Robotic Radiosurgical Boost After Whole-Brain Radiotherapy for 12 Brain Metastases: En Bloc Consecutive Irradiation With Comprehensively Optimized Single Plan for Eight Lesions Totaling 118 cc

Kazuhiro Ohtakara; Kuniaki Tanahashi; Takehiro Yamada; Nobuyuki Tsunoda; Kojiro Suzuki

doi:10.7759/cureus.51367

Robotic Radiosurgical Boost After Whole-Brain Radiotherapy for 12 Brain Metastases: En Bloc Consecutive Irradiation With Comprehensively Optimized Single Plan for Eight Lesions Totaling 118 cc

Cureus. 2023 Dec 30;15(12):e51367. doi: 10.7759/cureus.51367. eCollection 2023 Dec.

Authors

Kazuhiro Ohtakara^{1

2}, Kuniaki Tanahashi^{3

4}, Takehiro Yamada⁵, Nobuyuki Tsunoda^{6

7}, Kojiro Suzuki²

Affiliations

¹ Department of Radiation Oncology, Kainan Hospital Aichi Prefectural Welfare Federation of Agricultural Cooperatives, Yatomi, JPN.
² Department of Radiology, Aichi Medical University, Nagakute, JPN.
³ Department of Neurosurgery, Gifu Prefectural Tajimi Hospital, Tajimi, JPN.
⁴ Department of Neurosurgery, Nagoya University Graduate School of Medicine, Nagoya, JPN.
⁵ Department of Radiology, Nagoya University Hospital, Nagoya, JPN.
⁶ Department of Breast Surgery, Japanese Red Cross Aichi Medical Center Nagoya Daiichi Hospital, Nagoya, JPN.
⁷ Department of Breast and Endocrine Surgery, Nagoya University Graduate School of Medicine, Nagoya, JPN.

Abstract

General radiotherapeutic management for >10 brain metastases (BMs) totaling >100 cm³, including multiple large lesions (>10-30 cm³) in close proximity, demonstrated limited efficacy and/or safety. We describe a case of 12 BMs, summating 122.2 cm³, including a 39.6 cm³ maximum lesion and adjacent ones. The patient had an 8.1-year treatment history for recurrent/metastatic breast cancer refractory to endocrine and chemotherapy. BMs were treated with conventional whole-brain radiotherapy (WBRT) with 30 Gy/10 fractions (fr), followed by an immediate stereotactic radiosurgery (SRS) boost with 27 Gy/5 fr (52-64% isodoses) which covers the gross tumor boundaries of selected eight lesions (total 118.4 cm³). The SRS dose was defined to ensure the cumulative biologically effective dose (BED₁₀) of just ≥80 Gy while minimizing the risk of radiation injury. The SRS was performed using a CyberKnife (CK) robotic system (Accuray Incorporated, Sunnyvale, California, United States) with a variable-sized collimator (10-40 mm), for which en bloc consecutive irradiation, using 215 beams based on a comprehensively optimized single plan (path), was adopted. The treatment time per fraction was ≤45 min (mean 5.6 min per lesion). Afterward, BMs demonstrated remarkable regression over six months, causing the total residual visible lesions of 12.6 cm³ (10.3%) at 11.4 months, despite the absence of obvious lesion shrinkage during the radiotherapy. WBRT, followed by an immediate 5-fr SRS boost with a total BED₁₀ of 80 Gy to large and/or culprit lesions, can be an efficacious and safe treatment option for multiple BMs, totaling >120 cm³. En bloc consecutive irradiation with a single path provides overwhelmingly more efficient delivery for treating multiple lesions using CK in terms of irradiation time and comprehensive reduction of normal brain dose compared to individual planning. Volumetric-modulated arc-based >10-fr SRS with simultaneously integrated reduced-dose WBRT may be an alternative to further enhance efficacy and safety.

Keywords: biologically effective dose; brain metastases; breast cancer; fractionation; large tumor; multiple tumors; radiosurgical boost; robotic radiosurgery; stereotactic radiosurgery; whole-brain radiotherapy.

Publication types

Case Reports

Grants and funding

This study was supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant-in-Aid for Scientific Research C with the grant number JP21K07561.