ESTRO 2021 Abstract Book

S1101

ESTRO 2021

PO-1340 Prostate cancer reirradiation with stereotactic V-MAT IGRT : interim analysis of a phase II trial. A. Di Marzo 1 , F. Trippa 1 , P. Anselmo 2 , L. Draghini 1 , F. Arcidiacono 1 , S. Terenzi 1 , M. Italiani 3 , M. Muti 1 , M. Casale 1 , S. Fabiani 1 , E. Maranzano 1 1 Santa Maria Hospital Terni, Radiotherapy Oncology Centre, Terni, Italy; 2 Santa Maria Hospital Terni, Radiotherapy Oncology Centre , Terni, Italy; 3 Santa Maria Hospital Terni, Radiotherapy Oncology Centre, Terni, Italy Purpose or Objective The management of the locally recurrent prostate cancer patients (pts) continues to be debated. The aim of this phase II study is to explore the efficacy and safety of prostate re-irradiation with stereotactic volumetric modulate arc image-guided radiation therapy (VMAT-IGRT). We present our preliminary results. Materials and Methods Men affected by isolated local recurrence of prostate cancer, proven by a 18F-Choline or PSMA positron emission tomography and 3Tmultiparametric magnetic resonance, who underwent previous prostate external beam radiation therapy were enrolled in this study. Between may 2018 and February 2020 17 pts were re- irradiated to the prostate with stereotactic VMAT-IGRT, the total dose was 30Gy in 5 daily fractions. Pts were followed by clinical examination and PSA value 1 month after treatment and every 3 months thereafter. The primary outcome is to estimate the efficacy of the salvage stereotactic VMAT-IGRT in terms of biochemical relapse-free survival (bRFS,), local control (Lc), and androgen deprivation therapy free interval (ADTFI). Secondary outcomes are acute and late genitourinary and gastrointestinal toxicities evaluated according to Common Terminology Criteria for Adverse Events version 4.03. Results After a median follow-up of 9,5 months (range 1-33), 14 of 17 pts accrued were evaluable. No G3 acute urinary toxicity was registered, whereas gastrointestinal acute toxicity was not observed. In the first six months all but one pts had a decrease in serum level PSA, three pts had a progressive increase in serum PSA at the ninth, twelfth and fifteenth months, respectively. The four pts with biochemical failure showed a metastatic progression without evidence of local recurrence at choline or PSMA PET. Conclusion Our preliminary report showed that stereotactic V-MAT-IGRT re-irradiation could be a safe and effective treatment in selected pts with local recurrence prostate cancer, with an excellent acute toxicity profile. We reserve further evaluations regarding late toxicity and analysis of other outcomes. PO-1341 SBRT for Japanese patients with prostate cancer: prediction of acute genitourinary toxicities M. Ito 1 , Y. Takase 2 , J. Suzuki 3 , T. Matsunaga 3 , H. Takahashi 3 , A. Takeuchi 1 , S. Adachi 1 , S. Abe 1 , Y. Oshima 1 , K. Ohtakara 4 , Y. Yoshioka 5 , K. Suzuki 1 , T. Okuda 3 1 Aichi Medical University Hospital, Radiology, Nagakute, Japan; 2 Nagoya University Hospital, Radiology, Nagoya, Japan; 3 Toyota Memorial Hospital, Radiation Oncology, Toyota, Japan; 4 Kainan Hospital Aichi Prefectural Welfare Federation of Agricultural Cooperatives, Radiation Oncology, Yatomi, Japan; 5 Cancer Institute Hospital of Japanese Foundation for Cancer Research, Radiation Oncology, Koto, Japan 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. Materials 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.

PO-1342 Trends and predictors of worsening at RT end of anxiety and depression during RT for prostate