TITLE:
Evaluating IMRT and VMAT Dose Verification: Capability Index Analysis for Quality Assurance in Radiotherapy
AUTHORS:
Ayman G. Ibrahim, Hesham S. El-Bahkiry, Ismail Emam, Osama Abbas, Doaa G. Mahmoud
KEYWORDS:
IMRT, VMAT, EPID, 2D Array, Capability Index, Quality Assurance
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.14 No.4,
November
25,
2025
ABSTRACT: Introduction: Advanced radiotherapy methods include Intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) requiring stringent quality assurance (QA) to ensure accurate dose delivery. This study assesses the effectiveness of IMRT and VMAT dosage verification by gamma index analysis and capability index (Cpml), which are statistical process control (SPC) tools, to assess QA process reliability and compare dosimetrical outcomes for head and neck and rectal cancer treatment plans. Materials and Methods: For 28 cases of head and neck (14 IMRT and 14 VMAT) were generated utilizing treatment planning system (TPS) Eclipse, which delivered 6 MV photon beam linear accelerator (Varian, Clinac IX). Dose distributions were measured using an aSi-1000 electronic portal imaging device (EPID) and OCTAVIUS Detector 1500 2D array, compared against TPS calculations using gamma index criteria (3%/3 mm). Control charts and Cpml evaluated QA process stability for 25 cases. Dosimetrical comparisons for rectal cancer assessed planning target volume coverage, organ-at-risk doses, and monitor units. Result: For head and neck the gamma passing rates showed strong agreement, with means of 99.24% ± 0.37 (EPID) and 98.76% ± 0.61 (2D array) for IMRT, and 99.00% ± 0.38 (EPID) and 98.91% ± 0.43 (2D array) for VMAT. For rectal cancer the capability index (Cpml) values of 1.36 (IMRT) and 1.47 (VMAT) indicated optimal QA performance. VMAT plans for rectal cancer reduced MUs and treatment time by approximately 50% while achieving comparable PTV coverage and OAR sparing. Conclusion: VMAT demonstrates efficiency advantages over IMRT, with robust QA processes, supported by SPC and capability index assessments, enhancing treatment precision and patient outcomes.