LAUSR

INTRODUCTION Patients with lower mediastinal lymphoma (LML) benefit dosimetrically from proton therapy (PT) compared with intensity-modulated radiotherapy (IMRT). The added dosimetric benefit of deep-inspiration breath-hold (DIBH) is unknown; therefore, we evaluated IMRT versus PT and free-breathing (FB) versus DIBH among patients with LML. MATERIALS AND METHODS Twenty-one patients with LML underwent 4-dimensional CT and 3 sequential DIBH scans at simulation. Involved-site radiotherapy (ISRT) target volumes and organ-at-risk contours were developed for both DIBH and FB scans. FB-IMRT, DIBH-IMRT, FB-PT, and DIBH-PT plans were generated for each patient for comparison. RESULTS The median difference in lung volume between the DIBH and FB scans was 1275mL; the average difference in CTV volume was 5.7mL. DIBH-IMRT produced a lower mean lung dose (10.8Gy vs 11.9Gy, p<0.001) than FB-IMRT, with no difference in mean heart dose (MHD; 16.1Gy vs 15.0Gy, p=0.992). Both PT plans produced a significantly lower mean dose to the lung, heart, left ventricle, esophagus, and non-target body than DIBH-IMRT. DIBH-PT reduced the median MHD by 4.2Gy (p<0.0001); left ventricle dose by 5.1Gy (p<0.0001); and lung V5 by 26% (p<0.0001) versus DIBH-IMRT. The two PT plans were comparable, with DIBH-PT reducing mean lung dose (7.0Gy vs 7.7Gy; p=0.063), with no difference in MHD (10.3Gy vs 9.5Gy; p=0.992). CONCLUSIONS Among patients with LML, DIBH (IMRT or PT) improved lung dosimetry over FB but had little impact on MHD. PT (DIBH and FB) significantly reduced lung, heart, esophagus, and non-target body dose compared with DIBH IMRT, potentially reducing the risk of late complications.