Skin surface brachytherapy practice-pattern survey
ForBCC and cSCC treated with skin surface brachytherapy
TL;DR16 ABS respondents: gross-disease margin 3-15mm (median 5mm), doses 30 Gy/5fx to 64 Gy/32fx (EQD2 40-65 Gy), no consensus on dosimetric constraints.
The transferable read is pretibial dosing: 10 respondents (63%) dropped to 2-3 Gy per fraction there, and eight reported severe toxicity on the lower extremity. With max skin dose ranging 125-150% and fractionation cut points spanning 2-5 cm, a reader building a skin HDR program has a variance map, not a constraint set.
For a BCC or cSCC on the pretibial skin, this survey supports treating site as a reason for gentler fractionation; it does not inform lesions deeper than 3 mm or with perineural invasion, which respondents steered away from brachytherapy.
The transferable read is pretibial dosing: 10 respondents (63%) dropped to 2-3 Gy per fraction there, and eight reported severe lower-extremity toxicity. Max skin dose 125-150% and fractionation cut points of 2-5 cm mean a skin HDR program must set and audit its own constraints.
12 details
30-question electronic survey sent to ~400 American Brachytherapy Society clinician members. 16 fully completed surveys analyzed; one incomplete survey excluded. Nearly all US respondents, one from Spain.
Radiation oncologists using skin surface brachytherapy for cSCC and BCC. Practice settings spanned academic, hospital-based and private; aggregate experience ranged 8 to 1800 cases.
Hypofractionation preferred; clinical-scenario doses ranged 30 Gy in 5 fractions to 64 Gy in 32 fractions (EQD2 40 Gy-65 Gy). Median max prescription depth 5 mm; shielded applicators most common, custom molds for large or curved areas. Respondents avoided daily schedules when hypofractionating.
Margin on gross disease 3-15mm, median 5mm. Max skin dose 125-150% (median 135%) of prescription; CTV coverage 90-100% (median 95%). No consensus on dosimetric constraints.
| Parameter | All respondents | >100 cases in career |
|---|---|---|
| Max dose at skin surface | 13 (81%) | 7 (78%) |
| Min dose to CTV | 8 (50%) | 3 (33%) |
| Depth of 90% isodose line | 6 (38%) | 3 (33%) |
| Min dose to skin surface | 5 (31%) | 4 (44%) |
| V150 | 4 (25%) | 2 (22%) |
| D95 | 2 (13%) | 1 (11%) |
Eight respondents described severe acute and late toxicity on the lower extremity, especially pretibial skin. Three referred non-healing in-field ulcers for hyperbaric oxygen.
The cited prior literature (Guix custom-mold HDR, Paravati electronic brachytherapy, van Hezewijk hypofractionated electrons) reports single-series outcomes. This survey adds no outcomes; it documents how widely dose, margin and constraints vary across practices using the technique.
Several key tables carry ambiguous row-value pairing in the source, and the scenario table (Table 4) was not captured. Toxicity is anecdotal recall with no denominators.
The useful output is the spread itself: margins, skin-dose ceilings and the lesion-size threshold for gentler fractionation all vary several-fold. Prospective trials and expert consensus are what the authors call for, and this survey cannot substitute for either.
Practice survey of 16 self-selected respondents; no efficacy or toxicity endpoints measured, so the authors' 'convenient and safe' conclusion is not testable from this design.
- Which dosimetric constraints predict late skin toxicity?
- Optimal fractionation for pretibial and lower-extremity lesions
- Brachytherapy vs electrons or orthovoltage for cosmesis
📚 Sources · 📄 1 paper
The longer read
This paper is best read as a census of variation rather than evidence about the technique. Sixteen completed surveys from roughly 400 invitations is a small, self-selected sample, and the people who answer a voluntary ABS questionnaire about skin brachytherapy are plausibly those most invested in it. That selection cuts in a predictable direction: it likely overstates comfort with large fraction sizes and understates the frequency of abandonment after a bad outcome. The authors' conclusion that skin brachytherapy can be convenient and safe does not follow from the design, because no outcome was measured; safety here is the absence of reported catastrophe in recall, alongside eight respondents who did recall severe lower-extremity toxicity.
What the survey does establish is that there was no shared dosimetric language among users. Max skin dose ceilings of 125-150% of prescription, CTV coverage targets of 90-100%, and no respondent using D2cc, D1cc or D0.1cc means two programs can call the same plan acceptable or unacceptable. Some respondents planned only with applicator depth calculations, which is reasonable for flat shielded cones but leaves no common metric for comparing toxicity across centers. Any future outcomes series pooled across institutions inherits that heterogeneity.
Against the single-institution outcome series the authors cite, including custom-mold HDR for facial carcinomas and electronic brachytherapy reports, this survey sits one level lower in the evidence chain. Those series at least tie a schedule to a result. Here the dose range, 30 Gy in 5 fractions to 64 Gy in 32 fractions with EQD2 40 Gy-65 Gy, spans regimens that are not radiobiologically interchangeable for late skin effects, and the paper cannot say which end of that range buys better cosmesis or control.
The pretibial signal is the one finding with face validity for practice. Nearly unanimous de-escalation to 2-3 Gy per fraction on pretibial skin, plus the concentration of recalled severe toxicity there, matches the clinical intuition that poorly vascularized, edema-prone lower-leg skin tolerates large fractions badly. The non-healing ulcer case driven by post-treatment edema from systemic causes is a reminder that host factors, not just dose, determine the lower-extremity outcome.
The survey does not settle margin selection, the depth limit for surface brachytherapy beyond the respondents' 3 mm avoidance threshold, or whether brachytherapy's shorter course offsets any cosmetic cost relative to electrons or orthovoltage. Several respondents pointed to NCCN low- and high-risk definitions to set margins, which is the most portable takeaway: anchor margin decisions to histologic risk rather than to applicator convenience. For a program writing its own protocol, the value is knowing that the published practice range is wide enough that local constraints must be defined and audited internally.