bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐17: A Feasibility Study for the Transit Dosimetry with a Glass Dosimeter in Brachytherapy
Authors: Moon S , Yoon M , Chung W , Chung M , Kim D 
Published: July 2016

Purpose:Confirming the dose delivered to a patient is important to make sure the treatment quality and safety of the radiotherapy. Measuring a transit dose of the patient during the radiotherapy could be an interesting way to confirm the patient dose. In this study, we evaluated the feasibility of the transit dosimetry with a glass dosimeter in brachytherapy.Methods:We made a phantom that inserted the glass dosimeters and placed under patient lying on a couch for cervix cancer brachytherapy. The 18 glass dosimeters were placed in the phantom arranged 6 per row. A point putting 1cm vertically from the source was prescribed as 500.00 cGy. Solid phantoms of 0, 2, 4, 6, 8, 10 cm were placed between the source and the glass dosimeter. The transit dose was measured each thickness using the glass dosimeters and compared with a treatment planning system (TPS).Results:When the transit dose was smaller than 10 cGy, the average of the differences between measured values and calculated values by TPS was 0.50 cGy and the standard deviation was 0.69 cGy. If the transit dose was smaller than 100 cGy, the average of the error was 1.67 ± 4.01 cGy. The error to a point near the prescription point was −14.02 cGy per 500.00 cGy of the prescription dose.Conclusion:The distances from the sources to skin of the patient generally are within 10 cm for cervix cancer cases in brachytherapy. The results of this preliminary study showed the probability of the glass dosimeter as the transit dosimeter in brachytherapy.
SU‐F‐T‐24: Impact of Source Position and Dose Distribution Due to Curvature of HDR Transfer Tubes
Authors: Khan A , Yue N 
Published: July 2016

Purpose:Brachytherapy is a highly targeted from of radiotherapy. While this may lead to ideal dose distributions on the treatment planning system, a small error in source location can lead to change in the dose distribution. The purpose of this study is to quantify the impact on source position error due to curvature of the transfer tubes and the impact this may have on the dose distribution.Methods:Since the source travels along the midline of the tube, an estimate of the positioning error for various angles of curvature was determined using geometric properties of the tube. Based on the range of values a specific shift was chosen to alter the treatment plans for a number of cervical cancer patients who had undergone HDR brachytherapy boost using tandem and ovoids. Impact of dose to target and organs at risk were determined and checked against guidelines outlined by radiation oncologist.Results:The estimate of the positioning error was 2mm short of the expected position (the curved tube can only cause the source to not reach as far as with a flat tube). Quantitative impact on the dose distribution is still in the process of being analyzed.Conclusion:The accepted positioning tolerance for the source position of a HDR brachytherapy unit is plus or minus 1mm. If there is an additional 2mm discrepancy due to tube curvature, this can result in a source being 1mm to 3mm short of the expected location. While we do always attempt to keep the tubes straight, in some cases such as with tandem and ovoids, the tandem connector does not extend as far out from the patient so the ovoid tubes always contain some degree of curvature. The dose impact of this may be significant.
SU‐F‐T‐26: A Study of the Consistency of Brachytherapy Treatments for Vaginal Cuff
Authors: Shojaei M , Pella S , Dumitru N 
Published: July 2016

Purpose:To evaluate to treatment consistency over the total number of fractions when treatment what HDR brachytherapy using the ML cylinders. At the same time the dosimetric impact on the critical organs is monitored over the total number of fractions.Methods:A retrospective analysis of 10 patients treated with Cylinder applicators, from 2015–2016 were considered for this study. The CT scans of these patients, taken before each treatment were separately imported in to the treatment planning system and paired with the initial CT scan after completing the contouring. Two sets of CT images were fused together with respective to the applicator, using landmark registration. The doses of each plan were imported as well and a cumulative dosimetric analysis was made for bladder, bowels, and rectum and PTV.Results:No contour of any of the OAR was exactly similar when CT images were fused on each other. The PTV volumes vary from fraction to fraction. There was always a difference between the doses received by the OARs between treatments. The maximum dose varied between 5% and 30% in rectum and bladder. The minimum dose varied between 5% and 8% in rectum and bladder. The average dose varied between 15% and 20% in rectum and bladder. Deviation in placement were noticed between fractions.Conclusion:The variation in volumes of OARs and isodoses near the OARs, indicate that the estimated doses to OARs on the planning system may not be the same dose delivered to the patient in all the fractions. There are no major differences between the prescribed dose and the delivered dose over the total number of fractions. In some cases the critical organs will benefit if the consecutive plans will made after the CT scans will be registered with the initial scan and then planned.
SU‐F‐T‐31: Shape and Isodose Distributions in Co60 HDR Brachytherapy for Different Utero‐Vaginal Time Ratios
Authors: Gonzalez‐Sprinberg G , Piriz G 
Published: July 2016

Purpose:To optimize the dose in bladder and rectum and show the different shapes of the isodose volumes in Co60‐HDR brachytherapy, considering different utero and vaginal sources dwell ratio times (TU:TV).Methods:Besides Ir192‐HDR, new Co60‐HDR sources are being incorporated. We considered different TU:TV times and computed the dosis in bladder, rectum and at the reference points of the Manchester system. Also, we calculated the isodose volume and shape in each case. We used a EZAG‐BEBIG Co0.A86 model with TPS HDRplus3.0.4. and LCT42‐7, LCT42‐2(R,L) applicators. A reference dose RA= 1.00 Gy was given to the A‐right point. We considered the TU:TV dwell time ratios 1:0.25, 1:0.33, 1:0.5, 1:1, 1:2, 1:3, and 1:4. Given TU:TV, the stop time at each dwell position is fixed for each applicator.Results:Increasing TU:TV systematically results in a decreasing of the dose in bladder and rectum, e.g. 9% and 27% reduction were found in 1:0.25 with respect to 1:1, while 12% and 34% increase were found in 1:4 with respect to 1:1. Also, the isodose volume parameters height (h), width (w), thickness (t) and volume (hwt) increased from the 1:0.25 case to the 1:4 value: hwt is 25% lower and 31% higher than the 1:1 reference volume in these cases. Also w decreased for higher TU:TV and may compromise the tumoral volume coverage, decreasing 17% in the 1:0.25 case compared to the 1:1 case. The shape of the isodose volume was obtained for the different TU:TV considered.Conclusion:We obtained the shape of isodose volumes for different TU:TV values in gynecological Co60‐HDR. We studied the dose reduction in bladder and rectum for different TU:TV ratios. The volume parameters and hwt are strongly dependent on this ratio. This information is useful for a quantitative check of the TPS and as a starting point towards optimization.
SU‐F‐T‐34: Transition Form CT‐Based to Ultrasound‐Based HDR Treatment Planning for Prostate Cancer
Authors: Veltchev I , Price R , Horwitz E , Ma C 
Published: July 2016

Purpose:We discuss our experience with the transition from CT‐based to ultrasound‐based HDR treatment planning for prostate cancer in a high‐volume clinical setting. The details of switching from one afterloader vendor to another are also discussed. The four main stages of prostate HDR planning (image acquisition, target delineation, needle reconstruction, and plan optimization) are significantly modified when ultrasound imaging is used.Methods:We employ a time‐efficient needle reconstruction procedure that provides the necessary level of accuracy to rival the traditional CT‐based method. A total of 80 consecutive prostate treatments are part of this comparative study: 40 CT‐based and 40 ultrasound‐based. Various dosimetric parameters are investigated as points of comparison: target DVH points (V100, V150, V200) and dose non‐homogeneity ratio (DNR). An ultrasound‐guided peripheral needle‐placement strategy with two central needles is maintained for both groups of patients. Any differences in plan quality can therefore be attributed to target delineation, accuracy of needle reconstruction, and plan optimization capabilities of the two planning systems.Results:Statistical analysis of the dosimetric end‐points suggests that as a result of the implementation of ultrasound planning, target delineation consistency was improved; target volumes were reduced, leading to lower normal tissue dose while consistently improving all dosimetric parameters (DNR is reduced by ∼4%) as compared to the CT‐based treatment work‐flow.Conclusion:The introduction of ultrasound‐based real‐time treatment planning significantly reduced the operating room time for all patients ‐ from 4 hours to 2.5 hours, allowing us to double the patient load in a single 5 hour slot. Dosimetric quality of the plans was only slightly improved after the switch to ultrasound planning. Reproducibility however, saw the greatest improvement, eliminating the needle position uncertainties associated with the addition of a CT scan.
SU‐F‐T‐42: MRI and TRUS Image Fusion as a Mode of Generating More Accurate Prostate Contours
Authors: Petronek M , Purysko A , Balik S , Ciezki J , Klein E , Wilkinson D 
Published: July 2016

Purpose:Transrectal Ultrasound (TRUS) imaging is utilized intra‐operatively for LDR permanent prostate seed implant treatment planning. Prostate contouring with TRUS can be challenging at the apex and base. This study attempts to improve accuracy of prostate contouring with MRI‐TRUS fusion to prevent over‐ or under‐estimation of the prostate volume.Methods:14 patients with previous MRI guided prostate biopsy and undergone an LDR permanent prostate seed implant have been selected. The prostate was contoured on the MRI images (1 mm slice thickness) by a radiologist. The prostate was also contoured on TRUS images (5 mm slice thickness) during LDR procedure by a urologist. MRI and TRUS images were rigidly fused manually and the prostate contours from MRI and TRUS were compared using Dice similarity coefficient, percentage volume difference and length, height and width differences.Results:The prostate volume was overestimated by 8 ± 18% (range: 34% to −25%) in TRUS images compared to MRI. The mean Dice was 0.77 ± 0.09 (range: 0.53 to 0.88). The mean difference (TRUS‐MRI) in the prostate width was 0 ± 4 mm (range: −11 to 5 mm), height was −3 ± 6 mm (range: −13 to 6 mm) and length was 6 ± 6 (range: −10 to 16 mm). Prostate was overestimated with TRUS imaging at the base for 6 cases (mean: 8 ± 4 mm and range: 5 to 14 mm), at the apex for 6 cases (mean: 11 ± 3 mm and range: 5 to 15 mm) and 1 case was underestimated at both base and apex by 4 mm.Conclusion:Use of intra‐operative TRUS and MRI image fusion can help to improve the accuracy of prostate contouring by accurately accounting for prostate over‐ or under‐estimations, especially at the base and apex. The mean amount of discrepancy is within a range that is significant for LDR sources.
SU‐F‐T‐46: The Effect of Inter‐Seed Attenuation and Tissue Composition in Prostate 125I Brachytherapy Dose Calculations
Authors: Tamura K , Araki F , Ohno T 
Published: July 2016

Purpose:To investigate the difference of dose distributions with/without the effect of inter‐seed attenuation and tissue compositions in prostate 125I brachytherapy dose calculations, using Monte Carlo simulations of Particle and Heavy Ion Transport code System (PHITS).Methods:The dose distributions in 125I prostate brachytherapy were calculated using PHITS for non‐simultaneous and simultaneous alignments of STM1251 sources in water or prostate phantom for six patients. The PHITS input file was created from DICOM‐RT file which includes source coordinates and structures for clinical target volume (CTV) and organs at risk (OARs) of urethra and rectum, using in‐house Matlab software. Photon and electron cutoff energies were set to 1 keV and 100 MeV, respectively. The dose distributions were calculated with the kerma approximation and the voxel size of 1 × 1 × 1 mm3. The number of incident photon was set to be the statistical uncertainty (1σ) of less than 1%. The effect of inter‐seed attenuation and prostate tissue compositions was evaluated from dose volume histograms (DVHs) for each structure, by comparing to results of the AAPM TG‐43 dose calculation (without the effect of inter‐seed attenuation and prostate tissue compositions).Results:The dose reduction due to the inter‐seed attenuation by source capsules was approximately 2% for CTV and OARs compared to those of TG‐43. In additions, by considering prostate tissue composition, the D90 and V100 of CTV reduced by 6% and 1%, respectively.Conclusion:It needs to consider the dose reduction due to the inter‐seed attenuation and tissue composition in prostate 125I brachytherapy dose calculations.
SU‐F‐T‐50: Evaluation of Monte Carlo Simulations Performance for Pediatric Brachytherapy Dosimetry
Authors: Chatzipapas C , Papadimitroulas P , Loudos G , Papanikolaou N , Kagadis G 
Published: July 2016

Purpose:Pediatric tumors are generally treated with multi‐modal procedures. Brachytherapy can be used with pediatric tumors, especially given that in this patient population low toxicity on normal tissues is critical as is the suppression of the probability for late malignancies. Our goal is to validate the GATE toolkit on realistic brachytherapy applications, and evaluate brachytherapy plans on pediatrics for accurate dosimetry on sensitive and critical organs of interest.Methods:The GATE Monte Carlo (MC) toolkit was used. Two High Dose Rate (HDR) 192Ir brachytherapy sources were simulated (Nucletron mHDR‐v1 and Varian VS2000), and fully validated using the AAPM and ESTRO protocols. A realistic brachytherapy plan was also simulated using the XCAT anthropomorphic computational model .The simulated data were compared to the clinical dose points. Finally, a 14 years old girl with vaginal rhabdomyosarcoma was modelled based on clinical procedures for the calculation of the absorbed dose per organ.Results:The MC simulations resulted in accurate dosimetry in terms of dose rate constant (Λ), radial dose gL(r) and anisotropy function F(r,θ) for both sources.The simulations were executed using ∼1010 number of primaries resulting in statistical uncertainties lower than 2%.The differences between the theoretical values and the simulated ones ranged from 0.01% up to 3.3%, with the largest discrepancy (6%) being observed in the dose rate constant calculation.The simulated DVH using an adult female XCAT model was also compared to a clinical one resulting in differences smaller than 5%. Finally, a realistic pediatric brachytherapy simulation was performed to evaluate the absorbed dose per organ and to calculate DVH with respect to heterogeneities of the human anatomy.Conclusion:GATE is a reliable tool for brachytherapy simulations both for source modeling and for dosimetry in anthropomorphic voxelized models. Our project aims to evaluate a variety of pediatric brachytherapy schemes using a population of pediatric phantoms for several pathological cases.This study is part of a project that has received funding from the European Union Horizon2020 research and innovation programme under the MarieSklodowska‐Curiegrantagreement.No691203.The results published in this study reflect only the authors view and the Research Executive Agency (REA) and the European Commission is not responsible for any use that may be madeof the information it contains.
SU‐F‐T‐52: Study of Energy Dependent Effect of Dosimetry Systems Used in Therapeutic Soft X‐Ray Energy Range
Authors: Souri S , Qian X , Gill G , Jamshidi A , Cao Y , Chen Y 
Published: July 2016

Purpose:To investigate energy dependent effects of different dosimetry systems which can be used as in vivo dosimetry monitoring for intraoperative radiotherapy in therapeutic soft x‐ray energy range.Methods:Three dosimetry systems were evaluated in therapeutic soft x‐ray energy range: optically stimulated luminescent dosimeter (OSLD) nanoDots, radiochromic EBT2 and EBT3 films. The x‐ray photons were produced by a Zeiss Intrabeam 50 kV x‐ray radiotherapy system. Solid water and bolus slabs with different thicknesses were used in the process of irradiation. An aluminum filter set was used to measure HVLs of X‐rays. Calibration curves were made at different depth of boluses.Results:Half Value Layers at depths of 0, 3, 10, and 20 mm of solid water were measured to represent the energy change versus depth, yielding 0.306, 0.482, 0.865 and 0.901 respectively and indicating nearly unchanged HVL beyond 1 cm depth. The responses of each system at different depths were normalized to the response at 2 cm depth. In film dosimetry, the response is calculated as optical density (OD). The results show that there is nearly the same energy dependence for EBT2 and EBT3. At a HVL of 0.482 mm Al, the relative responses of nanoDots and EBT3 are 0.85 ± 0.04 and 0.89 ± 0.03 compared to those at 0.901 mm Al HVL, respectively, indicating no obvious difference between those two systems within the measurement uncertainty.Conclusion:It was observed that the studied dosimeter response increases about 13% from the x‐ray energy of 0.48 mm Al to 0.90 mm Al. Therefore, caution should be exercised in using an appropriate calibration curve, and x‐ray beam hardening effect has to be taken into account.
SU‐F‐T‐72: Experimental Determination of the Positionuncertainties for ROOS Ionization Chambers in Clinical Electron Beams
Authors: von Voigts‐Rhetz P , Pretzsch T , Czarnecki D , Vorwerk H , Zink K 
Published: July 2016

Purpose:National and international dosimetry protocols assume a position accuracy for ionization chambers of less than 0.2mm. To follow this precept the manufacturer PTW‐Freiburg introduced a positioning assistance system (TRUFIX) for their particular ion chambers. Aim of this study is an experimental investigation of the positioning uncertainties for ROOS‐type ionization chambers.Methods:For all measurements a linear accelerator Elekta Synergie was used. The experiments were performed in a water‐phantom. To collimate the electron beam a 10×10cm2 applicator was installed. All measured depth dose curves were normalized to their maximum. In all cases the TRUFIX system was applied for chamber positioning. For the first measurement series, to determine the positioning reproducibility of a ROOS chamber, one person placed the chamber three times in a 6 MeV electron beam. The mean value of this three measurements was the reference for further six random persons who repeated this procedure. The results were compared for different depths (R50, zref and Rp). To investigate the impact of different individual chambers of the same type 10 different ROOS chambers were placed by the same person in a 6, 12 and 18MeV electron beam and the measured reference depths zref were compared.Results:The absolute positioning reproducibility is less than 0.1mm for the same person. The positioning uncertainties are increasing up to +/−0.3mm if different persons perform the chamber's positioning within the water phantom. The comparison of the 10 different ROOS chambers resulted in reference depths zref with deviations in the range of +/−0.45mm for all energies.Conclusion:The position accuracy of 0.2mm can be fulfilled with the TRUFIX system. The comparison of the 10 different ROOS ionization chambers showed noticeable deviations in the determined reference depth. The impact of a positioning uncertainty of about 0.3–0.4mm on the total perturbation correction will be considered.
SU‐F‐T‐79: Monte Carlo Investigation of Optimizing Parameters for Modulated Electron Arc Therapy
Authors: Al Ashkar E , Eldib A , Eraba K , Imam M , Ma C 
Published: July 2016

Purpose:Electron arc therapy provides excellent dose distributions for treating superficial tumors along curved surfaces. However this modality has not received widespread application due to the lack of needed advancement in electron beam delivery, accurate electron dose calculation and treatment plan optimization. The aim of the current work is to investigate possible parameters that can be optimized for electron arc (eARC) therapy.Methods:The MCBEAM code was used to generate phase space files for 6 and 12MeV electron beam energies from a Varian trilogy machine. An Electron Multi‐leaf collimator eMLC of 2cm thickness positioned at 82 cm source collimated distance was used in the study. Dose distributions for electron arcs were calculated inside a cylindrical phantom using the MCSIM code. The Cylindrical phantom was constructed with 0.2cm voxels and a 15cm diameter. Electron arcs were delivered with two different approaches. The first approach was to deliver the arc as segments of very small field widths. In this approach we also tested the impact of the segment size and the arc increment angle. The second approach is to deliver the arc as a sum of large fields each covering the whole target as seen from the beam eye view.Results:In considering 90 % as the prescription isodose line, the first approach showed a region of buildup proceeding before the prescription zone. This build up is minimizing with the second approach neglecting need for bolus. The second approach also showed less x‐ray contamination. In both approaches the variation of the segment size changed the size and location of the prescription isodose line. The optimization process for eARC could involve interplay between small and large segments to achieve desired coverage.Conclusion:An advanced modulation of eARCs will allow for tailored dose distribution for superficial curved target as with challenging scalp cases
SU‐F‐T‐82: Dosimetric Evaluation of a Shield Used for Hemi‐Body Skin Electron Irradiation
Authors: Rivers C , AlDahlawi I , Wang I , Singh A , Podgorsak M 
Published: July 2016

Purpose:We had several mycosis fungoides patients with a limited disease to about half of the skin surface. A custom‐made plywood shield was used to protect the non‐targeted skin region with our total skin electron irradiation (TSEI) technique. We report a dosimetric evaluation for our “hemi‐body” skin electron irradiation technique.Methods:The technique is similar to our clinical total skin electron irradiation (TSEI), performed with a six‐pair dual field (Stanford technique) at an extended source‐to‐skin distance (SSD) of 377 cm, with the addition of a plywood shield placed 50 cm from the patient. The shield is made of three layers of standard 5/8″ thick plywood (total thickness of 4.75 cm) that are clamped securely on an adjustable‐height stand. Gafchromic EBT3 films were used in assessing the shield's transmission factor and the extend of the dose penumbra region. To verify the dose delivered for hemi‐body skin radiation in a real patient treatment, in‐vivo dosimetry using Gafchromic EBT3 films were performed. Film pieces were taped on the patient skin to measure the dose received during the first two fractions, placed on the forehead and upper body (shielded region); and also at the level of pelvic area, left thigh, and left ankle.Results:The shield transmission factor was found to be 10%, and the width of the penumbra (80‐to‐20% dose fall‐off) was about 12 cm. In‐vivo dosimetry of a real case confirmed the expected shielded area dose.Conclusion:Hemi‐Body skin electron irradiation at an extended SSD is feasible with the addition of a plywood shield at a distance from patient skin. The penumbra dose region and the shield's transmission factor should be evaluated prior to clinical use. We have treated several hemi‐body skin patients with our custom‐made plywood shield, the current patient measurements are representative of these for other patients as well.