Abstract
A patient-specific quality assurance (QA) test is conducted to verify the accuracy of dose delivery. It generally consists of three verification processes: the absolute point dose difference, the planar dose differences at each gantry angle, and the planar dose differences by 3D composite irradiation. However, this imposes a substantial workload on medical physicists. The objective of this study was to determine whether our novel method that predicts the 3D delivered dose allows certain patient-specific IMRT QAs to be curtailed. The object was IMRT QA for the pelvic region with regard to point dose and composite planar dose differences. We compared measured doses, doses calculated in the treatment planning system, and doses predicted by in-house software. The 3D predicted dose was reconstructed from the per-field measurement by incorporating the relative dose error distribution into the original dose grid of each beam. All point dose differences between the measured and the calculated dose were within ±3%, whereas 93.3% of them between the predicted and the calculated dose were within ±3%. As for planar dose differences, the gamma passing rates between the calculated and the predicted dose were higher than those between the calculated and the measured dose. Comparison and statistical analysis revealed a correlation between the predicted and the measured dose with regard to both point dose and planar dose differences. We concluded that the prediction-based approach is an accurate substitute for the conventional measurement-based approach in IMRT QA for the pelvic region. Our novel approach will help medical physicists save time on IMRT QA.
Highlights
Intensity-modulated radiation therapy (IMRT) enables complex dose distribution around a target with minimized damage to normal tissues [1]
We concluded that the prediction-based approach is an accurate substitute for the conventional measurement-based approach in IMRT quality assurance (QA) for the pelvic region
It requires multiple fluctuating beam intensities to conform the dose to targets; a patient-specific quality assurance (QA) test is conducted to verify the accuracy of dose delivery
Summary
Intensity-modulated radiation therapy (IMRT) enables complex dose distribution around a target with minimized damage to normal tissues [1]. It requires multiple fluctuating beam intensities to conform the dose to targets; a patient-specific quality assurance (QA) test is conducted to verify the accuracy of dose delivery. The American Association of Physicists in Medicine (AAPM) Task Group 119 recommended that point dose measurement and planar dose verification would provide confidence for IMRT commissioning [2]. Film verifies the planar dose by 3D composite irradiation with the same configuration in clinical treatments. Per-field measurement verifies the dose distribution on the coronal plane at a gantry angle of 0° using 2D diode array detectors or film. Patient-specific IMRT QA imposes a significant workload on medical physicists. The time required to ascertain point dose difference and planar dose differences was 3–10 h per patient
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