ESTRO 2024 - Abstract Book

S5996

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

2109

Digital Poster

Ultrahypofractionation in breast cancer: Retrospective study of dosimetry features

Daniela Saraiva, Raquel Rocha, Patrícia Varzim, Alice Alves, Gabriel Farinha, Armanda Monteiro, Catarina Dias, João Casalta Lopes, Pedro Meireles, Gabriela Pinto

Centro Hospitalar Universitário de São João, E.P.E., Radiotherapy, Porto, Portugal

Purpose/Objective:

Adjuvant radiotherapy is the standard of care for the treatment of early-stage breast cancer. Ultrahypofractionation represents a new paradigm after the results of the Fast-Forward trial emerged, demonstrating that 26 Gy in 5 fractions, ultrahypofractionation, is not inferior to 40 Gy in 15 fractions, moderate hypofractionation, with a five-year follow-up.

The main objective of this study is to assess the compliance of dosimetric features in patients with breast cancer that underwent ultrahypofractionated adjuvant radiotherapy at our department.

Material/Methods:

A retrospective study was conducted, including all breast cancer patients that underwent ultrahypofractionated adjuvant radiotherapy between March 2020 and June 2023. All patients proposed for whole-breast (WBI) and partial breast irradiation (PBI) were included; adjuvant chest wall irradiation patients were excluded from this analysis. Dosimetric features were analyzed for target-volume coverage (V95, V105 and V107) and organ-at-risk assessment (heart V5 and V25; ipsilateral lung V30). Optimal and mandatory constraints were defined according to the Fast Forward trial criteria. Statistical analysis was performed using IBM SPSS version 29. For descriptive purposes, mean±standard deviation were used for normally distributed quantitative variables; otherwise median and interquartile range were described. For qualitative variables, absolute and relative frequencies were used. For inferential analysis, Mann-Whitney tests were used to compare dosimetric parameters between groups (considering deep-inspiration breath-hold [DIBH] and WBI vs. PBI). For the comparison of compliance of optimal and mandatory constraints, Qui-square and Fisher’s exact tests were used, depending on the criteria of Cochran’s rule. A type I error of .05 was considered for all comparisons.

Results:

A total of 377 patients were included, 376 (99.7%) female, with a mean age of 60.8±11.7 years; three patients underwent bilateral breast irradiation, encompassing a total of 380 breasts. Most breast tumors presented on the left side (63.9%), with luminal subtypes encompassing 75.0%. WBI was performed in 337 cases (88.7%), with DIBH in 285 (75.0%), lower axillary irradiation in 28 (7.4%) and boost in 31 (8.2%), with doses ranging from 10Gy to 13.35Gy. Considering optimal target-volume dosimetric criteria, V95 was fulfilled in 348 (91.6%) plans and V105 was fulfilled in 379 (99.7%); mandatory criteria for target volume were met for all except one plan, where V105 was not accomplished. Heart dosimetric criteria were met for all except one plan (where V25 was not accomplished) and mandatory