Impact of Active Breathing Control-Deep Inspiration Breath Hold (ABC-DIBH) on the dose to surrounding normal structures in tangential field left breast radiotherapy

Background: Adjuvant radiotherapy after breast conserving surgery (BCS) is considered standard of care. For greater homogeneity of target dose and better normal tissue sparing, several radiotherapy modalities evolved. Therefore, we aimed to evaluate the organ-sparing potential of deep inspiration breath hold (DIBH) technique by comparing with the treatment plans among different respiratory phases based on the images retrieved from deep breathing 4D-CT. Methods: This retrospective study was conducted from August 2017 to February 2019, and included 14 patients with left-sided breast cancer who received adjuvant radiotherapy after BCS. Two sets of CT scans were performed, including 3D-CT images of DIBH with the active breathing control (ABC) device, and deep breathing 4D-CT images. We used tangential angle IMRT plans with four portals for treatment planning. Three plans were generated for each patient. One plan was based on the 3D-CT images of DIBH, and the others were based on the 4D-CT images of middle of lung expansion (MLE) and start of lung expansion (SLE). Adjuvant radiotherapy was prescribed with a total radiation dose of 50 Gy in 25 fractions. Results: The mean heart dose was 4.01 Gy in SLE, 3.76 Gy in MLE, and 2.72 Gy in DIBH (P<0.001). The plans with DIBH showed significantly lower dose for the heart, left ventricle (LV), left anterior descending coronary artery (LAD), and left lung when compared with the plans of either MLE or SLE images (P<0.05). Through inhalation cycle, the irradiated dose to heart and LV gradually decreased. There was no significant difference in right lung mean dose and V5right lung (P>0.05). Conclusions: For the adjuvant treatment of breast cancer, the use of DIBH technique resulted in a significant dose reduction in heart, LV, LAD, and left lung, especially with enough deep inhalation. Hence, the DIBH technique could be considered as a promising tool for normal organ sparing.