Advantage of using deep inspiration breath hold with active breathing control and image-guided radiation therapy for patients treated with lung cancers

Purpose: The aim of this study was to evaluate the irradiated volume and doses to the target, heart, left lung, right lung and spinal cord, the number of segments and treatment time by using moderated deep inspiration breath hold (mDIBH) with active breathing control (ABC) and image-guided radiotherapy (IGRT) for patients treated with lung cancers. Methods: The suitability of this technique for lung patient treated with ABC was investigated and the solutions to achieve better treatments were discussed. Eleven lung cancer patients (3 left-sided and 8 right sided lesions) with stages I-III underwent standard free breath (FB) and ABC computed tomography (CT) scans in the treatment supine position. This can be achieved by applying respiratory manoeuvres, such as mDIBH, during which the threshold volume utilized is defined as 75-80% of the maximum aspiratory capacity. Five to seven, 6-MV photon beams with optimized gantry angles were designed according to the tumor location to conform to the PTV while sparing as much heart, spinal cord, and contra lateral lung as possible. For eleven patients, treatment planning using mDIBH CT data with intensity modulated radiation therapy (IMRT) was then reoptimized on the free breathing data set for comparison. The studied parameters of the plans for each patient were evaluated based on the average of the minimum, mean, and maximum difference in dose, the range of difference, and the p-value using two-tailed paired t test assuming equal variance. Results: The average volume of the planning target volume (PTV) in 11 patients increased to 1.32% in ABC compared to FB. The average volume of heart in 11 patients decreased to 2.9% in ABC compared to free breathing IMRT. In the case of lungs, the volume increased to 27.5% and 25.85% for left and right lungs, respectively. The range of mean difference in dose to the PTV in 11 patients was -54 cGy to 230 cGy with ABC technique when compared with free breathing. The range of mean dose difference of heart in 11 patients observed were -88 cGy to 66 cGy (p < 0.0410) between ABC and FB. The range of maximum dose difference to the spinal cord in 11 patients were -1592 cGy to 190 cGy (p < 0.041) with ABC technique when compared with FB IMRT. Monitor units (MUs) were -22.9% less in ABC compared to FB. Segments were more in ABC compared to FB for about 16.39% on an average. The average of minimum, mean and maximum difference in dose to the right lung and left lung were less in ABC compared with FB. Conclusion: In most of the cases, IGRT with ABC significantly reduces the mean dose to heart, right lung, left lung, and spinal cord compared with FB. Discrepancy observed in few cases made the statistical data inconsistent. Depending on anatomy and arbitrary phase of the breathing cycle, the results may vary and for better outcome of the results optimum treatment procedures need to follow.