ESTRO 2023 - Abstract Book

S1192

Digital Posters

ESTRO 2023

Urology, Munich, Germany; 3 University Hospital Klinikum rechts der Isar, Technical University of Munich (TUM), Departmetn of Nuclear Medicine, Munich, Germany Purpose or Objective Definitive radiotherapy (RT) is an important treatment option for patients with prostate cancer (PC). A PSMA-PET has become indispensable in the salvage situation. However, little is known about the outcome and feasibility of PSMA-PET based definitive RT. Materials and Methods After screening 381 patients with definitive RT, we retrospectivley evaluated 102 patients with PSMA-PET-guided definitive RT. Each patient received a PET scan with a [68Ga] or [18F]-labeled PSMA targeting ligand ([18F]PSMA-1007, [18F]rhPSMA- , or [18F]rhPSMA-7.3). The primary endpoint was biochemical failure-free survival (bFS) according to the ASTRO Phoenix criteria (PSA nadir + 2 ng/mL). Secondary endpoints were metastasis-free survival (MFS) as well as gastrointestinal (GI) and genitourinary (GU) toxicity rates. For evaluation we used the Kaplan Meier method. The median follow-up was 35.1 months (range: 1.2-87.8 months). Results According to the D’Amico risk classification, the cohort consisted of 2/102 low risk patients (1.9%), 7/102 intermediate risk patients (6.9%), 67/102 high risk patients (65.7%), and 26/102 nodal positive patients (25.5%). Within these nodal positive patients, most of the lymph nodes (LNs) were located in the external iliac (69.2%, 18/26), internal iliac (46.2%, 12/26) and common iliac (34.6%, 9/26) areas. LNs were also seen in the obturatoric (11.5%, 3/26), preacetabular (11.5%, 3/26), pararectal (11.5%, 3/26), as well as presacral (3.8%, 1/26) areas. The median initial PSA before PET was 12.4 ng/mL (range: 2.1-678.0 ng/mL). 53/102 patients (52.0%) received a [68Ga]PSMA-PET, while 49/102 patients (48.0%) underwent a [18F]PSMA-PET scan. In 44/102 patients (43.1%) we treated the prostate only, in 32/102 patients (32.4%) we treated the prostate and the elective LNs, and in 26/102 patients (25.5%) we treated the prostate, the elective LNs and we prescribed a simultaneous integrated boost to PET-positive LNs. 25/102 (24.5%) patients received additive androgen deprivation therapy with a median time of 10.1 months (range: 0.2-134.9 months). Of all, 7/102 (6.9%) patients developed a biochemical failure. 2/102 patients (2.0%) developed a local recurrence and 8/102 (7.8%) patients developed distant metastases. The mean bFS was 80.68 months (range: 75.71-85.65 months, median not reached), while the mean MFS was 79.78 months (range: 74.55-85.01 months, median not reached). Early (< 6 months) and late toxicity rates ( ≥ 6 months) were low. Cumulative early GI toxicity rates ≥ grade 1 were 6.9%, while cumulative late GI toxicity was 28.4%. Early and late cumulative GU side effects (excluding erectile dysfunction) ≥ grade 1 were 32.4% and 29.4%, respectively. No grade 4 or 5 side effects were documented. Conclusion PSMA-PET-based definitive RT showed excellent control rates with a good tolerability in terms of toxicity. Therefore, PSMA PET should be considered for RT planning in the definitive situation, especially for patients with high risk PC. Purpose or Objective To evaluate treatment outcomes and toxicity of the moderately hypofractionated schedule with the total dose of 52.8 Gy in 16 daily fractions delivered with IMRT/VMAT. The treatment schedule selection was motivated by limited technology resources. Materials and Methods One hundred consecutive M0 patients with post-prostatectomy radiotherapy were evaluated based on intention to treat. Median age was 64 years. Radiotherapy indication was adjuvant in 19%, early salvage in 46% and salvage (PSA >0,5 ng/ml) in 35%. Clinical target volume was limited to the prostate bed (PB) in 89% and in 11% pelvic nodes irradiation was included. The dose prescription for PTV_PB was 52.8 Gy in 16 fractions of 3.3 Gy and 40 Gy in 16 fractions of 2.5 Gy for PTV_pelvis and treatment was delivered daily by image-guided step-and-shoot IMRT or VMAT. No androgen deprivation treatment (ADT) was administered in 42%, short-term LHRHa in 30%, 2-years bicalutamide in 12% and long-term LHRHa in 16%. Patients were followed with PSA every 3 to 6 months. If indicated, conventional imaging was used before radiotherapy and at PSA progression. The Common Terminology Criteria v.4 for Adverse Events scale was used for toxicity evaluation. Results The median follow-up was 61 months. Five-year freedom from biochemical failure (FFBF) was 79.7%, distant metastases free survival was 93.8% and overall survival was 98.8%. The multivariate analysis showed the treatment indication was the only significant factor for 5-year FFBF which was 86.3% vs. 67.6% for adjuvant and early salvage vs. salvage radiotherapy respectively (HR 0.15, 95% CI 0.05 – 0.47, p = 0.001). Acute GI toxicity grade 2 was recorded in 24% (mostly rectal mucositis and rectal pain), grade G3 in 2% (one small intestine obstruction after completion of adjuvant radiotherapy and one diarrhea) and acute GU toxicity grade 2 in v 10% (mostly cystitis and urinary frequency) and no grade 3. Cumulative rate of late GI toxicity grade ≥ 2 was observed in 9% (rectal hemorrhage and fecal incontinence) and late GU toxicity grade ≥ 2 in 16% (urinary retention, urinary frequency, and progression of urinary incontinence). Metachronous malignancies were recorded in 6% (2 NMIBC, 2 colon cancers, 1 lung cancer and 1 pancreatic cancer). PO-1472 Hypofractionated post-prostatectomy radiotherapy in 16 fractions: a single institution outcome P. Dubinsky 1 , K. Belanova 1 , N. Janickova 1 , V. Vojtek 1 , N. Balazova 1 , Z. Tomkova 1 1 East Slovakia Institute of Oncology, Radiation Oncology, Kosice, Slovakia

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