Evaluation of In-room Volumetric Imaging Doses for Image-guided Radiotherapy: A Multi-institutional Study

Yusuke Sakai; Hajime Monzen; Yoshiki Takei; Hiroyuki Kosaka; Kenji Nakamura; Yuya Yanagi; Kazuki Wakabayashi; Makoto Hosono; Yasumasa Nishimura

doi:10.4103/jmp.jmp_109_22

Evaluation of In-room Volumetric Imaging Doses for Image-guided Radiotherapy: A Multi-institutional Study

J Med Phys. 2023 Apr-Jun;48(2):189-194. doi: 10.4103/jmp.jmp_109_22. Epub 2023 Jun 29.

Authors

Yusuke Sakai^{1

2}, Hajime Monzen¹, Yoshiki Takei³, Hiroyuki Kosaka¹, Kenji Nakamura¹, Yuya Yanagi¹, Kazuki Wakabayashi¹, Makoto Hosono⁴, Yasumasa Nishimura⁴

Affiliations

¹ Department of Medical Physics, Graduate School of Medical Sciences, Kindai University, Hyogo, Japan.
² Department of Radiotherapy, Takarazuka City Hospital, Takarazuka, Hyogo, Japan.
³ Department of Radiology, Kindai University Nara Hospital, Ikoma, Nara, Japan.
⁴ Department of Radiation Oncology, Faculty of Medicine, Kindai University, Osakasayama, Osaka, Japan.

Abstract

Aims: We investigated imaging dose and noise under clinical scan conditions at multiple institutions using a simple and unified method, and demonstrated the need for diagnostic reference levels in image-guided radiotherapy (IGRT).

Materials and methods: Nine cone-beam and helical computed tomography (CT) scanners (Varian, Elekta, Accuray Inc., and BrainLAB) from seven institutions were investigated in this study. The weighted cone-beam dose index (CBDI_w) was calculated for head and pelvic protocols using a 100 mm pencil chamber under the conditions used in actual clinical practice at each institution. Cone-beam CT image noise was evaluated using polymethylmethacrylate head and body phantoms with diameters of 16 and 32 cm, respectively.

Results: For head and pelvic protocols, CBDI_w values ranged from 0.94-6.59 and 1.47-20.9 mGy, respectively. Similarly, standard deviation (SD) values ranged from 9.3-34.0 and 26.9-97.4 HU, respectively. The SD values tended to increase with decreasing imaging dose (r = -0.33 and -0.61 for the head and pelvic protocols, respectively).

Conclusions: Among the nine machines, the imaging dose for high imaging dose institutions was approximately 20 mGy to the pelvic phantom, and there was a 14-fold difference in dose compared with the other institutions. These results suggest the need to establish DRLs for IGRT to guide clinical decision-making.

Keywords: Diagnostic reference level; image-guided radiotherapy; imaging dose.