ESTRO 2024 - Abstract Book

S6004

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

Adjuvant RT for women with early breast cancer was proven very effective in local cancer control and overall survival. With the evolution of techniques, there is no consensus on which technique is most suitable to treat breast cancer. 1

The objective of this study was to explore if there are better alternatives to the FiF technique (the current local gold standard in a single RT department) that is non-inferior to the current technique in concerning OAR sparing and target coverage. Four techniques were compared with FiF: IMRT, Hybrid-IMRT, VMAT and Hybrid-VMAT.

Material/Methods:

In this treatment planning study, five different treatment plans were generated using Eclipse TM treatment planning system version 15.6 (Varian Medical Systems, Palo Alto, CA). A small sample of five anonymized patients with early stage left breast tumours who provided consent was included in this feasibility study before the research team proceeds with a larger-sample study. The delineation of the CTV and OAR was based on the ESTRO guidelines. 2 The total prescription dose was 26Gy in five fractions of 5.2Gy each, delivered in one week. The dose constraints for OAR and upper and lower limits for PTV suggested in the FAST-FORWARD protocol, the conformity index, the planning time, and the beam-on time were collected and compared among the different techniques. 3 Wilcoxon matched-pair signed rank test (two-tailed, p<0.05) was used for statistical analysis.

Results:

The results are summarised in Table 1. This feasibility study indicates that some of the comparison techniques (IMRT, hybrid-IMRT, and hybrid-VMAT) show statistically significant improvements in OARs sparing without compromising the PTV coverage. Table 1. Mean values, standard deviations, and range of dosimetric parameters: from the FAST-FOWARD protocol, CI, D max , Planning Time and Beam-on Time. Bold values are the best values across all techniques for each parameter, while underlined values mean the worst. Mandatory objectives of the FAST-FOWARD protocol are presented between '( )' while the optimal ones appear between '[ ]'. Green highlighted cells correspond to statistically significantly better than FiF, while Red highlighted cells correspond to significantly worse.