There may be no threshold dose below which radiation to cardiac substructures does not increase the risk for later cardiac diseases in children with cancer.
Review of 25,481 patients in the Childhood Cancer Survivor Study who had no cardiac complications in the first 5 years following cancer treatment from 1970-1999; nearly half (48.2%) had been exposed to radiotherapy.
Radiation doses to the coronary arteries, heart chambers, heart valves, and whole heart were calculated based on radiotherapy records.
Median age at follow up was 29.8 years and ranged from 5.6 to 65.9 years.
Mean radiation doses of 5.0–9.9 Gy to the whole heart did not increase the risk for later cardiac disease.
Mean doses of 5.0–9.9 Gy to the right coronary artery (rate ratio [RR], 2.6) and left ventricle (RR, 2.2) did increase the risk for subsequent coronary artery disease.
Mean doses of 5.0–9.9 Gy to the tricuspid valve (RR, 5.5) and right ventricle (RR, 8.4) increased the risk for later valvular disease.
Linear modeling adequately described the dose-response relationship for many cardiac substructures, suggesting there is no threshold dose necessary for cardiac damage.
“These findings solidify the need to consider cardiac substructure doses in [pediatric] radiation treatment planning and in survivorship care. Future work to ascertain optimal cardiac dose constraints, especially in the era of highly conformal [radiotherapy] techniques such as [intensity-modulated radiotherapy] and proton therapy, remains critical,” the authors conclude.
The study was led by James Bates, MD, of Emory University, Atlanta, and published June 12 in the Journal of Clinical Oncology.
Chronic conditions were self-reported.
Current radiotherapy techniques are much more precise than in the decades when these cancer survivors were treated, allowing preferential sparing of various heart structures.
The study did not assess other treatments and lifestyle issues that may have affected heart health.
The work was funded by the National Cancer Institute. Investigators reported ties to Doximity, Abbott, Merck, Grail, and other companies.
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