ESTRO 2022 - Abstract Book

S1345

Abstract book

ESTRO 2022

The following table summarizes the data of the cumulative doses in the brachial plexus:

At twelve months after the end of the radiotherapy, fourteen patients (34.14%) reported a radiation-induced brachial plexitis (grade 2 in 13 cases and grade 3 in only one case). For all these patients, the Dmax was > 40 Gy and the Dmean > 30 Gy. Conclusion The radiation-induced brachial plexitis is one of the most underestimated complications in the locoregional treatment of localized breast cancers. In the absence of radiation-induced plexitis prevention guidelines, we propose a systematic delineation of the brachial plexus in case of locoregional breast cancer irradiation in order to minimize as much as possible the cumulative doses at its level. The results of this study show that these constraints could be reasonable to respect during dosimetric optimization: Dmoy £30 Gy, Dmax £40 Gy and V41 £23%. However, these results should to be confirmed by larger series.

PO-1563 What are the oesophagus dosimetric constraints during breast cancer hypofractionated radiotherapy?

F. Dhouib 1 , M. Frikha 2 , N. Fourati 3 , Z. Fessi 3 , L. Farhat 3 , W. Mnejja 3 , J. Daoud 3

1 Habib Bourguiba University Hospital, oncology-radiotherapy, Sfax, Tunisia; 2 Habib Bourguiba University Hospital, oncology-Radiotherapy, Sfax, Tunisia; 3 Habib Bourguiba University Hospital, Oncology-radiotherapy, Sfax, Tunisia Purpose or Objective Hypofractionated radiotherapy (HRT) is becoming a valid option in the treatment of breast cancer. However, data are missing concerning the normal tissues dosimetric constraints. The purpose of this study is to evaluate the cumulative doses in the oesophagus during HRT for breast cancer with a clinical toxicities correlation in order to propose dosimetric constraints adapted to this type of fractionation. Materials and Methods This is a retrospective study analyzing the dosimetric plans of 41 patients treated with adjuvant locoregional (LR) radiotherapy for localized breast cancer between January and December 2020. The treatment plan was carried out according to a three dimensional (3D) conformational technique. The total dose prescribed was 42.5 Gy in 16 fractions with a boost of 10 Gy in 4 fractions in the tumor bed in case of a conservative treatment (35%) and 40 Gy in 15 fractions in case of a radical treatment (65%) at a rate of 5 fractions per week. The whole esophagus was delineated. By analyzing the dose- volume histogram, we retrospectively recorded the mean dose (Dmean), the maximum dose (Dmax), the volume receiving more than: 17 Gy (V17) , 30 Gy (V30) and 35 Gy (V35). These dosimetric constraint levels were defined by calculating the biological equivalent dose. Clinical assessment of esophageal toxicity was performed at the end of the radiotherapy sessions and 6 months later, using a questionnaire based on the RTOG clinical scales. Data analysis was performed by SPSS version 20. Results The median of Dmean, Dmax, V17, V30, and V35 were respectively of 4.14Gy [0.8-12.85], 37Gy [2.5-43], 8% [0-33.87], 2.2% [0-25.7] and 0.02% [0-18.26] . The 3 rd quartile (Q3) of Dmean, Dmax, V17, V30 and V35 were respectively of 7.3 Gy, 39 Gy, 18.3%, 9% and 2.7%. The following table summarizes the data of the cumulative doses in the oesophagus:

At the end of radiotherapy sessions, seven patients (17.07%) have reported a radiation-induced esophagitis (garde 1 in 6 cases and grade 2 in only one case). Of these seven patients, the Dmax in the oesophagus was > 35 Gy in 6 cases and > 38 Gy in 5 cases. At six months after the end of the radiotherapy, no patient had clinical signs of esophagitis. Conclusion Radiation-induced esophagitis is one of the most underestimated complications in locoregional treatment of localized breast cancers. In the absence of radiation-induced esophagitis prevention guidelines, we propose a systematic delineation of the whole esophagus in case of LR HRT in order to minimize as much as possible the cumulative doses at its level. The results of this study show that these constraints could be reasonable to respect during dosimetric optimization: Dmean <= 8 Gy, Dmax <= 38 Gy, V17 <= 19% and V30 <= 9%. However, these results should to be confirmed by larger series.