Session Item

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.

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).

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.

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.