Comparison of HDR-brachytherapy and tomotherapy for the treatment of non-melanoma skin cancers of the head and neck

Purpose: This study aims to investigate and compare High Dose Rate Brachytherapy (HDR-BT) with Helical Tomotherapy (HT) treatment plans. The focus is on small target volumes near radiation-sensitive organs in the ocular region, to evaluate the advantages of these techniques in treating skin cancer.

Methods: This retrospective observational analysis included patients who underwent skin cancer HDR-BT Freiburg flap treatment between 2019 and 2023. An expert radiation oncologist contoured the planning target volumes (PTVs) and marked their visible extension with a radio-opaque tin wire. Each patient had two treatment plans: an individually shaped HDR-BT surface mold and an HT calculation used specifically for this study. Quality assurance of treatment plan was performed in both HDR-BT and HT. The plans were then compared using organ at risk (OAR) maximum doses and the conformity index CI. Radiation oncologists assessed their quality using their routine workflow evaluation plan.

Results: Twelve patients were selected for the inclusion in this study. HT provided more consistent target coverage than HDR-BT, with a statistically significant difference (p < 0.05) at t-test. HT showed higher CIs and maximum dose for the optic nerve, optic chiasm, and lens in the homolateral part. Radiation oncologists preferred the overall quality of HT treatment due to its superior PTV coverage, especially for convex surfaces, while maintaining effective OAR sparing. HDR-BT is preferred when concave surfaces are present.

Conclusion: HT offers more conformal treatment, although some OAR parameters are statistically significantly better with HDR-BT, which may also be superior for complex geometries.