ASTRO guideline: definitive and postoperative RT for BCC and cSCC
TL;DRThe guideline gives explicit strength and evidence grades for definitive RT, PORT, nodal RT, BED10 dose ranges and concurrent systemic therapy in non-metastatic BCC and cSCC. Most rest on low-to-moderate evidence.
The nodal dose ceiling is the practical read. The adjuvant dose is 6000-6600 cGy after lymphadenectomy, and the panel says no data support 6600 cGy even for positive margins or ECE. It also exempts a single <3 cm cervical node without ECE from adjuvant RT, so de-escalation in both directions has explicit cover.
In resected cSCC with close or positive margins that cannot be re-excised, this supports PORT as a Strong recommendation. The same margin scenario in BCC gets only a conditional recommendation, which leaves room for shared decision-making.
Nodal dosing has an explicit ceiling: 6000-6600 cGy after lymphadenectomy, with no data supporting 6600 cGy for positive margins or ECE. Elective nodal RT is narrowed to cSCC thicker than 6 mm with a primary field overlapping the basin. Primary-site dosing is given as BED10 ranges, so modality choice stays open.
Concurrent carboplatin with adjuvant RT for resected locally advanced cSCC is a Strong recommendation against, based on a negative randomized trial. Concurrent drug therapy with definitive RT is only conditionally recommended for unresected disease, on Low QoE. Hedgehog inhibitors and cemiplimab were positioned as palliative where curative local therapy is feasible.
Clinically apparent nodes go to therapeutic lymphadenectomy first, with definitive nodal RT reserved for inoperable or unresectable disease. Imaging plus SLNB is conditionally recommended for high-risk cSCC to guide nodal RT. PORT triggers in cSCC hinge on whether close or positive margins can be corrected surgically.
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ASTRO task force guideline: systematic MEDLINE review (May 1988 through June 2018) graded by strength × QoE. Consensus came from a modified Delphi process with a ≥75% agreement threshold (≥90% for expert opinion). Endorsed by AAPM, ABS, ACR, AHNS and SSO.
Adults with non-metastatic invasive BCC or cSCC treated with curative-intent RT. Re-irradiation, palliation and dosimetric studies were excluded. Minimum cohort size was ≥100 pts for KQ1, ≥50 for KQ2 to 4 and ≥15 for KQ5.
Primary-site dosing is given as BED10 ranges, not fixed schedules. Definitive: conventional 70-93.5, hypofractionated 56-88. Postoperative: conventional 59.5-79.2, hypofractionated 56-70.2. Gross perineural spread on imaging gets definitive-equivalent dose, preferably conventionally fractionated.
Cisplatin with adjuvant RT has randomized support in mucosal head and neck SCC. The one randomized trial in high-risk resected cSCC found no benefit from weekly carboplatin added to PORT, which is why the guideline recommends against it. Nodal dosing and the 6-week start window are extrapolated from mucosal H&N practice.
AJCC eighth edition skin staging covers head and neck only, so the T3/T4 PORT trigger has no staged equivalent on the trunk or limbs. Microscopic perineural invasion has no recommendation; only gross spread is addressed.
Strength and evidence diverge on purpose: several Strong recommendations sit on Low QoE and reflect panel conviction, not measured benefit. The cSCC vs BCC split in PORT strength is the guideline's most usable distinction. The panel considered recommending against routine elective nodal RT but judged the data insufficient either way.
| Scenario | Strength | QoE |
|---|---|---|
| Cannot undergo or decline surgery | Strong | Moderate |
| Surgery would compromise function or cosmesis | Conditional | Moderate |
| Genetic radiosensitivity (ataxia telangiectasia, Gorlin, Li-Fraumeni) | Conditionally not recommended | Expert Opinion |
| Indication | Histology | Strength | QoE |
|---|---|---|---|
| Gross perineural spread, clinical or radiologic | BCC + cSCC | Strong | Moderate |
| Close/positive margins, not correctable surgically | cSCC | Strong | Low |
| Recurrence after margin-negative resection | cSCC | Strong | Moderate |
| T3/T4 | cSCC | Strong | Moderate |
| Desmoplastic/infiltrative + chronic immunosuppression | cSCC | Strong | Moderate |
| Close/positive margins, not correctable surgically | BCC | Conditional | Low |
| Recurrence after margin-negative resection | BCC | Conditional | Low |
| Locally advanced/neglected, into bone or muscle | BCC | Conditional | Low |
| Scenario | Strength | QoE |
|---|---|---|
| Clinically apparent nodes → lymphadenectomy + adjuvant RT (except single <3 cm cervical node, no ECE) | Strong | Moderate |
| Definitive nodal RT only if inoperable or unresectable | Strong | Moderate |
| Imaging + SLNB to guide nodal RT, high-risk cSCC | Conditional | Expert Opinion |
| Elective nodal RT, cSCC thickness >6 mm, only if primary field overlaps basin | Conditional | Low |
| Adjuvant after lymphadenectomy: 6000-6600 cGy at 180-200 cGy/fx | Strong | Moderate |
| Elective, no lymphadenectomy: 5000-5400 cGy at 180-200 cGy/fx | Strong | Moderate |
| Setting | Conventional (180-200 cGy/fx) | Hypofractionation (210-500 cGy/fx) |
|---|---|---|
| Definitive | BED10 70-93.5 | BED10 56-88 |
| Postoperative | BED10 59.5-79.2 | BED10 56-70.2 |
- Optimal management of microscopic perineural invasion recruiting Study of a Strategy Integrating Adjuvant Radiation Therapy Versus Strategy Based on Monitoring in the Treatment of Carcinomas Spinocellular With High Risk of Recurrence Phase 3n=266 · primary completion 2031-06 · phase 3 adjuvant RT vs surveillance, high-risk cSCC
- Standardized fractionation schemes across skin RT modalities
- Role of systemic therapy with RT: neoadjuvant, adjuvant, concurrent n=27 · primary completion 2025-06 · neoadjuvant pembro before surgery + PORT, HN cSCCn=34 · primary completion 2027-10 · RT + cemiplimab, unresectable locally advanced cSCC
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The longer read
This document is best read as a codification of radiation practice that already existed, not as a shift in it. The evidence review itself concedes that few well-conducted modern randomized trials support RT in BCC or cSCC, so most recommendations rest on retrospective series and expert opinion. The grading is honest about that. Several recommendations pair a Strong label with Low quality of evidence, including PORT for cSCC with uncorrectable close or positive margins and the KQ4 BED10 ranges. ASTRO's grading system separates strength from evidence quality on purpose, but a reader should take a Strong/Low recommendation as panel conviction rather than a measured effect.
The most useful asymmetry for a radiation oncologist is between histologies after surgery. The same scenarios (margins that cannot be corrected surgically, recurrence after a margin-negative resection) earn a Strong recommendation in cSCC and only a Conditional one in BCC. The stated rationale is that cSCC carries far greater regional and nodal risk. For a post-excision referral, that split is explicit cover for shared decision-making in BCC while treating the equivalent cSCC.
The nodal section leans heavily on mucosal head and neck practice. The adjuvant dose of 6000-6600 cGy, the statement that no data support escalating to 6600 cGy for positive margins or extranodal extension, and the start window of within 6 weeks of surgery are all extrapolations. The elective nodal recommendation is deliberately narrow: cSCC thicker than 6 mm, and only when the primary field already overlaps the draining basin. The text records that the panel considered recommending against routine elective nodal RT but judged the data insufficient. The median 5-year regional relapse-free survival of 99% it cites comes from selected retrospective series and cannot separate treatment effect from patient selection.
On systemic therapy, the one randomized input is negative: weekly carboplatin added to PORT did not help high-risk resected cSCC. That is why the guideline declines to carry the mucosal SCC chemoradiation paradigm across. The advice to avoid hedgehog inhibitors and cemiplimab where curative surgery or RT is feasible reflects their palliative approval status at publication. It is also the section most likely to be outdated by later perioperative immunotherapy data, and the guideline commits to replacement or reaffirmation within 5 years of publication, so a reader should check for an update before relying on KQ5.
Two structural limits affect how well the recommendations transfer. AJCC eighth edition staging for skin covers only the head and neck, so the T3/T4 PORT trigger has no staged equivalent on the trunk or limbs, where the panel also notes that salvage re-resection is less morbid. And giving BED10 ranges rather than fixed schedules keeps flexibility across ELS, HDR brachytherapy, electrons and MV photons but leaves fractionation unstandardized. The task force names standardization as a research priority, along with microscopic perineural invasion, which it leaves without a recommendation.