Leukemia/Lymphoma/Hematologic

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

176 - The Relationship of Mean Heart Dose and Cardiac Substructure Dose over Evolving Radiation Techniques in Mediastinal Lymphoma

Tuesday, October 23
1:10 PM - 1:20 PM
Location: Room 004

The Relationship of Mean Heart Dose and Cardiac Substructure Dose over Evolving Radiation Techniques in Mediastinal Lymphoma
B. S. Hoppe1, J. E. Bates2, N. P. Mendenhall2, R. T. Hoppe3, C. G. Morris4, Z. Li4, and S. Flampouri4; 1Department of Radiation Oncology, University of Florida College of Medicine, Jacksonville, FL, 2Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, 3Stanford University School of Medicine, Stanford, CA, 4University of Florida Health Proton Therapy Institute, Jacksonville, FL

Purpose/Objective(s): Our understanding of the relationship between cardiac morbidity and mean heart dose among survivors of mediastinal lymphoma (mHL) dates back to the use of standard large-field 2D techniques. Over time, RT treatment in mHL has evolved with smaller, more personalized radiation fields and more conformal techniques, like 3D conformal RT (3D), intensity-modulated RT (IMRT), and proton therapy (PT). We investigated the relationship between mean heart dose and cardiac substructures across treatment fields and delivery techniques.

Materials/Methods: We retrospectively developed IFRT (n=37) plans among selected patients with mHL treated with involved-site radiation therapy (ISRT) between 2008 and 2017. Doses to the cardiac substructures were exported to a dosimetric database of ISRT plans for mHL, including 3D (n=25), IMRT (n=28), and PT (n=36). The structures included the heart, left anterior descending artery (LAD), mitral valve (MV), tricuspid valve (TV), aortic valve (AV), left and right ventricles (LV, RV), and left and right atriam (LA, RAPlans were scaled to a prescription dose of 30 Gy and the mean heart dose was evaluated for correlation (R2) and slope (beta) of the relationship with mean dose to the cardiac substructures.

Results: The table reports the correlation coefficient (R2) and slope for the relationships between mean heart dose and mean cardiac substructure dose, demonstrating less correlation with increasingly conformal delivery. A strong correlation (R2≥70%) was seen for IFRT with RV, LV, and LAD; for 3D with RV and LV; and for IMRT with RV and LV. No strong correlation was observed for PT. When evaluating the slope (beta) for a relationship between mean heart dose and mean LAD dose, the slope was steepest for IFRT (1.86) and PT (1.69) compared to IMRT (1.36) and 3D (1.14), suggesting that a lower mean heart dose can be associated in some instances with a higher mean LAD dose with IFRT and PT compared to IMRT or 3D RT. For the LV, the slope was steepest for IFRT (2.07) followed by 3D (1.25), IMRT (1.17), and then PT (0.98).

Conclusion: The relationship between mean heart dose and mean substructure dose changes with increasingly conformal techniques. Calculating mean heart dose as a surrogate for cardiac risk is no longer sufficient. Contouring the cardiac substructures, especially the LAD and LV, is important in understanding the late cardiac risks in the modern era of RT.
IFRT 3DCRT IMRT PROTONS
Structure Rho BETA Rho BETA Rho BETA Rho BETA
Name (R2) (Slope) (R2) (Slope) (R2) (Slope) (R2) (Slope)
Aortic Valve 6% 0.07 7% 0.10 35% 0.71 43% 1.47
Left Atrium 48% 0.29 65% 0.54 53% 0.84 44% 1.41
Right Atrium 11% 0.10 34% 0.92 36% 0.87 26% 0.85
Left Ant. Desc. art 76% 1.86 62% 1.14 60% 1.36 52% 1.69
Mitral Valve 50% 0.72 52% 0.61 38% 0.82 37% 1.34
Tricuspid Valve 5% 0.08 50% 1.22 43% 0.96 16% 0.51
Left Ventricle 95% 2.07 72% 1.25 74% 1.17 61% 0.98
Right Ventricle 80% 0.90 85% 1.13 81% 1.09 37% 0.79

Author Disclosure: 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. J.E. Bates: None. N.P. Mendenhall: None. R.T. Hoppe: Employee; Stanford University. Honoraria; NCCN. Board Member; ISCL. C.G. Morris: None. Z. Li: None. S. Flampouri: None.

Bradford Hoppe, MD, MPH

Disclosure:
Employment
University of Florida: Associate Professor: Employee

Compensation
Children Oncology Group: Travel Expenses; NRG: Research Grants; Proton Collaborative Group: Advisory Board

Leadership
American College of Radiology: Member of the Lymphoma Sub-committee; Proton Collaborative Group: Secretary, see below; RTOG: Co-Chair of RTOG 1308

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