ESTRO 2024 - Abstract Book

S2463

Clinical - Urology

ESTRO 2024

The long-term clinical impact of using fiducial markers (FMs) in image-guided radiotherapy for prostate cancer remains unclear and has been sparsely investigated. We conducted this study to investigate the impact of FMs vs. non-FMs based image-guided radiotherapy for prostate cancer on late gastrointestinal and genitourinary toxicity and the long-term oncological outcome.

Material/Methods:

The study population was composed of all prostate cancer patients (with or without FMs), treated in our center with curative radiotherapy since the introduction of our standard prospective follow-up program in 2005 with minimum follow-up of 5 years. The radiotherapy dose was 78 Gy in 39 fractions to the PTV of the prostate. The used PTV margin was 10 mm. Position verification in the non-FM group was based on bony structures, and on FMs in the FM group. Toxicity was reported according to EORTC-RTOG criteria using both (prospectively collected) patient-reported questionnaires and physician-reported toxicities. The biochemical recurrence was defined according to Phoenix criteria. Kaplan Meier estimate was used to calculate the cumulative incidence of gastrointestinal and genitourinary toxicities and biochemical recurrence. Univariable and multivariable (factors with p<0.100 in univariable analysis) Cox regression analyses were applied to identify independent association factors for late toxicities and biochemical recurrence. Propensity score matching was employed to balance baseline characteristics with sensitivity analyses to validate the findings. Data of 985 patients treated from March 2005 to July 2014 were collected. 25 patients were excluded for lacking late toxicity data (8) or not using FMs for medical reasons (17), resulted in 960 patients for analyses (281 patients in the non-FM group and 679 patients in the FM group). Baseline characteristics are shown in Table 1. The compliance rates for patient-reported outcomes were 98.5% for acute toxicity and 85.6% for late toxicity. The 5-year cumulative late grade ≥ 2 gastrointestinal toxicity was 22.4% [95% CI 17.0 -27.4] in the non-FM group; compared to 32.6% [95% CI 28.6-36.5] in the FM group, p=0.011. The rate of proctitis was 3.6% in the non-FM group versus 9.3% in the FM group, p=0.004. The rate of diarrhea was 11.0% in the non-FM group versus 17.5% in the non-FM group, p=0.015. The 5- year cumulative grade ≥ 2 late genitourinary toxicity was 36.3% in both groups. The 5 -year cumulative biochemical recurrence rate was 17.4% [95% CI 12.5-21.9] in the non-FM group compared to 22.8% [95% CI 19.2 26.3] in the FM group, p=0.018. In multivariable analysis the following factors were associated with increased late grade ≥ 2 gastrointestinal toxicity: the use of FMs (Hazard ratio [HR] 1.37, 95% CI 1.02-1.83, p=0.036), intermediate risk comparing to low risk (HR 1.68, 95% CI 1.09- 2.59, p=0.018), and the presence of baseline grade ≥ 2 gastrointestinal symptoms (HR 2.13, 95% CI 1.36 3.34, p= 0.001). Factors independently associated with increased late grade ≥ 2 genitourinary toxicity included: transurethral resection of prostate (HR 1.44, 95% CI 1.12-1.84, p=0.004), hormone therapy (HR 1.31, 95% CI 1.01 1.69, p=0.042) and the presence of baseline grade ≥ 2 genitourinary symptoms (HR 2.51, 95% CI 1.91 -3.30, p<0.001); Age < 71 years (HR 0.75, 95% CI 0.60- 0.95, p=0.015) was associated with a lower incidence of late grade ≥ 2 genitourinary toxicity. Intermediate risk was associated with increased biochemical recurrence rate compared to low risk (HR 2.09, 95% CI 1.36-3.22, p=0.001). In contrast, hormone therapy (HR 0.59, 95% CI 0.45-0.78, p<0.001) was associated with a lower biochemical recurrence rate. Analyses of the propensity score matched data (262 patients in the non-FM group and 463 patients in the FM group), which used nearest-neighbor matching with a caliper of 0.05, confirmed these results. The 5-year cumulative late grade ≥ 2 gastrointestinal toxicity was 22.1% [95% CI 16.7 -27.3] in the non-FM group versus 31.9% Results: