ESTRO 2024 - Abstract Book

S5972

RTT - Treatment planning, OAR and target definitions

ESTRO 2024

1448

Digital Poster

ESTRO versus RTOG atlases for breast radiation therapy: what impact on organs-at-risk ?

Wafaa Merssetti 1 , Nabila Sellal 1 , Mohamed sami Amraoui 1 , Lamiae Baztaoui 2 , Mohamed El hfid 1

1 University hospital mohammed 6, Radiotherapy, Tangier, Morocco. 2 University hospital mohammed 6, Physics, Tangier, Morocco

Purpose/Objective:

In the realm of advanced radiation therapy technologies, precision in defining target volumes stands as a pivotal stride in the planning of radiotherapy. International atlases have been drawn up for breast radiation therapy, such as ESTRO (European society for radiotherapy and oncology) and RTOG (radiation therapy oncology group) to standardize delineation of target volumes and reduce inconsistencies.

The aim of our study is to evaluate the delivered organ at risk (OAR) dose according to each atlas.

Material/Methods:

This comparative dosimetric analysis encompassed 50 patients undergoing treatment for left-sided breast cancer with indication for nodal irradiation at the radiotherapy department of university hospital Mohammed VI. Target volumes were delineated twice adhering to the guidelines provided by "RTOG" and "ESTRO". Two dosimetric plans were meticulously created for all patients using 3D conformal technique. The dosimetric data were extracted from dose volume histogram and compared for each plan.

Results:

The delineated target volumes following the RTOG guidelines were notably larger than those delineated by ESTRO (836.7+/-287.9 vs. 626.75+/-292.7 cm³, p < 0.001). In terms of target volume coverage, the average D95% was 41.88+/- 4.14 Gy for RTOG, compared to 46.19+/-3.39 for ESTRO and the D2% was 109.8+/-1.6% vs 108.44+/-0.8% respectively in RTOG and ESTRO. In assessing organ-at-risk constraints, the mean dose (Dmean) received by the heart was 4+/-0.83 Gy in the ESTRO group, contrasting with 4.63+/-0.71 Gy in the RTOG group. For the lungs, the average V20 and V30 were 26.7+/-2.43% and 23.1+/-2% in RTOG, respectively, and 25+/-1.51% and 21.2+/-1.54% in ESTRO (p<0.001). In the RTOG group, the Dmean received by the larynx was 2.13+/-1.12 Gy, whereas it was 1.16+/-1.54 Gy in ESTRO. The Dmoy to the thyroid was 8.3+/-4.2Gy in RTOG vs 2.5+/-1.9 in ESTRO (p<0.001).

Conclusion: