Risk of major cardiac events following adjuvant proton versus photon radiation therapy for patients with thymic malignancies.
BACKGROUND
While often managed with surgery alone, patients with thymic malignancies with high-risk features may benefit from adjuvant radiation therapy but are at risk for late toxicities. Previously, the risk of major cardiac events (MCEs) was reported to increase by 7% per one Gray (Gy) to the heart. In this study, we compare dose to organs at risk (OARs) with intensity-modulated (IMRT) versus proton beam therapy (PBT). We hypothesize a decrease risk of predicted MCEs with PBT.


METHODS
Patients requiring adjuvant therapy for thymic malignancies were treated with double scattered proton beam therapy (DS-PBT). Clinical backup IMRT plans were generated. Predicted MCEs were calculated based on median dose to the heart. A Wilcoxon rank sum test was used for statistical comparisons.


RESULTS
Twenty-two consecutive patients were evaluated. DS-PBT resulted in statistically significant decreases in dose to the heart, lungs, left ventricle, esophagus, and spinal cord (all p ≤ .01). The increase in risk of MCEs from 0 to ≥20 years was lower with PBT (74% versus 135%, p = .04).


CONCLUSIONS
DS-PBT results in decreased dose to OARs and may reduce the risk of MCEs compared with IMRT. Long-term follow-up is required to assess for clinical benefit from DS-PBT.
a Department of Radiation Oncology , Hospital of the University of Pennsylvania , Philadelphia , PA , USA.
Jennifer
J
Vogel
a Department of Radiation Oncology , Hospital of the University of Pennsylvania , Philadelphia , PA , USA.
Liyong
http://orcid.org/0000-0002-0820-8063
L
Lin
b Department of Radiation Oncology , University of Maryland Medical Center, Maryland Proton Treatment Center , Baltimore , MD , USA.
Charles B
CB
Simone
a Department of Radiation Oncology , Hospital of the University of Pennsylvania , Philadelphia , PA , USA.
Abigail T
AT
Berman
D000328:Adult; D000368:Aged; D005260:Female; D006331:Heart Diseases / Q000453:epidemiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D058958:Organs at Risk / Q000528:radiation effects; D015143:Philadelphia / Q000453:epidemiology; D015995:Prevalence; D011446:Prospective Studies; D061766:Proton Therapy / Q000379:methods*; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013953:Thymus Neoplasms / Q000532:radiotherapy*