Kidney
2026-07-31
IROCK Contouring Guidelines (RCC SABR)
ForLocalized RCC considered for SABR, including IVC thrombus, post-RN or post-RFA recurrence
TL;DRFirst international consensus contouring atlas for RCC SABR: median DSC 0.85 across 16 experts, 4 scenario-specific iGTV statements.
The two hardest scenarios are named and quantified: Case 1 (IVC thrombus) and Case 4 (post-RFA cavity) carried the worst agreement (DSC 0.85 and 0.75, HD 64.60 and 9.00 mm), driven by how far superiorly thrombus was covered and how much cavity was included. Both statements push toward larger volumes, so OAR priority and a 5 mm PTV are the gates on whether that transfers.
In a patient with post-RFA residual RCC or an IVC tumor thrombus being planned for SABR, this defines the target as the whole ablation cavity or the full thrombus rather than the visible nodule alone; it does not address dose selection or whether SABR beats nephrectomy.
Case 1 (IVC thrombus) and Case 4 (post-RFA cavity) carried the worst agreement, DSC 0.85 and 0.75 with HD 64.60 and 9.00 mm, and both consensus statements push toward the larger volume: full thrombus, entire ablation cavity. OAR constraints outrank coverage, and the 5 mm PTV assumes 4D-CT with daily CBCT.
12 details
International contouring consensus under IROCK, convened at ASTRO 2023. 16 radiation oncologists contoured 4** RCC SABR scenarios on CT alone via EduCase; a STAPLE algorithm generated the 95% consensus contour, refined across 2 online meetings in May and June 2024. Statements were revised to uniform (100%) agreement**.
Panelists, not patients: inclusion required ≥10 prior RCC SABR cases, with 14 of 16 having treated ≥10 in the preceding 12 months. Cases were a >10 cm RCC with IVC tumor thrombus, a central tumor abutting the hilum, a local recurrence post-nephrectomy, and a post-RFA cavity recurrence.
Target is the iGTV (GTV incorporating internal motion); no participant added a microscopic-spread margin, so no separate ITV is recommended. The most common PTV expansion was a uniform 5 mm, predicated on supine vacuum-cushion setup, 4D-CT sim, IV contrast and daily CBCT. Dose objectives and OAR constraints for 1, 3, or 5 fractions are tabulated from FASTRACK-II and AQuOS-II.
Overall median DSC 0.85 (range 0.40-0.95), median MDA 2.17 mm (0.71-10.82), median HD 9.00 mm (4.00-89.31), with DSC above 0.70 in every case. Two-way ANOVA showed all three metrics differed by case (P < .05); only MDA differed by participant (P = .03).
| Case | DSC | MDA (mm) | HD (mm) |
|---|---|---|---|
| 1: >10 cm RCC + IVC thrombus | 0.85, 0.79-0.85 | 6.69, 5.88-8.79 | 64.60, 64.44-86.40 |
| 2: central tumor at hilum | 0.90, 0.84-0.93 | 1.55, 1.00-2.09 | 7.92, 5.35-9.98 |
| 3: local recurrence post-RN | 0.91, 0.88-0.93 | 1.42, 1.18-1.89 | 6.18, 6.00-7.12 |
| 4: post-RFA cavity recurrence | 0.75, 0.60-0.79 | 2.50, 2.12-2.99 | 9.00, 9.00-12.39 |
IROCK previously supplied the outcome evidence (its pooled international analyses and the FASTRACK-II phase 2), and both showed heterogeneous dose, fractionation and planning conventions across contributing centers. This fills the delineation gap those datasets left open, and it borrows its constraint table from FASTRACK-II and the ongoing AQuOS-II rather than deriving new dose-response thresholds.
The renal substructure question is left deliberately unsettled: cortex is defined for use, hilum is explicitly not a dose-limiting OAR, on the reasoning that sparing an unvalidated structure would redistribute dose into parenchyma that does correlate with renal function. AQuOS-II is the trial that may resolve it.
CT-only images were supplied on purpose, for international accessibility, so measured variation likely overstates what an MRI-equipped center would see. Participants never recontoured post-consensus, so the guideline's own effect on agreement is unmeasured, and adoption assumes urology, radiology and nephrology collaboration plus advanced planning technology.
Expert consensus atlas, not an outcome study: 16-panel STAPLE contours with unanimous statements, no efficacy or toxicity endpoint, unvalidated prospectively.
- Does renal hilum sparing reduce artery stenosis or ureteric stricture?
- Does guideline adherence improve local control or reduce toxicity?
- Would MRI-based simulation narrow contour variability?
📚 Sources · 📄 1 paper
2026-05-18 ESTRO Congress 2026
FASTRACK II NCT02613819
ForPrimary RCC ≤10cm, T1b-dominant, medically inoperable or declined surgery
100% at 36, 60, 84 mo
ITT population, RECIST-assessed, median f/u 62 mo
TL;DR100% freedom from local progression at 36, 60, and 84mo after single-fraction 26Gy or 42Gy/3fx SABR in inoperable primary RCC.
The transferable detail is the size-adapted prescription: 26Gy in one fraction under 4cm, 42Gy/3fx above it, with median tumour 46mm and 65% T1b or higher. That is a larger-tumour cohort than most ablation series, and zero local failures out to 84mo supports offering SABR when a 77-year-old is turned down for nephrectomy.
In a medically inoperable or surgery-declining patient with a primary RCC up to 10cm, including T1b and larger where thermal ablation is a poor fit, this supports SABR as a durable local option; it does not speak to the operable patient, where nephrectomy remains untested against it.
The transferable detail is the size-adapted prescription: 26Gy single fraction under 4cm, 42Gy/3fx above it, in a cohort with median tumour 46mm and 65% at least T1b. Zero local failures to 84mo supports offering SABR when the patient is turned down for nephrectomy; bowel toxicity (two colonic obstructions) sets the technical ceiling.
This is the non-surgical arm of the small-renal-mass conversation getting real prospective follow-up, at a median tumour of 46mm where thermal ablation performs worst. It changes what you can tell a high-risk or surgery-declining patient at referral; it does not test SABR against partial nephrectomy in an operable patient, which remains unstudied.
10 details
Non-randomised phase 2, eight hospitals in Australia and the Netherlands, run by TROG and ANZUP. Enrolment July 28 2016 to Feb 27 2020; 71 enrolled, one withdrew consent before treatment. This report is the pre-planned final follow-up at a median of 62 months (IQR 60-72).
Histologically confirmed primary RCC, medically inoperable, high risk, or declined surgery, ECOG ≤2, tumours ≤10 cm, N0-N1. Median age 77 years (70-82), 49 (70%) male. Median tumour size 46 mm (37-55), with 39 (56%) T1b, six (9%) T2a and one (1%) T3a.
Size-adapted prescription: 26 Gy in a single fraction for tumours ≤4 cm, 42 Gy in three fractions 48 h apart for tumours >4 cm. Histological confirmation was required before treatment, so this is a biopsy-proven cohort rather than a radiographic-diagnosis one.
Primary: freedom from local progression by RECIST, assessed in the intention-to-treat population, as was safety.
100% local control at 36, 60 and 84 months, with no local recurrences and no cancer-related deaths reported in the cohort.
Seven (10%) patients had at least one treatment-related grade 3 event within 9 months: pain in four (6%), nausea and vomiting in three (4%), colonic obstruction in two (3%), diarrhoea in one (1%). No grade 4 events and no treatment-related deaths; no new long-term safety signals emerged with extended follow-up.
A 100% point estimate in 70 pts carries a wide confidence bound that the headline hides, and RECIST is an imperfect local-control instrument after ablative RT, where a treated mass commonly persists without viable tumour. Renal function trajectory, the endpoint that actually competes with nephrectomy, is not reported in this source.
Prior SABR evidence in primary RCC was retrospective and pooled, so a prospective multicentre dataset at 84 months is the new contribution rather than the effect size itself. Comparison to partial nephrectomy and thermal ablation remains indirect: no randomised trial has run, and this cohort was selected against surgery by definition.
The finding that transfers is durability at a tumour size where thermal ablation performs worst, with a median of 46 mm and 65% at least T1b. What it does not settle is whether SABR is a choice rather than a fallback, which needs a randomised or matched comparison in operable pts, with renal function as a co-primary.
Single-arm phase 2, N=70, inoperable or surgery-declining pts only. No randomised comparator vs partial nephrectomy or thermal ablation. Maturity gate holds despite 62mo f/u.
- SABR vs partial nephrectomy in operable pts
- Renal function trajectory after SABR vs nephrectomy
- SABR vs thermal ablation in T1b tumours
📚 Sources · 📄 1 paper
Abstract
2026-05-17 ESTRO Congress 2026
RCC SBRT (5-year local control)
ForPrimary RCC treated with SBRT; stage and operability not stated in source
TL;DR100% local control at 5 years for RCC treated with SBRT, per a conference slide; no N, dose, or CI in source.
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Not reported in source. The tweet gives a 5-year local control figure with no study type, N, institution, or registry identifier, so design cannot be inferred.
SBRT to primary RCC; dose, fractionation, number of fractions, and target definition are not reported in source. These are the parameters that gate transfer to practice, and none are available here.
100% local control at 5 years as stated in the source tweet. No confidence interval, no n-at-risk, and no statement of whether this is a Kaplan-Meier estimate or a crude proportion.
Beyond the missing design, the specific risk is effective follow-up: a medically inoperable RCC cohort loses pts to non-cancer death well before 5y, so a 100% figure can rest on very few pts at risk. Local control definition (RECIST-style size change vs absence of growth vs biopsy) is also unstated and swings the estimate.
Single tweet with one number, no N, design, dose, or LC definition. Cannot judge whether the 100% figure reflects efficacy or short effective follow-up.
- Dose and fractionation behind the reported 5-year local control
- Local control definition and n-at-risk at 5 years
- SBRT vs partial nephrectomy in operable primary RCC
📚 Sources · 🐦 1 tweet
These results are so impressive!! 💯 local control at 5 years for RCC treated with SBRT@DrRanaMcKay @AdityaBagrodia @DrTylerStewart @DrYukselUrun @OncoAlert https://t.co/fUB3airM5g
— Tyler Seibert MD PhD (@TylerSbrt) May 17, 2026