Verification system for intensity-modulated radiation therapy with scintillator
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SCIENTIFIC PAPER
Verification system for intensity‑modulated radiation therapy with scintillator Yasuharu Ando1 · Kentaro Miki2 · Jun Araki1 · Masato Tsuneda3 · Hiroshi Kiriu1 · Teiji Nishio3 · Yasushi Nagata2 Received: 7 April 2020 / Accepted: 6 November 2020 © Australasian College of Physical Scientists and Engineers in Medicine 2020
Abstract In the preparation of intensity-modulated radiation therapy (IMRT), patient-specific verification is widely employed to optimize the treatment. To accurately estimate the accumulated dose and obtain the field-by-field or segment-by-segment verification, an original IMRT verification tool using scintillator light and an analysis workflow was developed in this study. The raw light distribution was calibrated with respect to the irradiated field size dependency and light diffusion in the water. The calibrated distribution was converted to dose quantity and subsequently compared with the results of the clinically employed plan. A criterion of 2-mm dose-to-agreement and 3% dose difference was specified in the gamma analysis with a 10% dose threshold. By applying the light diffusion calibration, the maximum dose difference was corrected from 7.7 cGy to 3.9 cGy around the field edge for a 60 cGy dose, 7 × 7 cm2 irradiation field, and 10 MV beam energy. Equivalent performance was confirmed in the chromodynamic film. The average dose difference and gamma pass rate of the accumulated dose distributions in six patients were 0.8 ± 4.5 cGy and 97.4%, respectively. In the field-by-field analysis, the average dose difference and gamma pass rate in seven fields of Patient 1 were 0.2 ± 1.2 cGy and 93.9%, respectively. In the segment-bysegment analysis, the average dose difference and gamma pass rate in nine segments of Patient 1 and a 305° gantry angle were − 0.03 ± 0.2 cGy and 93.9%, respectively. This system allowed the simultaneous and independent analysis of each field or segment in the accumulated dose analysis. Keywords Dose verification · IMRT · Scintillator · Radiation therapy
Introduction In recent years, external beam radiation therapy facilities have shifted towards the use of intensity-modulated radiation therapy (IMRT) as the standard. This technique delivers a more appropriate dose to the tumor tissue, as compared to the dose in conventional methods, while suppressing the dose delivered to normal tissues. [1, 2] IMRT significantly improves the outcomes of prostate cancer, specifically compared to conventional radiation therapy, [3] while IMRT treatment in the head and neck region has demonstrated a reduction of adverse events, such as dysphagia and dry mouth. [4, 5] IMRT generates a dose distribution to fit * Yasuharu Ando ibanez‑[email protected] 1
Hiroshima City Asa Citizens Hospital, Hiroshima, Japan
2
Hiroshima University Hospital, Hiroshima, Japan
3
Tokyo Women’s Medical University, Tokyo, Japan
the shape of the tumor volume using a multi-leaf collimator (MLC) by integrating multiple irradiation fields from the same gantry angle. Because IMRT dose d
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