International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationAssociation Between Tangential Beam Treatment Parameters and Cardiac Abnormalities After Definitive Radiation Treatment for Left-Sided Breast Cancer
Introduction
Radiation treatment (RT) is an effective treatment modality for early-stage breast cancer, resulting in a two-thirds reduction in local cancer recurrence and a decrease in breast cancer deaths 1, 2. However, several long-term follow-up studies have demonstrated increased cardiovascular mortality among irradiated breast cancer patients 3, 4. In the most recent update of the Early Breast Cancer Trialists' Collaborative Group meta-analysis, RT compared with no RT was associated with excess mortality (rate ratio 1.3) from heart disease (3). Many of the trials included in this overview were composed of irradiated mastectomy patients, used older techniques such as Co60 or orthovoltage radiation, large fraction sizes, or anterior photon internal mammary node irradiation 5, 6, 7. As compared with older techniques, contemporary coplanar, megavoltage tangential beam RT results in a much smaller amount of radiation delivered to cardiovascular structures 8, 9, 10, 11, 12.
The clinical cardiac effects of modern RT for early-stage breast cancer are not fully quantified. Mortality by laterality studies with the Ontario and Swedish Cancer Registries and the Surveillance Epidemiology and End Results (SEER) database revealed an increased mortality from myocardial infarction and ischemic heart disease among irradiated patients with left-sided breast cancer as compared to similar patients with right-sided breast cancer 13, 14, 15. In contrast, several single-institution studies evaluating a smaller number of patients have not reported an increased cardiac mortality (16) or incidence of myocardial infarctions (17) among left vs. right-sided irradiated early-stage breast cancer patients. In addition, two SEER studies that analyzed patients treated after the early 1980s found no increased risk of cardiovascular mortality (4) or ischemic heart disease (15) among left-sided irradiated patients.
One method to evaluate the cardiac effects of RT for early-stage breast cancer is to study cardiac diagnostic test findings among left-sided irradiated patients. Recent studies have demonstrated that myocardial perfusion defects can result after adjuvant RT among patients with left-sided breast cancer 18, 19, 20, 21, 22, 23, 24. Evaluation of patient's dosimetry plans indicates that abnormal cardiac findings may be dose dependent and sensitive to RT parameters 10, 19, 20, 23, 24, 25. The long-term clinical significance of these cardiac test abnormalities, which indicate early cardiac damage, is uncertain, but potential adverse cardiac consequences may be avoidable with appropriate modification of RT parameters.
We have previously shown an increased rate of chest pain, coronary artery disease, and myocardial infarction among left- as compared to right-sided irradiated, early-stage breast conservation patients treated with conventional tangential beam RT 21, 22. In the present study, the findings from diagnostic studies of the heart among symptomatic patients who underwent RT for left-sided early-stage breast cancer are reported. The incidence of cardiac study abnormalities and the association of RT parameters with these abnormalities were evaluated. Also, the association between RT parameters and clinical cardiac diagnoses of coronary artery disease, myocardial infarction, and congestive heart failure among tested patients was assessed.
Section snippets
Methods and Materials
Institutional Review Board permission was granted for this study. The medical records of women with left-sided breast cancer treated with coplanar, megavoltage tangential beam RT for early-stage breast cancer at the Hospital of the University of Pennsylvania between 1977 and 1995 were retrospectively reviewed (n = 599). Patients excluded from analysis were those with less than 2 years of follow-up (n = 96), preexisting cardiac disease (n = 19), or internal mammary node irradiation (n = 68). Of
Incidence of cardiac diagnostic test abnormalities
A total of 62 patients had 84 diagnostic studies of the heart performed at a median time of 12 years post-RT (mean, 12 years; range, 2–24 years) for cardiovascular symptoms: 38 of 84 (45%) myocardial perfusion and 46 of 84 (55%) echocardiogram. Twenty-two patients underwent both myocardial perfusion imaging and echocardiography. Results from these tests showed consistent findings in both tests in 20 of these patients (either normal findings, findings consistent with coronary artery disease on
Discussion
We have previously demonstrated an increased risk of late cardiac morbidity in terms of chest pain, coronary artery disease, and myocardial infarction diagnosis among left vs. right-sided irradiated early-stage breast cancer patients treated with conventional tangential beam RT 21, 22. The present study found a higher incidence of cardiac diagnostic test abnormalities among early-stage breast cancer patients who received RT for left-sided disease than expected from the patients' cardiovascular
Conclusions
In this study, a higher than expected incidence of late cardiac diagnostic test abnormalities was found among symptomatic patients with left-sided breast cancer treated with conventional tangential beam RT. The majority of test abnormalities were localized to the left anterior descending coronary artery region, which is included within the portion of the heart potentially irradiated by tangential beams. Cardiac diagnostic test abnormalities, coronary artery disease, and congestive heart failure
Acknowledgments
The authors thank Ms. Elizabeth Patton for help with data management.
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Conflict of interest: none.
Presented in part at the 90th Annual Meeting of the Radiological Society of North America (RSNA), Chicago, IL, November 28–December 3, 2004.
Supported in part by a grant from The Breast Cancer Research Foundation and a research award from RSNA.