Acute and Late Toxicity of Prostate-Only or Pelvic SBRT in Prostate Cancer: A Comparative Study

Abstract

<h3>Purpose/Objective(s)</h3> To compare the urinary and gastrointestinal toxicity with or without the inclusion of pelvic nodal regions in patients treated with extreme hypofractionated stereotactic radiotherapy (SBRT) for prostate cancer. <h3>Materials/Methods</h3> Patients treated with definitive SBRT for non-metastatic adenocarcinoma prostate were identified from a prospectively maintained institutional database and details of radiotherapy volume, dose, acute and late adverse effects were analyzed. Symptoms of acute (within 90 days of completing SBRT) and late gastrointestinal and urinary toxicities were graded using CTCAE version 5.0. Each symptom was scored according to the worst reported grading during treatment and follow-up period. ‘Non-infective cystitis' was considered as ‘urinary toxicity' because it encompasses all other urinary symptoms. Cumulative toxicity rates between prostate-only SBRT (PO-SBRT) and whole pelvic SBRT (WP-SBRT) were compared using chi-square test. <h3>Results</h3> Total 220 patients were analyzed (PO-SBRT=118, WP-SBRT=102), with most having locally advanced disease (PO-SBRT 60% high risk, 40% intermediate risk; WP-SBRT 79% node positive, 21% high risk). Median SBRT dose was 36.25Gy (IQR 35-36.25) to the prostate (EQD2=90.6Gy, a/b=1.5Gy) and simultaneous integrated 25Gy to the pelvis (EQD2=46.3Gy) in five fractions on alternate days. No grade 3-4 acute toxicities were observed except one grade 3 urinary obstruction (PO-SBRT). WP-SBRT was associated with significantly higher grade 2 acute GI toxicity (29.4% vs 14.7%, p=0.008), acute proctitis (23.5% vs 11.2%, p=0.016) and acute diarrhea (13.7% vs 1.7%, p=0.001). At a median follow-up of 28 months, grade 2 late urinary toxicity was significantly higher with WP-SBRT (45.6% vs 25.0%, p=0.003), while gastrointestinal toxicity was similar in both the groups (18.9% vs 13.4% p=0.1). Grade 3 late toxicities were low in both the groups (urinary 2.5%, gastrointestinal 1%). <h3>Conclusion</h3> WP-SBRT is associated with significant increase in acute GI and late urinary toxicities compared to PO-SBRT. Prospective validation of these findings is ongoing.