Background
Prospective phase II, N=32, locally advanced rectal cancer. Tests whether early intratreatment MRI response (≥20% volume reduction at 3 wk) can guide adaptive radiation dose escalation.
Interventions and follow up
Arm A (early responders): Standard CRT to 54 Gy + 5-FU
Arm B (non-responders at 3 wk): IMRT dose escalation, SIB to 60 Gy + 5-FU
Primary endpoint: Feasibility of MRI response-adapted dose escalation; pCR
mFollow up: Not reported
Arm B (non-responders at 3 wk): IMRT dose escalation, SIB to 60 Gy + 5-FU
Primary endpoint: Feasibility of MRI response-adapted dose escalation; pCR
mFollow up: Not reported
Results
MRI response at 3 wk: 63% responders vs 37% non-responders
pCR: 33% (non-responders escalated to 60 Gy) vs 30% (responders at 54 Gy) — similar
R0 resection: 100% both groups
Grade ≥3 toxicity (60 Gy arm): 25%
pCR: 33% (non-responders escalated to 60 Gy) vs 30% (responders at 54 Gy) — similar
R0 resection: 100% both groups
Grade ≥3 toxicity (60 Gy arm): 25%
Adverse events
Grade ≥3 acute GI (60 Gy): 25%
Grade ≥3 acute GI (54 Gy): 15%
Surgical complications: No increase in escalated group
Grade ≥3 acute GI (54 Gy): 15%
Surgical complications: No increase in escalated group
Conclusions
Early MRI response at 3 wk can identify non-responders; escalation to 60 Gy with IMRT is feasible with manageable toxicity and yields pCR (33%) similar to early responders at 54 Gy (30%), suggesting dose escalation can overcome early radioresistance.
Key Limitations
Small single-arm feasibility study (N=32); non-randomized response-adaptive design; surrogate endpoint (pCR) rather than survival; follow-up not reported; results hypothesis-generating only.
Clinical Context
Proof-of-concept for biomarker/imaging-adapted radiotherapy in rectal cancer; not practice-changing but supports investigation of functional-imaging-guided dose escalation in non-responders within total neoadjuvant therapy strategies.