adaptive Treatment Planning Optimization for IMRT
Authors: Lee E , Cha K
Published: April 2010

We present an adaptive IMRT treatment planning approach that is guided by 3D/4D images and that allows exploration of a wide range of beam angles for optimal treatment design. Computational advances to improve solution times are highlight, and robustness of the method and quality of the resulting plans are compared.

We focus on column generation of adaptable and clinically acceptable plans. Binary (0/1)variables are used to capture “on”/“off” for each beam. Guided by the tumor image, these candidate beams are generated dynamically throughout the solution process. The treatment model includes explicit clinical constraints, including constraints based on upper/lower/mean dose, approximate organs‐at‐risks dose‐volume relationships, and PTV homogeneity and coverage. During the solution process, at most k active beams are allowed in the branch‐and‐price framework(where k is input by clinicians and is patient/tumor‐specific).

Compared to clinical plans, for prostate cases, PTV homogeneity improves by 8–11%, whereas mean‐dose to rectum and bladder reduce uniformly by over 50%. For head‐and‐neck cases, left‐parotid mean dose reduces uniformly by over 50%. In particular, all critical structures receive significantly less dose, as the adaptive approach focuses the radiation onto the tumor volume. The adaptive plans provide over 95% PTV coverage, as requested by the clinicians.

The adaptive branch‐and‐price approach proves efficient to simultaneously optimize the beam orientations over the entire space of gantry angles and the fluence map. Two significant advances were made: 1) We efficiently and rapidly solved previously intractable large‐scale treatment instances with important clinical constraints to optimality. 2)We designed a rapid column‐generation approach where candidate beams are chosen adaptively and dynamically, and where the set of active beams are set to clinically acceptable values. These properties allow for generation of plans that are practical for actual delivery and guided in real‐time by tumor images. Clinical experiments showed that our approach produces superior plans.
SU‐FF‐T‐89: Comparison of RADPOS 4D in Vivo Dosimetry System with Phillips Bellows and Varian RPM Systems
Authors: Cherpak A , Andrusyk S , Pourmoghaddas A , Wells G , Cygler J
Published: April 2010

Purpose: To present the latest data on the newly‐developed RADPOS 4D in vivo dosimetry system including comparisons with the Phillips Bellows and Varian RPM systems. Methods and Materials: A 4D Quasar phantom was set‐up on the couch of a Phillips Brilliance CT scanner and set to move in a sinusoidal pattern with amplitude of 1 cm. The Phillips Bellows belt was secured around the moving translation stage and was used to record the motion of the stage. The same motion was also measured by a RADPOS detector. This procedure was repeated on the couch of a PET/CT scanner using the Varian RPM system. A RADPOS detector and the RPM optical block were placed on top of the phantom's translation stage and the motion was recorded by both systems. The feasibility of using the RAPDOS system for in vivo dosimetry during daily external beam radiation therapy is also being studied. Results: When used to measure simulated breathing motion on a 4D Quasar phantom, the RADPOS‐measured displacements were on average within 0.13 and 0.05 mm of those recorded by the Phillips Bellows and Varian RPM systems, respectively. The correlation between the RADPOS displacements and those measured by the Bellows and RPM systems were 0.96 and 0.99, respectively. Initial results for clinical use in radiation therapy treatments show that the RADPOS system can be set‐up quickly, requiring minimal additional time for each scheduled treatment fraction. Conclusions: In conclusion, the RADPOS system agrees well with currently accepted position monitoring systems and provides sufficient information to identify changes in the patients breathing pattern and other patient motion. Acknowledgements: This project is supported by grants from HTX and ORCC Foundation. Financial and technical support from Best medical Canada is also acknowledged.
SU‐FF‐T‐110: Evaluating Head and Neck IMRT Plans with a Computational Tool for Spatial Dose‐Volume Histograms
Authors: Myint K , Pyakuryal A , Gopalakrishnan M , Sathiaseelan V , Mittal BB
Published: April 2010

Purpose: To evaluate head and neck IMRT plans with spatial dose‐volume histograms (DVHs) that have been calculated with a computational tool for DVH analysis. Method and Materials: A computational tool called HART (Histogram Analysis in Radiation Therapy) was developed for the efficient analysis of treatment plan DVHs. Notable functions include user‐defined DVH endpoints, an outcome analysis toolbox for biological endpoints such as tumor control probability (TCP) and normal tissue complication probability (NTCP) and a user‐friendly graphical interface. A recent addition to the HART package is the ability to calculate spatial DVHs in all three dimensions (xDVH, yDVH and zDVH). In this study, spatial DVHs in all three directions were extracted for ten head and neck IMRT plans and compared to conventional DVHs. Dose‐volume data was examined for all targets and 26 critical structures. Results: The attraction of the conventional DVH has been that it can summarize a 3‐D isodose distribution onto a 2‐D plot. Unfortunately, the cost of this transformation is the loss of spatial information. Spatial DVHs have been shown to provide information on the position of “hot” and “cold” spots in the dose distribution while still maintaining the simplicity of a 2‐D plot. This additional spatial data can then be used for correlation to complications in normal tissues. By automating the extraction and computation of all DVH data, it was shown that HART is a useful tool for the evaluation of IMRT treatment plans with spatial and conventional DVHs. Conclusion: Spatial DVHs can be used as a complementary tool to conventional DVHs in the evaluation of head and neck IMRT plans. Automating these computations with software such as HART allows for the routine clinical use of spatial DVHs.
SU‐FF‐T‐124: Comparison of Eclipse Step‐And‐Shoot IMRT Plans with Direct Aperture Optimized Treatment Plans
Authors: Weldon M , Zhang D , Korytko T , Radawski J , Gupta N
Published: April 2010

Purpose: The purpose of this work was to investigate possible improvements in plan quality and efficiency for step‐and‐shoot IMRT plans computed using a Direct Step‐and‐Shoot (DSS) optimization engine to those calculated by Eclipse TPS. Method and Materials: Eclipse uses a gradient based fluence optimization algorithm for IMRT planning, followed by a Leaf Motion Calculation Algorithm to compute MLC segments, followed by Monitor Units (MU's) calculation for the optimal fluence maps obtained. IMRT plans previously delivered in our clinic for different target complexities ranging from prostate, head and neck and abdomen were re‐planned using the same target and normal tissue constraints with a commercially developed DSS algorithm based IMRT planning prototype software. The DSS planning software was further constrained to produce less than or equal to the number of segments as the clinically treated Eclipse treatment plan. These plans were compared using several dose‐volume based plan comparison parameters for both the PTV and Organs at Risk (OAR), along with the total number of MU's and segments required to deliver a comparable or better plan. For comparison purpose, the DSS plans were scaled to have the same D50 as the Eclipse plans. Results: Our results show that DSS always result in better quality plans than the fluence based optimization. The DSS plans gave more homogenous PTV coverage, reduction of hot spots, and better dose sparing in most OAR's e.g. H&N (spinal cord, brainstem), Pelvis (bladder, rectum). The total MU's calculated by the DSS plans in our cases were sometimes less or greater than the Eclipse plans. Conclusions: For our study DSS consistently resulted in overall better quality, compared to our Eclipse fluence based optimized plans. There was no consistent improvement of plan efficiency. However, further optimization of constraining the number of segments may yield more efficient plans.
SU‐FF‐T‐128: A Novel Approach for Measurement of Dosimetric Leaf Gap for a Rounded Leaf End Multi‐Leaf Collimator
Authors: Weinberg R , Boyer A
Published: April 2010

Purpose: For Varian multi‐leaf collimators (MLCs), the rounded leaf ends of the MLC cause a mismatch between the edges of the light field and the radiation field in the plane of isocenter. The radiation field edge is defined as the point at the edge of the radiation field at which the intensity drops to 50% of the intensity within the field. The dosimetric leaf gap is defined in the Eclipse treatment planning system (TPS) as twice the displacement between the leaf tip projection and the radiation field edge. Method and Materials: A step and shoot sequence of MLC fields generated nominally 2‐cm wide strips narrower at their tops and wider at their bottoms. Pairs of strips were abutted with a 2‐mm gap at the narrow ends. The gaps between the strips decreased by 0.1 mm for every subsequent leaf pair until the wide ends of the strips overlapped by 2 mm, creating a narrow under‐dose triangle at one end of the strips and a narrow over‐dose triangle at the other end. The dosimetric leaf gap was derived from the settings of the leaf pairs along the strips at which the tips of these triangles met. Results: To measure the location at which the triangles met, a region of interest (ROI) was drawn in imaging software and moved along the intensity strip pattern, measuring the standard deviation (SD) of intensity values within the ROI at each location. These SDs were fit to a second‐order polynomial whose minimum identified the leaf tip positions used to determine the dosimetric leaf gap. These measurements determined a 0.6‐mm dosimetric leaf gap. Conclusion: The dosimetric leaf gap value used for commissioning a TPS can be determined for a rounded‐leaf MLC by analyzing a step‐and‐shoot MLC sequence that employs abutting strips creating an over‐ and under‐dose pattern.