SBRT for Japanese patients with prostate cancer: prediction of acute genitourinary toxicities
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Abstract
SBRT for Japanese patients with prostate cancer: prediction of acute genitourinary toxicities
Authors: Makoto Ito1, Yuuki Takase2, Junji Suzuki3, Takuma Matsunaga3, Hironori Takahashi3, Arisa Takeuchi1, Sou Adachi1, Souichirou Abe1, Yukihiko Oshima1, Kazuhiro Ohtakara4, Yasuo Yoshioka5, Kojiro Suzuki1, Takahito Okuda3
1Aichi Medical University Hospital, Radiology, Nagakute, Japan; 2Nagoya University Hospital, Radiology, Nagoya, Japan; 3Toyota Memorial Hospital, Radiation Oncology, Toyota, Japan; 4Kainan Hospital Aichi Prefectural Welfare Federation of Agricultural Cooperatives, Radiation Oncology, Yatomi, Japan; 5Cancer Institute Hospital of Japanese Foundation for Cancer Research, Radiation Oncology, Koto, Japan
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Purpose or Objective
To report the preliminary results of SBRT for prostate cancer, and to identify the clinical and dosimetric factors predicting acute genitourinary (GU) toxicities for Japanese patients.
Material and Methods
Medical records of non-metastatic prostate cancer patients were reviewed retrospectively between June 2017 and August 2020. Patients were treated by SBRT with a total dose of 36.25 Gy in 5 fractions over 5 consecutive weekdays using CyberKnife. Radiotherapy alone was offered to low-risk patients, while intermediate-risk patients also received 6-month neoadjuvant androgen deprivation therapy (ADT), and high-risk patients received neoadjuvant and adjuvant ADT for 2 years principally. Only 2 patients were injected with periprostatic hydrogel spacer. Toxicities were measured according to CTCAE v5.0 scale. Furthermore, patient-reported outcomes were evaluated based on the IPSS and QOL score.
Results
A total of 104 patients, including 10 low-, 60 intermediate-, and 34 high-risk patients, were analyzed. Ninety-five (91%) patients, including 1 exceptional low-risk patient, underwent ADT. The median prostate volume at the time of SBRT was 23.9 cc (range, 11.7-61.6). The median follow-up time was 2.0 years (range, 0.5–3.6). None of any biochemical/clinical recurrence, distant metastasis, or death from prostate cancer has been observed thus far. Only 1 patient died with another cause than prostate cancer. Grade 2 acute GU toxicity was observed in 40 (38%) patients. In multivariate analysis, age (HR: 1.09, p = 0.021), GU toxicity at baseline ≥ grade 1 (HR: 4.35, p = 0.023), and bladder mean dose (HR: 1.33, p = 0.047) were significantly associated with the incidence of grade 2 acute GU toxicity. Based on ROC analysis, the cut-off values of 65 years for age and 10.3 Gy for bladder mean dose were considered as appropriate. In contrast, prostate volume was not associated with grade 2 acute GU toxicity (HR: 0.99, p = 0.984). Based on IPSS and QOL score, symptoms reached the peak by 4 weeks after SBRT and returned to the baseline by 3 months. Grade 2 acute gastrointestinal toxicity was observed in only 5 (5%) patients. No grade ≥3 acute or late toxicity has been observed thus far.
Conclusion
SBRT for Japanese patients with prostate cancer was feasible, and its acute toxicity was acceptable. Age, GU toxicity at baseline ≥ grade 1, and the bladder mean dose were identified as the predictive factors for grade 2 acute GU toxicity.