Cardiac Dose in Locally Advanced Lung Cancer: Results From a Statewide Consortium

The heart has been identified as a potential significant organ at risk in patients with locally advanced non-small cell lung cancer treated with radiation. Practice patterns and radiation dose delivered to the heart in routine practice in academic and community settings are unknown.

Between 2012 and 2017, 746 patients with stage III non-small cell lung cancer were treated with radiation within the statewide Michigan Radiation Oncology Quality Consortium (MROQC). Cardiac radiation dose was characterized, including mean and those exceeding historical or recently proposed Radiation Therapy Oncology Group and NRG Oncology constraints. Sites were surveyed to determine dose constraints used in practice. Patient-, anatomic-, and treatment-related associations with cardiac dose were analyzed using multivariable regression analysis and inverse probability weighting.

Thirty-eight percent of patients had a left-sided primary, and 80% had N2 or N3 disease. Median prescription was 60 Gy (interquartile range, 60-66 Gy). Twenty-two percent of patients were prescribed 60 Gy in 2012, which increased to 62% by 2017 (P < .001). Median mean heart dose was 12 Gy (interquartile range, 5-19 Gy). The volume receiving 30 Gy (V30 Gy) exceeded 50% in 5% of patients, and V40 Gy was >35% in 3% of cases. No heart dose constraint was uniformly applied. Intensity modulated radiation therapy (IMRT) usage increased from 33% in 2012 to 86% in 2017 (P < .001) and was significantly associated with more complex cases (larger planning target volume, higher stage, and preexisting cardiac disease). In multivariable regression analysis, IMRT was associated with a lower percent of the heart receiving V30 Gy (absolute reduction = 3.0%; 95% confidence interval, 0.5%-5.4%) and V50 Gy (absolute reduction = 3.6%; 95% confidence interval, 2.4%-4.8%) but not mean dose. In inverse probability weighting analysis, IMRT was associated with 29% to 48% relative reduction in percent of the heart receiving V40-V60 Gy without increasing lung or esophageal dose or compromising planning target volume coverage.

Within MROQC, historical cardiac constraints were met in most cases, yet 1 in 4 patients received a mean heart dose exceeding 20 Gy. Future work is required to standardize heart dose constraints and to develop treatment approaches that allow for constraints to be met without compromising other planning goals.