Radiation injury to the heart

Feasibility of intracoronary beta-irradiation to reduce restenosis after balloon angioplasty. A clinical pilot study

BACKGROUND

With the aim of decreasing the incidence of restenosis after coronary balloon angioplasty, we developed a technique of intracoronary beta-irradiation using an endoluminally centered pure metallic 90Y source. The purpose of the present study was to evaluate the clinical feasibility and safety profile of this approach with a dose of 18 Gy delivered to the inner arterial surface.

METHODS AND RESULTS

Between June 21 and November 15, 1995, fifteen patients (6 women and 9 men; mean age, 71 +/- 5 years) underwent intracoronary beta-irradiation immediately after a conventional percutaneous transluminal coronary angioplasty (PTCA) procedure. The PTCA/irradiation procedure was technically feasible in all attempted cases, and the delivery of the 18 Gy dose was accomplished without complications. In 4 patients, the intervention was completed through intra-arterial stent implantation because of dissection induced by the initial PTCA. During the follow-up period of 178 +/- 17 days (range, 150 to 225 days), no complication occurred that could be attributed to radiation therapy. No aneurysm or angiographically detectable thrombus was observed in any of the irradiated arterial segments. The clinical event rate (4 of 15 patients underwent further target lesion revascularization) and the angiographic follow-up (6 of 15 patients had a > 50%-diameter stenosis at the previously treated site) did not suggest a marked impact on the expected restenosis rate.

CONCLUSIONS

This early experience demonstrates that our approach is feasible, and no side effects attributable to radiation were noted during a 6-month period of follow-up. Whether higher doses of beta-irradiation will favorably affect post-PTCA restenosis in patients must await further evaluation.

Cardiotoxicity from intensive chemotherapy combined with radiotherapy in breast cancer

Cardiac function was evaluated in 86 breast cancer patients after standard chemotherapy, followed by ablative chemotherapy and chest irradiation. One patient died of subacute heart failure 3 months after ablative chemotherapy. At a minimum of 1 year's follow-up (range 1-11 years) left vertricular ejection fraction (LVEF) was marginally abnormal in 4 of 27 disease-free survivors. One exceptional patient who received two transplantations is alive, with serious heart failure occurring after the second ablative chemotherapy. Including this patient, the percentage of patients free of clinical and subclinical cardiac dysfunction at 7 years is 78% (95% CI 61-95%). After ablative chemotherapy, cardiotoxicity was rarely life-threatening. The impact of subclinical cardiotoxicity in the long term is not clear and needs continued evaluation.

Electron arc irradiation of the postmastectomy chest wall: clinical results

BACKGROUND AND PURPOSE

Since 1980 electron arc irradiation of the postmastectomy chest wall has been the preferred technique for patients with advanced breast cancer at our institution. Here we report the results of this technique in 140 consecutive patients treated from 1980 to 1993.

MATERIALS AND METHODS

Thoracic computerized tomography was used to determine internal mammary lymph node depth and chest wall thickness, and for computerized dosimetry calculations. Total doses of 45-50 Gy in 5 to 5 1/2 weeks were delivered to the chest wall and internal mammary lymph nodes via electron arc and, in most cases, supraclavicular and axillary nodes were treated with a matching photon field. Patients were assessed for acute and late radiation changes, local and distant control of disease, and survival. Patients had a minimum follow-up of 1 year after completion of radiation treatment, and a mean follow up interval of 49 months and a median of 33 months. All patients had advanced disease: T stages 1, 2, 3, and 4 represented 21%, 39%, 21% and 19% of the study population, with a mean number of positive axillary lymph nodes of 6.5 (range, 0-29). Analysis was performed according to adjuvant status (no residual disease, n = 90), residual disease (positive margin, n = 15, and primary radiation, n = 2), or recurrent disease (n = 33).

RESULTS

Acute radiation reactions were generally mild and self limiting. A total of 26% of patients developed moist desquamation, and 32% had brisk erythema. Actuarial 5 year local-regional control, freedom from distant failure, and cause-specific survival was 91%, 64%, and 75% in the adjuvant group; 84%, 50%, and 53% in the residual disease group; and 63%, 34%, and 32% in the recurrent disease group, respectively. In univariate Cox regressions, the number of positive lymph nodes was predictive for local failure in the adjuvant group (P = 0.037). Chronic complications were minimal with 11% of patients having arm edema, 17% hyperpigmentation, and 13% telangectasia formation.

CONCLUSION

These data demonstrate that local-regional control with electron are therapy of the postmastectomy chest wall is comparable to photon techniques. Acute radiation reactions are well tolerated and mostly of minor extent. A previous report demonstrated a significant reduction in the dose-volume relationship of the lung using the electron arc compared with two photon techniques. Consequently, with careful attention to treatment planning and dosimetry, electron arc therapy of the postmastectomy chest wall is safe and effective. The radiation dose to heart and lung is minimized without compromise on local control.

The potential role of external beam radiation in preventing restenosis after coronary angioplasty

The potential role of radiation in the prevention of coronary artery restenosis after angioplasty has generated much recent interest. Animal research and pilot clinical efforts have focused primarily on intraluminal methods of radiation delivery. This article reviews the experience to date with external beam radiation in restenosis prevention and suggests issues that should be considered from the standpoint of both external beam and intravascular radiotherapy. External beam radiation can certainly play an effective role in clinical studies of coronary artery restenosis, and a multicenter randomized trial of external beam radiation after coronary angioplasty has been initiated.

Myocardial damage in breast cancer patients treated with adjuvant radiotherapy: a prospective study

PURPOSE

To look for early and late signs of cardiac side effects of postoperative radiotherapy in patients with left-sided breast cancer.

METHODS AND MATERIALS

Seventeen left-sided primary (Stage I-III) breast cancer patients considered eligible were recruited. Their computer tomography-based dose planning showed a part of the heart's left ventricle irradiated with at least 85-95% of the total dose. Twelve patients were examined both before treatment and an average of 13 months later, at a first follow-up. In partially mastectomized patients tangential opposed photon fields were used to the breast tissue, while in patients with modified radical mastectomy electrons were given to the thorax. Echocardiography and a bicycle ergometry stress test with myocardial perfusion scintigraphy were carried out before and after radiotherapy to assess if any myocardial damage could be detected.

RESULTS

Six of the 12 patients exhibited new fixed scintigraphic defects after radiotherapy indicating regional hypoperfusion. Four of them received treatment only to the breast after breast-conserving surgery. The localization of the defects corresponded well with the irradiated volume of the left ventricle. No deterioration in left ventricular systolic or diastolic function could be detected by echocardiography.

CONCLUSIONS

In this study half of the patients exhibited new scintigraphic defects that indicate radiation-induced myocardial damage, probably affecting the microcirculation. There were no changes on electrocardiography or any deterioration of the left ventricular function at this stage. Long-term follow-up is necessary to assess whether this finding is a prognostic sign for developing radiation-induced coronary artery disease.

The radiobiology of intravascular irradiation

PURPOSE

There is increasing interest in the use of vascular irradiation, from an internally introduced radioactive source to control restenosis after balloon angioplasty. Both animal experiments and early clinical studies appear to show promising results in this regard. We consider various mechanistic interpretations of the experimental and clinical observations that doses of 12-20 Gy appear to be efficacious in preventing restenosis. We develop and investigate simple models, both experimental and theoretical, of the kinetics of radiation-induced smooth muscle cell (SMC) inactivation and regrowth, as a first step toward optimizing the design of clinical vascular irradiation.

METHODS AND MATERIALS

Using in vitro models of human SMCs, we investigate the relative radiosensitivity of SMCs compared with endothelial cells and measure the dose-dependent ability of SMCs to repopulate a denuded region in a confluent layer of cells. We then use quantitative information on the number, radiation sensitivity, and growth rate of the potential arterial target cells to model the time course of the SMC population after irradiation.

RESULTS AND CONCLUSION

Doses >20 Gy, which would be required to completely eliminate the SMC population which has the potential to cause restenosis, are too large to be practical because of the unacceptable risk of late complications. However, doses that can be practically given in vascular irradiation (<20 Gy) will certainly delay restenosis by 1-3 years, with larger doses producing longer delays. Whether such doses can avert restenosis permanently is unclear, as permanent prevention at realistic doses depends critically on the assumption that those SMCs which survive irradiation have a significantly limited capacity for proliferation. With regard to current animal model experiments, routine follow-up of <1 year, which is standard practice, is probably too short to address some of the key mechanistic question in intravascular radiation therapy.

Long-term cardiac mortality after radiotherapy of breast cancer--application of the relative seriality model

Effects on the heart constitute a potentially significant and serious clinical problem in primary radiation therapy of early breast cancer. Increased cardiac mortality among irradiated patients may offset the potential benefit in terms of a reduced risk of recurrence or of death from breast cancer. Clinical data on long-term cardiac mortality among breast cancer patients included in two randomized trials (the Stockholm and Oslo studies) of radiation therapy as an adjunct to primary surgery were analysed using the relative seriality model of radiation response. Five different radiation therapy techniques were used in the trials. The original treatment plans were recalculated on a group of model patients using a three-dimensional treatment planning system. A mean dose-volume histogram (DVH) was calculated for each treatment technique. Both heart and myocardium, i.e. excluding circulating blood within the heart, were separately investigated as risk organs. Model parameters, (D50, i.e. the dose giving 50% complication probability; gamma, i.e. the maximum relative slope of the dose-response curve; s, describing the organ relative seriality) were determined by a chi 2 fitting of the calculated probability of excess cardiac mortality, based on the DVHs, to the incidence data. Computed complication probabilities for each treatment technique were modelled within the 95% confidence interval (CI) of the clinical incidence data. It was shown that the relative seriality model, assuming a homogeneous radiation sensitivity within the volume of the heart/myocardium can be used to describe the incidence data. A small dependence on the volume was found. The results do not, however, exclude the possibility that more sensitive structures within the myocardium are the main target for radiation.

Evaluation of meta-[211At]astatobenzylguanidine in an athymic mouse human neuroblastoma xenograft model

A paired-label biodistribution was performed in athymic mice bearing SK-N-SH human neuroblastoma xenografts to compare the tissue uptake of meta-[211At]astatobenzylguanidine ([211At]MABG) and [131I]MIBG. Significantly higher (p < 0.05) uptake of [211At]MABG was seen in tumor (3.8 +/- 0.8% ID/g vs. 3.1 +/- 0.7% ID/g at 8 h) compared to [131I]MIBG. Desipramine reduced tumor uptake of [211At] MABG by 43%, suggesting that its accumulation was related to the specific uptake-1 mechanism. Higher uptake of [211At]MABG was also seen in normal tissue targets such as heart (6.0 +/- 0.9% ID/g vs. 4.5 +/- 0.8% ID/g at 8 h; p < 0.05). Pretreatment of mice with unlabeled MIBG increased tumor uptake of [211At]MABG by 1.5-fold while reducing uptake in heart and several other normal tissues. The vesicular uptake inhibitor tetrabenazine reduced heart uptake by 30% without reducing the tumor uptake. These results suggest such strategies might be useful for improving [211At]MABG tumor-to-normal tissue ratios.