ESTRO 2024 - Abstract Book

S306

Brachytherapy - Head & neck, skin, eye

ESTRO 2024

Basal Cell Carcinoma (BCC) and Cutaneous Squamous Cell Carcinoma (cSCC) are persistent challenges in oncology, often manifesting on the face (1). When surgical intervention is limited due to various reasons like patient refusal or anatomic constraints, alternative treatments are considered (2). High-Dose Rate (HDR) Interstitial Brachytherapy (iBT) is one such emerging modality, which involves the precise implantation of a radioactive source, such as Iridium-192, into tumor or peritumoral tissue. The objective of this study is to explore the outcomes and procedural details of HDR iBT in treating early-stage nasal BCC and cSCC at the Institut Godinot, thereby shedding light on its potential advantages and challenges.

Material/Methods:

Utilizing the MOSAIQ system, ten patients with nasal carcinoma underwent treatment with HDR iBT between May 2021 and February 2023. Flexible plastic implant tubes with a 6F diameter (Elekta, Sweden) were configured in single or multiple parallel rows, maintaining a catheter spacing of 7-10 mm. These tubes were subdermally implanted at a depth of at least 3 mm to minimize the risk of skin necrosis and other late toxicities. A margin of 7 10 mm around the tumor was included to account for potential microscopic invasion, adhering to GEC-ESTRO guidelines (3). To mitigate long-term septal risks, a non-piercing implantation method was predominantly employed. This involved a longitudinal positioning of catheters, ensuring nasal septum integrity (4). Radio-opaque buttons (6F diameter, Elekta, Sweden) secured catheters at each extremity before they were cut to the desired length. Subsequent to implantation, a dosimetric CT scan featuring 1 mm slices was executed. Oncentra Brachy v4.6 software (Elekta, Sweden) facilitated both the delineation and dosimetric planning phases. Post-importing CT images and outlining the Clinical Target Volume (CTV) and Organs at Risk (OARs), each implanted interstitial catheter was manually identified and modeled to establish the trajectory for the Iridium-192 radioactive source. The CTV was demarcated as the entire tissue span between fixation buttons. Eyes and mandible were the sole OARs considered. Treatment schedules entailed 9-10 fractions administered twice daily, at intervals of at least 6 hours, with each session lasting only a few minutes. Dosing varied from 40 to 45 Gy in 9-10 fractions, based on both GEC-ESTRO and ASTRO guidelines for skin and head and neck brachytherapy. The reference isodose was set at 90% of the prescribed dose. Aesthetic outcomes were gauged using the Global Aesthetic Improvement Scale (GAIS). Data were analyzed statistically with SPSS v29.0, and quantitative variables were expressed either as mean ± standard deviation or as median [range]. Qualitative metrics were presented in terms of numbers and percentages.

Results: