Abstract Book

S836

ESTRO 37

Medicine, Zurich, Switzerland 3 University Hospital Zürich, Department of Urology, Zurich, Switzerland Purpose or Objective After treatment of localized prostate cancer (PCa) recurrence rates are approximately 40-80%. Until recently, standard of care treatment has been salvage radiotherapy (SRT) of the prostate bed. However, in approximately 20-40% of patients recurrences are located outside this area. As PSMA PET has become available for identification of recurrences at low PSA-levels, RT of PSMA-positive oligometastatic recurrences (ORT) has become a frequently practiced option in order to improve prognosis or quality of life by delaying start of ADT. Material and Methods Retrospectively, data of 43 patients with oligometastatic PSMA-positive PCa recurrences were evaluated, who underwent ORT of all metastatic sites between 06/2016 and 10/2017 in one academic center. Most (84%) did not receive ADT. Radiation treatment planning, PSA- progression free survival (PSA-PFS) and toxicity were analyzed. Results Median age was 70 (52-85)y, 58% were initially high-, and 42% intermediate-risk. 67% were R1-resected; 84% did not reach a PSA <0.03ng/ml after initial radical prostatectomy (RP), 37% received previous SRT after RP. Time to biochemical recurrence was 20.8 mo (range 0- 106). Median PSA at time of PSMA-PET was 0.28 ( 0.04- 22.1) ng/ml. PSA-DT at time of PSMA-PET was median 6 (0-48) mo. Median number of irradiated PSMA-positive metastases was 2 (1-11): 26 lymph node (LN) metastases, 9 bone metastases (BM) and 1 lung metastasis. 11 patients had a PSMA-positive prostate bed recurrence. Median dose (EQD2/1.5) to prostate bed recurrences was 72 (63.4-83) Gy and to positive LN 65.8 (46.4-98.6) Gy. Elective pelvic lymphatic irradiation was performed in all patients with positive PSMA-positive LN and combined with an integrated/stereotactic boost. BM and the lung metastasis were stereotactically irradiated with median 85 (62.8-108.6) Gy. Median FU was 3 (0-13) mo, PSA-PFS at 6 mo was 48%, 4 out of 33 showed PSA-progression immediately after ORT, all other patients showed a PSA response. Overall, PSA levels reduced significantly following ORT: in the cohort w/o ADT, average PSA prior to ORT was 4.55(0.14-27.3)ng/ml which dropped significantly to 2.9 ( 0-17.93) ng/ml (p=0.018) 1-5 mo after ORT. In the cohort with ADT, mean PSA prior to SRT was 0.96 (0.12-2.49)ng/ml, which dropped to 0.05 (0- 0.13) ng/ml (p=0.06) 1-5 mo thereafter. Acute toxicity consisted of 1 Gr 2 urinary frequency and 1 Gr 2 diarrhea. Conclusion Our preliminary experience of definitive radiotherapy in this cohort of mainly high-risk, mostly ADT-naïve PCa patients with oligometastatic recurrent PCa, is that PSMA-targeted radiotherapy was feasible and safe. Although the follow-up was short, at 6 months approximately half of patients presented with regredient PSA-levels. This shows that irradiating PSMA-positive oligometastatic PCa recurrences might play a role in prolonging the time to start of ADT. Prospective trials are needed to select patient subgroups that would benefit most from this treatment.

oral nanocurcumin in prostate cancer patients undergoing radiotherapy (RT). Material and Methods Between March 2016 and April 2017, 64 intermediate- or high-risk prostate cancer patients were randomised to receive either oral nanocurcumin or placebo three days before and during the RT course (120mg/day). The nanocurcumin 40mg or placebo capsules were taken three times daily, so two capsules were administered in the morning and another capsule at bedtime. All patients were stratified by treatment schedule and received either conventional fractionated (70Gy, 2Gy/fraction) or hypofractionated schedule (70.2Gy, 2.7Gy/fraction). All patients received neoadjuvant hormone therapy. An intention to treat approach was used as the analysis strategy. Acute toxicities were assessed weekly during the treatment and once thereafter according to CTCAE grading criteria. The patients are followed to evaluate the treatment response. Pearson’s chi-square and fisher’s exact test were used to compare the number of patients with acute toxicities in the two groups. The duration of acute toxicities was compared using Mann–Whitney U test. A p value <0.05 (two-sided test) was considered significant. Results Nanocurcumin was well tolerated. Differences between the two groups with respect to the bowel and urinary endpoints are illustrated in the table below. Placebo group (n=31) Nanocurcumin group (n=33) P value

Acute toxicity, n (%) Proctitis

18 (58.1) 15 (45.5)

0.313

Cystitis

23 (74.2) 29 (87.9)

0.161

Duration toxicity,

of

Mean

weeks (SD) Proctitis

1.3 (1.4) 1.2 (1.5)

0.651

Cystitis

2.5 (2)

3.3 (1.6)

0.309

There was no significant difference between placebo and nanocurcumin group in terms of two major clinical endpoints including proctitis and Cystitis. Furthermore, no significant difference was observed between the two groups in relation to duration of the toxicities. No patient except one in the nanocurcumin group experienced grade 3 or higher acute toxicity during the treatment. Conclusion In contrast to very encouraging preclinical evidence, we demonstrated that nanocurcumin is not an effective radioprotector for prostate cancer patients undergoing radiotherapy. Therefore, clinical application of nanocurcumin as a promising radioprotector was not confirmed in this setting. EP-1550 Radiotherapy of PSMA-positive oligometastatic recurrent prostate cancer: a single- center experience. S.G.C. Kroeze 1 , I.A. Burger 2 , H. Garcia-Schüler 1 , T. Hermanns 3 , M. Guckenberger 1 1 University Hospital Zürich, Department of Radiation Oncology, Zurich, Switzerland 2 University Hospital Zürich, Department of Nuclear