ESTRO 2024 - Abstract Book

S2309

Clinical - Urology

ESTRO 2024

Ghent, Belgium. 5 University Hospitals Leuven, Radiation-Oncology, Leuven, Belgium. 6 CH-Mouscron, Radiation Oncology, Mouscron, Belgium. 7 AZ Groeninge, Radiation-Oncology, Kortrijk, Belgium. 8 Limburg Oncology Centre, Radiotherapy-Oncology, Hasselt, Belgium

Purpose/Objective:

Patients with muscle-invasive bladder cancer (MIBC) with high-risk pathological features following radical cystectomy (RC) have a poor prognosis. Up to 30% of patients with ≥pT3 tumors develop a pelvic recurrence, which is rarely salvageable and is often associated with debilitating sequels (1, 2).

This trial aims to evaluate the safety and efficacy of adjuvant EBRT in reducing the incidence of locoregional failure. We report on the secondary endpoints: updated survival outcomes and hematological toxicity.

Material/Methods:

This is a multicentric phase 2 trial. From August 2014 till October 2020, we treated 72 high-risk MIBC patients with adjuvant EBRT after RC. High- risk MIBC is defined as ≥1 of the following characteristics being present:

• Pathological (p)T3 stage + presence of lymphovascular invasion on pathological examination • pT4 stage • <10 lymph nodes removed • positive lymph nodes • positive surgical margins

A median dose of 50 Gy was prescribed to the pelvic lymph nodes ± bladder bed (in case of a positive surgical margin), delivered in 25 fractions over 5 days a week using Volumetric Modulated Arc Therapy (VMAT).

Follow up consisted of CT-imaging (thorax/abdomen/pelvis) 3-6 monthly after the end of EBRT during the first year and 6-monthly thereafter up to a period of 5 years or until disease progression. Kaplan-Meier statistics were applied to calculate the 2-yr and 5-yr survival outcomes: local relapse-free rate (LRFR; time from EBRT without evidence of recurrence within the pelvis), clinical relapse-free survival (CRFS; time from EBRT without evidence of disease recurrence or death of any cause), and overall survival (OS; time from EBRT till death of any cause). Blood analyses, which included assessment of erythrocytes, leucocytes (including formula), and thrombocytes, were planned before the initiation of EBRT, after the last fraction, and at 1, 3, 6, 9, 12, 18, and 24 months following adjuvant EBRT. Hematological toxicity assessment was only performed for patients who completed the full course of EBRT and for whom baseline blood counts and at least one post-EBRT blood analysis were available. CTCAE v. 5.0 was used for this analysis. We used univariate analysis to evaluate the influence of administering neo-adjuvant chemotherapy on both the baseline blood count values and the post-EBRT blood count values (median of the blood count values of all measured time points after EBRT). Statistical significance was set at p < 0.05.

Results:

Median follow up time was 22 months (IQR 9-47). For the 25 patients (35%) who were still alive at the last assessment the median follow-up time was 52 months (IQR 37-60). Thirteen patients (18%) developed a local recurrence, with 12 of these recurrences occurring within the first year after EBRT (Figure 1). The 2-yr LRFR was 78% ± 5%. A total of 43 patients (60%) developed distant metastases of whom 10 patients were simultaneously