Figure 1 - available via license: Creative Commons Attribution 4.0 International
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A box plot of the gamma-passing rate (phase 0% versus phase 50%) of all 13 plans as a function of the motion amplitude, for different number of breaths, with 10% (A) and 50% (B) dose thresholds. The solid line represents the 90% tolerance level.
Source publication
Introduction
Stereotactic ablative radiotherapy (SABR) is susceptible to challenges for tumours affected by intrafraction organ motion. This study aims to investigate the effect of breathing characteristics and plan complexity on the interplay effect.
Methods
A patient-specific interplay effect evaluation was performed using in-house software with...
Context in source publication
Context 1
... 1 and 2 demonstrate the results of the comparison of the dose distribution in the plans of 13 patients between the endinhalation 0% and end-exhalation 50% breathing phases simulated with a range-of-motion amplitudes that cover the range of lung tumour motion and range of NBs from low (5) to high (50). A general trend of reduction in the gamma-passing rate was observed as the motion amplitude exceeded 5 mm for both thresholds in Figures 1A and 1B. The dominant effect of the NBs as the motion amplitudes increase is shown in Figures 2A and 2B. ...
Citations
... While simple ion chamber measurements can provide one-dimensional (1D) information, it may not be sufficient for identifying errors in complex volumetric-modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) plans. To obtain two-dimensional (2D) or three-dimensional (3D) dose information, many commercial array-based detectors are available, [3][4][5][6][7] equipped with built-in analyzing software. The planned dose and measured dose can be compared using the gamma index, quantifying the gamma passing rate (GPR) in percentage. ...
Purpose
This study aimed to investigate the influence of calibration field size on the gamma passing rate (GPR) in patient-specific quality assurance (PSQA).
Methods
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 cm ² field sizes. Gamma analysis was conducted with 2%2mm, 2%3mm and 3%3mm gamma criteria.
Results
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.
Conclusion
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.
