ESTRO 2021 Abstract Book

S1127

ESTRO 2021

axial plane

A: NVB dose constraints met bilaterally; B: NVB dose constraints met unilaterally; C: NVB dose constraints not met. Patient 9 and 10 had 2 GTVs. Conclusion Neurovascular sparing MRgRT for localized PCa is feasible. The extent of NVB sparing largely depends on the patient’s anatomy and GTV location. We will initiate a phase II clinical trial to investigate the effect of neurovascular sparing MRgRT on erectile function in intermediate risk PCa patients with a satisfactory erectile function at baseline. PO-1376 Preliminary mono-institutional report of prostate/prostate bed SBRT re-irradiation F. Cuccia 1 , L. Nicosia 2 , R. Mazzola 1 , V. Figlia 1 , N. Giaj-Levra 1 , F. Ricchetti 1 , M. Rigo 1 , C. Vitale 1 , G. Attinà 1 , E. Pastorello 1 , S. Corradini 3 , R. Ruggieri 1 , F. Alongi 1,4 1 Sacro Cuore Don Calabria Hospital, Advanced Radiation Oncology Department, Negrar di Valpolicella (VR), Italy; 2 Sacro Cuore Don Calabria Hospital, Advanced Radiation Oncology Department, Negrar di Valpolicella (VR), Italy; 3 LMU, Munich University Hospital, Radiation Oncology , Munich, Germany; 4 University of Brescia, Radiation Oncology, Brescia, Italy Purpose or Objective The management of prostate cancer (PC) recurrence after definitive or post-operative radiotherapy is still controversial. To date, few data about the use of salvage stereotactic re-irradiation are available and mostly based on the use of robotic techniques. Herein we present acute and late toxicity data and preliminary clinical outcomes of a mono-institutional series of xx patients treated VMAT-based or MR-guided SBRT for recurrent prostate cancer after previous radiotherapy. Materials and Methods Inclusion criteria were: previous definitive or adjuvant/salvage radiotherapy, evidence of biochemical recurrence and radiological detection of local relapse (either with MRI or PSMA/Choline-PET), IPSS<10. CTV was delineated as the prostate gland or as the PET+ area within the prostate bed, and PTV was generated by adding a margin of 5 mm in all directions, except for the posterior margin of 3 mm. Re-irradiation was performed with volumetric modulated arc therapy (VMAT) technique. Toxicity was assessed according to CTCAE v4.0. Assuming p values ≤0.05 as significant, Chi-squared tests were applied for statistical analysis. Kaplan-Meier method and log-rank test were adopted for survival estimates. Results From July 2014 to December 2020 37 patients with a median age of 76 years (65-89) underwent re-irradiation for PC. Relapsed disease occurred within the prostate in 24 cases and within the prostate bed in 13. Median PSA prior to the second RT was 3.2 ng/ml (0.18 – 10.74 ng/ml). ADT was administered in 6 patients. 32 cases were treated with VMAT SBRT for a median total dose of 30 Gy (range, 20-36 Gy) in 5-6 fractions.; 5 cases were treated with MR-guided SBRT for a median total dose of 30 Gy in 5-6 fractions. Treatment was performed every other day in 31 cases, and on consecutive fractions in 6; no interruption occurred. Median CTV and PTV were 28.5cc (1.1-84.9cc) and 54.6 cc (3.6-147cc). Acute toxicity was: G1 in 20.5% and G2 in 18% for GU, and only G1 in 3% for GI. Concerning late events, data were available for 29 patients: G≥2 GU was recorded in 13.7% including one case of G3 urethral stenosis. For GI late toxicity we observed G1 in 7%, no G≥2 occurred. At the last follow-up, 3 patients died by non-prostate cancer specific causes, resulting in 1- and 2-years overall survival (OS) rates of 90% and 79%. Median PSA-nadir after SBRT was 0.38 ng/ml (range, 0.01 – 4.7 ng/ml). Our 1- and 2-years biochemical relapse-free survival (BRFS) and progression-free survival (PFS) rates were respectively and 72% and 61%. The most frequent sites of progression were pelvic lymph nodes in 5 cases and bone in 4. One patient developed a further prostate bed relapse successfully treated with a second SBRT re-irradiation. Conclusion Our data support the use of Linac-based SBRT for the salvage treatment of radio-recurrent PC as a safe and feasible treatment option, with only one case of late G3 GU toxicity. Preliminary rates of BRFS and PFS are encouraging and long-term data are warranted.

PO-1377 Dosimetric study of scanning method for prostate cancer patients in comparison with wobbler and VMAT

M. Takagi 1 , Y. Hasegawa 1 , K. Tateoka 1 , Y. Takada 1 , M. Hareyama 1 1 Sapporo Teishinkai Hospital, Proton Therapy Center, Sapporo, Japan