bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐684: Robustness Versus Plan Quality for IMPT
Authors: Gorissen BL , Depauw N , Unkelbach J 
Published: June 2015

Purpose:Range and set‐up uncertainties in intensity‐modulated proton therapy cannot be addressed with margins. Instead, several robust optimization (RO) models have been developed that explicitly take uncertainty into account. RO optimizes the worst case at the cost of the treatment outcome in more likely scenarios. The goal is to provide insight in the trade‐off between robustness and plan quality and the behavior of different trade‐off methods.Methods:We present four methods to trade‐off robustness with plan quality that can be applied to any of the worst case methods found in literature. Each trade‐off is a mixture between worst case, expected value, and non‐robust planning, which effectively corresponds to assigning different importance weights to error scenarios. Each method is tested on several worst case methods for a sarcoma case, a paraspinal case and a benchmark case from literature.Results:Each trade‐off method yields a unique dose distribution in the border region between target volume and adjacent normal tissues, corresponding to a specific trade‐off between robustness and nominal plan quality. The fully robust solutions perform badly when the realized errors are smaller than the maximum projected errors. Compared to fully robust solutions, significant improvements are possible for non‐extreme scenarios while only slightly deteriorating plan quality at an extreme scenario. It is further observed that trade‐off methods cannot be mimicked by putting different weights on objectives for the tumor and the normal tissue.Conclusion:The method to trade‐off robustness with plan quality should be chosen carefully, as each method has a different impact on plan quality. Two of the methods can directly be implemented in any framework for multicriteria optimization, hopefully leading to their quick dissemination.
SU‐E‐T‐685: Root Cause Analysis of in Vivo Dosimetry Controls for Dynamic Arc Treatments
Authors: Celi S , Wessels C , Francois P 
Published: June 2015

Purpose:To produce an insight on the influence of selected parameters on the pass/fail rates of in‐vivo dosimetry (IVD) controls for dynamic arc treatments.Methods:A group of 25 patient treatment plans optimized with the treatment planning system Eclipse™ (Varian) for dual‐arc RapidArc treatment was analyzed. All plans were tracked with the IVD solution EPIgray (DOSIsoft S.A) over all sessions of the treatment course. Based on the acquired a‐Si EPID images, the dose differences to the TPS at given reference points and the corresponding gamma indices were computed. In addition, the dose difference variations over the course were determined post‐treatment. Five parameters — considered as possible fail or pass causes of IVD for dynamic arc plans — were chosen. Based on the treatment plan, two types of modulation indices qualifying the movement of the MLC were calculated. An “in‐field” coefficient and a “weighted‐in‐field” coefficient were established to quantify the position of the dose reference points in the planned volume. Finally, the dose rate variations for each arc were also determined. The described parameters were confronted to the results of the IVD controls.Results:The analyzed plans have a mean relative dose difference of 0.2% (±7.2%). No correlation could be established between the modulation indices and the dose differences, the gamma indices or the dose difference variation. Slightly better passing rates for individual sessions and total treatment plans were observed for “in‐field” coefficients superior to 50%. Similar passing rates were observed for arcs with below and above average dose rate deviations.Conclusion:Though all the analyzed parameters are cited as possible pass/fail criteria, only the position of the dose reference point can be linked to dose differences in IVD controls. Automatically generated dose measurement points could avoid false interpretations and an overflow of false negative alerts.The author's PhD research is funded by DOSIsoft S.A.
SU‐E‐T‐686: SBRT 4‐Dimensional Treatment Planning for Vero Dynamic Tumor Tracking Lung Patients
Authors: Su Z , Dagan R , Li Z 
Published: June 2015

Purpose:To investigate 4‐dimensional (4D) treatment planning for Vero dynamic tumor tracking (DTT) SBRT lung patients and to compare its dosimetry to one single‐phase (50%) CT based treatment plan as well as to 4D average‐intensity CT based plan.Methods:7 lung patients with total of 10 tumors were retrospectively selected. Tumor and organ‐at‐risks (OARs), which include lung, heart, esophagus, spinal cord and proximal airways, were contoured on each phase of the 4DCTs and 4D average‐intensity CTs. GTV averages and standard deviations (SD) among phases were obtained for target deformation evaluation. For each tumor, treatment plans of 50Gy in 5 fractions with same beam arrangements were generated for the 3 planning approaches. MimVista was used to deform phase dose matrices to the 50% phase. Doses to the OARs were compared between 4D deformed plans and single‐phase plans (clinical DTT plans). Single‐phase CT plans were also compared to 4D average‐intensity CT plans.Results:The relative SD of phase GTV volume is mostly in an inverse relationship with GTV volume. Compared to 4D average‐intensity plan, single‐phase DTT plan shows up to 253.9cc reduction of lung volume at 12.5Gy, and reduction of 28.1Gy, 4.8Gy, 5.3Gy of maximum dose to proximal airways, to heart and to spinal cord, respectively; Compared to single‐phase DTT plan, 4D deformed plan shows up to 70.3cc reduction of lung volume at 12.5Gy, and reduction of 1.6Gy, 3.4Gy, 1.3Gy of maximum dose to proximal airways, to heart and to spinal cord, respectively.Conclusion:This study showed that small tumors are potentially prone to phase deformation. This study also demonstrated that DTT can significantly reduce doses to OARs for lung SBRT patients. Furthermore, 4D treatment planning with phase dose deformation to 50% phase is more representative of actual dose to OARs than single‐phase CT based planning for lung patients treated with DTT.This study is partially supported by Brainlab Inc.
SU‐E‐T‐692: Should the Machine‐Related Range Shifter (MRS) Be Replaced by a Patient‐Related Range Shifter (PRS) to Preserve the Scanning Beam Dosimetric Advantages?
Authors: Lin H , Shen J , McDonough J , Tochner Z , Both S 
Published: June 2015

Purpose:To present and evaluate the impact of PRS relative to MRS on PBS spot size.Methods:Three PRS: U‐shape bolus (USB), anterior‐lateral bridge bolus (ALBB), couch top bolus (CTB)) and MRS mounted on the nozzle are currently employed in our institution. Homogeneous materials with different densities were employed for each device. In‐air spot sizes were simulated and compared for 6 conditions: open field, MRS with 15cm, 20cm, and 35 cm air gaps and PRS with 2cm and 8cm air gaps to reproduce clinical treatment conditions. The pros and cons of MRS are evaluated against PRS.Results:Spot sizes increased with greater air gaps, which are more significant for low energy protons. PRS can be consistently placed close to the patient surface; therefore spot sizes don't change significantly relative to the open beam. MRS may have the same effect for small air gaps. While PRS is overall superior in avoiding patient collision, its impact on the quality of the verification imaging increases as Z increases, in particular for CTB. However, lower Z‐material CTB may increase collision and still affect CBCT quality. The main advantages of the PRS are spot size preservation (<2mm change for air gaps of 2 to 8cm), increased uniformity and conformality of the dose distributions and patient collision avoidance. This cannot be achieved consistently for Brain and HN treatment using MRS as the air gap may increase greater than 15cm (maximal increase of 4.5 mm on spot size) due to clearance issues.Conclusion:The spot size and PBS dosimetrical advantages can be maintained with minimized air gap for both PRS and MRS. However; the PRS non‐removable device (CTB) affects CBCT imaging quality. Therefore, an ideal approach would be a combination between the USB for the brain and HN treatments and an automated MRS for body and extremities.
SU‐E‐T‐697: Simple and Efficient Modeling of the Varian TrueBeam Linac Using the GATE Monte Carlo Platform
Authors: Roth B , Ploquin N , Wiebe J 
Published: June 2015

Purpose:To investigate the use of the relatively new Geant4 Application for Tomographic Emission (GATE) Monte Carlo (MC) platform for radiotherapy applications, by developing a model of the Varian TrueBeam™ linac.Methods:Multiple 6 MV phase space files were provided by Varian, serving as a simulation particle source. Modeling of the jaws and multileaf collimator (MLC) in GATE's macro structured environment was automated through the use of an in‐house developed Python program. Profiles and percentage depth doses (PDD) were compared between MC calculations, diode, ion chamber and radiochromic film measurements for six square fields ranging in size from 1 × 1 cm2 to 40 × 40 cm2 at five different depths. The MLC model was evaluated through comparison to radiochromic film for an “E” shaped field defined by the MLCs at two different depths.Results:Profiles and PDDs of MC calculated values for each field size and depth were evaluated against measurements using a tight 3%/1 mm gamma criteria. It was found that 28 out of 30 square field profiles have a gamma pass rate of ≥90%, 20 of which achieved at least a 95% pass rate. All PDDs were found to have at least a 97% pass rate. When compared to film measurements, 97% and 99% of points met the gamma criteria for the MLC shaped field along the inline and crossline axes respectively, while 100% of points achieved the criteria along both axes at a depth of 50 mm.Conclusion:GATE provides a valid, efficient and simple to use MC platform to model medical linear accelerators for the purpose of radiotherapy dose calculation.
SU‐E‐T‐704: Skin Dose in Proton Pencil Beam Scanning for Pediatric Patients
Authors: Axente M , Moskvin V , Shin J , Tsiamas P , Merchant T , Farr J 
Published: June 2015

Purpose:Optimize intensity modulated proton therapy (IMPT) treatment planning guidelines with regard to skin dose reduction in pediatric patients.Methods:Phantom and patient CTs were used to evaluate skin dose using a pre‐clinical proton beam modeled using Monte Carlo (TOPAS) in a commercial radiotherapy planning system (RTP). Single‐spot and single‐beam doses were analyzed in phantom environment. Fractional surface dose was evaluated vs. spot spacing and maximum range for beams optimized for increasingly deep targets. Both RTP automatic variable spacing (0.5xσprojected) and constant spacing (0.2–1.2cm) were evaluated. 3 spine IMPT plans were obtained with/without objectives for skin dose, with automatic and constant spot spacing. Dosimetric parameters and spot weight/energy statistics were evaluated.Results:Single‐spot primary fluence depletion raises the spot axial relative skin dose above Bragg peak dose for E0>139MeV. Dose heterogeneity and maximum skin dose increases with maximum beam energy and spot spacing non‐linearly. Exponential fitting of maximum skin‐to‐target dose ratio against spot spacing suggested an optimum constant spacing <3mm for minimizing skin dose. Automatic spacing did not produce optimal results for deep tumors. For patient plans, heterogeneous and high skin dose were observed where >50% MU weight was carried by spots with energy >135MeV, and had spots >155MeV. Introducing skin optimization objectives/constraints, decreased high energy spots weights, while that for >135MeV spots increased. Hence, skin D50 increased with skin‐optimized plans, while coverage remained constant. Average dose, D1 and D0.1cc decreased compared to plans without skin objectives. Constant spacing did not produce superior skin dose distributions without skin optimization objectives.Conclusion:IMPT inverse planning can produce high skin doses with heterogeneous distributions, effects that can be mitigated via optimization. Careful coordination between RTP techniques and accurate skin dosimetric parameters will allow minimization of clinical skin effects and establishment of threshold doses for acute/late effects in pediatric population treated with IMPT.
SU‐E‐T‐719: Surface Dose Evaluation of the Equivalent Quality Flattening Filter‐Free Photon Beams
Authors: Meshram M , Pramanik S , Ranjith C P , Meshram M 
Published: June 2015

Purpose:To provide data on the relative surface dose of photon beams of Versa HD linear accelerator designed to delivered the Flattening Filter Free (FFF) beam having beam quality equivalent to the corresponding Flattened beam.This study involves the comparative evaluation of the entrance dose of FFF and Flattened photon beams in the buildup region.Methods:Surface dose was measured using Markus parallel plate chamber with the thin flat entrance window thickness of 0.025mm of water equivalent material in solid water phantom. Data were collected for square fields of 2×2cm2, 3×3cm2,4×4cm2,5×5cm2,7×7cm2,10×10cm2 and 20×20cm2 created in Monaco Treatment Planning System.The surface dose was define for this study as the relative dose at depth of 0.5mm with respect to the dose at dmax.The same Markus chamber was used to investigate the dose in the buildup region for all the square fields.The buildup depths for 6MV flattened and FFF beams were 0 to 18mm and for 10MV Flattened and FFF beams were 0 to 24mm. All values were determined in relation to the depth at dose maximum dmax.Results:The relation of surface dose for both Flattened and FFF beams with field sizes were linear. The surface dose for smaller field size upto 10×10cm2 for both FFF beams were higher than Flattened beams but the variation was marginal. The difference was 0.3 percentage at 6MV and 1.9 percentage at 10MV for a 10×10cm2 field but for the larger field the relative surface dose was lower for FFF beam with difference of 3.6 percentage at 6MV and 4.3 percentage at 10MV for a 20×20cm2 field.Conclusion:The equivalent quality FFF Photons produce higher surface dose for smaller field sizes upto 10×10cm2 but lower surface dose for large field sizes than the conventional flattened beam. The percentage variation was marginal for smaller field sizes and may not be clinically significant.
SU‐E‐T‐725: The Analysis of Different Diagonal Profiles Used for Commissioning in Eclipse
Authors: Mabhouti H , Acar H , Kucuk N , Kucukmorkoc E , Doyuran M , Caglar M , Altinok A , Cebe M , Yilidir G , Caglar H 
Published: June 2015

Purpose:The effect of diagonal profiles measured with different types of detectors to the improvement of the quality of the algorithm configuration is analysed.Methods:For commissioning of Truebeam STx machine, Eclipse requires a diagonal profiles of the largest field size. The left side of the beam profile with 5cm overscan at depths of 30cm for a 40×40cm2 field at 100cm SSD was scanned. The scan was made using PTW 0.125cc semiflex ionization chamber and PTW microDiamond with 0.004mm3 sensitive volume. Two different machnines were created in Eclipse with the same beam data except for diagonal profiles. A single 6 FFF beam with zero gantry and collimator angle for 10×10cm2 field size was planned on the CT scan of RW3 solid water. The dose calculation was done with 1mm grid size using AcurosXB v13 algorithm. Dose profile measurements were made in a RW3 solid water phantom at depths of 5, 10, 15cm using EBT3 Gafchromic film extending from field edge up to 15cm. The gamma index analysis of measured and calculated dose profiles were compared.Result:For the plan using semiflex configured machine, the measured and the calculated dose distributions gamma analysis passing rate was 98.1% within ±2% dose difference and ±2mm distance‐to‐agreement for in field doses. However they decreases to 96.8% for out of field doses. For the plan using microDiamond configured machine had 98.9% passing rate for ±2% in field but it decreases to 97.6% for out of field doses. Although passing rates were increasing with the depth for in field doses they were decreasing with depth for out of field doses.Conclusion:Diagonal profiles are used for source configuration in Eclipse. Because of that it can be advisable to use fine resolution detector.
SU‐E‐T‐726: The Analysis of Different Percentage Depth Dose Curves Used for Commissioning in Eclipse
Authors: Cebe M , Acar H , Kucuk N , Kucukmorkoc E , Doyuran M , Caglar M , Altinok A , Yilidir G , Mabhouti H , Caglar H 
Published: June 2015

Purpose:Percentage Depth Doses (PDDs) used for balance fitting of the calculation model in Eclipse. The effect of PDD curves measured with two different detectors for the commissioning of Truebeam STx machine to the improvement of the quality of the algorithm configuration is analysed.Methods:The measurement of open field PDD for 2×2cm2 to 40×40cm2 field sizes were done with two different detector types. The scan was made using 0.125cc semiflex thimble ionization chamber (PTW TM31010) and PTW 60019 microDiamond with 0.004mm3 sensitive volume. Two different machines were created in Eclipse with the same beam data except for PDD measured with two different detector types. A single 6 FFF beam with zero gantry and collimator angles for 2×2, 3×3, 5×5cm2 field sizes were planned on the CT scan of RW3 solid water. The dose calculation was done with 1mm grid size using AcurosXB v13 algorithm using two different machine created. PDD measurements were made in a RW3 solid water phantom using EBT3 Gafchromic film extending from surface to 30cm. The gamma index analysis of measured and calculated PDD curves were compared.Result:For the plan made using machine configured with semiflex measured PDD curves, the measured and the calculated dose distributions for 2×2cm2 field size gamma analysis passing rate was 97.6% within 2% dose difference and 2mm distance‐to‐agreement. For the plan made using machine configured with microDiamond measured PDD curves had 98.1% passing rate for ±2% in field but the passing rates. Passing rates were increasing with the field sizes. For 5×5cm2 field size they are 98.3% and 99.1% respectively.Conclusion:The agrement with treatment planning system and measurement was better when fine resolution detector was used especially for small field sizes.
SU‐E‐T‐729: The Dosimetric Impact of Moving Small Size Lung Tumor Using Helical Tomotherapy
Authors: Tu P , Nien H , Lee H , Wu C , Lin C , Lin C 
Published: June 2015

Purpose:Respiration during radiotherapy irradiation causes dose delivery uncertainty to the lung tumor. This phantom study was designed to investigate the dosimetric impact of tumor motion during respiration with TomoTherapy treatment.Methods:Dynamic thorax phantom (CIRS. Inc, Norfolk, VA), was used to mimic small size lung tumors (1, 2, and 3cm in diameter) motion during respiration. CT images of tumors under static condition were imported into TomoTherapy Hi‐Art system. Plans were calculated with different jaw sizes for each size of tumor. Dose measurement was performed under both static and respiratory simulation produced by dynamic thorax phantom. Our respiratory simulation setting was chosen due to more compatible with clinical breathing cycle pattern including 1cm amplitude movement in SI direction, 4s breathing period and cos6 breathing pattern. Two‐dimensional dose of DQA plans were measured by EBT3 films. The point dose was measured in the center of each tumor using A1SL ion chamber.Results:The point dose of 1 cm motion tumor was 9% higher than plan dose, and decreased variation by increasing jaw size. The point dose of 1 cm and 2 cm motion tumors were greater than static tumors, but the results of 3 cm tumor were in contrast. Dose coverage was improved by increasing tumor size and jaw size. The width of 50% dose level of motion tumors on horizontal 2D dose profile were similar with widths of static tumor, but dose distribution shifted toward inferior direction. The widths of 60% dose level of motion tumors were smaller than widths of static tumor and difference decreased by increasing tumor and jaw size.Conclusion:Small size motion tumor has greater dose difference than bigger tumors. Large jaw size leads to more penumbra but provides better dose coverage. Larger margin was suggested at the longitudinal superior direction to compensate the dose distribution deviation during respiration.
SU‐E‐T‐731: The Effect of Thermoplatic Mask to the Surface Dose in Sterotactic Brain Treatments with Flattening Filter Free Beams with EBT3 Gafchromic Film and OSL Dosimeter
Authors: Yilidir G , Acar H , Kucuk N , Kucukmorkoc E , Doyuran M , Caglar M , Altinok A , Cebe M , Mabhouti H , Caglar H 
Published: June 2015

Purpose:The surface dose of flattening filter free beams is higher than conventional flattening filter beams. In this study, The effect of thermoplatic mask to the surface dose in sterotactic brain treatments was compared using EBT3 Gafchromic film and OSL dosimeter.Methods:Treatment planning were done using 2 full arc VMAT technique with 6 FFF beam on the CT scan of Randophantom simulating the treatment of sterotactic treatments for one brain metastasis.1×1 cm2 Gafchromic EBT 3 film pieces were placed under the thermoplastic mask on the lens of the phantom. Then OSL dosimeter was also placed at the same way in the same place. Then phantom was irradiated without mask with film and OSL again. The surface doses with or without mask was compared for film and OSL dosimeter seperately.Results:The calibration of film and OSL dosimetry were done at first. Surface dosemeasurements made using the EBT3 film showed good agreement with results of the OSL dosimetry for standard fields of FFF beams within the measurement uncertainty of 3.1%. The surface dose determined using EBT3 film was found to change from 57 % to 93 % to with the mask. The surface dose determined using OSL dosimeter was found to change from 56 % to 93 % to with the mask. This study also demonstrates the suitability of Gafchromic EBT3 film and OSL dosimeter for surface dose measurements in FFF beams.Conclusion:The skin sparing effect FFF beams are lower than conventional beams. Significant bolus effect on skin dose in the presence of thermoplastic mask was seen. The skin reactions resulting from thermoplastic masks should be monitored especially for FFF beams and corrective measures should be taken during treatment to avoid skin toxicity.