2886 - A Prospective Pilot Study of Acute Symptoms and Toxicities Among Patients Undergoing Curative or Palliative-Intent Non-Ablative Short Course Pelvic Radiotherapy for De Novo or Locally Recurrent Rectal or Rectosigmoid Cancer (SHORT-TOX Study)

Purpose/Objective(s):

Short-course radiotherapy (SCRT), defined as 1-5 fractions of hypofractionated RT, is commonly administered for both curative-intent and palliative treatment of rectal and rectosigmoid cancer. While efficacy and long-term safety of SCRT are well-studied, there is a lack of data describing its acute toxicities, for which our understanding remains largely anecdotal. This study aims to address this knowledge gap and quantitatively characterize the timing, incidence, and nature of toxicities experienced following SCRT.

Materials/Methods:

Patients undergoing SCRT for rectal or rectosigmoid cancer were prospectively followed up to 8 weeks post-treatment. Any history of previous pelvic radiotherapy or systemic therapy was permitted. Patient-reported quality of life and toxicity outcomes were collected at baseline, on the final day of SCRT, and on weeks 1, 2, 4, and 8 following completion of SCRT using the EORTC QLQ-C30, QLQ-PRT20, and PRO-CTCAE questionnaires. At each timepoint, clinician-reported adverse events were documented using the CTCAE v5.0 scale, and the use of supportive care interventions and medications was recorded.

Results:

Between May 2024 and January 2026, 40 patients were enrolled into this study. 36/40 patients received a 5-fraction course of SCRT, with the remainder receiving between 1-3 fractions. 15/40 patients received SCRT as part of curative-intent treatment, with the remainder treated in the palliative setting.

At the time of interim analysis, 32 patients had completed follow-up. 16/32 experienced grade 3 acute toxicities, and no grade 4-5 acute toxicities were recorded. The most frequently described grade 3 acute toxicities were proctitis, diarrhea, and abdominal pain. Only 1 instance of grade 3 nausea and 1 instance of grade 2 vomiting were reported. These most commonly occurred at the end of SCRT or within 1-2 weeks of competing SCRT, with symptoms generally improving by week 4. This is reflected in patient-reported outcomes from the QLQ-C30, which demonstrate a 5-point decrease in standardized quality of life scores at 1 week post-SCRT before returning to baseline by week 8. Similar patterns are seen across all proctitis domains captured in the QLQ-PRT20; while average scores for symptomology such as bloating, bowel control, and pain were worse at 1 week post-SCRT, they improved to be better than baseline by week 8.

Conclusion:

Overall, this study reports prospective, quantitative insights into the character, timing, and impact of acute toxicities following SCRT for rectal and rectosigmoid cancers. These results provide clinicians with an evidence-based approach to better guide the use of supportive care interventions, predict toxicity patterns, and educate patients on treatment expectations.