ESTRO 2024 - Abstract Book

S2369

Clinical - Urology

ESTRO 2024

Akita University Hospital, Department of Radiation Oncology, Akita, Japan

Purpose/Objective:

OBJECTIVE.

Moderate hypofractionated external beam radiotherapy (EBRT) for localised prostate cancer has the advantages of comparable outcomes and shorter treatment times compared to conventional EBRT. Hydrogel spacers (SpaceOAR), it also has the advantage of minimising adverse rectal events. In this study, we evaluated the safety of moderately fractionated EBRT using SpaceOAR in elderly patients with prostate cancer at our institution.

Material/Methods:

METHODS:

To assess acute and late (after 6 months) adverse events, we retrospectively evaluated patients (aged 75 years or older) who underwent moderate hypofractionated EBRT of 60 Gy in 20 fractions for localised prostate cancer between May 2019 and August 2022. We also analysed the association between patient characteristics, SpaceOAR implantation status, and adverse events using Pearson's chi-square test.

Results:

This study included 29 patients (median age [range] = 77 [75-87] years). The median observation period was 19.0 months (range 1-48 months). The patients were grouped using the NCCN risk classification (2, 8, 15, 2, and 2 patients in the low-, favourable intermediate-, unfavourable intermediate-, high-, and very high-risk groups, respectively). The median initial PSA was 7.9 (range 4.3-26.8) ng/mL. All but one patient received androgen deprivation therapy for a median duration of 16 months (6-36 months). All treatments comprised volumetric modulated arc therapy (VMAT) using a linear accelerator (True Beam STx; Varian Medical Systems) and image guided-radiotherapy (IGRT) with embedded gold markers. No biological recurrence was observed at the time of observation. Acute adverse events according to CTCAE v5.0 included genitourinary (GU) grade 1 (G1) in 15 of 29 patients (51.7%), G2 in 14 patients (45.5%) and no G3 or higher. Gastrointestinal (GI) G1 rectal haemorrhage was present in 2 (6.9%). Late (6 months later) adverse events were GU G1 in 7 of 25 patients (28.0%), G2 in 1 patient (4.0%) and GI G1 in 1 patient (4.0%). SpaceOAR was implanted in all patients but inadvertently migrated into the rectal wall in 19 of 29 patients (65.5%) and into the prostate in two (6.9%). The SpaceOAR implantation position was biased craniocaudally or laterally in eight (27.9%) cases. There was no significant correlation between the presence or absence of SpaceOARs inadvertently migrating into the rectal wall or prostate and the presence or absence of rectal adverse events (p=0.29, 0.69). Notably, the presence or absence of pretreatment dysuria of G2 or higher significantly correlated with the presence or absence of acute urinary tract adverse events (p=0.014).