Urinary toxicity after salvage re-irradiation for prostate cancer local failure after definitive radiotherapy: a clinical and dosimetric prognostic factors analysis

Purpose: Predictors of long-term toxicity after prostate cancer re-irradiation are scarce. In this study, we retrospectively assessed the impact of clinical/dosimetric data on late genitourinary (GU) toxicity on fourteen radio-recurrent prostate cancer patients treated with salvage radiotherapy (RT).

Material and methods: To identify dose parameters and clinical factors potentially associated to severe long-term GU toxicity, study population was stratified in two groups according to toxicity, including one low-grade group (grade ≤ 2, n = 6) and one high-grade group (grade ≥ 3, n = 8). Dose prescription at primary and salvage-RT in 2 Gy equivalent dose (EQD_2Gy) per fraction, treatment techniques, and clinical factors potentially associated to severe GU toxicity were analyzed.

Results: At salvage-RT, the median EQD_2Gy α/β = 3 Gy was significantly higher in the high-toxicity group (85 Gy, range, 71-85 Gy) compared to the low-toxicity group (77 Gy, range, 61-85 Gy) (p = 0.01). All patients treated using salvage-RT with a brachytherapy (BT) boost and with a baseline Framingham risk-score of > 20% (n = 8) developed severe GU toxicity, while none of the remaining patients developed a grade 3 or more GU toxicity (p = 0.0003). V₇₀ > 0 and V₇₅ > 0 of the primary treatment were associated with an increased rate of toxicity.

Conclusions: Our analysis shows that the delivery of doses up to 75-80 Gy (EQD_2Gy, α/β = 3 Gy) in salvage-RT can be safe in terms of severe GU toxicity avoidance. Furthermore, concomitant cardiovascular comorbidities seem to increase the risk to develop severe GU toxicity.