Development of a novel delivery quality assurance system based on simultaneous verification of dose distribution and binary multi-leaf collimator opening in helical tomotherapy

Yuichi Tanaka; Masatoshi Hashimoto; Minoru Ishigami; Masahiro Nakano; Tomoyuki Hasegawa

doi:10.1186/s13014-023-02366-6

Development of a novel delivery quality assurance system based on simultaneous verification of dose distribution and binary multi-leaf collimator opening in helical tomotherapy

Radiat Oncol. 2023 Nov 2;18(1):180. doi: 10.1186/s13014-023-02366-6.

Authors

Yuichi Tanaka^#¹, Masatoshi Hashimoto^#², Minoru Ishigami³, Masahiro Nakano⁴, Tomoyuki Hasegawa²

Affiliations

¹ Graduate School of Medical Sciences, Kitasato University, 1-15-1 Kitazato, Minami-ku, Sagamihara-shi, Kanagawa, Japan. dm20018@st.kitasato-u.ac.jp.
² School of Allied Health Sciences, Kitasato University, 1-15-1 Kitazato, Minami-ku, Sagamihara-shi, Kanagawa, Japan.
³ Department of Radiology, Kitasato University Hospital, 1-15-1 Kitazato, Minami-ku, Sagamihara-shi, Kanagawa, Japan.
⁴ Department of Radiation Oncology, Kitasato University School of Medicine, 1-15-1 Kitazato, Minami-ku, Sagamihara-shi, Kanagawa, Japan.

^# Contributed equally.

Abstract

Background: Intensity-modulated radiation therapy (IMRT) requires delivery quality assurance (DQA) to ensure treatment accuracy and safety. Irradiation techniques such as helical tomotherapy (HT) have become increasingly complex, rendering conventional verification methods insufficient. This study aims to develop a novel DQA system to simultaneously verify dose distribution and multi-leaf collimator (MLC) opening during HT.

Methods: We developed a prototype detector consisting of a cylindrical plastic scintillator (PS) and a cooled charge-coupled device (CCD) camera. Scintillation light was recorded using a CCD camera. A TomoHDA (Accuray Inc.) was used as the irradiation device. The characteristics of the developed system were evaluated based on the light intensity. The IMRT plan was irradiated onto the PS to record a moving image of the scintillation light. MLC opening and light distribution were obtained from the recorded images. To detect MLC opening, we placed a region of interest (ROI) on the image, corresponding to the leaf position, and analyzed the temporal change in the light intensity within each ROI. Corrections were made for light changes due to differences in the PS shape and irradiation position. The corrected light intensity was converted into the leaf opening time (LOT), and an MLC sinogram was constructed. The reconstructed MLC sinogram was compared with that calculated using the treatment planning system (TPS). Light distribution was obtained by integrating all frames obtained during IMRT irradiation. The light distribution was compared with the dose distribution calculated using the TPS.

Results: The LOT and the light intensity followed a linear relationship. Owing to MLC movements, the sensitivity and specificity of the reconstructed sinogram exceeded 97%, with an LOT error of - 3.9 ± 7.8%. The light distribution pattern closely resembled that of the dose distribution. The average dose difference and the pass rate of gamma analysis with 3%/3 mm were 1.4 ± 0.2% and 99%, respectively.

Conclusion: We developed a DQA system for simultaneous and accurate verification of both dose distribution and MLC opening during HT.

Keywords: CCD camera; Delivery quality assurance; Helical tomotherapy; IMRT; Plastic scintillator.

MeSH terms

Humans
Phantoms, Imaging
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Radiotherapy, Intensity-Modulated* / methods