3775 - Pelvic Radiation Therapy in Patients Aged 80 and Older: Predictive Factors of Treatment Completion

Purpose/Objective(s): The completion rates of pelvic radiation therapy (RT) in patients aged 80 and older remain poorly characterized, often leading to treatment hesitancy based on chronological age alone. We sought to evaluate treatment completion rates, characterize patterns of care, and identify clinical predictors of non-completion in patients aged 80 and older receiving pelvic RT.

Materials/Methods: We performed a retrospective single-institution review of patients aged 80 and older who received external beam pelvic RT between 2015 and 2025. Brachytherapy-only cases were excluded. Patient demographics, Karnofsky Performance Status (KPS), tumor site, treatment technique, fractionation, concurrent chemotherapy use, completion rate, and survival status were collected. Treatment completion was defined as delivery of 100% of planned fractions. KPS was stratified into Good (80-100), Moderate (60-70), and Poor (=50). Completion rates and survival were compared across subgroups using two-sample t-tests. Linear regression assessed age and KPS as continuous predictors of completion and survival.

Results: Of 2,734 patients treated with pelvic RT, 154 patients (5.6%) met inclusion criteria. Median age was 84 years (range 80-99). Tumor sites included prostate (41%), uterus (16%), rectum (15%), bladder (12%), anus (7%), cervix (4%), vulva (3%), and vagina (1%). Techniques included IMRT (70%), 3D-CRT (15%), and SBRT (9%). Completion rates were high across all KPS groups: Good 99.2% (n=114), Moderate 95.4% (n=25), and Poor 99.2% (n=13). Patients with good KPS patients had significantly higher completion than patients with moderate KPS (p=0.015). When palliative cases were excluded, this difference persisted (99.6% vs 97.4%, p=0.025). Patients with poor KPS were prescribed significantly fewer fractions than patients with good KPS (11.7 vs 24.1, p=0.001), while patients with moderate KPS received a similar number of fractions to patients with good KPS (21.6 vs 24.1, p=0.326). Age did not predict completion on linear regression (R²=0.012, p=0.185). KPS was strongly predictive of survival (R²=0.173, p<0.001) while age was a weaker predictor (R²=0.028, p=0.037). Concurrent chemotherapy trended toward lower completion (97.0% vs 99.1%, p=0.081) but did not affect survival (p=0.533).

Conclusion: Pelvic radiation in patients aged 80 and older confers high completion rates across all performance status groups. Patients with moderate KPS (60-70) receiving definitive intent courses represent the highest-risk group for non-completion, potentially due to receiving treatment courses of similar length to higher-functioning patients. KPS was a far stronger predictor of survival than chronological age. These findings support offering pelvic radiation based on functional assessment rather than age and underscore the importance of tailoring treatment intensity to performance status.