ESTRO 2023 - Abstract Book

S1782

Digital Posters

ESTRO 2023

Figure 2. Differences in R50 and D2cm for both systems

Conclusion For both systems, plan calculations provided substantially good results. Although R50 and D2cm values were seen to be more easily achievable in Eclipse, leading to more conformable plans, these had intrinsically more MU compared to Monaco. One of the main differences could be related to distinct Agility MLC segmentation algorithms between TPS.

PO-2009 Mono isocentric technique versus dual isocentric technique for breast cancer radiotherapy

N. Bouzid 1 , R. Zanzouri 2 , B. Amri 2 , M. Souissi 2 , S. Tbessi 2 , S. Belaajouza 2 , S. Tebra 2

1 Farhat Hached Hospital , Radiation Oncology Department, Sousse, Tunisia; 2 Farhat Hached Hospital, Radiation Oncology Department, Sousse, Tunisia Purpose or Objective To compare the dosimetry of the monoisocentric technique (MIT) and the dual isocentric technique (DIT) for adjuvant radiation in breast cancer. Materials and Methods A descriptive, analytical study carried out with 50 breast cancer patients after radical surgery, treated with hypofractionated locoregional radiotherapy (RT), delivering 40 Gy in 15 fractions over 3 weeks, using either the MIT (n=25) or the DIT (n=25), at the Radiation Oncology department of the Farhat Hached Hospital, Sousse, Tunisia between 2021 and 2022. Clinical history and therapeutic characteristics were collected. Techniques were compared according to dose volume histograms (DVHs) analysis in terms of PTV coverage and OARs (Organs at Risk) dose and volume parameters. Results The average age was 51.2 [29-75]. 54% of patients had right-sided tumours. The histopathological analysis showed Invasive Ductal Carcinoma in 92% of cases. All patients had a radical surgery, and 96% had axillary lymph nodes dissection and 4% had sentinel lymph node dissection. Chemotherapy was administered in the neoadjuvant and adjuvant setting in 30% and 64% of patients, respectively. Hormone therapy was prescribed in 78% of cases and Trastuzumab was indicated for 24% of cases. All patients recieved three-dimensional conformal RT of the chest wall, internal mammary chain and supra- and infraclavicular areas, without boost. According to the DVHs of the target volumes, the MIT provides better coverage of the chest wall with a significant increase in V95% (Median 97.2 for MIT and 88 for DIT ; p=0.001). However, no significant difference was found between the dose coverage of the internal mammary chain, the supra- and infraclavicular lymph nodes using the MIT and the DIT.

The maximum dose at the field junction was significantly higher with DIT compared to the MIT : Median Dmax was 45.2Gy