PD 08 - Hematologic 1 - Poster Discussion

1067 - Comparison of Radiation Techniques in Lower Mediastinal Lymphoma

Monday, October 22
4:39 PM - 4:45 PM
Location: Room 217 A/B

Comparison of Radiation Techniques in Lower Mediastinal Lymphoma
A. Everett1, S. Flampouri2, D. Louis2, A. M. McDonald1, N. P. Mendenhall3, Z. Li2, and B. S. Hoppe2,4; 1University of Alabama at Birmingham, Birmingham, AL, 2University of Florida Health Proton Therapy Institute, Jacksonville, FL, 3Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, 4Department of Radiation Oncology, University of Florida College of Medicine, Jacksonville, FL

Purpose/Objective(s): Intensity modulated radiation therapy (IMRT), deep inspiratory breath hold (DIBH) and proton therapy (PT) have been implemented to decrease radiation to organs at risk (OARs), and minimize late effects of treatment among patients with mediastinal lymphoma. Recent ILROG guidelines identified patients with disease extending below the left main stem artery (LM) as those who might benefit the most from PT. Yet, clinical data is lacking and the potential additional benefit with DIBH is unknown in the lower mediastinum. The aim of this study is to evaluate IMRT vs PT and free breathing (FB) vs DIBH among patients with lower mediastinal lymphoma.

Materials/Methods: After IRB approval, patients who underwent 4D-CT and 3 sequential DIBH scans (to assess reproducibility) at the time of simulation were retrospectively identified. For each patient, involved site radiation therapy (ISRT) target volumes and OAR contours were developed for both DIBH and 4DCT scans using pre-treatment PET-CT scans. An ITV was developed using all 10 phases of the 4DCT scan, or using the 3 sequential DIBH scans. The same patient specific PTV margin was used (5-8 mm). Plans were generated for FB IMRT, DIBH IMRT, FB PT, and DIBH PT (n=84). Dose volume histograms (DVH) for each technique were generated and compared.

Results: Twenty-two patients with mediastinal lymphoma treated with ISRT were identified. One patient with only disease above the LM was omitted from the analysis, while 21 had disease extending below the LM, including 12 with cardiophrenic (CP) nodes or extension of a bulky mass into the CP recess. The average difference in lung volume between the DIBH and FB scans was 1275 mL, while the average difference in CTV volume was 5 mL. Comparing IMRT plans, DIBH produced lower mean lung (10.7 vs 11.7 Gy), lung V5 (60% vs 65%), and lung V20 (20% vs 23%) compared to FB IMRT, but no difference in mean heart dose (15.2 vs 14.8 Gy). Either PT modality compared to DIBH IMRT produced substantially lower and statistically significant mean dose to lung, lung V5, heart, left ventricle (LV), esophagus, and non-target body. On average PT reduced the mean heart dose by 4.5 Gy (p<0.001); LV dose by 5.5 Gy (p<0.001); and lung V5 by 26% (p<0.001) compared with DIBH IMRT. PT reduced the breast dose by > 4 Gy in 3 patients, but no statistically significant difference in mean breast dose was detected among females (n=16). The two PT modalities were comparable, with DIBH PT producing reduced mean lung dose (7.6 vs 8.3 Gy; p=0.01), but no difference in mean heart dose (10.9 vs 10.8 Gy; p=0.7).

Conclusion: Among patients with lower mediastinal involvement, DIBH (IMRT or PT) improved lung dosimetry compared to FB slightly, but had little impact on mean heart dose. Proton therapy (DIBH and FB) significantly reduced dose to the lung, heart, esophagus, and non-target body compared with DIBH IMRT, potentially reducing the risk of late complications. Among patients with lower mediastinal involvement, utilization of PT (DIBH or FB) can provide significant benefit over DIBH IMRT.

Author Disclosure: A. Everett: None. S. Flampouri: None. D. Louis: None. A.M. McDonald: None. N.P. Mendenhall: None. Z. Li: None. B.S. Hoppe: Advisory Board; Proton Collaborative Group. Travel Expenses; Children Oncology Group. see below; Proton Collaborative Group. Co-Chair of RTOG 1308; RTOG. Member of the Lymphoma Sub-committee; American College of Radiology.

Ashlyn Everett, MD

No relationships to disclose.

Dr. Ashlyn Everett is currently a PGY-4 resident in the Department of Radiation Oncology at the University of Alabama at Birmingham (UAB). She earned her medical degree at UAB, and completed a transitional year internship at the Brookwood-Baptist Health System. Her clinical research interests include breast, lung, and lymphoma. Dr. Everett also serves on many departmental and hospital-wide committees for quality improvement and patient safety.


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