ESTRO 2024 - Abstract Book

S387

Beachytherapy - Physics

ESTRO 2024

Interventional radiotherapy (IRT), also referred to as brachytherapy, represents a highly effective treatment modality for non-melanoma skin cancer (NMSC) [1]. Traditionally, only NMSC lesions with a maximum depth of 5 mm were deemed suitable for contact IRT. However, based on findings from national surveys and recent recommendations, this criterion has evolved, and contact IRT can now be used for lesions exceeding 5 mm in thickness. The precise utilization of image guidance to determine lesion depth accurately during NMSC treatment is pivotal for delineating the clinical target volume (CTV) and averting unwarranted toxicity.

Material/Methods:

In this study, we employed a solid water phantom, and a CT scan was conducted with a slice thickness of 0.625 mm utilizing a GE Medical System Discovery CT590RT CT scanner. The Oncentra Brachy treatment planning system (TPS v.4.6.2 Elekta, Sweden) was employed for contouring and planning both organs at risk (OARs) and the clinical target volume (CTV). Traditionally, the "therapeutic window" (TW) denotes the space between achieving tumor control and encountering adverse events in a clinical context. In the context of skin IRT, tumor control closely hinges on achieving comprehensive coverage with the 100% isoline (dose prescription) while restraining the maximum isoline to avert toxicity [1][2]. Several studies have reported the maximum isoline reaching as high as 150%, as illustrated in Figure 1A-1B

Consequently, in this report, we characterize the TW as the gap between the 100% and the 150% isoline. We use, also, the multilayer arrangement for 4 NMSC patients in head and neck region in Figure 1D, previously treated with a single flap setting. The coverage of CTV and the percentage of high dose isodose in skin was evaluated.