Dosimetric evaluation of the benefit of deep inspiration breath hold (DIBH) for locoregional irradiation of right breast cancer with volumetric modulated arctherapy (VMAT)

International audienceIntroduction:Right-lateralized cardiac substructures can be substantially exposed during right breastcancer (R-BC) radiotherapy. The cardiac benefit of deep inspiration breath hold (DIBH) is established incombination with volumetric modulated arctherapy (VMAT) for left breast cancer with regional nodeirradiation but is unknown for R-BC. This study evaluated the dosimetric benefit of DIBH for locore-gional irradiation of R-BC with VMAT.Material and Methods:All patients treated for R-BC with adjuvant locoregional DIBH-VMAT in theDepartment of Radiation Oncology of the Institut Curie (Paris, France) until December 2022 wereincluded, corresponding to 15 patients. FB- and DIBH-VMAT plans were compared both for a normo-fractionated regimen (50Gy/25fx) used for treatment and a replanned hypofractionated regimen(40Gy/15fx). Dose to the heart, cardiac substructures (sinoatrial node (SAN), atrio-ventricular node(AVN), right coronary artery, left anterior descending coronary artery, left ventricle), ipsilateral lung andliver were retrieved and compared.Results: Mean heart dose (MHD) was 3.33 Gy with FB vs. 3.10 Gy with DIBH on normofractionated plans (p¼0.489), and 2.58 Gy with FB vs. 2.41 Gy with DIBH on hypofractionated plan (p¼0.489). Thebenefit of DIBH was not significant for any cardiac substructure. The most exposed cardiac substruc-ture were the SAN (mean dose of 6.62 Gy for FB- and 5.64 Gy for DIBH-VMAT on normofractionatedplans) and the RCA (mean dose of 4.21 Gy for FB- and 4.06 Gy for DIBH-VMAT on normofractionatedplans). The maximum benefit was observed for the RCA with a median individual dose reduction of0.84 Gy on normofractionated plans (p¼0.599). No significant dosimetric difference were observed forright lung. Liver mean dose was significantly lower with DIBH with median values decreasing from2.54 Gy to 0.87 Gy (p¼0.01).Conclusion:Adding DIBH to efficient cardiac-sparing radiotherapy techniques, such as VMAT, is notjustified in the general case for locoregional R-BC irradiation. Specific R-BC patient subpopulationswho could benefit from additional DIBH combination with locoregional VMAT are yet to be identified