ESTRO 2024 - Abstract Book

S304

Brachytherapy - Head & neck, skin, eye

ESTRO 2024

patients and reviewed the clinical outcomes in our practice. We also have developed a combination of IS and SC (IS+SC), to improve target coverage in part of the cases, and compared dosimetry with IS and SC techniques.

Material/Methods:

An interstitial (IS), surface custom mold (SC), or a combination of IS and SC applicator (IS + SC) was used for treatments based on the depth of tumor invasion. Clinical target volume (CTV) was determined by adding 1 cm to the initial visible lesion (gross tumor volume (GTV)). Brachytherapy prescription dose was 24 Gy in 6 fractions in addition to 45-50 Gy for EBRT. If brachytherapy was used as a monotherapy, 50 Gy in 10 fractions was prescribed. Interstitial technique was considered first because of conformal irradiated volume and treatment accuracy. Typically, 1 to 3 interstitial tubes have been evaluated as sufficient for the planned volume. Optimal spacing between tubes is 1.1-1.3 cm. During the evaluation and optimization (Fig.1) of the treatment plan, if adding one or more catheters superficially helped the dose distribution and coverage, one or two additional catheters were added for IS+SC. For tumors less than 5mm deep, SCs were created manually or 3D-printed and used for treatment. Since some implantations and applicator design were suboptimal, manual or inverse planning followed by graphical optimization was used to meet target coverage goal and OAR constraints. Target coverage parameters (CTV D90 and V100), hot spots (V150), and treated volume were obtained from each technique and compared with a paired t-test.

Fig. 1. Isodose distributions from HDR-BT (A), 3D view of the reconstruction of interstitial tubes (B)

Results:

A total of 33 cases of lip cancer from two institutions were treated from 2015 to 2021. The median age of the patients was 63 years (range, 42-85). Sixty percent of the patients were males, and forty percent were females. Three patients underwent immunosuppression after lung transplant. By using TNM staging classification, there were 14 stage I (42.4%), 15 stage II (45.5%), and 4 stage III (12.1%) lip cancers. Thirty-one patients (93.9%) had complete responses to treatment (Fig.2). Only 2 patients (6.1%) displayed local recurrences. Grade 1, 2, and 3 acute toxicities were observed in 30.3%, 51.5%, and 18.2% of patients, respectively. Grade 1, 2, and 3 late toxicities were observed in 39.4%, 21.2%, and 0.0% of cases. Cosmetic results were excellent in 21.2%, good in 54.5%, fair in 18.2%, and poor in 6.1% of patients. The median CTV volume was measured to be 5.8cc (2-19cc). Similar target coverages were achieved (V100 = 94.9±2.6% from IS+SC, 94.8±2.4% from IS (P=0.4), 94.8±2.5% from SC (P=0.7)).