pmp Progress in Medical Physics Progress in Medical Physics 2508-4445 2508-4453 Korean Society of Medical Physics 10.14316/pmp.2017.28.2.61 pmp-28-61 Original Article Gamma Evaluation with Portal Dosimetry for Volumetric Modulated Arc Therapy and Intensity-Modulated Radiation Therapy KimJung-in ∗ † ‡ ChoiChang Heon ∗ † ‡ ParkSo-Yeon ∗ † ‡ AnHyunJoon ∗ † ‡ WuHong-Gyun ∗ † ‡ § ParkJong Min ∗ † ‡ ∥ Department of Radiation Oncology, Seoul National University Hospital, Seoul, Korea Biomedical Research Institute, Seoul National University Hospital, Seoul, Korea Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Korea Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea Robotics Research Laboratory for Extreme Environments, Advanced Institutes of Convergence Technology, Suwon, Korea Corresponding author Jong Min Park (leodavinci@naver.com) Tel: 82-2-2072-2527 Fax: 82-2-765-3317 62017 1762017 282 6166 30062017 10072017 10072017 Copyright © 2017 Korean Society of Medical Physics 2017 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract

The aim of this study is to investigate the characteristics of portal dosimetry in comparison with the MapCHECK2 measurments. In this study, a total of 65 treatment plans including both volumetric modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) were retrospectively selected and analyzed (45 VMAT plans and 20 IMRT plans). A total of 4 types of linac models (VitalBeam, Trilogy, Clinac 21EXS, and Clianc iX) were used for the comparison between portal dosimetry and the MapCHECK2 measurements. The VMAT plans were delivered with two VitalBeam linacs (VitalBeam1 and VitalBeam2) and one Trilogy while the IMRT plans were delivered with one Clinac 21EXS and one Clinacl iX. The global gamma passing rates of portal dosimetry and the MapCHECK2 measurements were analyzed with a gamma criterion of 3%/3 mm for IMRT while those were analyzed with a gamma criterion of 2%/2 mm for VMAT. Spearman's correlation coefficients (r) were calculated between the gamma passing rates of portal dosimetry and those of the MapCHECK2 measurements. For VMAT, the gamma passing rates of portal dosimetry with the VitalBeam1, VitalBeam2, and Trilogy were 97.3%±3.5%, 97.1%±3.4%, and 97.5%±1.9%, respectively. Those of the MapCHECK2 measurements were 96.8%±2.5%, 96.3%±2.7%, and 97.4%±1.3%, respectively. For IMRT, the gamma passing rates of portal dosimetry with Clinac 21EXS and Clinac iX were 99.7%±0.3% and 99.8%±0.2%, respectively. Those of the MapCHECK2 measurements were 96.5%±3.3% and 97.7%±3.2%, respectively. Except for the result with the Trilogy, no correlations were observed between the gamma passing rates of portal dosimetry and those of the MapCHECK2 measurements. Therefore, both the MapCHECK2 measurements and portal dosimetry can be used as an alternative to each other for patient-specific QA for both IMRT and VMAT.

 Volumetric modulated arc therapy Intensity modulated radiation therapy Gamma analysis Portal dosimetry REFERENCES Zhang P Happersett L Hunt M Jackson A Zelefsky M Mageras G Volumetric modulated arc therapy: planning and evaluation for prostate cancer cases Int J Radiat Oncol Biol Phys. 2010765 145662 Studenski MT Bar-Ad V Siglin J Cognetti D Curry J Tuluc M Clinical experience transitioning from IMRT to VMAT for head and neck cancer Med Dosim. 2013382 1715 Ezzell GA Burmeister JW Dogan N LoSasso TJ Mechalakos JG Mihailidis D IMRT commissioning: multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119 Med Phys. 20093611 535973 Brahme A Optimization of stationary and moving beam radiation therapy techniques Radiother Oncol. 1988122 12940 Otto K Volumetric modulated arc therapy: IMRT in a single gantry arc Med Phys. 2008351 3107 Kang JK Kim MS Jang WI Seo YS Kim HJ Cho CK The clinical utilization of radiation therapy in Korea between 2009 and 2013 Radiat Oncol J. 2016342 8895 Park JM Park SY Kim H Modulation index for VMAT considering both mechanical and dose calculation uncertainties Phys Med Biol. 20156018 710125 Park SY Kim IH Ye SJ Carlson J Park JM Texture analysis on the fluence map to evaluate the degree of modulation for volumetric modulated arc therapy Med Phys. 20144111 111718 Fredh A Scherman JB Fog LS Munck af Rosenschold P Patient QA systems for rotational radiation therapy: a comparative experimental study with intentional errors Med Phys. 2013403 031716 Heilemann G Poppe B Laub W On the sensitivity of common gamma-index evaluation methods to MLC misalignments in Rapidarc quality assurance Med Phys. 2013403 031702 Kim JI Park SY Kim HJ Kim JH Ye SJ Park JM The sensitivity of gamma-index method to the positioning errors of high-definition MLC in patient-specific VMAT QA for SBRT Radiat Oncol. 20149 167 Low DA Harms WB Mutic S Purdy JA A technique for the quantitative evaluation of dose distributions Med Phys. 1998255 65661 Fogliata A Clivio A Fenoglietto P Hrbacek J Kloeck S Lattuada P Quality assurance of RapidArc in clinical practice using portal dosimetry Br J Radiol. 2011841002 53445 Sharma DS Mhatre V Heigrujam M Talapatra K Mallik S Portal dosimetry for pretreatment verification of IMRT plan: a comparison with 2D ion chamber array J Appl Clin Med Phys. 2010114 3268 Martinez Ortega J Gomez Gonzalez N Castro Tejero P Pinto Monedero M Tolani NB Nunez Martin L A portal dosimetry dose prediction method based on collapsed cone algorithm using the clinical beam model Med Phys. 2017441 33341 Yoon J Jung JW Kim JO Yeo I A Monte Carlo calculation model of electronic portal imaging device for transit dosimetry through heterogeneous media Med Phys. 2016435): 2242. Millin AE Windle RS Lewis DG A comparison of electronic portal dosimetry verification methods for use in stereotactic radiotherapy Phys Med. 2016321 18896 Spreeuw H Rozendaal R Camargo P Mans A Wendling M Olaciregui-Ruiz I Portal dosimetry in wedged beams J Appl Clin Med Phys. 2015163 5375 Tables

Gamma passing rates of portal dosimetry and the MapCHECK2 measurements for volumetric modulated arc therapy with a gamma criterion of 2%/2 mm.

Machine Portal dosimetry MapCHECK2 p
VitalBeam 1 97.3±3.5 96.8±2.5 0.543
  (89.1~100.0) (90.0~100.0)  
VitalBeam 2 97.1±3.4 96.3±2.7 0.476
  (89.1~100.0) (90.0~100.0)  
Trilogy 97.5±1.9 97.4±1.3 0.876
  (93.9~99.9) (95.3~99.8)  

Gamma passing rates of portal dosimetry and the MapCHECK2 measurements for intensity-modulated radiation therapy with a gamma criterion of 3%/3 mm.

Machine Portal dosimetry MapCHECK2 p
Clianc 21EXS 99.7±0.3 96.5±3.3 0.020
  (99.0~99.9) (90.7~99.9)  
Clinac iX 99.8±0.2 97.7±3.2 0.076
  (99.3~100.0) (91.1~99.3)  

Correlations between the gamma passing rates of portal dosimetry and those of MapCHECK2 measurements.

Technique Machine Gamma criterion N r p
VMAT VitalBeam 1 2%/2 mm 20 0.381 0.097
  VitalBeam 2   15 0.221 0.429
  Trilogy   10 0.658 0.038
IMRT 21EXS 3%/3 mm 10 −0.075 0.836
  iX   10 0.107 0.769

VMAT: volumetric modulated arc therapy, IMRT: intensity-modulated radiation therapy, N: number, r: Spearman's correlation coefficient.