GI Lower
Dose escalation in LARC, with the survival signal running ahead of the local-control mechanism that should drive it.
SIB-CRT vs Standard CRT for LARC (NCT02195141) NCT02195141
ForStage II/III rectal adenocarcinoma, neoadjuvant chemoRT candidates
15.2% vs 18.4%
P=0.695, primary endpoint not met
TL;DR9yr LC 87.1% vs 70.1% (HR 0.40, P=0.038) and OS 74.3% vs 48.9% (HR 0.43) favoring SIB dose escalation.
The boost was 56 Gy to PGTV and 60 Gy to involved lateral nodes on a 50 Gy/25 fx pelvic base, a deliverable prescription with acute G3 toxicity 14.5% vs 19.6%. LC 87.1% vs 70.1% is the mechanistically coherent signal; the OS and MFS separation on 106 pts is not, and gates any move to boost outside a trial.
In stage II/III LARC where perioperative chemotherapy is not planned or not tolerated, this supports testing an integrated boost to gross disease and involved lateral nodes; it gives no read on pts receiving modern TNT, where the subgroup showed no added benefit. The longer read
The prescription is deliverable and specified: 56 Gy to PGTV, 60 Gy to involved lateral nodes, on a 50 Gy/25 fx pelvic base, with acute G3 toxicity 14.5% vs 19.6% and no late toxicity reported. LC 87.1% vs 70.1% is the endpoint a boost can own; treat the OS and MFS separation as hypothesis-generating for a boost trial, not license to escalate off-protocol.
The benefit was confined to pts who did not receive perioperative chemotherapy (9yr DFS 70.8%, HR 0.343, P=.014), with no additional benefit in those who did, and chemo receipt was not randomized. Read as a signal about RT dose in chemotherapy-ineligible pts rather than any argument against systemic intensification.
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Prospective randomized phase 2, 1:1, N=106 (55 SIB-CRT, 51 CRT), accrued August 2013 to February 2015. Median follow-up 116.6 months, which is the study's real asset.
Stage II/III rectal adenocarcinoma. Radical surgery planned 6 to 8 weeks after chemoradiotherapy. Perioperative chemotherapy was not randomized, and its receipt defines the subgroup that carries the result.
Both arms received 50 Gy/25 fx to the pelvis. The experimental arm added a simultaneous integrated boost of 56 Gy to PGTV and 60 Gy to lateral metastatic nodes where present, so the escalation targets gross primary and involved lateral nodes rather than the elective volume.
Primary: pCR rate. Secondary: DFS, OS, MFS, LC, CSS and toxicity. Every result the conclusion rests on is secondary.
Acute grade 3 toxicity 14.5% (SIB-CRT) vs 19.6% (CRT), primarily radiation dermatitis. Late toxicity is not reported in the source, which matters most for a boost delivered near bowel and for pts followed nearly a decade.
Neoadjuvant dose escalation in LARC has repeatedly raised pCR without translating to survival; this trial reports the mirror image, a null pCR (15.2% vs 18.4%) with survival separation. The result also sits against the TNT era, where systemic intensification rather than RT dose is the current lever, and the chemo-receiving subgroup here showed no additional benefit.
The survival claim is a secondary-endpoint result from 51 vs 55 pts, so a handful of events moves each HR, and no confidence intervals are reported in the source. The driving subgroup is defined by non-randomized chemotherapy receipt, and the higher rate of curative treatment in the SIB arm (89.1% vs 78.4%) is itself a plausible route to the OS difference independent of dose.
A pelvic boost has a defensible mechanism for LC 87.1% vs 70.1% and essentially none for MFS 70.8% vs 47.2%. The authors attribute the distant benefit to intensified control of micrometastases; the simpler reading is that a small trial with a large curative-treatment imbalance produced correlated secondary endpoints.
| Endpoint | SIB-CRT | CRT | Effect |
|---|---|---|---|
| DFS | 70.8% | 47.4% | HR 0.46, P=0.013 |
| OS | 74.3% | 48.9% | HR 0.43, P=0.008 |
| MFS | 70.8% | 47.2% | HR 0.48, P=0.017 |
| LC | 87.1% | 70.1% | HR 0.40, P=0.038 |
| CSS | 77.4% | 57.2% | P=0.027 |
| pCR | 15.2% | 18.4% | P=0.695 |
CONSORT flow
Randomized phase 2, N=106, primary endpoint (pCR) missed; survival gains are secondary endpoints with wide implied precision and a non-randomized chemo subgroup driving them.
- Does SIB add anything on a total neoadjuvant therapy backbone n=37 · primary completion 2026-05 · SIB-SCRT plus CAPOX and PD-1 in high-risk LARCn=156 · primary completion 2026-12 · randomises GTV SIB 58.75 vs 50 Gy/25f for CRrecruiting THeragnostic Utilities for Neoplastic DisEases of the Rectum by MRI Guided Radiotherapy Phase NAn=179 · primary completion 2027-01 · RT dose escalation gated by early regression index
- Late GI and GU toxicity of the boost beyond 9 years active Safety of a Boost (CXB or EBRT) in Combination With Neoadjuvant Chemoradiotherapy for Early Rectal Adenocarcinoma Phase 3n=148 · primary completion 2023-06 · safety endpoint for CXB vs EBRT boost after nCRTrecruiting Standard Dose Versus High Dose of Radiotherapy in Rectal Preservation With Chemo-radiotherapy in Rectal Cancer Patients Phase 3n=162 · primary completion 2026-12 · 62 Gy vs 50.4 Gy phase 3, dose-escalation toxicity
- Whether the curative-treatment rate imbalance explains the OS gap