bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐03: Radiobiological Evaluation of a Directional Brachytherapy Device Surgically Implanted Following EBRT
Authors: Rivard MJ , Emrich JG , Poli J 
Published: July 2016

Purpose:Preceding surgical implantation following external‐beam radiotherapy (EBRT) delivery, a radiobiological evaluation was performed for a new LDR Pd‐103 directional brachytherapy device (CivaSheet). As this was the first case with the device used in combination with EBRT, there was concern to determine the appropriate prescription dose.Methods:The radiobiological model of Dale (1985, 1989) was used for a permanent LDR implant including radioactive decay. The biological effective dose (BED) was converted to the equivalent dose in 2 Gy fractions (EQD2) for comparison with EBRT prescription expectations. Given IMRT delivery of 50.4 Gy, an LDR brachytherapy dose of approximately 15–20 Gy EQD2 was desired. To be specific to the treatment site (leiomyosarcoma T2bN0M0, grade 2 with R1 surgical margin), the radiobiological model required several radiobiological parameters with values taken from the literature. A sensitivity analysis was performed to determine their relative importance on the calculated BED and subsequent EQD2. The Pd‐103 decay constant (λ=0.0017 h−1) was also used. DVHs were prepared for pre‐ and post‐surgical geometries to glean the possible and realized implant geometric configuration. DVHs prepared in VariSeed9 were converted to BEDVHs and subsequently EQD2 values for each volume‐element.Results:For a physical dose of 28 Gy to a 0.5 cm depth, BED=21.7 Gy and EQD2=17.6 Gy, which was near the center of the desired EQD2 range. Tumor bed (CTV=4 cm3) coverage was 99.2% with 48 sources implanted. In order of decreasing importance from the sensitivity analysis, the radiobiological parameters were α=0.25 Gy−1, TPOT=23 days, α/β=8.6 Gy, and T=1.5 h. Percentage variations in these values produced EQD2 variations of 40%, 20%, 18%, and 1%, respectively.Conclusion:This radiobiological evaluation indicated that prescription dose may be determined for comparison with the desired EQD2, and that radiobiologicalparameter uncertainties produce smaller EQD2 differences than had physical dose been simply added to EBRT dose.Research support provided in part by CivaTech Oncology, Inc. for Dr. Rivard.
SU‐F‐T‐06: Development of a Formalism for Practical Dose Measurements in Brachytherapy in the German Standard DIN 6803
Authors: Hensley F , Chofor N , Schoenfeld A , Harder D 
Published: July 2016

Purpose:In the steep dose gradients in the vicinity of a radiation source and due to the properties of the changing photon spectra, dose measurements in Brachytherapy usually have large uncertainties. Working group DIN 6803‐3 is presently discussing recommendations for practical brachytherapy dosimetry incorporating recent theoretical developments in the description of brachytherapy radiation fields as well as new detectors and phantom materials. The goal is to prepare methods and instruments to verify dose calculation algorithms and for clinical dose verification with reduced uncertainties.Methods:After analysis of the distance dependent spectral changes of the radiation field surrounding brachytherapy sources, the energy dependent response of typical brachytherapy detectors was examined with Monte Carlo simulations. A dosimetric formalism was developed allowing the correction of their energy dependence as function of source distance for a Co‐60 calibrated detector. Water equivalent phantom materials were examined with Monte Carlo calculations for their influence on brachytherapy photon spectra and for their water equivalence in terms of generating equivalent distributions of photon spectra and absorbed dose to water.Results:The energy dependence of a detector in the vicinity of a brachytherapy source can be described by defining an energy correction factor kQ for brachytherapy in the same manner as in existing dosimetry protocols which incorporates volume averaging and radiation field distortion by the detector. Solid phantom materials were identified which allow precise positioning of a detector together with small correctable deviations from absorbed dose to water. Recommendations for the selection of detectors and phantom materials are being developed for different measurements in brachytherapy.Conclusion:The introduction of kQ for brachytherapy sources may allow more systematic and comparable dose measurements. In principle, the corrections can be verified or even determined by measurement in a water phantom and comparison with dose distributions calculated using the TG43 dosimetry formalism.Project is supported by DIN Deutsches Institut fuer Normung
SU‐F‐T‐09: In Phantom Full‐Implant Validation of Plastic Scintillation Detectors for in Vivo Dosimetry During Low Dose Rate Brachytherapy
Authors: Therriault‐Proulx F , Beaulieu L , Bruno T , Beddar S 
Published: July 2016

Purpose:To validate in a water phantom the use of plastic scintillation detectors to measure dose to the urethra and the rectal wall during a clinically realistic low dose rate (LDR) brachytherapy implant.Methods:A template was designed to replicate a clinically realistic LDR brachytherapy prostate implant inside a water phantom. Twenty‐two catheters were inserted, including one mimicking the urethra and another the rectal wall. The needles inserted in the remaining 20 catheters were composed of thin‐walled nylon tubes in which I‐125 radioactive seeds (Air Kerma Strengths of (0.328±0.020)U) were abutted together with plastic spacers to replicate a typical loading. A plastic scintillation detector (PSD) with a 5‐mm long × 1‐mm diameter sensitive element was first placed inside the urethra and 1‐second measurements were performed for 60s after each needle implant. Measurements were also performed at multiple positions along the urethra once all the needles were inserted. The procedure was then repeated with the PSD placed at the rectal wall.Results:Individual dose‐rates ranging from 0.07µGy/s to 1.5µGy/s were measured after each needle implant. The average absolute relative differences were (6.2±3.6)% and (6.9±6.5)% to the values calculated with the TG‐43 formalism, for the urethra and rectal wall respectively. These results are within expectations from the error uncertainty budget once accounting for uncertainties in seeds’ strength and positioning. Interestingly, the PSD allowed for unplanned error detection as the study was performed. Finally, the measured dose after the full implant at different positions along the mimicked organs at risk were in agreement with TG‐43 values for all of the positions tested.Conclusion:Plastic scintillation detectors could be used as in vivo detectors for LDR brachytherapy as they would provide accurate dose information after each needle implant as well as along the organs at risk at the end of the implant.
SU‐F‐T‐10: Validation of ELP Dosimetry Using PRESAGE Dosimeter: Feasibility Test and Practical Considerations
Authors: Lambson K , Lafata K , Schaal J , Miles D , Yoon S , Liu W , Oldham M , Cai J 
Published: July 2016

Purpose:To validate the use of a PRESAGE dosimeter as a method to quantitatively measure dose distributions of injectable brachytherapy based on elastin‐like polypeptide (ELP) nanoparticles. PRESAGE is a solid, transparent polyurethane‐based dosimeter whose dose is proportional to a change in optical density, making it useful for visualizing the dose from a radionuclide‐tagged‐ELP injection.Methods:A PRESAGE dosimeter was designed to simulate an ELP injection. To calibrate, cuvette samples from the batch of PRESAGE were exposed to varying levels of radiation from 0–35.9Gy applied via a linear accelerator, then placed into a spectrophotometer to obtain the optical density change as a function of dose. A pre‐optical‐CT scan was acquired of the phantom to obtain a baseline tomographic optical density. A 1cc saline solution of I‐125 tagged‐ELP with and activity concentration of 1mCi/cc was injected into the phantom and left for five days. After five days, the ELP was removed and the cavity cleaned of all remaining radioactive material. Post tomographic optical images were acquired to obtain a differential optical density dataset.Results:Initial results after the 5‐day exposure revealed an opaque white film that resembled the volume of the ELP solution injected into the phantom. We think this is possibly due to the saline solution diffusing into the PRESAGE and causing a change in the index of refraction at this shallow depth. Therefore, initially the optical scanner yielded inconclusive results. After several more days, the saline seemed to have evaporated out of the injection site and the ELP dose distribution was visible via color change in the dosimeter.Conclusion:We have created the first experimental design to measure the dose distribution of I‐125‐tagged‐ELP. The PRESAGE formulation proves to be a feasible option for such measurements. Future experimental measurements need to be obtained to further characterize ELP dosimetry.
SU‐F‐T‐11: Scintillator Based Quality Assurance Device for HDR Brachytherapy
Authors: Jozsef G 
Published: July 2016

Purpose:To build a test device for HDR afterloaders capable of checking source positions, times at positions and estimate the activity of the source.Methods:A catheter is taped on a plastic scintillation sheet. When a source travels through the catheter, the scintillator sheet lights up around the source. The sheet is monitored with a video camera, and records the movement of the light spot. The center of the spot on each image on the video provides the source location, and the time stamps of the images can provide the dwell time the source spend in each location. Finally, the brightness of the light spot is related to the activity of the source. A code was developed for noise removal, calibrate the scale of the image to centimeters, eliminate the distortion caused by the oblique view angle, identifying the boundaries of the light spot, transforming the image into binary and detect and calculate the source motion, positions and times. The images are much less noisy if the camera is shielded. That requires that the light spot is monitored in a mirror, rather than directly. The whole assembly is covered from external light and has a size of approximately 17×35×25cm (H×L×W)Results:A cheap camera in BW mode proved to be sufficient with a plastic scintillator sheet. The best images were resulted by a 3mm thick sheet with ZnS:Ag surface coating. The shielding of the camera decreased the noise, but could not eliminate it. A test run even in noisy condition resulted in approximately 1 mm and 1 sec difference from the planned positions and dwell times. Activity tests are in progress.Conclusion:The proposed method is feasible. It might simplify the monthly QA process of HDR Brachytherapy units.
SU‐F‐T‐13: Transit Dose Comparisons for Co‐60 and Ir‐192 HDR Sources
Authors: Gimenez‐Alventosa V , Vijande J , Ballester F , Perez‐Calatayud J 
Published: July 2016

Purpose:The purpose of this study is to compare the transit dose due to the movement of high dose rate (HDR) Ir‐192 and Co‐60 sources along the transfer tube. This is performed by evaluating air‐kerma differences in the vicinity of the transfer tube when both sources are moved with the same velocity from a HDR brachytherapy afterloader into a patient.Methods:Monte Carlo simulations have been performed using PENELOPE2014. mHDR‐v2 and Flexisource sources have been considered. Collisional kerma has been scored. The sources were simulated within a plastic catheter located in an infinite air phantom. The movement of the seed was included by displacing their positions along the connecting catheter from z=−75 cm to z=+75 cm and combining them. Backscatter from the afterloader and the patient was not considered. Since modern afterloaders like Flexitron (Elekta) or Saginova (Bebig) are able to use equally Ir‐192 and Co‐60 sources it was assumed that both sources are displaced with equal speed. Typical content activity values were provided by the manufacturer (460 GBq for Ir‐192 and 75 GBq for Co‐60).Results:2D distributions were obtained with type‐A uncertainties (k=2) less than 0.01%. From those, the air kerma ratio Co‐60/Ir‐192 was evaluated weighted by their corresponding activities. It was found that it varies slowly with distance (less than 10% variation) but strongly in time due to the shorter half‐life of the Ir‐192 (73.83 days). The maximum ratio is located close to the catheter with a value of 0.57 when both sources are installed by the manufacturer, while increasing up to 1.25 at the end of the recommended working life (90 days) of the Ir‐192 source.Conclusion:Air‐kerma ratios are almost constant (0.51–0.57) in the vicinity of the source. Nevertheless, air‐kerma ratios increase rapidly whenever the Ir‐192 is approaching the end of its life.
SU‐F‐T‐14: Dosimetric Impacts of Various Uncertainties in Cervical Cancer HDR Brachytherapy: Are Conventional Point Doses Good Surrogates for 3D Dosimetry?
Authors: Liang X , Zheng D , Zhang X , Narayanasamy G , Morrill S , Penagaricano J , Paudel N , Li Z 
Published: July 2016

Purpose:In the context of evaluating dosimetric impacts of a variety of uncertainties involved in HDR Tandem‐and‐Ovoid treatment, to study the correlations between conventional point doses and 3D volumetric doses.Methods:For 5 cervical cancer patients treated with HDR T&O, 150 plans were retrospectively created to study dosimetric impacts of the following uncertainties: (1) inter‐fractional applicator displacement between two treatment fractions within a single insertion by applying Fraction#1 plan to Fraction#2 CT; (2) positional dwell error simulated from −5mm to 5mm in 1mm steps; (3) simulated temporal dwell error of 0.05s, 0.1s, 0.5s, and 1s. The original plans were based on point dose prescription, from which the volume covered by the prescription dose was generated as the pseudo target volume to study the 3D target dose effect. OARs were contoured. The point and volumetric dose errors were calculated by taking the differences between original and simulated plans. The correlations between the point and volumetric dose errors were analyzed.Results:For the most clinically relevant positional dwell uncertainty of 1mm, temporal uncertainty of 0.05s, and inter‐fractional applicator displacement within the same insertion, the mean target D90 and V100 deviation were within 1%. Among these uncertainties, the applicator displacement showed the largest potential target coverage impact (2.6% on D90) as well as the OAR dose impact (2.5% and 3.4% on bladder D2cc and rectum D2cc). The Spearman correlation analysis shows a correlation coefficient of 0.43 with a p‐value of 0.11 between target D90 coverage and H point dose.Conclusion:With the most clinically relevant positional and temporal dwell uncertainties and patient interfractional applicator displacement within the same insertion, the dose error is within clinical acceptable range. The lack of correlation between H point and 3D volumetric dose errors is a motivator for the use of 3D treatment planning in cervical HDR brachytherapy.
SU‐F‐T‐15: Evaluation of 192Ir, 60Co and 169Yb Sources for High Dose Rate Prostate Brachytherapy Inverse Planning Using An Interior Point Constraint Generation Algorithm
Authors: Mok Tsze Chung E , Safigholi H , Nicolae A , Davidson M , Ravi A , Aleman D , Song W 
Published: July 2016

Purpose:The effectiveness of using a combination of three sources, 60Co, 192Ir and 169Yb, is analyzed. Different combinations are compared against a single 192Ir source on prostate cancer cases. A novel inverse planning interior point algorithm is developed in‐house to generate the treatment plans.Methods:Thirteen prostate cancer patients are separated into two groups: Group A includes eight patients with the prostate as target volume, while group B consists of four patients with a boost nodule inside the prostate that is assigned 150% of the prescription dose. The mean target volume is 35.7±9.3cc and 30.6±8.5cc for groups A and B, respectively. All patients are treated with each source individually, then with paired sources, and finally with all three sources. To compare the results, boost volume V150 and D90, urethra Dmax and D10, and rectum Dmax and V80 are evaluated. For fair comparison, all plans are normalized to a uniform V100=100.Results:Overall, double‐ and triple‐source plans were better than single‐source plans. The triple‐source plans resulted in an average decrease of 21.7% and 1.5% in urethra Dmax and D10, respectively, and 8.0% and 0.8% in rectum Dmax and V80, respectively, for group A. For group B, boost volume V150 and D90 increased by 4.7% and 3.0%, respectively, while keeping similar dose delivered to the urethra and rectum. 60Co and 192Ir produced better plans than their counterparts in the double‐source category, whereas 60Co produced more favorable results than the remaining individual sources.Conclusion:This study demonstrates the potential advantage of using a combination of two or three sources, reflected in dose reduction to organs‐at‐risk and more conformal dose to the target. three sources, reflected in dose reduction to organs‐at‐risk and more conformal dose to the target. Our results show that 60Co, 192Ir and 169Yb produce the best plans when used simultaneously and can thus be an alternative to 192Ir‐only in high‐dose‐rate prostate brachytherapy.
SU‐F‐T‐16: Experimental Determination of Ionization Chamber Correction Factors for In‐Phantom Measurements of Reference Air Kerma Rate and Absorbed Water Dose Rate of Brachytherapy 192Ir Source
Authors: Chan M , Lee V , Wong M , Leung R , Law G , Lee K , Cheung S , Tung S 
Published: July 2016

Purpose:Following the method of in‐phantom measurements of reference air kerma rate (Ka) at 100cm and absorbed water dose rate (Dw1) at 1cm of high‐dose‐rate 192Ir brachytherapy source using 60Co absorbed‐dose‐to‐water calibrated (ND,w,60Co) ionization chamber (IC), we experimentally determined the in‐phantom correction factors (kglob) of the PTW30013 (PTW, Freiburg, Germany) IC by comparing the Monte Carlo (MC)‐calculated kglob of the other PTW30016 IC.Methods:The Dw1 formalism of in‐phantom measurement is: M*ND,w,60Co*(kglob)Dw1, where M is the collected charges, and (kglob)Dw1 the in‐phantom Dw1 correction factor. Similarly, Ka is determined by M*ND,w,60Co*(kglob)ka, where (kglob)ka the in‐phantom Ka correction factor. Two thimble ICs PTW30013 and another PTW30016 having a ND,w,60Co from the German primary standard laboratory (PTB) were simultaneously exposed to the microselectron 192Ir v2 source at 8cm in a PMMA phantom. A reference well chamber (PTW33004) with a PTB transfer Ka calibration Nka was used for comparing the in‐phantom measurements to derive the experimental (kglob)ka factors. We determined the experimental (kglob)Dw1 of the PTW30013 by comparing the PTW30016 measurements with MC‐calculated (kglob)Dw1.Results:Ka results of the PTW30016 based on ND,w,60Co and MC‐calculated (kglob)ka differ from the well chamber results based on Nka by 1.6% and from the manufacturer by 1.0%. Experimental (kglob)ka factors for the PTW30016 and two other PTW30013 are 0.00683, 0.00681 and 0.00679, and vary <0.5% with 1mm source positioning uncertainty. Experimental (kglob)Dw1 of the PTW30013 ICs are 75.3 and 75.6, and differ by 1.6% from the conversion by dose rate constant from the AAPM report 229.Conclusion:The 1.7% difference between MC and experimental (kglob)ka for the PTW30016 IC is within the PTB 2.5% expanded uncertainty in Ka calibration standard. Using a single IC with ND,w,60Co to calibrate the brachytherapy source and dose output in external radiotherapy is feasible. MC validation of the PTW30013(kglob)Dw1 is warranted.
SU‐F‐T‐18: The Importance of Immobilization Devices in Brachytherapy Treatments of Vaginal Cuff
Authors: Shojaei M , Dumitru N , Pella S 
Published: July 2016

Purpose:High dose rate brachytherapy is a highly localized radiation therapy that has a very high dose gradient. Thus one of the most important parts of the treatment is the immobilization. The smallest movement of the patient or applicator can result in dose variation to the surrounding tissues as well as to the tumor to be treated. We will revise the ML Cylinder treatments and their localization challenges.Methods:A retrospective study of 25 patients with 5 treatments each looking into the applicator's placement in regard to the organs at risk. Motion possibilities for each applicator intra and inter fractionation with their dosimetric implications were covered and measured in regard with their dose variance. The localization immobilization devices used were assessed for the capability to prevent motion before and during the treatment delivery.Results:We focused on the 100% isodose on central axis and a 15 degree displacement due to possible rotation analyzing the dose variations to the bladder and rectum walls. The average dose variation for bladder was 15% of the accepted tolerance, with a minimum variance of 11.1% and a maximum one of 23.14% on the central axis. For the off axis measurements we found an average variation of 16.84% of the accepted tolerance, with a minimum variance of 11.47% and a maximum one of 27.69%. For the rectum we focused on the rectum wall closest to the 120% isodose line. The average dose variation was 19.4%, minimum 11.3% and a maximum of 34.02% from the accepted tolerance valuesConclusion:Improved immobilization devices are recommended. For inter‐fractionation, localization devices are recommended in place with consistent planning in regards with the initial fraction. Many of the present immobilization devices produced for external radiotherapy can be used to improve the localization of HDR applicators during transportation of the patient and during treatment
SU‐F‐T‐20: Novel Catheter Lumen Recognition Algorithm for Rapid Digitization
Authors: Dise J , McDonald D , Ashenafi M , Peng J , Mart C , Koch N , Vanek K 
Published: July 2016

Purpose:Manual catheter recognition remains a time‐consuming aspect of high‐dose‐rate brachytherapy (HDR) treatment planning. In this work, a novel catheter lumen recognition algorithm was created for accurate and rapid digitization.Methods:MatLab v8.5 was used to create the catheter recognition algorithm. Initially, the algorithm searches the patient CT dataset using an intensity based k‐means filter designed to locate catheters. Once the catheters have been located, seed points are manually selected to initialize digitization of each catheter. From each seed point, the algorithm searches locally in order to automatically digitize the remaining catheter. This digitization is accomplished by finding pixels with similar image curvature and divergence parameters compared to the seed pixel. Newly digitized pixels are treated as new seed positions, and hessian image analysis is used to direct the algorithm toward neighboring catheter pixels, and to make the algorithm insensitive to adjacent catheters that are unresolvable on CT, air pockets, and high Z artifacts. The algorithm was tested using 11 HDR treatment plans, including the Syed template, tandem and ovoid applicator, and multi‐catheter lung brachytherapy. Digitization error was calculated by comparing manually determined catheter positions to those determined by the algorithm.Results:he digitization error was 0.23 mm ± 0.14 mm axially and 0.62 mm ± 0.13 mm longitudinally at the tip. The time of digitization, following initial seed placement was less than 1 second per catheter. The maximum total time required to digitize all tested applicators was 4 minutes (Syed template with 15 needles).Conclusion:This algorithm successfully digitizes HDR catheters for a variety of applicators with or without CT markers. The minimal axial error demonstrates the accuracy of the algorithm, and its insensitivity to image artifacts and challenging catheter positioning. Future work to automatically place initial seed positions would improve the algorithm speed.