Gamma Evaluation with Portal Dosimetry for Volumetric Modulated Arc Therapy and Intensity-Modulated Radiation Therapy

Jung-in Kim; Chang Heon Choi; So-Yeon Park; HyunJoon An; Hong-Gyun Wu; Jong Min Park

doi:10.14316/pmp.2017.28.2.61

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Kim, Choi, Park, An, Wu, and Park: Gamma Evaluation with Portal Dosimetry for Volumetric Modulated Arc Therapy and Intensity-Modulated Radiation Therapy

Original Article

Progress in Medical Physics 2017;28(2):61-66.

Published online: 17 June 2017

DOI: https://doi.org/10.14316/pmp.2017.28.2.61

Gamma Evaluation with Portal Dosimetry for Volumetric Modulated Arc Therapy and Intensity-Modulated Radiation Therapy

Jung-in Kim^∗,^†,^‡, Chang Heon Choi^∗,^†,^‡, So-Yeon Park^∗,^†,^‡, HyunJoon An^∗,^†,^‡, Hong-Gyun Wu^∗,^†,^‡,^§, Jong Min Park^∗,^†,^‡,^∥,

^∗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

Received 30 June 201710 July 2017 Accepted 10 July 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.

Keywords: Volumetric modulated arc therapy, Intensity modulated radiation therapy, Gamma analysis, Portal dosimetry

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Table 1.

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)

Table 2.

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)

Table 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.

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