Cardiac events are “relatively common,” affecting 23% of patients, and occur earlier than previously thought following radiotherapy for non–small-cell lung cancer (NSCLC), according to a report in the Journal of Clinical Oncology.
Radiation-associated cardiac toxicity has long been recognized in patients treated for other thoracic cancers, but the conventional wisdom has been that it isn’t a consideration in patients with stage III NSCLC because “there are few long-term survivors to experience toxicity, given the typically long latency of radiotherapy-associated heart injury and the poor prognosis” of this cancer. However, the findings “challenge the perception that minimizing heart dose is not important in the treatment of patients with stage III NSCLC,” said Kyle Wang, MD, of University of North Carolina Hospitals, Chapel Hill, and his associates.
“Our data support minimization of heart radiation exposure whenever possible to doses lower than commonly recommended in patients with stage III NSCLC, to reduce risks of [cardiac] toxicity,” they noted.
Dr. Wang and his associates performed a retrospective post hoc analysis of data pooled from six prospective phase I and II trials that the University of North Carolina was involved in between 1996 and 2009. The studies assessed both dose-escalated radiotherapy and various chemotherapeutic regimens in 112 patients who were followed for a median of 8.8 years (range, 2.3-17.3 years). All the patients received induction chemotherapy, 90% received concurrent chemotherapy, and 25% received consolidation chemotherapy.
A total of 26 patients (23%) had at least one symptomatic cardiac event following radiotherapy: pericardial effusion (7 patients), MI (5 patients), unstable angina (3 patients), pericarditis (2 patients), significant arrhythmia (12 patients), and heart failure (1 patient). After the data were adjusted to account for competing risks of death, the 2-year rate of symptomatic cardiac toxicity was 10% and the 4-year rate was 18%. The first adverse cardiac event occurred at a median of 26 months (range, 1-84 months).
The risk of cardiac toxicities rose with increasing radiation exposure: At 2 years, the rate of cardiac events was 4% for those exposed to less than 10 Gy, 7% for those exposed to 10-20 Gy, and 21% for those exposed to greater than 20 Gy. At 4 years, those rates were 4%, 13%, and 41%, respectively. Patients whose hearts were exposed to greater than 20 Gy had a significantly higher rate of cardiac events than did those exposed to less than 10 Gy (HR, 5.47) or to 10-20 Gy (HR, 2.76).
Even though the prognosis may be poor in patients with stage III NSCLC, “they generally receive higher heart doses and may also have more comorbidities and smoking history, thus increasing risk and perhaps shortening the latency between radiotherapy and resultant heart disease,” Dr. Wang and his associates said (J Clin Oncol. 2017 Jan 23 [doi: 10.1200/JCO.2016.70.0229]).
“In our opinion, tumor coverage should rarely be compromised to meet a heart dose constraint. However, it would be reasonable to try to limit heart mean dose to less than 20 Gy (lower if possible) on the basis of the high event rate we observed in patients exceeding this dose (21% at 2 years and 41% at 4 years). Sophisticated radiation treatment planning techniques (e.g., [intensity-modulated radiation therapy]) and charged-particle therapy with protons or carbon ions may provide increased flexibility to generate more conformal treatment plans and reduce heart dose, which could potentially improve the clinical outcomes in patients with stage III NSCLC,” they added.