Intensity modulated radiotherapy (IMRT) for breast and lymph node irradiation

Background:Since 2009, the use of IMRT for the treatment of breast cancer with lymph node involvement has been considerably growing at our institution. Helical Tomotherapy (HT) was chosen as main technique using field width of 2.5 cm (HT_FW_2.5). Alternatively HT using field width of 5 cm (HT_FW_5), Volumetric Modulated Arc Therapy (VMAT), or Proton Therapy with Pencil Beam Scanning (PT-PBS) were used to reduce treatment duration or optimize organs at risk (OAR) sparing. Purpose: the aim of this study is to compare the 4 modalities of treatment available at our site. Patients and methods: We studied 10 patients treated for breast cancer with lymph node involvement. The prescribed dose was 51.8 Gy to breast with simultaneous integrated boost till 63 Gy, 50.4 Gy to the lymph nodes in 28 fractions for all studied patients. The CTV (clinical target volume) were delineated using ESTRO Guidelines. Dosimetric plan used in routine clinical practice was done using HT_FW_2.5. Clinical plan approved was compared to the plan using the 3 others IMRT techniques. Dosimetric parameters were noted down. For Planning Target Volume (PTV) coverage, dosimetric goals were D95% ≥ 95% and D2% ≤ 107% of the prescribed dose. Regarding OAR, mean dose were noted for heart, contralateral/ipsilateral lung and contralateral breast. Maximum dose in the spinal cord was also recorded. Dosimetric score was made to evaluate plan quality. For both PTV score (PTVs) and OAR score (OARs), 1 was the best and 4 the worst achievable score. Results:HT_FW_5 and VMAT plans ensure an equivalent or even better PTV coverage than the initial clinically approved plan (PTVs = 2.3 and 2.0 VS 2.5) but at the cost of a deterioration of OAR sparing (OARs = 3.3 and 3.2 VS 2.3). PT_PBS plans show that an excellent PTV coverage can be maintained with significantly lower doses to OAR (PTVs = 2.0; OARs = 1.1) Conclusion:HT_FW_5 and VMAT plans allow significantly reducing treatment duration and can be good alternative to HT_FW_2.5 for specified population which has already a good OAR sparing and needs to reduce treatment duration. HT_FW_2.5 could be chosen for patient with higher risk of side effect. In addition PT_PBS treatment should be considered in the near future as it showed great potential benefit to lower the risk of side effects without deteriorating PTV coverage. Citation Format: Wassim El Amine, Laurent Bartolucci, Camille Adrien, Marie Lejars, Alain Fourquet, Marion Vaillant, Magalie Robilliard, Emilie Costa, Alejandro Mazal, Farid Goudjil, Youlia Kirova. Intensity modulated radiotherapy (IMRT) for breast and lymph node irradiation [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-12-32.