A dosimetric study of electron beam therapy vs. high-dose-rate mould brachytherapy in adjuvant treatment of non-melanoma skin carcinomas of the head and neck region

PURPOSE: Radiation for superficial tumours of the head and neck region can be given either by brachytherapy or electrons. Brachytherapy (BT), due to rapid dose fall-off and minor set-up errors, should be superior to external beam radiotherapy (EBRT) for treatment of lesions in difficult locations such as the nose and earlobe. The present study is a dosimetric comparison of computed tomography (CT)-based mould brachytherapy treatment plans with 3D conformal electron beam therapy in the treatment of non-melanoma skin cancers (NMSC). MATERIAL AND METHODS: From December 2017 to November 2018 10 patients with NMSC of the head and neck region (forehead, nose, cheek) who underwent adjuvant radiation with HDR brachytherapy (BT) with a surface mould individual applicator were enrolled for analysis. We evaluated dose coverage by minimal dose to 90% of planning target volume (PTV, D(90)), volumes of PTV receiving 90-150% of prescribed dose (PD) (VPTV(90-150)), conformal index for 90% and 100% of PD (COIN(90), COIN(100)), dose homogeneity index (DHI), dose nonuniformity ratio (DNR), and exposure of organs at risk (OARs) (eyes, lens, underlying bone and skin). Prospectively, we created CT-based treatment plans for electron beam therapy. We compared conformity (COIN(90), COIN(100)), dose coverage of PTV (D(90), VPTV(90), VPTV(100)), volumes of body receiving 10-90% of PD (V(10)-V(90)), doses to OARs (D(0.1cc) and D(2cc)) of BT and electron plans. RESULTS: We obtained mean BT-DHI 0.81, BT-DNR 0.608, Electron-DHI 1.25. We observed no significant differences in VPTV(90,100) and D(90) between BT and electron beam. Mean BT-VPTV(125,150) were significantly higher than Electron-VPTV(100,125). COIN(90) was superior for BT plans. CONCLUSIONS: CT-based surface mould brachytherapy results in better conformity of superficial lesions on small, irregular surfaces such as the nose and inner canthus than electrons with a slightly higher skin dose.