Dosimetric Comparison of Intensity-Modulated Radiation Therapy via Breath Hold Technique and Proton Therapy With or Without Breath Hold for Mediastinal Lymphoma

Abstract

Treating patients affected with mediastinal lymphoma with radiation therapy (RT) has been associated with long-term late side effects. Deep inspiration breath-hold (BH) can result in significant dosimetric benefits to the heart and lung. We hypothesized that RT to the mediastinum with intensity modulated radiation therapy (IMRT) would be comparable to proton-free breathing (P-FB) plans but inferior to theoretical proton breath-hold (P-BH) plans in regards to dosimetry of organs at risk (OAR). Ten patients (including 5 females) that received mediastinal involved site RT with “butterfly” IMRT-BH and had 4D-CT treatment planning scans available were included. Female patients were positioned on a 15 degree inclined board for breast sparing. The Eclipse Treatment Planning System was used to generate two additional plans per patient (P-FB and P-BH), optimized to deliver 30.6 Gy or CGE in 17 fractions. We calculated total volume, mean dose, V30, V25, V15 and V5 for OAR including heart, left ventricle (LV), coronary arteries, lungs, and breasts. Comparisons were made using a non-parametric two tailed paired t test with a significant P value of < 0.05. All plans had to have comparable coverage of the PTV. Heart dose was not significantly different comparing IMRT-BH to P-FB, while P-BH significantly improved high and low doses to the heart (Table 1). There was a significant lower LV mean dose in favor of P-BH compared to IMRT-BH (1.0 Gy versus 3.3 Gy; P = 0.01). P-BH resulted in lower lung high and low doses compared to IMRT-BH and P-FB. Although lung V5 was significantly higher with IMRT-BH compared to both P-FB and P-BH, IMRT-BH significantly lowered the V30 and V25 (Table 1). In all plans, there were no statistically significant differences in mean dose, V30, V25, V15 or V5 for the left main/left anterior descending artery, right coronary artery, and bilateral breasts. Owing to its physical properties, proton RT can be advantageous for the treatment of lymphoma patients receiving RT to the mediastinum contingent on using deep inspiration BH technique; IMRT-BH was able to achieve comparable doses to the heart, breasts, and coronary arteries compared with P-FB plans.Tabled 1Abstract 130; Table 1OrganIMRT-BHP-FBP valueIMRT-BH vs. P-FBP-BHP valueIMRT-BH vs. P-BHP valueP-FB vs. P-BHLung Volume (cc)4369.62438.4.001 Mean Dose (Gy)861.9753.6.03664.7<.001.008 V306.810.8<.0018.7.004.001 V2513.916.2.00813.3.18.001 V2019.319.5.8616.4.001.001 V1524.523.4.4520.4.001.008 V540.533.8.00731.0<.001.03Heart Volume (cc)625.2653.1.23 Mean Dose (Gy)9.67.6.077.0.001.37 V3016.016.6.7415.0.43.32 V2521.719.9.5118.1.03.31 V1527.123.9.3522.1.02.35 V536.928.9.1026.8.004.36 Open table in a new tab