Prospective Dosimetric Analysis of the Impact of Prone Positioning with Deep Inspiration Breath Hold in the Treatment of Left Sided Breast Cancers with Radiation

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Treatment of left sided breast cancer has always presented a challenge due to concerns regarding the delivery of significant radiation doses to cardiac structures. Attempts to reduce cardiac doses have included prone patient positioning and using deep inspiratory breath hold (DIBH). Although prone positioning and DIBH techniques have independently shown to reduce radiation doses to cardiac structures, whether the combination of these modalities provides a further dose reduction is yet to be determined. The aim of this study was to prospectively assess the radiation doses to the heart, left anterior descending artery (LAD), and lungs, in patients treated in the prone position with free breathing (FB) vs. those treated in the prone position with DIBH to determine whether the combined modality leads to a more favorable dosimetric profile. We enrolled 25 patients with early stage, left sided breast cancer in this prospective analysis. All patients underwent FB and DIBH CT simulation scans in the prone position. Heart, lungs, and LAD were contoured on both CT simulation scans and two separate treatment plans were created. The mean heart, LAD, ipsilateral lung, and the total lung doses were recorded. Ultimately, all patients were treated in the prone FB position and the prone DIBH scans were simply used for dosimetric comparisons. Two tailed paired T-tests were performed to compare the dose values of lung and cardiac structures between the two modalities. All patients tolerated the prone position in combination with DIBH without difficulty. The mean total lung dose was slightly higher at 0.10 Gy in the prone DIBH patients in comparison to 0.08 Gy in the prone FB patients. The mean ipsilateral lung dose was slightly lower at 0.09 Gy in the prone FB patients vs. 0.166 in the prone DIBH group. Despite these small variations, lung doses did not differ significantly between the two patient cohorts. Interestingly, the mean heart dose was significantly lower at 0.48 Gy in the prone DIBH group compared to 0.56 Gy in the prone FB group (p = 0. 02). Similarly, the mean LAD dose was significantly lower at 2.80 Gy in the prone DIBH group vs. 6.30 Gy in the prone FB cohort (p = 0.04). The heart dose was reduced by 14% and LAD dose was reduced by 56% through the use of prone DIBH positioning. Our preliminary work indicates that the treatment of left sided breast cancer with prone DIBH positioning leads to a significant decrease in the heart and LAD doses in comparison to prone positioning with free breathing. Additionally, prone DIBH is well tolerated and does not appear to impact lung doses significantly. Although further studies are needed to determine whether this favorable dosimetry translates to a clinical benefit, our results suggest that prone DIBH positioning should be considered in the treatment of left sided breast cancer.