Abstract Book

S850

ESTRO 37

1 AUSL-IRCCS- Reggio Emilia, Oncology and advanced technologies- U.O.C. Radioterapia Oncologica, Reggio Emilia, Italy 2 AUSL-IRCCS- Reggio Emilia, Oncology and advanced technologies- Servizio di Fisica Medica, Reggio Emilia, Italy Purpose or Objective The optimal management of limited nodal prostate cancer (PCa) recurrences after primary treatment remains largely undefined. These patients are usually treated by androgen deprivation therapy (ADT), with detrimental effect on general health and quality of life. In the recent years there is a growing interest for the locoregional treatment. Stereotactic body radiation therapy (SBRT), that allows the delivery of high tumor ablative doses with low toxicity, can potentially cure or, at least, improve prognosis and prolong tumor control and survival. The aim of this monocentric prospective trial is to explore the role of SBRT in patients affected by PCa with limited nodal relapse in order to assess the overall response rates and the delay of systemic treatments (and related toxicity). Material and Methods PCa patients with limited (<3) nodal recurrence were treated with SBRT, defined as a radiotherapy dose of at least 5 Gy per fraction to a biological effective dose of at least 80 Gy to all metastatic sites. Relapses after SBRT were recorded and compared with the initially treated site. Secondary end points were local control, time to ADT and acute and late toxicity. Results Between November 2014 and June 2017 45 metastases in 29 patients were treated with SBRT. Median age of treated patients was 73.5 years (range 64-88). Regarding the primary treatment of PCa, 22 patients underwent surgery and 7 underwent radical radiotherapy. After surgery, 6 patients underwent adjuvant and 12 salvage radiotherapy. All patients were free from androgen deprivation therapy (ADT) at the time of nodal recurrence detection and all, except one, underwent choline-PET before SBRT. Most patients (67%) received 40 Gy in 5 fractions, while 33% received 45 in 6 fractions. A major biochemical response (≥70% in PSA reduction) was achieved in 16 patients (57%), a partial response (30- 69% in PSA reduction) in 6 patients (19%), a stability in 3 (10%) and a biochemical progression in 4 patients (14%). During follow-up period, with a median of 20.8 months (range 2-48), 12 patients (43%) underwent biochemical progression and 6 patients (24%) underwent imaging- documented progression with bone metastasis. No in-field recurrences were reported. 11 patients (52%) are currently free from progression/recurrence and from any systemic therapy. SBRT was well tolerated: we did not observe any acute or late event. Conclusion Our experience shows that SBRT is a safe, effective and minimally invasive treatment for limited nodal recurrence in oligometastatic prostate cancer. Because of its low toxicity and excellent local control, this treatment represent a feasible option not only to improve the outcome, but also to delay further systemic treatments (and related toxicity) in this subset of patients.

EP-1578 Early biochemical response following PSMA PET-directed salvage nodal irradiation for prostate cancer J. Wake 1,2 , A. Hayden 1,2 , V. Do 1,2 , S. Turner 1 , V. Gebski 1,3 1 Westmead Hospital, Radiation Oncology, Westmead, Australia 2 Nepean Hospital, Radiation Oncology, Penrith, Australia 3 University of Sydney, NHMRC Clinical Trials Centre, Sydney, Australia Purpose or Objective Purpose: To determine the rate of biochemical response, acute toxicity and early biochemical progression following salvage radiation therapy to the pelvic lymph nodes in the setting of 68 Ga-PSMA PET detected prostate cancer lymph node recurrence. Material and Methods Methods and Materials: Between June 2015 and November 2016, 34 prostate cancer patients with a rising PSA following previous curative treatment underwent salvage nodal radiotherapy (SNRT) for pelvic lymph node recurrence identified on 68 Ga-PSMA PET scan. Prior treatment included radical prostatectomy +/- prostate bed radiotherapy (N=32) or definitive prostate radiotherapy +/-androgen deprivation therapy (ADT) (N=2). Patients with nodal recurrence confined to the pelvis (up to and including common iliac lymph nodes) were included in this analysis. Treatment consisted of 45-56Gy to the bilateral elective pelvic lymph nodes, with a simultaneous integrated boost of 55-70Gy to the involved node(s), delivered in 25-33 fractions. The prostate bed was treated to 59.4-66Gy in 10 post-prostatectomy patients who had not received prior prostate bed RT. No patients received concurrent ADT during treatment. Acute toxicity was documented electronically, and graded retrospectively in accordance with CTCAE v4.03. Following treatment, patients attended for clinical review and PSA evaluation on a 3-6 monthly basis. Results Results: 34 patients with nodal relapse detected on 68 Ga-PSMA PET underwent SNRT, with a median follow- up of 13.6 months (range 3-17 months). The median PSA prior to treatment was 0.86 (range 0.15-9.2). 91%(31/34) men had a reduction in the PSA post-treatment, with 32%(11/34) achieving a PSA nadir of <=0.1 (post RP) or <2ng/mL (post definitive RT). Grade 1 or 2 toxicity was experienced by 28 and 5 patients respectively, consisting of genitourinary or gastrointestinal side effects, or fatigue. At last follow-up, 38%(13/34) patients have experienced biochemical progression; of these - 6 have been commenced on ADT at a median of 8.7 months (range 3- 15) post-treatment. No patients have had clinical progression or have died. Conclusion Conclusion: Nodal salvage radiotherapy is well tolerated with minimal acute toxicity. Clinically significant biochemical response is observed in the majority of patients without ADT. Longer follow-up is required to assess rates of biochemical and clinical progression and prognostic features to aid in patient selection for SNRT. EP-1579 SBRT for limited lymph node recurrence in patients with prostate cancer I. Renna 1 , E. Lattanzi 1 , M. Galaverni 1 , G. Timon 1 , F. Vigo 1 , M. Galeandro 1 , A. Rosca 1 , D. Ramundo 1 , P. Ciammella 1 , L. Giaccherini 1 , F. Bellafiore 1 , M.P. Ruggieri 1 , R. Sghedoni 2 , A. Botti 2 , M. Orlandi 2 , C. Iotti 1