Dose-Escalated RT for Muscle-Invasive Bladder Cancer
ForMIBC (T2-T3, N0-N1) post-TURBT, curative-intent trimodality or RT alone
TL;DR2yr invasive local recurrence 5.5% vs 27.5% with SIB dose escalation, adjusted SHR 0.20 (0.05-0.89), p=0.035; no OS or MFS difference.
The boost was a simultaneous integrated boost to the primary lesion, 60Gy/20fx or 70Gy/32fx, deliverable on daily CBCT without an elective-volume change, and G2+ GU toxicity did not rise (17.9% vs 22.1%). Half the cohort got no chemotherapy, so this speaks directly to the chemo-ineligible pt where RT intensity is the only lever left.
In an MIBC pt going to bladder preservation who cannot take concurrent chemotherapy, this supports discussing a boost to the primary lesion as the available intensification; it says nothing about pts with multifocal disease, who were entirely absent from the escalated cohort.
The boost was simultaneous integrated, 60Gy/20fx or 70Gy/32fx to the primary lesion, elective volume unchanged, on daily CBCT with MRI/PET fusion for delineation, and G2+ GU toxicity did not rise (17.9% vs 22.1%). That combination makes the escalation technically transferable today, and moves the dose decision for the chemo-ineligible pt.
Half the cohort (51%) received no concurrent chemotherapy, mostly for performance status, and absence of chemo carried worse OS (HR 2.83 [1.42, 5.63], p<0.01). Chemo showed no association with invasive local recurrence on univariable analysis, so this frames RT dose, not the radiosensitiser, as the intensification available when a pt cannot take cisplatin.
Salvage cystectomy was performed in only 2 standard-dose and 1 escalated pt, because most pts with invasive relapse were judged unfit for surgery at recurrence. Bladder preservation rates here therefore reflect operability as much as disease control, which matters when counselling a marginal-fitness pt that salvage is a real fallback.
10 details
Multicentre retrospective cohort across three centres, March 2015 to May 2025, chosen to capture the daily-CBCT image-guidance era. N=107 (39 dose-escalated, 68 standard), median follow-up 23 months (range 3 to 104).
MIBC after TURBT treated with curative intent, with or without concurrent chemotherapy; node-positive pts eligible if non-metastatic. Metastatic or palliative-intent pts excluded. T2 86%, ECOG 2-3 in half the cohort, hypofractionation in 91%.
Standard cohort received 55Gy/20fx or 64Gy/32fx to the whole bladder. Escalated cohort received a simultaneous integrated boost to the primary lesion, up to 60Gy/20fx or 70Gy/32fx. CT simulation with empty bladder; MRI and FDG PET fused for target delineation in selected pts; daily CBCT in all but one pt.
2-year local control for invasive and non-invasive disease, metastasis-free survival, overall survival, bladder preservation, and toxicity. Local control analysed by Fine-Gray competing-risk models, univariable then multivariable adjusted for T stage.
Dose escalation was associated with lower invasive local recurrence; non-invasive recurrence, metastasis, and survival did not differ. Numbers are in the outcomes table above.
| Endpoint | Dose escalation | Standard dose | Effect |
|---|---|---|---|
| 2yr invasive local recurrence (CI) | 5.5% | 27.5% | SHR 0.20 (0.05, 0.89), p=0.035 (adj T stage) |
| 2yr non-invasive recurrence (CI) | 6.7% | 9.9% | SHR 0.88 (0.23-3.33), p=0.98 |
| 2yr metastasis (CI) | 21.1% | 32.3% | p=0.79 univariable |
| 2yr overall survival | 71.1% | 64.4% | p=0.5 |
| G2+ GU toxicity | 17.9% (7) | 22.1% (15) | p=0.8 |
| G2+ GI toxicity | 5.1% (2) | 7.4% (5) | p=0.9 |
No difference in G2+ GU (17.9% vs 22.1%, p=0.8) or G2+ GI toxicity (5.1% vs 7.4%, p=0.9). Grade 3 toxicity in 2 pts (2.9%), both in the standard-dose arm. No pt required early cessation of treatment for toxicity.
The direction matches BC2001 and BCON, which established chemoradiation and hypoxic modification as ways to improve local control within bladder preservation but never randomised the RT dose itself. The open question these left, whether escalating the primary lesion adds control on top of a modern image-guided plan, is what this cohort probes, at retrospective strength rather than randomised.
The escalated cohort was systematically more favourable: 100% single-focus disease vs 65%, hydronephrosis in 10% vs 28%, T3 in 8% vs 16%. Only T stage entered the multivariable model, and with 18 invasive events total the model could not have supported more. Recurrence ascertainment differed by arm: 3 standard-dose recurrences were presumed invasive on CT and MDT consensus while every escalated-cohort recurrence was confirmed cystoscopically.
The local-control signal is real in this dataset but its magnitude is not transferable: an SHR of 0.20 resting on 2 events versus 16, in cohorts that differ on tumour focality, is an effect size that would be expected to shrink under randomisation. What survives the caveats is a tolerability finding, that an integrated boost to the primary did not raise G2+ GU or GI toxicity.
Retrospective, N=107, 18 total invasive events driving the SHR; boost cohort had single-focus disease and less hydronephrosis, with only T stage adjusted.
- Does the local-control benefit survive randomisation and balanced tumour focality?
- Can multifocal MIBC be boosted at all, or only unifocal disease?
- Late GU toxicity beyond 23 months with an integrated boost
📚 Sources · 📄 1 paper
The longer read
Bladder preservation has been intensified in almost every dimension except the one a radiation oncologist controls most directly. BC2001 established the concurrent radiosensitiser, BCON established hypoxic modification, and both improved locoregional control within trimodality therapy. Neither randomised the radiation dose to the tumour itself. That leaves a durable gap in the evidence, because roughly a quarter of pts still fail invasively in the bladder after standard-dose whole-bladder treatment, and the standard dose in wide use was set in an era of large margins and no daily volumetric imaging. This cohort asks the obvious follow-on question with the tool that modern practice actually provides: a simultaneous integrated boost to the visible primary lesion, planned on empty-bladder CT with MRI or PET fusion and delivered under daily CBCT.
The headline association is large. Invasive recurrence at two years was 5.5% with escalation and 27.5% without, and the adjusted subdistribution hazard ratio was 0.20 with a confidence interval reaching 0.89. A reader should treat that interval, rather than the point estimate, as the honest summary. It rests on 2 invasive events in the escalated group and 16 in the standard group. Effect sizes estimated from event counts that small are unstable in a specific and predictable direction: they are usually smaller when the same question is asked prospectively.
The more consequential problem is that the two cohorts were not the same patients. Every escalated patient had a single tumour focus; a third of the standard-dose cohort had multiple foci. Hydronephrosis, a well-recognised adverse feature in this disease, was present in 10% of escalated patients and 28% of standard-dose patients, and T3 disease was half as common in the escalated arm. This is not incidental noise, it is the expected footprint of the clinical decision that generated the groups: a clinician boosts a lesion they can see, contour, and cover, which is exactly the patient whose disease is unifocal and less locally advanced. The multivariable model adjusted for T stage alone, and with 18 events it could not honestly have adjusted for more. So the confounding that most plausibly drives the result, tumour focality, is the one variable the analysis could not address. Ascertainment adds a second, smaller asymmetry in the same direction: three standard-dose recurrences were classified as invasive from CT appearance and multidisciplinary consensus in patients too comorbid for cystoscopy, while every recurrence in the escalated cohort was cystoscopically confirmed.
What holds up better than the efficacy estimate is tolerability, and it is arguably the more useful finding. G2+ GU toxicity was 17.9% with the boost and 22.1% without, G2+ GI toxicity 5.1% and 7.4%, and the only two grade 3 events occurred in the standard-dose arm. Because the boost was integrated rather than sequential and the elective volume was unchanged, this is a plausible dosimetric result rather than a surprising one, and it is the observation that makes a prospective dose-escalation trial straightforward to justify. The absence of any signal on metastasis-free or overall survival is unremarkable at 23 months in a cohort with ECOG 2-3 in half its patients, where competing mortality dominates. The finding most likely to change a decision this week is contextual rather than comparative: 51% of these patients received no concurrent chemotherapy, and in that group the local dose is the only lever left. That is the population in whom this data is worth raising, and the population in whom multifocal disease, unrepresented here, should stop the extrapolation.