Coronary arteriosclerosis and atherosclerosis in fast neutron or photon irradiated dogs

Coronary Artery Stenosis following Mediastinal Radiation Therapy. Case Report and Review of the Literature

A case of coronary artery stenosis following mediastinal radiation therapy in a young woman and a review of the literature offer indications on the criteria to follow in the diagnosis of coronary artery disease secondary to mediastinal radiation therapy.

Cardiac complications of thoracic irradiation

Adjuvant radiation therapy in the management of early stage breast cancer, Hodgkin's disease, and to a lesser extent other thoracic malignancies has led to a significant improvement in disease-specific survival. Cardiovascular disease is now the most common nonmalignancy cause of death in radiation-treated cancer survivors, most often occurring decades after treatment. The spectrum of radiation-induced cardiac disease is broad, potentially involving any component of the heart. The relative risk of coronary artery disease, congestive heart failure, valvular heart disease, pericardial disease, conduction abnormalities, and sudden cardiac death is particularly increased. Over the years contemporary techniques have been introduced to reduce cardiac morbidity and mortality in radiation-treated cancer survivors; however, the long-term effects on the heart still remain unclear, mandating longer follow-up. Awareness and early identification of potential cardiac complications is crucial in cancer survivors, with the management often being quite complex. This review examines the epidemiology of radiation-induced cardiac disease together with its pathophysiology and explores the available treatment strategies and the potential utility of various screening strategies for affected cancer survivors.

Cardioprotective radiotherapy: the circadian way

Radiotherapy (RT) has been established to improve both local control as well as overall survival rates in breast cancer. However, RT especially in left-sided breast cancer also irradiates a portion of the heart. Radiation associated toxicity to the heart assumes significance because of improval in survival of breast cancer patients. A circadian pattern has been reported in the myocardial oxygen demand and myocardial ischaemia with the cardiac tissue being more susceptible to injury between 6 am and noon. Radiation damages blood vessels of all sizes causing an increase in capillary wall permeability and dilatation of vessels leading to the characteristic radiation erythema followed by an inflammatory cell infiltrate. Coronary artery spasm may be the reason behind some cases of sudden death occurring in patients after radiation therapy. Endothelial behaviour also has a circadian variation and vasodilation is significantly attenuated in the morning. Critical coronary artery disease occurs 10-15 years after radiotherapy. Radiation in the morning hours may be one of the associated risk factor. The application of chrono-therapeutics with radiation therapy in carcinoma breast and in other chest wall irradiation, could possibly decrease the radiation associated cardiac toxicity.

A population-based case-cohort study of the risk of myocardial infarction following radiation therapy for breast cancer

OBJECTIVE

To describe the risk of acute myocardial infarction (AMI) after radiation therapy (RT) for breast cancer (BrCa) in an exposed population.

METHODS

We identified and validated cases of AMI (vAMI), by electrocardiographic or enzyme criteria, among all 6680 women who received post-operative RT following lumpectomy or mastectomy, within 12 months following diagnosis of BrCa between 1982 and 1988 in Ontario, Canada. We identified women without vAMI whose death certification was ascribed to AMI (dAMI). We abstracted risk factors and treatment exposures for a random sample of women from the 6680, and for all with vAMI or dAMI. The hazards of vAMI and of dAMI were estimated using multivariate Cox proportional hazards models, corrected for study design.

RESULTS

We validated 121 cases of vAMI and identified 92 cases of dAMI. The risk of vAMI associated with RT to the left breast HR=1.96 (1.09,3.54) among women at age >/= 60 at time of RT, adjusted for history of smoking and prior MI. The adjusted HR dAMI=1.90 (1.08,3.35) for exposure to anterior internal mammary node (IMC) RT. Among women who received anterior left breast boost RT, increasing area of the boost is associated with adjusted HR vAMI=1.02 (1.00,1.03)/cm(2), and adjusted HR dAMI=1.02 (1.01,1.03)/cm(2).

CONCLUSION

The risks of vAMI and dAMI following RT for BrCa are related to anatomic sites of RT (left breast, area of anterior left breast boost field, and anterior IMC field).

Cardiac Morbidity of Adjuvant Radiotherapy for Breast Cancer

Purpose

Adjuvant breast irradiation has been associated with an increase in cardiac mortality, because left-sided breast radiation can produce cardiac damage. The purpose of this study was to determine whether modern adjuvant radiotherapy is associated with increased risk of cardiac morbidity.

Patients and Methods

Data from the Surveillance, Epidemiology, and End Results–Medicare database were used for women who were diagnosed with nonmetastatic breast cancer from 1986 to 1993, had known disease laterality, underwent breast surgery, and received adjuvant radiotherapy. The Cox proportional-hazards model was used to compare patients with left- versus right-sided breast cancer for the end points of hospitalization with the following discharge diagnoses (International Classification of Diseases, 9th Revision codes): ischemic heart disease (410-414, 36.0, and 36.1), valvular heart disease (394-397, 424, 35), congestive heart failure (428, 402.01, 402.11, 402.91, and 425), and conduction abnormalities (426, 427, 37.7-37.8, and 37.94-37.99).

Results

Eight thousand three hundred sixty-three patients had left-sided breast cancer, and 7,907 had right-sided breast cancer. Mean follow-up was 9.5 years (range, 0 to 15 years). There were no significant differences in patients with left- versus right-sided cancers for hospitalization for ischemic heart disease (9.9% v 9.7%), valvular heart disease (2.9% v 2.8%), conduction abnormalities (9.7% v 9.6%), or heart failure (9.7% v 9.7%). The adjusted hazard ratio for left- versus right-sided breast cancer was 1.05 (95% CI, 0.94 to 1.16) for ischemic heart disease, 1.07 (95% CI, 0.89 to 1.30) for valvular heart disease, 1.07 (95% CI, 0.96 to 1.19) for conduction abnormalities, and 1.05 (95% CI, 0.95 to 1.17) for heart failure.

Conclusion

With up to 15 years of follow-up there were no significant differences in cardiac morbidity after radiation for left- versus right-sided breast cancer.

Pathology of radiation and anthracycline cardiotoxicity

Radiation-induced heart disease (RIHD) and anthracycline cardiotoxicity are two patterns of cardiac dysfunction caused by therapeutic interventions to treat malignancies. They occur in both the pediatric and adult populations and there is evidence to suggest that pediatric patients are at greater risk. This is due in part to the longer survival rates but also reflects increased susceptibility to the attendant complications caused by both therapies. Radiation can cause injury to all the components of the heart, including the vasculature, while anthracycline toxicity is generally limited to the myocardium.

Radiation-associated cardiovascular disease

As the number of cancer survivors grows because of advances in therapy, it has become more important to understand the long-term complications of these treatments. This article presents the current knowledge of adverse cardiovascular effects of radiotherapy to the chest. Emphasis is on clinical presentations, recommendations for follow-up, and treatment of patients previously exposed to irradiation. Medline literature searches were performed, and abstracts related to this topic from oncology and cardiology meetings were reviewed. Potential adverse effects of mediastinal irradiation are numerous and can include coronary artery disease, pericarditis, cardiomyopathy, valvular disease and conduction abnormalities. Damage appears to be related to dose, volume and technique of chest irradiation. Effects may initially present as subclinical abnormalities on screening tests or as catastrophic clinical events. Estimates of relative risk of fatal cardiovascular events after mediastinal irradiation for Hodgkin's disease ranges between 2.2 and 7.2 and after irradiation for left-sided breast cancer from 1.0 to 2.2. Risk is life long, and absolute risk appears to increase with length of time since exposure. Radiation-associated cardiovascular toxicity may in fact be progressive. Long-term cardiac follow-up of these patients is therefore essential, and the range of appropriate cardiac screening is discussed, although no specific, evidence-based screening regimen was found in the literature.

Pathophysiological effects of radiation on atherosclerosis development and progression, and the incidence of cardiovascular complications

Radiation therapy while important in the management of several diseases, is implicated in the causation of atherosclerosis and other cardiovascular complications. Cancer and atherosclerosis go through the same stages of initiation, promotion, and complication, beginning with a mutation in a single cell. Clinical observations before the 1960s lead to the belief that the heart is relatively resistant to the doses of radiation used in radiotherapy. Subsequently, it was discovered that the heart is sensitive to radiation and many cardiac structures may be damaged by radiation exposure. A significantly higher risk of death due to ischemic heart disease has been reported for patients treated with radiation for Hodgkin's disease and breast cancer. Certain cytokines and growth factors, such as TGF-beta1 and IL-1 beta, may stimulate radiation-induced endothelial proliferation, fibroblast proliferation, collagen deposition, and fibrosis leading to advanced lesions of atherosclerosis. The treatment for radiation-induced ischemic heart disease includes conventional pharmacological therapy, balloon angioplasty, and bypass surgery. Endovascular irradiation has been shown to be effective in reducing restenosis-like response to balloon-catheter injury in animal models. Caution must be exercised when radiation therapy is combined with doxorubicin because there appears to be a synergistic toxic effect on the myocardium. Damage to endothelial cells is a central event in the pathogenesis of damage to the coronary arteries. Certain growth factors that interfere with the apoptotic pathway may provide new therapeutic strategies for reducing the risk of radiation-induced damage to the heart. Exposure to low level occupational or environmental radiation appears to pose no undue risk of atherosclerosis development or cardiovascular mortality. But, other radiation-induced processes such as the bystander effects, abscopal effects, hormesis, and individual variations in radiosensitivity may be important in certain circumstances.

Mortality from myocardial infarction following postlumpectomy radiotherapy for breast cancer: a population-based study in Ontario, Canada

PURPOSE

To compare the risk of mortality from myocardial infarction (MI) after left-sided postlumpectomy radiotherapy (RT) to the risk after right-sided postlumpectomy RT.

METHODS

We conducted a population-based cohort study of cases of invasive female breast cancer in Ontario, diagnosed between January 1, 1982 and December 31, 1987 (n = 25,570). Records of the Ontario Cancer Registry (OCR) were linked to hospital procedure and discharge abstracts and to RT records from Ontario cancer centers. A case was labelled as lumpectomy if this was the maximum breast surgery within 4 months of diagnosis. Postlumpectomy RT occurred up to 1 year postdiagnosis. Laterality was assigned from the laterality descriptor of the RT records. A case was labelled as having had a fatal MI if ICD code 410 (myocardial infarction) was recorded as the cause of death in the OCR. We used logistic regression to compare the likelihood of utilization of: 1. Dose per fraction > 2.00 Gy; 2. cobalt vs. linac; and 3. boost RT. We used life table analysis and the log rank test comparing the time to fatal MI from diagnosis of breast cancer between women who received left-sided postlumpectomy RT and women who received right-sided. We used Cox proportional hazards models to study the relative risk for left-sided cases overall, and stratified by age, RT characteristics, and among conditional survival cohorts.

RESULTS

Postlumpectomy RT was received by 1,555 left-sided and 1,451 right-sided cases. With follow-up to December 31, 1995, 2% of women with left-sided RT had a fatal MI compared to 1% of women with right-sided RT. Comparison of the time to failure between women who had left-sided RT and women who had right-sided RT showed the left-sided RT group to be associated with a higher risk of fatal MI (p = 0.02). Adjusting for age at diagnosis, the relative risk for fatal MI with left-sided postlumpectomy RT was 2.10 (1.11, 3.95).

CONCLUSION

Among women who received postlumpectomy RT for breast cancer in Ontario between 1982-1987, left-sided postlumpectomy RT was associated with a higher risk of fatal MI compared to right-sided.

Directional coronary atherectomy for the diagnosis and treatment of radiation-induced coronary artery stenosis

While radiation therapy has been known to cause myocardial and pericardial damage, its role in accentuating coronary artery disease in the absence of traditional cardiovascular risk factors has been controversial. As younger patients with treatable cancers are being treated with mediastinal radiation, coronary artery disease as a cause for severe chest pain should be entertained as a possible diagnosis. We describe a 25-year-old male who presented with an inferior wall myocardial infarction 6 years after receiving mediastinal radiation and chemotherapy for Hodgkin's disease. He was subsequently treated by directional atherectomy to a 95% lesion in the right coronary artery. Histological examination of the atherectomy specimen revealed evidence of radiation-induced endothelial damage that had resulted in plaque formation and subsequent ischemia. Possible mechanisms for radiation-induced coronary artery disease and treatment options are discussed.

Radiation therapy-induced cardiac injury

Radiation therapy is currently standard treatment for a number of malignancies, including Hodgkin's disease. With the advent of techniques (e.g., subcarnial blocks) that limit the dose of radiation to which the heart is exposed, the incidence of radiation-induced heart disease can be minimized. However, a small percentage of patients will eventually suffer iatrogenic effects. Most commonly seen is pericardial disease, but valvular, conduction system, and coronary artery disease are also seen. Further, because these patients are now surviving longer after therapy, those effects with a longer latent period may be seen with increasing frequency.

Radiation-induced coronary artery disease

Excessive unprotected radiation to the heart appears to lead to the development of CAD, even in the absence of significant cardiovascular risk factors. The coexistence of such factors may enhance the probability of CAD. The presence of hypercholesterolemia and concomitant or sequential use of chemotherapeutic agents (especially doxorubicin) could further increase this risk. Therapeutic decisions, as with any other manifestation of CAD, relate to the extent of myocardium at jeopardy and to the overall diffuseness of CAD. Management options possible are PTCA or coronary artery bypass surgery. The latter may be required in left main artery stenosis and complicated ostial lesions. Use of shielding should decrease the associated risk of radiation-induced CAD in future years. However, clinicians should continue to have a high degree of suspicion of CAD in patients treated with thoracic radiation without cardiac shielding.

Morphologic effects of fast neutrons or photons on the canine kidney

Thirty-nine adult male Beagles received either fast neutron or photon irradiation to the right thorax to determine the relative biological effectiveness of fast neutrons on normal pulmonary tissue. The right anterior abdomen, including the cranial half of the right kidney, was included in the field of irradiation. Twenty-four dogs (six/group) received fast neutrons with an average energy of 15 MeV to total doses of 1000, 1500, 2250, or 3375 cGy in four fractions per week for 6 weeks. Fifteen dogs received 3000, 4500, or 6750 cGy of photons (five/group) in an identical fractionation pattern. All 12 neutron irradiated dogs receiving 3375 and 2250 cGy and 1 of 6 receiving 1500 cGy, developed clinical and clinical pathologic signs of hepatic, pancreatic, and gastrointestinal disturbances, but no signs of renal injury were seen. These 13 dogs died or were euthanatized 47-367 days after irradiation. Only 1 of 5 dogs receiving 6750 cGy of photons developed similar signs and died 708 days post-irradiation. The remaining 11 neutron irradiated dogs and 14 photon irradiated dogs eventually died of other causes. All 39 dogs were necropsied and their kidneys were compared to each other and to control dogs. Radiation induced lesions included hemorrhages, necrosis and disappearance of tubular epithelia, glomerulosclerosis, atrophy and fibrosis. These lesions were associated with degenerative and occlusive vascular changes and were much more severe in the neutron irradiated dogs. The relative biologic effectiveness of fast neutrons for canine kidney assessed by gross and microscopic pathology is approximately 4.5 (6750/1500).

Cardiovascular sequelae of therapeutic thoracic radiation

Mediastinal radiation damages endothelial cells, with resulting loss of capillaries and ischemia at the level of the microcirculation. These changes lead to increases in collagen and proliferation of fibrous tissue throughout the heart. Cardiac dysfunction following radiotherapy is surprisingly common and may be due to pericardial, myocardial, valvular, conduction system, or coronary artery disease. Greater awareness of cardiotoxicity has prompted changes in radiation techniques that appear to reduce clinical cardiovascular complications.

Pathologic effects of fractionated fast neutrons or photons on the pancreas, pylorus and duodenum of dogs

Thirty-nine adult male Beagles received either fast neutron or photon irradiation to the right thorax to determine the relative biological effectiveness (RBE) of fast neutrons on normal pulmonary tissue. The right anterior abdomen was included in the field of radiation. Twenty-four dogs (six/group) received fast neutrons with an average energy of 15 MeV to total doses of 1000, 1500, 2250 or 3375 rad in four fractions per week for six weeks. Fifteen dogs received 3000, 4500 or 6750 rad of photons (five/group) in an identical fractionation pattern. All neutron irradiated dogs receiving 3375 and 2250 rad and one receiving 1500 rad developed clinical signs of pancreatic, hepatic and gastrointestinal disturbances. The liver enzymes of these dogs became elevated and they died or were euthanatized in extremis 47-367 days after irradiation. Only one 6750 rad photon dog developed similar signs and died 708 days post-irradiation. Five neutron and 10 photon exposed dogs died of other causes. Neutron-induced lesions in the stomach and duodenum included hemorrhages, erosions, ulcerations and fibrosis. Ulcers perforated the GI tract of five dogs. Pancreatic lesions included degranulation and necrosis of acinar cells, fibrosis ans atrophy. Islet cells were not obviously damaged. All lesions were associated with degenerative and occlusive vascular changes. The RBE of fast neutrons, assessed by clinical signs, gross and microscopic pathology, is approximately 3-4.5 for pancreas and about 4.5 for pylorus and duodenum.