Radiobiological evaluation considering the treatment time with stereotactic radiosurgery for brain metastases

Hisashi Nakano; Takeshi Takizawa; Daisuke Kawahara; Satoshi Tanabe; Satoru Utsunomiya; Motoki Kaidu; Katsuya Maruyama; Shigekazu Takeuchi; Kiyoshi Onda; Masahiko Koizumi; Teiji Nishio; Hiroyuki Ishikawa

doi:10.1259/bjro.20220013

Radiobiological evaluation considering the treatment time with stereotactic radiosurgery for brain metastases

BJR Open. 2022 Nov 24;4(1):20220013. doi: 10.1259/bjro.20220013. eCollection 2022.

Authors

Affiliations

¹ Department of Radiation Oncology, Institute of Biomedical and Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima-shi, Hiroshima, Japan.
² Department of Radiation Oncology, Niigata University Medical and Dental Hospital, 1-757 Asahimachi-dori, Chuo-ku, Niigata-shi, Niigata, Japan.
³ Department of Radiological Technology, Niigata University Graduate School of Health Sciences, 2-746 Asahimachi-dori, Chuo-ku, Niigata-shi, Niigata, Japan.
⁴ Department of Radiology and Radiation Oncology, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachi-dori, Chuo-ku, Niigata-shi, Niigata, Japan.
⁵ Department of Radiation Oncology, Niigata Neurosurgical Hospital, 3057 Yamada, Nishi-ku, Niigata-shi, Niigata, Japan.
⁶ Department of Neurosurgery, Niigata Neurosurgical Hospital, 3057 Yamada, Nishi-ku, Niigata-shi, Niigata, Japan.
⁷ Department of Medical Physics and Engineering, Osaka University Graduate School of Medicine, 1-7 Yamadaoka, Suita-shi, Osaka, Japan.

Abstract

Objective: We evaluated the radiobiological effect of the irradiation time with the interruption time of stereotactic radiosurgery (SRS) using CyberKnife^® (CK) systemfor brain metastases.

Methods: We used the DICOM data and irradiation log file of the 10 patients with brain metastases from non-small-cell lung cancer (NSCLC) who underwent brain SRS. We defined the treatment time as the sum of the dose-delivery time and the interruption time during irradiations, and we used a microdosimetric kinetic model (MKM) to evaluate the radiobiological effects of the treatment time. The biological parameters, i.e. α₀, β₀, and the DNA repair constant rate (a + c), were acquired from NCI-H460 cell for the MKM. We calculated the radiobiological dose for the gross tumor volume (GTV_bio) to evaluate the treatment time's effect compared with no treatment time as a reference. The D95 (%) and the Radiation Therapy Oncology Group conformity index (RCI) and Paddick conformity index (PCI) were calculated as dosimetric indices. We used several DNA repair constant rates (a + c) (0.46, 1.0, and 2.0) to assess the radiobiological effect by varying the DNA repair date (a + c) values.

Results: The mean values of D95 (%), RCI, and PCI for GTV_bio were 98.8%, 0.90, and 0.80, respectively, and decreased with increasing treatment time. The mean values of D95 (%), RCI, and PCI of GTV_bio at 2.0 (a+c) value were 94.9%, 0.71, and 0.49, respectively.

Conclusion: The radiobiological effect of the treatment time on tumors was accurately evaluated with brain SRS using CK.

Advances in knowledge: There has been no published investigation of the radiobiological impact of the longer treatment time with multiple interruptions of SRS using a CK on the target dose distribution in a comparison with the use of a linac. Radiobiological dose assessment that takes into account treatment time in the physical dose in this study may allow more accurate dose assessment in SRS for metastatic brain tumors using CK.