bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐CAMPUS‐J‐06: The Impact of CT‐Scan Energy On Range Uncertainty in Proton Therapy Planning
Authors: Grantham K , Li H , Zhao T , Klein E 
Published: July 2014

Purpose:To investigate the impact of tube potential (kVp) on the CTnumber (HU) to proton stopping power ratio (PSPR) conversion table; the range uncertainty and the dosimetric change introduced by a mismatch in kVp between the CT and the HU to PSPR table used to calculate dose are analyzed.Methods:A CIRS CT‐ED phantom was scanned with a Philips Brilliance 64‐slice scanner under 90kVp and 120kVp tube potentials. Two HU to PSPR curves were then created. Using Eclipse (Varian) a treatment plan was created for a single beam in a water phantom (HU=0) passing through a wedge‐shaped heterogeneity (HU=1488). The dose was recalculated by changing only the HU to PSPR table used in the dose calculation. The change in range (the distal 90% isodose line) relative to a distal structure was recorded as a function of heterogeneity thickness in the beam. To show the dosimetric impact of a mismatch in kVp between the CT and the HU to PSPR table, we repeated this procedure using a clinical plan comparing DVH data.Results:The HU to PSPR tables diverge for low‐density bone and higher density structures. In the phantom plan, the divergence of the tables results in a change in range of ~1mm per cm of bone in the beam path for the HU used. For the clinical plan, a mismatch in kVp showed a 28% increase in mean dose to the brainstem along with a 10% increase in maximum dose to the brainstem center.Conclusion:A mismatch in kVp between the CT and the HU to PSPR table can introduce significant uncertainty in the proton beam range. For dense bone, the measured range uncertainty is about 1mm per cm of bone in the beam. CT‐scan energy verification should be employed, particularly when high‐density media is in the proton beam path.
SU‐F‐19A‐01: APBI Brachytherapy Treatment Planning: The Impact of Heterogeneous Dose Calculations
Authors: Loupot S , Han T , Salehpour M , Gifford K 
Published: July 2014

Purpose:To quantify the difference in dose to PTV_EVAL and OARs (skin and rib) as calculated by (TG43) and heterogeneous calculations (CCC).Methods:25 patient plans (5 Contura and 20 SAVI) were selected for analysis. Clinical dose distributions were computed with a commercially available treatment planning algorithm (TG43‐D_(w,w)) and then recomputed with a pre‐clinical collapsed cone convolution algorithm (CCCD_(m,m)). PTV_EVAL coverage (V90%, V95%), and rib and skin maximum dose were compared via percent difference. Differences in dose to normal tissue (V150cc, V200cc of PTV_EVAL) were also compared. Changes in coverage and maximum dose to organs at risk are reported in percent change, (100*(TG43 − CCC) / TG43)), and changes in maximum dose to normal tissue are absolute change in cc (TG43 − CCC).Results:Mean differences in V90, V95, V150, and V200 for the SAVI cases were −0.2%, −0.4%, −0.03cc, and −0.14cc, respectively, with maximum differences of −0.78%, −1.7%, 1.28cc, and 1.01cc, respectively. Mean differences in the 0.1cc dose to the rib and skin were −1.4% and −0.22%, respectively, with maximum differences of −4.5% and 16%, respectively. Mean differences in V90, V95, V150, and V200 for the Contura cases were −1.2%, −2.1%, −1.8cc, and −0.59cc, respectively, with maximum differences of −2.0%, −3.16%, −2.9cc, and −0.76cc, respectively. Mean differences in the 0.1cc dose to the rib and skin were −2.6% and −3.9%, respectively, with maximum differences of −3.2% and −5.7%, respectively.Conclusion:The effects of translating clinical knowledge based on D_(w,w) to plans reported in D_(m,m) are minimal (2% or less) on average, but vary based on the type and placement of the device, source, and heterogeneity information.
SU‐F‐19A‐02: Comparison of Absorbed Dose to Water Standards for HDR Ir‐192 Brachytherapy Between the LCR, Brazil and NRC, Canada
Authors: Salata C , David M , de Almeida C , El Gamal I , Cojocaru C , Mainegra‐Hing E , McEwen M 
Published: July 2014

Purpose:To compare absorbed dose to water standards for HDR brachytherapy dosimetry developed by the Radiological Science Laboratory of Rio de Janeiro State University (LCR) and the National Research Council, Canada (NRC).Methods:The two institutions have separately developed absorbed dose standards based on the Fricke dosimetry system. There are important differences between the two standards, including: preparation and read‐out of the Fricke solution, irradiation geometry of the Fricke holder in relation to the Ir‐192 source, and determination of the G‐value to be used at Ir‐192 energies. All measurements for both standards were made directly at the NRC laboratory (i.e., no transfer instrument was used) using a single Ir‐192 source (microSelectron v2). In addition, the NRC group has established a self‐consistent method to determine the G‐value for Ir‐192, based on an interpolation between G‐values obtained at Co‐60 and 250kVp X‐rays, and this measurement was repeated using the LCR Fricke solution to investigate possible systematic uncertainties.Results:G‐values for Co‐60 and 250 kVp x‐rays, obtained using the LCR Fricke system, agreed with the NRC values within 0.5 % and 1 % respectively, indicating that the general assumption of universal G‐values is appropriate in this case. The standard uncertainty in the determination of G for Ir‐192 is estimated to be 0.6 %. For the comparison of absorbed dose measurements at the reference point for Ir‐192 (1 cm depth in water, perpendicular to the seed long‐axis), the ratio Dw(NRC)/Dw(LCR) was found to be 1.011 with a combined standard uncertainty of 1.7 %, k=1.Conclusion:The agreement in the absorbed dose to water values for the LCR and NRC systems is very encouraging. Combined with the lower uncertainty in this approach compared to the present air‐kerma approach, these results reaffirm the use of Fricke solution as a potential primary standard for HDR Ir‐192 brachytherapy.
SU‐F‐19A‐03: Dosimetric Advantages in Critical Structure Dose Sparing by Using a Multichannel Cylinder in High Dose Rate Brachytherapy to Treat Vaginal Cuff Cancer
Authors: Syh J , Syh J , Patel B , Zhang J , Wu H , Rosen L 
Published: July 2014

Purpose:The multichannel cylindrical vaginal applicator is a variation of traditional single channel cylindrical vaginal applicator. The multichannel applicator has additional peripheral channels that provide more flexibility in the planning process. The dosimetric advantage is to reduce dose to adjacent organ at risk (OAR) such as bladder and rectum while maintaining target coverage with the dose optimization from additional channels.Methods:Vaginal HDR brachytherapy plans are all CT based. CT images were acquired in 2 mm thickness to keep integrity of cylinder contouring. The CTV of 5mm Rind with prescribed treatment length was reconstructed from 5mm expansion of inserted cylinder. The goal was 95% of CTV covered by 95% of prescribed dose in both single channel planning (SCP)and multichannel planning (MCP) before proceeding any further optimization for dose reduction to critical structures with emphasis on D2cc and V2Gy .Results:This study demonstrated noticeable dose reduction to OAR was apparent in multichannel plans. The D2cc of the rectum and bladder were showing the reduced dose for multichannel versus single channel. The V2Gy of the rectum was 93.72% and 83.79% (p=0.007) for single channel and multichannel respectively (Figure 1 and Table 1). To assure adequate coverage to target while reducing the dose to the OAR without any compromise is the main goal in using multichannel vaginal applicator in HDR brachytherapy.Conclusion:Multichannel plans were optimized using anatomical based inverse optimization algorithm of inverse planning simulation annealing. The optimization solution of the algorithm was to improve the clinical target volume dose coverage while reducing the dose to critical organs such as bladder, rectum and bowels. The comparison between SCP and MCP demonstrated MCP is superior to SCP where the dwell positions were based on geometric array only. It concluded that MCP is preferable and is able to provide certain features superior to SCP.
SU‐F‐19A‐04: Dosimetric Evaluation of a Novel CT/MR Compatible Fletcher Applicator for Intracavitary Brachytherapy of the Cervix Uteri
Authors: Gifford K , Han T , Mourtada F , Eifel P 
Published: July 2014

Purpose:To validate a Monte Carlo model and evaluate the dosimetric capabilities of a novel commercial CT/MR compatible Fletcher applicator for cervical cancer brachytherapy.Methods:MCNPX 2.7.0 was used to model the Fletcher CT/MR shielded applicator (FA) and 192Ir HDR source. Energy deposition was calculated with a track length estimator modified by an energy‐dependent heating function. A high density polystyrene phantom was constructed with three film pockets for validation of the MCNPX model. Three planes of data were calculated with the MCNPX model corresponding to the three film planes in phantom. The planes were located 1 cm from the most anterior, posterior, and medial extents of the FA right ovoid. Unshielded distributions were calculated by modeling the shielded cells as air instead of the tungsten alloy. A third order polynomial fit to the OD to dose curve was used to convert OD of the three film planes to dose. Each film and MCNPX plane dose distribution was normalized to a point 2 cm from the center of the film plane and in a region of low dose gradient. MCNPX and film were overlaid and compared with a distance‐to‐agreement criterion of (±2%/±2mm). Shielded and unshielded distributions were overlaid and a percent shielded plot was created.Results:85.2%, 97.1%, and 96.6% of the MCNPX points passed the (±2%/±2mm) criterion respectively for the anterior, lateral, and posterior film comparison planes. A majority of the points in the anterior plane that exceeded the DTA criterion were either along edges of where the film was cut or near the terminal edges of the film. The percent shielded matrices indicated that the maximum % shielding was 50%.Conclusion:These data confirm the validity of the FA Monte Carlo model. The FA ovoid can shield up to 50% of the dose in the anteroposterior direction.
SU‐F‐19A‐05: Experimental and Monte Carlo Characterization of the 1 Cm CivaString 103Pd Brachytherapy Source
Authors: Reed J , Rivard M , Micka J , Culberson W , DeWerd L 
Published: July 2014

Purpose:To determine the in‐air azimuthal anisotropy and in‐water dose distribution for the 1 cm length of the CivaString 103Pd brachytherapy source through measurements and Monte Carlo (MC) simulations. American Association of Physicists in Medicine Task Group No. 43 (TG‐43) dosimetry parameters were also determined for this source.Methods:The in‐air azimuthal anisotropy of the source was measured with a NaI scintillation detector and simulated with the MCNP5 radiation transport code. Measured and simulated results were normalized to their respective mean values and compared. The TG‐43 dose‐rate constant, line‐source radial dose function, and 2D anisotropy function for this source were determined from LiF:Mg,Ti thermoluminescent dosimeter (TLD) measurements and MC simulations. The impact of 103Pd well‐loading variability on the in‐water dose distribution was investigated using MC simulations by comparing the dose distribution for a source model with four wells of equal strength to that for a source model with strengths increased by 1% for two of the four wells.Results:NaI scintillation detector measurements and MC simulations of the in‐air azimuthal anisotropy showed that ≥95% of the normalized data were within 1.2% of the mean value. TLD measurements and MC simulations of the TG‐43 dose‐rate constant, line‐source radial dose function, and 2D anisotropy function agreed to within the experimental TLD uncertainties (k=2). MC simulations showed that a 1% variability in 103Pd well‐loading resulted in changes of <0.1%, <0.1%, and <0.3% in the TG‐43 dose‐rate constant, radial dose distribution, and polar dose distribution, respectively.Conclusion:The CivaString source has a high degree of azimuthal symmetry as indicated by the NaI scintillation detector measurements and MC simulations of the in‐air azimuthal anisotropy. TG‐43 dosimetry parameters for this source were determined from TLD measurements and MC simulations. 103Pd well‐loading variability results in minimal variations in the in‐water dose distribution according to MC simulations.This work was partially supported by CivaTech Oncology, Inc. through an educational grant for Joshua Reed, John Micka, Wesley Culberson, and Larry DeWerd and through research support for Mark Rivard.
SU‐F‐19A‐06: Experimental Investigation of the Energy Dependence of TLD Sensitivity in Low‐Energy Photon Beams
Authors: Chen Z , Nath R 
Published: July 2014

Purpose:To measure the energy dependence of TLD sensitivity in lowenergy photon beams with equivalent mono‐energetic energy matching those of 103Pd, 125I and 131Cs brachytherapy sources.Methods:A Pantek DXT 300 x‐ray unit (Precision X‐ray, Branford, CT), with stable digital voltage control down to 20 kV, was used to establish three lowenergy photon beams with narrow energy spread and equivalent monoenergetic energies matching those of 103Pd, 125I and 131Cs brachytherapy sources. The low‐energy x‐ray beams and a reference 6 MV photon beam were calibrated according to the AAPM TG‐61 and TG‐51 protocols, respectively, using a parallel‐plate low‐energy chamber and a Farmer cylindrical chamber with NIST traceable calibration factors. The dose response of model TLD‐100 micro‐cubes (1×1×1 mm3) in each beam was measured for five different batches of TLDs (each contained approximately 100 TLDs) that have different histories of irradiation and usage. Relative absorbed dose sensitivity was determined as the quotient of the slope of dose response for a beam‐of‐interest to that of the reference beam.Results:Equivalent mono‐energetic photon energies of the low‐energy beams established for 103Pd, 125I and 131Cs sources were 20.5, 27.5, and 30.1 keV, respectively. Each beam exhibited narrow spectral spread with energyhomogeneity index close to 90%. The relative absorbed‐dose sensitivity was found to vary between different batches of TLD with maximum differences of up to 8%. The mean and standard deviation determined from the five TLD batches was 1.453 ± 0.026, 1.541 ± 0.035 and 1.529 ± 0.051 for the simulated 103P, 125I and 131Cs beams, respectively.Conclusion:Our measured relative absorbed‐dose sensitivities are greater than the historically measured value of 1.41. We find that the relative absorbed‐dose sensitivity of TLD in the 103P beam is approximately 5% lower than that of 125I and 131Cs beams. Comparison of our results with other studies will be presented.
SU‐F‐19A‐07: Is a Day30 Scan Necessary to Evaluate Activity‐Based Regulatory Compliance in Permanent Interstitial Brachytherapy for Prostate Cancer?
Authors: Kapur P , Ford J , Moghanaki D , Datsang R , Chang M , Hagan M , Palta J , Rosu M 
Published: July 2014

Purpose:To evaluate the Medical Event (ME) criteria for I‐125 prostate implants based on the assessment of post implant dosimetry on “Day0”/“Day30” imaging. The new ME criteria do not mandate a timeframe for this assessment. The compliance criteria are: more than 80% of the activity from the written directive for treatment site (TS) must be implanted inside TS, and doses to 1cc of either uninvolved rectum (D1_UR) or uninvolved bladder (D1_UB), or 2cc of other non‐specified tissue (D2_UT) must be less than 150% of the planned dose.Methods:“Day0”/“Day30” post‐implant analyses for 25 patients were evaluated. Treatment plans had a peripheral loading pattern with 2 core needles placed at least 10 mm away from urethra, with several seeds planned outside of the prostate for adequate target coverage. TS were a uniform 5 mm expansion of the prostate, except posteriorly (no expansion).Results:“Day0”/“Day30”analyses found no MEs. The relative changes for D1_UR, D1_UB, and D2_UT were (ranges): [−37.0, 38.2]%, [−96.5, 74.7]%, and [−41.2, 37.7]%. Furthermore, changes did not correlate with prostate volume changes of −18.7% [σ:16.0%, range:−60.5%, +6.4%]. These unfavorable changes did not lead to ME at “Day30” because these values were generally well below 150% at “Day0”. However, D2_UT dose values exceeded those for D1_UR and D1_UB at both “Day0”/“Day30”.Conclusion:The total activity was relatively insensitive to changes in target volume from “Day0” to ”Day30”. The dose metrics of interest, albeit susceptible to large, often unfavorable changes, remained less than the 150% threshold. Data from this study suggest that “Day0” can be used for the regulatory compliance evaluation. However, further evaluation at “Day30” is advisable if D2_UT is 110% or above (based on the largest D2_UT increase of 37.7% observed in this patient population). Future rigorous statistical analysis of a larger cohort will afford a refinement of this recommendation.
SU‐F‐19A‐08: Optimal Time Release Schedule of In‐Situ Drug Release During Permanent Prostate Brachytherapy
Authors: Cormack R , Ngwa W , Tangutoori S , Rajiv K , Sridhar S , Makrigiorgos G 
Published: July 2014

Purpose:Permanent prostate brachytherapy spacers can be used to deliver sustained doses of radiosentitizing drug directly to the target, in order to enhance the radiation effect. Implantable nanoplatforms for chemo‐radiation therapy (INCeRTs) have a maximum drug capacity and can be engineered to control the drug release schedule. The optimal schedule for sensitization during continuous low dose rate irradiation is unknown. This work studies the optimal release schedule of drug for both traditional sensitizers, and those that work by suppressing DNA repair processes.Methods:Six brachytherapy treatment plans were used to model the anatomy, implant geometry and calculate the spatial distribution of radiation dose and drug concentrations for a range of drug diffusion parameters. Three state partial differential equations (cells healthy, damaged or dead) modeled the effect of continuous radiation (radiosensitivities α,β) and cellular repair (time tr) on a cell population. Radiosensitization was modeled as concentration dependent change in α,β or tr which with variable duration under the constraint of fixed total drug release. Average cell kill was used to measure effectiveness. Sensitization by means of both enhanced damage and reduced repair were studied.Results:Optimal release duration is dependent on the concentration of radiosensitizer compared to the saturation concentration (csat) above which additional sensitization does not occur. Long duration drug release when enhancing α or β maximizes cell death when drug concentrations are generally over csat. Short term release is optimal for concentrations below saturation. Sensitization by suppressing repair has a similar though less distinct trend that is more affected by the radiation dose distribution.Conclusion:Models of sustained local radiosensitization show potential to increase the effectiveness of radiation in permanent prostate brachytherapy. INCeRTs with high drug capacity produce the greatest benefit with drug release over weeks. If in‐vivo drug concentrations are not able to approach saturation concentration, durations of days is optimal.DOD 1R21CA16977501; A. David Mazzone Awards Program 2012PD164
SU‐F‐19A‐09: Propagation of Organ at Risk Contours for High Dose Rate Brachytherapy Planning for Cervical Cancer: A Deformable Image Registration Comparison
Authors: Bellon M , Kumarasiri A , Kim J , Shah M , Elshaikh M , Chetty I 
Published: July 2014

Purpose:To compare the performance of two deformable image registration (DIR) algorithms for contour propagation and to evaluate the accuracy of DIR for use with high dose rate (HDR) brachytherapy planning for cervical cancer.Methods:Five patients undergoing HDR ring and tandem brachytherapy were included in this retrospective study. All patients underwent CT simulation and replanning prior to each fraction (3–5 fractions total). CT‐to‐CT DIR was performed using two commercially available software platforms: SmartAdapt, Varian Medical Systems (Demons) and Velocity AI, Velocity Medical Solutions (B‐spline). Fraction 1 contours were deformed and propagated to each subsequent image set and compared to contours manually drawn by an expert clinician. Dice similarity coefficients (DSC), defined as, DSC(A,B)=2(AandB)/(A+B) were calculated to quantify spatial overlap between manual (A) and deformed (B) contours. Additionally, clinician‐assigned visual scores were used to describe and compare the performance of each DIR method and ultimately evaluate which was more clinically acceptable. Scoring was based on a 1–5 scale—with 1 meaning, “clinically acceptable with no contour changes” and 5 meaning, “clinically unacceptable”.Results:Statistically significant differences were not observed between the two DIR algorithms. The average DSC for the bladder, rectum and rectosigmoid were 0.82±0.08, 0.67±0.13 and 0.48±0.18, respectively. The poorest contour agreement was observed for the rectosigmoid due to limited soft tissue contrast and drastic anatomical changes, i.e., organ shape/filling. Two clinicians gave nearly equivalent average scores of 2.75±0.91 for SmartAdapt and 2.75±0.94 for Velocity AI—indicating that for a majority of the cases, more than one of the three contours evaluated required major modifications.Conclusion:Limitations of both DIR algorithms resulted in inaccuracies in contour propagation in the pelvic region, thus hampering the clinical utility of this technology. Further work is required to optimize these algorithms and take advantage of the potential of DIR for HDR brachytherapy planning.
SU‐F‐19A‐10: Recalculation and Reporting Clinical HDR 192‐Ir Head and Neck Dose Distributions Using Model Based Dose Calculation
Authors: Carlsson Tedgren A , Persson M , Nilsson J 
Published: July 2014

Purpose:To retrospectively re‐calculate dose distributions for selected head and neck cancer patients, earlier treated with HDR 192Ir brachytherapy, using Monte Carlo (MC) simulations and compare results to distributions from the planning system derived using TG43 formalism. To study differences between dose to medium (as obtained with the MC code) and dose to water in medium as obtained through (1) ratios of stopping powers and (2) ratios of mass energy absorption coefficients between water and medium.Methods:The MC code Algebra was used to calculate dose distributions according to earlier actual treatment plans using anonymized plan data and CT images in DICOM format. Ratios of stopping power and mass energy absorption coefficients for water with various media obtained from 192‐Ir spectra were used in toggling between dose to water and dose to media.Results:Differences between initial planned TG43 dose distributions and the doses to media calculated by MC are insignificant in the target volume. Differences are moderate (within 4–5 % at distances of 3–4 cm) but increase with distance and are most notable in bone and at the patient surface. Differences between dose to water and dose to medium are within 1‐2% when using mass energy absorption coefficients to toggle between the two quantities but increase to above 10% for bone using stopping power ratios.Conclusion:MC predicts target doses for head and neck cancer patients in close agreement with TG43. MC yields improved dose estimations outside the target where a larger fraction of dose is from scattered photons. It is important with awareness and a clear reporting of absorbed dose values in using model based algorithms. Differences in bone media can exceed 10% depending on how dose to water in medium is defined.