Background
Phase III RCT (NRG Oncology/RTOG 1203). 278 patients with endometrial cancer (stage IB-IVA) or cervical cancer requiring adjuvant pelvic RT after primary surgery. Randomized to standard 4-field (box) EBRT (45 Gy in 25 fractions) vs pelvic IMRT (45 Gy in 25 fractions). Primary endpoint: bowel toxicity as measured by patient-reported outcomes (PRO). The trial was designed to determine whether IMRT reduces acute and late bowel toxicity vs conventional 3D-CRT in gynecologic cancer radiation. Long-term QoL and cancer outcomes published in Yeung JCO 2020.
Interventions and follow up
Arm A: Standard 4-field pelvic EBRT 45 Gy in 25 fractions (3D-CRT)
Arm B: Pelvic IMRT 45 Gy in 25 fractio
Primary endpoint: Patient-reported bowel toxicity at end of treatment
mFollow up: 36.1 months (Yeung 2020 long-term update)
Arm B: Pelvic IMRT 45 Gy in 25 fractio
Primary endpoint: Patient-reported bowel toxicity at end of treatment
mFollow up: 36.1 months (Yeung 2020 long-term update)
Results
Bowel toxicity (patient-reported, end of treatment): 38.3% (3D-CRT) vs 22.5% (IMRT), P=.007
Grade ≥2 GI toxicity (CTCAE): Significantly reduced with IMRT vs 3D-CRT at end of treatment
Urinary toxicity: Similar between arms
Late bowel symptoms (Yeung 2020): Durable reduction in bowel symptoms maintained at 24 months with IMRT
Recurrence-free survival: 64.7% (3D-CRT) vs 66.7% (IMRT) — not significantly different
Grade ≥2 GI toxicity (CTCAE): Significantly reduced with IMRT vs 3D-CRT at end of treatment
Urinary toxicity: Similar between arms
Late bowel symptoms (Yeung 2020): Durable reduction in bowel symptoms maintained at 24 months with IMRT
Recurrence-free survival: 64.7% (3D-CRT) vs 66.7% (IMRT) — not significantly different
Adverse events
Main adverse events: IMRT significantly reduced acute patient-reported bowel symptoms (diarrhea, fecal leakage, urgency) without compromising cancer control. Late bowel toxicity reduction maintained at 2–3 years. No significant difference in urinary toxicity or recurrence rates between arms. IMRT also reduced hematologic toxicity (bone marrow sparing).
Conclusions
Pelvic IMRT significantly reduced patient-reported acute and late bowel toxicity compared to standard 4-field 3D-CRT for adjuvant pelvic RT in endometrial and cervical cancer, without compromising cancer control, establishing IMRT as the preferred pelvic radiation technique in gynecologic cancer.
Key Limitations
Key Limitations: Not powered to detect differences in recurrence or survival — only PRO toxicity endpoint. Mixed population (endometrial and cervical cancer, various stages) limits generalizability to any one disease site. The control arm was a standard 4-field technique (not 3D-CRT with modern dose constraints), which may have overestimated the toxicity difference vs modern conventional RT. Concurrent chemotherapy was not standardized across all patients.
Clinical Context
RTOG 1203 established IMRT as the standard radiation technique for adjuvant pelvic RT in gynecologic cancer (endometrial and cervical), replacing conventional 4-field box technique. Most centers now use IMRT or VMAT routinely. The trial also validated patient-reported outcomes as primary endpoints in RT trials. The bowel sparing advantage is particularly important for patients with prior abdominal surgery, prior RT, or inflammatory bowel disease.