Leukemia/Lymphoma/Hematologic

SS 25 - Hematologic 2 - Translating Better Technology to Reduced Toxicity

177 - A Comparison of Proton and X-ray Therapy for Coronary Artery Sparing Using ECG-gated CT With Coronary Angiography for Mediastinal Lymphoma

Tuesday, October 23
1:20 PM - 1:30 PM
Location: Room 004

A Comparison of Proton and X-ray Therapy for Coronary Artery Sparing Using ECG-gated CT With Coronary Angiography for Mediastinal Lymphoma
K. Taparra1, S. C. Lester2, A. Hunzeker2, R. K. Funk2, M. Blanchard2, P. Young3, J. Herrmann4, A. Tasson2, S. Leng3, J. A. Martenson2, T. J. Whitaker2, E. E. Williamson3, and N. N. Laack II2; 1Mayo Clinic School of Medicine, Mayo Clinic, Rochester, MN, 2Department of Radiation Oncology, Mayo Clinic, Rochester, MN, 3Department of Diagnostic Radiology, Mayo Clinic, Rochester, MN, 4Department of Cardiology, Mayo Clinic, Rochester, MN

Purpose/Objective(s): We previously showed ECG-gated CT with coronary angiography (E-CTA) enables accurate delineation of coronary arteries to reduce dose with intensity modulated radiation therapy (IMRT). In this study, we expanded on our E-CTA analysis to compare maximal coronary-sparing with IMRT to pencil beam scanning proton therapy (PBT) in mediastinal lymphomas treatment.

Materials/Methods: Patients were prospectively enrolled in an IRB-approved, observational study. During simulation, each patient underwent a CT scan using deep inspiratory breath hold and an E-CTA. A study-specific, multidisciplinary-designed contouring atlas was used to delineate the left anterior descending (LAD), left circumflex (LCX), and right coronary arteries (RCA) in systole and diastole, then combined into PRVs. Target volumes were delineated using ISRT. IMRT and PBT plans were generated and normalized for 95% coverage of the CTV. Treatment plan selection was at the discretion of the treating physician. Absolute differences between IMRT and PBT plans were determined for V5-30Gy in increments of 5Gy. Due to expected dose differences based on adenopathy site, each vessel was analyzed independently. A dose difference of ≥10% for V15Gy of and/or ≥5% for V30Gy was considered to be potentially clinically impactful.

Results: 12 patients aged 14-53 years with stage IIA-IVB Hodgkin (n=10) or primary mediastinal B cell lymphoma (n =2) have undergone comparative planning. Median prescription dose and fractionation were 30 Gy in 15 fractions (r, 21-30 Gy in 14-15 fractions). The median mean heart dose was 9.4 vs 4.7 Gy (r, 2.6 - 18.8 Gy vs 0.9-13.5 Gy) for IMRT E-CTA vs PBT E-CTA. The number of patients who had a V15Gy with IMRT that met criteria for comparison and were included for analysis for LAD, RCA, and LCX were 7 of 12 (r, 31.5 – 95.1%), 6 of 12 (r, 28.4 – 100%), and 7 of 12 (r, 13.5 – 100%), respectively. Of these patients, PBT E-CTA led to a V15Gy median absolute reduction for LAD, RCA, and LCX of 10.7% (r, -1.2 – 66.0%), 9.8% (r, -0.2 – 57.7%), 8.3% (r, 0.0 – 47.8%), respectively. 3 patients had LAD V15Gy reductions of 28, 46, 66%, all with disease predominantly anterior and medial to the LAD. 1 patient had a RCA V15Gy reduction of 57% with disease predominantly anterior and medial to the RCA. The max increase in V15Gy to any coronary artery with PBT was 1.2%, occurring in the same patient who had a 57% reduction in RCA V15Gy. 5 patients had possibly clinically significant reductions in V30Gy to at least 1 coronary artery, including 3 arteries reduced by 20-45%. In general, patients with the max reductions had disease near the target volumes. Overall, 10 of 12 (83%) patients had ≥1 coronary artery achieve a potentially clinically impactful dose reduction.

Conclusion: For patients with mediastinal lymphomas, PBT provided additional coronary artery-sparing compared to IMRT, while also reducing mean heart dose.

Author Disclosure: K. Taparra: None. S.C. Lester: Employee; Mayo Clinic. A. Hunzeker: None. R.K. Funk: None. M. Blanchard: None. P. Young: None. S. Leng: None. J.A. Martenson: None. T.J. Whitaker: None. E.E. Williamson: None. N.N. Laack: Research Grant; Bristol Myers Squibb. Vice Chair, Bone Committee; Children's Oncology Group.

Kekoa Taparra, PhD

Disclosure:
No relationships to disclose.

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