Prog Med Phys.  2017 Jun;28(2):61-66. 10.14316/pmp.2017.28.2.61.

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

• Kim JI
• Choi CH
• Park SY
• An H
• Wu HG
• Park JM

• KMID: 2388210
• DOI: http://doi.org/10.14316/pmp.2017.28.2.61

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.

Keyword

Volumetric modulated arc therapy; Intensity modulated radiation therapy; Gamma analysis; Portal dosimetry

MeSH Terms

Radiotherapy, Intensity-Modulated*
Retrospective Studies

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