ESTRO 2024 - Abstract Book

S2582

Clinical - Urology

ESTRO 2024

up to 2 separate nodules were allowed. Intra-prostatic fiducial markers and recto-prostatic hydrogel spacer were placed under transrectal ultrasound guide. MRI-based SBRT-simulation was performed in all patients. SBRT was delivered with volumetric modulated arc therapy (VMAT), administering 36.25 Gy to the prostate with a simultaneous integrated boost (SIB) of 40 Gy (dose gradient range 100%-120%) to the DIL (Figure 1). Genitourinary (GU) and gastrointestinal (GI) toxicities were reported using the Common Terminology Criteria for Adverse Events (CTCAE) classification. The objective of the study was to evaluate the dosimetric parameters and the rate of acute toxicity of the SBRT-SIB approach. Results, in terms of toxicity and dosimetry, were compared with a group of patients treated with prostate SBRT without boost in the same period.

Results:

From January 2022 to December 2022, a total of 42 men underwent prostate SBRT at our Institution. Among these, 18 patients (43%) with mpMRI-defined DIL, confirmed by targeted biopsy, received prostate SBRT with simultaneous boost to the focal lesions. Median patient age was 75 years (range 56-80). Fifteen patients (83%) had cT2 disease, median iPSA was 7 ng/ml (range 3.6-19.2), and baseline IPSS score was mild and moderate in 61% and 39%, respectively. The majority of DILs were in the peripheral zone (89%). Most patients had either 3+4 (39%) or 4+3 Gleason (33%). In 7 (39%) patients androgen deprivation therapy (ADT) was administered in accordance with current clinical practice. All the SBRT-SIB plans met the predetermined target coverage objectives. Table 1 reports the results of the SBRT-SIB treatment plan analysis for DIL target volume and critical organs at risk (OARs). At a median follow up of 16.4 months (range 9.8- 20.1), no G≥3 GU or GI toxicity was observed. Furthermore, 90 days after SBRT SIB treatment, the cumulative acute G1-2 GU and GI toxicity rates were 44.4% and 16.7%, respectively. In comparison with the non-boost SBRT group (24 patients), the rectal V40Gy, V36Gy and V24 Gy, and the bladder V40 Gy, V37 Gy and V18.1 Gy did not differ significantly (all p > 0.05). Also, no differences were found between groups in terms of acute G2 GU (16.7% boost vs 20.8% no-boost; p = 0.74) and GI toxicity (5.6% boost vs 4.2% no-boost; p =0.83).