This study aimed to investigate the influence of calibration field size on the gamma passing rate (GPR) in patient-specific quality assurance (PSQA).

Two independent detectors, PTW OCTAVIUS 4D (4DOCT) and Arc Check, were utilised in volumetric modulated arc therapy plans for 26 patients (14 with Arc Check and 12 with 4DOCT). Plans were administered using Varian Unique machine (with 4DOCT) and Varian TrueBeam (with Arc Check), each employing different calibration factors (CFs): 4 × 4, 6 × 6, 8 × 8, 10 × 10, 12 × 12 and 15 × 15 cm2 field sizes. Gamma analysis was conducted with 2%2mm, 2%3mm and 3%3mm gamma criteria.

GPR exhibited variations across different CFs. GPR demonstrated an increasing trend below 10 × 10 cm² CFs, while it displayed a decreasing trend above 10 × 10 cm². Both detectors exhibited similar GPR patterns. The correlation between 4DOCT and Arc Check was strong in tighter criteria (2%2mm) with an R² value of 0·9957, moderate criteria (2%3mm) with an R² value of 0·9868, but reduced in liberal criteria (3%3mm) with an R² value of 0·4226.

This study demonstrates that calibration field sizes significantly influence GPR in PSQA. This study recommends the plan specific calibration field must obtain to calibrate the QA devices for modulated plans.

The aim of this work was to study the acceptability of plans prepared for prostate patients treated by volumetric modulated arc therapy (VMAT) with the vision to evaluate the quality of plans and test pre-treatment quality assurance (QA).

VMAT plans of 35 patients, planned on the Eclipse Treatment Planning System (Aria 15), were included in the study. Plan acceptability was checked using statistical analysis, which includes homogeneity index, radical and median homogeneity index, coverage and uniformity index. Dose–volume histograms (DVH) of the plans were also studied to check prescribed dose (PD), Dmax, Dmin, D5 and D95. Portal dosimetry was also done by gamma analysis using 3%/3 mm criterion. SD and mean SD error were also calculated and analysed.

Statistical analysis showed a mean HI of 1·054, coverage 0·959, UI 1·055, mDHI 0·962 and rDHI 0·866. SD of HI, coverage, UI, mDHI and rDHI was 0·019, 0·019, 0·014, 0·013 and 0·030, respectively. From the DVHs, mean of D5, D95, Dmin and Dmax was calculated at 6,252·9, 5,757·4, 6,413·3 and 5,657·7 cGy, respectively, with a prescribed dose of 6,000 cGy. According to gamma analysis, area gamma < 1 was 99·12% with a tolerance limit of 95%, maximum gamma was 1·466 with a tolerance limit of 3·5, average gamma was 0·388 with a tolerance limit of 0·5, area gamma > 1·2 was 0·242% with a tolerance limit of 0·5%, maximum dose difference was 0·6 with a tolerance limit of 1·0 and average dose difference was 0·029 with a tolerance limit of 0·2.

All three computations showed the results to be within acceptable limits. VMAT possesses a unique feature of delivering the whole treatment with only two rotations of the gantry. VMAT has an improved efficiency of delivery for equivalent dosimetric quality.

This study reported the justification and selection of acceptable γ criteria with respect to low (6 MV) and high (15 MV) photon beams for intensity-modulated radiation therapy quality assurance (IMRT QA) using the Gafchromic external beam therapy 3 (EBT3) film.

Five-field step-and-shoot IMRT was used to treat 16 brain IMRT patients using the dual-energy DHX-S linear accelerator (Varian Medical System, Palo Alto, CA, USA). Dose comparisons between computed values of the treatment planning system (TPS) and Gafchromic EBT3 film were evaluated based on γ analysis using the Film QA Pro software. The dose distribution was analysed with gamma area histograms (GAHs) generated using different γ criteria (3%/2 mm, 3%/3 mm and 5%/3 mm) for the 6 and 15 MV photon beams, to optimise the best distance-to-agreement (DTA) criteria with respect to the beam energy.

From the comparison between the dose distributions acquired from the TPS and EBT3 film, a DTA criterion of 3%/2 mm showed less dose differences (DDs) with passing rates up to 93% for the 6 MV photon beams, while for the 15 MV a relaxed DTA criterion of 5%/3 mm was consistent with the DD acceptability criteria with a 95% passing rate.

Our results suggested that high-energy photon beams required relaxed DTA criteria for the brain IMRT QA, while low-energy photon beams showed better results even with tight DTA criteria.