ESTRO 2024 - Abstract Book
S2512
Clinical - Urology
ESTRO 2024
This acute toxicity analysis pertains to a single-center cohort of patients (pts) treated with LINAC-based VMAT ultra hypofractionation (42.7 Gy/7 fractions every other day; 15-19 days). The treatment was delivered with daily IGRT (Cone-Beam CT). No fiducials nor spacers were employed. The CTV – PTV margin was 7 mm (5 mm towards the rectum). The CTV was defined as the prostate only for low-risk (LR) pts. CTV included proximal seminal vesicles (SVs) in intermediate-risk PCa and distal SVs for high-risk pts (HR). Whole SVs were included in the case of cT3b. Hormonal therapy prescription (HT) was at the physician's discretion in unfavorable-intermediate PCa (UIR) and mandatory in HR. Genitourinary (GU) and gastrointestinal (GI) toxicity were scored according to RTOG. The IPSS was also assessed. Timepoints of the toxicity report were: every fraction, 1 and 3 months from the RT end. A statistical analysis (logistic regression analysis) was also performed to identify the predictive risk factors of GU G2+ events. Among the investigated factors: risk-group, previous TURP, baseline alpha- blocker administration, baseline IPSS value (≤ or > 12), prostate volume ( ≤ or > 80cc), HT administration, overall treatment time (OTT, ≤17 or >17 days), bladder V37 Gy (≤10cc, ≤15cc, ≤20cc, >20cc). 244 patients were treated between May 2020 and June 2023. Most pts were UIR (54%), followed by favorable intermediate PCa (FIR, 28%), HR (14%), and LR (4%). HT was prescribed to 119 pts (49%): 68 pts treated with Bicalutamide 150 mg, and 51 with LHRH-analogues. A large prostate volume was observed in 46 pts (18.8%): 13.5%, 80 to 100 cc, and 5.3% >100cc. The 36% of the population had alpha-blocker therapy ongoing at baseline. Previous TURP was reported for 21% of pts. The median IPSS score at baseline was 7, in particular > 12 for 27% of the study population. GU G2+ toxicity events (mainly G2) were observed in 73 pts (30%). G3 was observed in just 4 pts (2%) and G4 in 2 pts (1%). The GU G2+ incidence peak was at the last RT fraction (26% of pts), followed by 6% at 1-month and 2% at 3-months. Only 3 (5%) of the 63 pts with GU G2+ toxicity recorded at the RT end had persistent toxicity at 3-months. The following risk factors for acute GU G2+ toxicity were identified: UIR (p=0.016) and HR (p=0.006) risk groups, large prostate volumes (as a continuous variable, p<0.001), baseline IPSS-assessed moderate to severe urinary symptoms (p=0.01 and p=0.009, respectively). The HT (p<0.001) and the OTT>17 days (p=0.045) resulted as significant protective factors for GU G2+ events. Noteworthy, among pts undergoing HT, LHRH-analogues emerged to be associated with more GU G2+ events than Bicalutamide (p=0.017). GI G2 toxicity was reported in 6 pts (2%). No G3-G4 GI toxicities were observed. Results:
Conclusion:
LINAC-based image-guided ultra-hypofractionation appears to be safe regarding early GU tolerance, with negligible rates of acute GI toxicity. Pts at higher risk of developing acute GU G2+ toxicity are those more symptomatic at baseline, those with enlarged prostates, and those with UIR/HR groups. Longer-lasting RT treatments and HT appeared protective regarding GU events' incidence. Our analysis further supports the favorable HYPO-RT-PC [1] and PACE-B [2] acute toxicity data.
Keywords: Prostate Cancer, Ultra-hypofractionation, Toxicity
References:
1) Widmark A, Gunnlaugsson A, Beckman L, Thellenberg-Karlsson C, Hoyer M, Lagerlund M, Kindblom J, Ginman C, Johansson B, Björnlinger K, Seke M, Agrup M, Fransson P, Tavelin B, Norman D, Zackrisson B, Anderson H, Kjellén E, Franzén L, Nilsson P. Ultra-hypofractionated versus conventionally fractionated radiotherapy for prostate cancer: 5-
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