Dosimetric and clinical advantages of adapting the DIBH technique to hybrid solitary dynamic portal radiotherapy for left-sided chest-wall plus regional nodal irradiation.

To evaluate the dosimetric and clinical advantages of using deep-inspiration breath-hold (DIBH) technique in hybrid solitary dynamic portal radiotherapy (hSDPRT) for left-sided chest-wall plus regional nodal irradiation and to demonstrate a simplified strategy for preclinical commissioning and calibration of DIBH-gating technique. Fifteen patients with left-sided breast cancer who underwent postmastectomy radiotherapy using hSDPRT were retrospectively evaluated. Two sets of planning-CT images were acquired for each patient, one with free/normal breathing and the other with DIBH. The hSDPRT plans were computed to deliver about 85% of the prescribed dose using static open fields and 15% of dose using a less complex solitary dynamic field. The dosimetric differences between the paired samples were compared using the Wilcoxon signed-rank test. For clinical commissioning of gated treatments, a respiratory simulator equipped with a microcontroller was programmed to simulate free-breathing and DIBH-patterns using a custom-developed android application. While both the hSDPRT plans displayed identical target coverage on both the image-sets, the DIBH technique resulted in statistically significant differences in various dose-volume metrics of heart, left-anterior-descending artery, and ipsilateral-lung structures. The hSDPRT plan with DIBH entails reduced total monitor unit (354.9 ± 13.6 MU) and breath-hold time ranging from 2.9 ± 0.3 to 13.7 ± 0.8 seconds/field, along with an acceptable impact on overall machine throughput. DIBH is a feasible method to effectively address the delivery uncertainty and produce substantial sparing of heart and lung when combined with hSDPRT. Streamlined procedures for commissioning and calibration of DIBH-gating technique are essential for more efficient clinical practice.