Sparing of the Cardiac Valves and Left Ventricle using Proton Therapy with ECG-gated CT with Coronary Angiography for the Treatment of Mediastinal Lymphoma

Abstract

ECG-gated CT with coronary angiography (E-CTA) enables accurate delineation of cardiac substructures in time and space. We compared IMRT and IMPT to assess doses to the cardiac valves and left ventricle for patients treated with mediastinal radiation for lymphoma. Patients were prospectively enrolled in an institutional review board-approved, observational study. During simulation, patients underwent a CT scan using deep inspiratory breath hold and an E-CTA. A study-specific, multidisciplinary-designed, cardiac substructure contouring atlas was used to delineate the cardiac substructures in systole and diastole, which were then combined into PRVs. Target volumes were delineated using involved site radiotherapy. IMRT and IMPT plans were generated and normalized for 95% coverage of the CTV. Absolute differences between IMRT and IMPT plans were determined for V5-30Gy in increments of 5Gy and mean doses. Due to expected dose differences based on adenopathy site, each cardiac structure was analyzed independently. A paired T-test was used to compare differences between mean doses to substructures by modality. Twelve patients aged 14-53 years with lymphoma involving the mediastinum underwent comparative planning. The median prescription dose was 30 Gy in 15 fractions (r, 21-30 Gy). The median mean heart dose was 9.4Gy and 4.7 Gy for IMRT vs IMPT. The average mean, V5Gy, and V15 Gy to the left ventricle were all significantly less with IMPT. The average V25Gy was nearly significant as well (5.2 vs 2.8%, p=0.06). No individual patient had an increase in the dose to the LV with IMPT. The pulmonic valve was the only valve with a significant reduction in V30 Gy (27.2 vs 15.0%, p = 0.05). The majority of patients did not have any V30 Gy to the mitral or tricuspid valve with either modality. One patient did have an increase in the aortic valve V30 Gy by 10.6% with IMPT, and no significant benefit for the other valves with IMPT. The average mean dose to all valves was significantly lower IMPT. For patients with mediastinal lymphomas, IMPT reduced average doses to the left ventricle and cardiac valves when using E-CTA for cardiac substructure delineation.Abstract MO_20_2648; Table 1Substructure ParameterIMRT Mean (range)IMPT Mean (range)Paired T-TestLeft Ventricle Mean Dose [Gy]6.4 (0.6 – 14.6)2.1 (0.0 – 7.9)< 0.01 V5Gy [%]41.2 (0.0 – 91.9)10.8 (0.0 – 35.4)0.01 V15Gy [%]10.9 (0.0 – 32.3)5.2 (0.0 – 24.0)0.01 V25Gy [%]5.2 (0.0 - 26.1)2.8 (0.0 – 16.1)0.06Aortic Valve Mean Dose [Gy]16.1 (5.7 – 25.8)8.6 (0.8 – 17.2)<0.01 V30Gy [%]7.9 (0.0 – 36.9)3.6 (0.0 – 15.8)0.22Mitral Valve Mean Dose [Gy]10.5 (2.2 – 21.1)3.7 (0.0 – 10.6)< 0.01 V30Gy [%]3.1 (0.0 – 27.9)1.21 (0.0 – 12.2)0.20Pulmonic Valve Mean Dose [Gy]19.3 (8.0 – 30.1)14.1 (2.1 – 29.2)< 0.01 V30Gy [%]27.2 (0.0 – 71.5)15.0 (0.0-68.5)0.05Tricuspid Valve Mean Dose [Gy]8.6 (0.7 – 28.9)3.1 (0.0 – 20.2)< 0.01 V30Gy [%]6.5 (0.0 – 49.9)3.9 (0.0 – 39.0)0.18 Open table in a new tab