Image-guided high-dose-rate interstitial brachytherapy with custom-made surface applicators for lower lip cancer as monotherapy. Technique, long-term clinical results, and quantitative dose-volume evaluation: A case series.

Abstract

Purpose: This study showed long-term clinical results and quantitative dose-volume evaluation of image-guided high-dose-rate interstitial brachytherapy (IG HDR-BT) with custom-made surface applicators for lower lip cancer as monotherapy.

Material and methods: Patients with localized lower lip cancer, who received IG HDR-BT with custom-made surface applicators as monotherapy at the NHO Osaka National Hospital between February 2012 and January 2015 were enrolled in this study. One to three applicators were implanted interstitially, and two to six were placed on tumor surface. Planning-aimed dose (PAD) was 54 Gy, 48 Gy for a recurrent case, and irradiation was delivered at 6 Gy/fraction, twice a day. Dosimetric goal was to achieve D₉₀: clinical target volume (CTV) > PAD without excessive dose to the mandible. A lead shield was placed between the gingiva and lower lip during irradiation to reduce the dose to the mandible in all but one edentulous patient. A gauze with 2% lidocaine was inserted intra-orally to reduce the dose to the upper lip and maxilla.

Results: Six patients (T1 : T2 : T3 = 3 : 2 : 1), including one recurrent case, were enrolled in this study. The CTV was contoured on computed tomography and in two cases, magnetic resonance imaging was used as a reference for contouring. The median follow-up was 69.5 months. The primary tumor was controlled in all cases. No serious late adverse reactions were observed. The median D₉₀ (CTV) and V₁₀₀ (PAD) were 108.9% PAD and 99.3% CTV, respectively. The median D_0.1cm3 (mandible) was 3.2 Gy per fraction.

Conclusions: IG HDR-BT with custom-made surface applicators for lower lip cancer as monotherapy showed an excellent CTV dose and acceptable doses to the mandible, with good long-term clinical results.