Andersen, Claus E.

Kertzscher Schwencke, Gustavo Adolfo Vladimir

Tanderup, K.

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 20, 2017Fast, Simple, and Accurate: In Vivo Dosimeter Calibration for HDR/PDR BrachytherapyKertzscher Schwencke, Gustavo Adolfo Vladimir; Andersen, Claus E.; Tanderup, K.Published in:International Journal of Radiation Oncology, Biology, PhysicsLink to article, DOI:10.1016/j.ijrobp.2014.05.2157Publication date:2014Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Kertzscher Schwencke, G. A. V., Andersen, C. E., & Tanderup, K. (2014). Fast, Simple, and Accurate: In VivoDosimeter Calibration for HDR/PDR Brachytherapy. International Journal of Radiation Oncology, Biology,Physics, 90(1), S742. DOI: 10.1016/j.ijrobp.2014.05.2157(H&N) plans. A new imaging insert was designed for the phantom tomeasure set-up error (rotations and translations) with respect to radiationisocenter through automated analysis of portal images acquired during thevisit.Results: Visits were completed at 14 centers with 17 prostate plans createdand tested (5 IMRT and 12 VMAT) and 14 H&N plans from Year 1 re-delivered. The average diode pass rate for the prostate plans was higher(96% for 3%/2mm composite analysis) than that of the H&N plans(92.3%) in Year 1, which reflects the different complexity in these sites.Mean pass rate for repeat delivery of the first year H&N plans remained thesame but important variations (+/-) were observed at the center level. Theprogram proved to be a useful tool to evaluate impact of practice andinfrastructure changes as 7 centers re-computed or re-planned the H&Ncase to test new practice or equipment. Quantification of phantom set-uperror (n Z 17) showed minimal rotational errors with only one rotationalerror greater than 0.5. Translational error was larger, with maximum er-rors in lateral, vertical and longitudinal directions of 1.7, 1.1 and 2.1 mmrespectively, but means of <0.1, 0.3 and 0.1 mm. There was no relation-ship between pass-rate and magnitude of set-up error.Conclusions: The CQA program provides a controlled testing environmentto assess planning and delivery performance for multiple clinical sites on avariety of planning and delivery platforms. Repeat delivery is a part of thecontinuous quality improvement loop to assess changes in quality ofplanning or delivery. Design and integration of a new phantom insert in theprogram showed that setup errors were small and had limited impact oncenters’ results. Third year development for the CQA program includes anew clinical site, and introduction of tests to isolate the impact of multileafcollimator calibration on IMRT performance.Author Disclosure: A.L. McNiven: None. D.A. Jaffray: None. D.Letourneau: None.3349Fast, Simple, and Accurate: In Vivo Dosimeter Calibration for HDR/PDR BrachytherapyG. Kertzscher,1 C.E. Andersen,1 and K. Tanderup2; 1Technical Universityof Denmark, Centre for Nuclear Technologies, Roskilde, Denmark,2Aarhus University Hospital, Department of Oncology, Aarhus, DenmarkPurpose/Objective(s): In vivo dosimetry (IVD) during brachytherapy(BT) provides with an independent verification of the agreement betweenplanned and delivered treatments. Despite several benefits from real-timeIVD, e.g. efficient detection of treatment errors, widespread use of IVD islimited due to factors that compromise the simplicity of the implementa-tion and the dosimetric accuracy. This study presents a fast and accuratecalibration procedure for real-time point dosimeters which substantiallysimplifies clinical implementations of cost efficient and accurate IVD.Materials/Methods: Impractical and time consuming procedures thatinvolve filling a water tank for dosimeter calibration were avoided bymeans of a custom made dry calibration phantom that was composed of a14x14x4 cm3 base piece and a 13x4x30 cm3 tower piece that weighted 2.1kg. Parallel 1 cm separated inserts in the tower piece for the dosimeterprobe and the source catheter provided positional accuracy in lateral di-rections. The inserts were 15 and 19 cm deep such that the BT sourcecould irradiate at positions below and along the dosimeter probe tip in thelongitudinal direction. The dosimeter was calibrated based on its responseduring a single fly-by BT source scan. The positional accuracy in thelongitudinal direction was provided using an iterative algorithm. In eachiteration, a chi-square fit between measured and calculated dose rates wasperformed for candidate relative longitudinal source-to-detector distances.The algorithm updated the longitudinal distance and calibration co-efficients in each iteration, and corrected for limited scatter conditions ofthe calibration phantom, temperature dependence of the detector, andenergy dependence of the detector material with respect to water. The finalcalibration coefficients and energy and temperature corrections were usedfor fiber-coupled Al2O3:C real-time dosimetry during water phantomdepth-dose measurements and IVD implementations into the BT treatmentworkflow.Results: The calibration was performed in less than 15 minutes includingthe time required to setup the calibration, power the computer, and run thecalibration and iterative algorithm. The water phantom dose rate mea-surements agreed with AAPM TG43 calculations within 2% for source-to-detector distances between 1.5 and 7.5 cm when energy corrections weremade, and within 5% without energy corrections. The calibration proce-dure was feasible to implement in the clinical routine.Conclusions: The calibration procedure allows for robust and accurateIVD and a time efficient implementation into the clinical routine. Thecalibration algorithm corrects for the for energy and temperature depen-dence of the detector material and can therefore be adapted for any pointdosimeter probe intended for real-time IVD during BT.Author Disclosure: G. Kertzscher: None. C.E. Andersen: None. K.Tanderup: None.3350VMAT Head and Neck Treatment Delivery: Benchmarking Accuracyof Patient DVH Based QA With Radiological Physics Center (RPC)Head and Neck Phantom ResultsR. Varadhan, A. Haven-Smith, S. Yerich, C. Overbeck, B. Garrity,and S. Way; Minneapolis Radiation Oncology, Minneapolis, MNPurpose/Objective(s): The purpose of this study is to a) investigate theaccuracy of patient DVH based QA using volumetric measurement guideddose reconstruction (MGDR) for head & neck Volumetric Modulated ArcTherapy (VMAT) delivery by benchmarking against RPC Head and NeckPhantom results, b) investigate the correlation of 3D detector phantombased QA using local gamma and global gamma results when comparedagainst patient DVH based QA.Materials/Methods: The RPC head and neck phantom was planned andirradiated using 2 arc VMAT delivery method. The results of point doses fromRPC TLDs at eight locations and dose profiles from radiochromic film throughcenter of primary PTVinside the phantomwere compared against the treatmentplanning system (TPS) and the results from the MGDR analysis based on 3Ddetector phantom QA. Also the 3D gamma value was calculated using theMGDR analysis which compares the TPS dose to the predicted dose distri-bution. Five head and neck patients were planned using VMAT deliverymethod and the QAwas performed using both 3D detector phantom based QAand patient DVH based analysis using MGDR. The correlation betweengamma pass rates using both global and local gamma criteria was comparedagainst the gamma pass rates using MGDR analysis.Results: The ratio of MGDR calculated dose to primary and secondaryplanning target volume (PTV) compared with both RPC TLD and EclipseTPS doses was  1.05. The ratio of estimated cord dose from MGDRanalysis was  1.09 and 1.03 when compared to RPC TLD and TPS dosesrespectively. The displacement between calculated dose gradient in theregion between primary PTV and organ at risk (OAR) in all 3 planes fromMGDR was within 3mm and 1mm when compared to RPC film and TPSprofiles respectively. The average 3D local gamma pass rate for the fiveclinical cases using MGDR was  97.5% and 92% when using 3% 3mmand 2% 2mm analysis criteria respectively. The average gamma pass rateusing global gamma 3%3mm criteria was 99.8%, compared to an averagelocal gamma pass rate of 87.1% using 3D detector phantom based QAwitha maximum increase of 18%.Conclusions: Benchmarking the accuracy of patient DVH based QA re-sults to the RPC head and neck phantom established a baseline accuracyand confidence in use of MGDR analysis for VMAT delivery in a realisticpatient geometry. For the 5 clinical test cases studied, the low pass ratesobtained using the local gamma evaluation criteria in phantom based QAhad no significant clinical impact for the patient when evaluated usingDVH based QA.Author Disclosure: R. Varadhan: None. A. Haven-Smith: None. S.Yerich: None. C. Overbeck: None. B. Garrity: None. S. Way: None.International Journal of Radiation Oncology  Biology  PhysicsS742

Fast, Simple, and Accurate: In Vivo Dosimeter Calibration for HDR/PDR Brachytherapy

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Fast, Simple, and Accurate: In Vivo Dosimeter Calibration for HDR/PDR Brachytherapy

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