ESTRO 2024 - Abstract Book

S702

Clinical - Breast

ESTRO 2024

Included cases of BC that underwent adjuvant ultrahypofractionated WBI or PBI between March 2020 and June 2023, aged ≥ 65. Adjuvant chest wall irradiation patients were excluded.

Demographic details, disease characteristics and treatment-related parameters were collected. The optimal and mandatory constraints were analyzed for target-volume coverage (V95, V105 and V107) and organ-at-risk assessment (heart V5 and V25; ipsilateral lung V30), according to the Fast-Forward trial criteria. Inferential analysis was performed using IBM SPSS version 29, with a type I error of .05. Chi-square and Mann-Whitney tests were used for comparisons.

Results:

A total of 187 patients (1 male), with a median age of 71 years, were included, with a total of 188 breasts (1 patient underwent bilateral RT). Most tumors were located on the left breast (51.1%), and the luminal subtypes represented 73.9% of the cases. WBI was used in 158 cases (84.0%), DIBH in 96 (51.1%), lower axillary irradiation in 13 (6.9%). We retrieved dosimetric parameters in 149 patients. The optimal target volume dosimetric criteria was fulfilled in V95 on 137 cases (91.9%) and in V105 on 148 cases (99.3%). Heart dosimetric parameters V25 and the mandatory V30 criterion in the lung were met in all cases. With respect to acute effects, 107 cases (56.9%) experienced skin-related effects (grade < 2). The most frequent subacute effects were pigmentation and edema in 28 cases (14.9%) and 95.8% of the cases achieved good esthetic results. There is a statistically significant difference (p<.005) between the type of irradiation (WBI vs. PBI) and the target volume and organ -at-risk dosimetric parameters with PTV V105, heart V5 and V25 and lung V30, higher for WBI. Also, a significant difference was observed in dosimetric parameters when comparing DIBH vs. no DIBH, with PTV V95, V105, heart V5 higher for no-DIBH patients.

With regards to acute cutaneous effects no significant difference was observed in relation to dosimetric parameters.