Sameer K. Nath
Higher doses of radiation to immune cells appeared associated with tumor progression and shorter OS among patients with stage III non-small cell lung cancer, according to results of a retrospective study published in International Journal of Radiation Oncology Biology Physics.
Researchers noted that adjusting radiation doses to spare the immune system may improve outcomes among this patient population.
“Over the last decade, a lot of research supports the idea that a functional immune system plays a key role in tumor cell killing following the DNA damage created by radiation therapy,” Sameer K. Nath, MD, investigator at University of Colorado Cancer Center and assistant professor in department of radiation oncology at CU School of Medicine, said in a press release. “Our hypothesis is that higher doses of radiation to the immune system contribute to worse survival in those patients.”
A secondary analysis of the phase 3 RTOG 0617 trial suggested that higher doses of radiation inhibited tumor control and reduced OS compared with the standard dose. Nath and colleagues sought to further explore the relationship between estimated dose of radiation to immune cells (EDRIC) and cancer-specific outcomes among 117 patients (median age, 63 years; range, 36-89; 53% women) with stage III NSCLC treated at University of Colorado Cancer Center between 2004 and 2017.
Patients received a median radiation dose of 60 Gy, with 60% undergoing intensity-modulated radiation therapy and 92% receiving concurrent platinum-based chemotherapy.
Researchers calculated EDRIC as a function of number of radiation fractions and mean doses to the lung, heart and the remaining body, using a model developed by researchers in the secondary analysis of RTOG 0617.
OS served as the study’s primary endpoint. Local PFS and DFS served as secondary endpoints.
Median follow-up was 15.7 months (range, 2.8-124.5), with 77% of patients followed until their death.
Results showed 5-year OS of 11.2%, with median survival of 17.3 months (95% CI, 14.6-24) and median EDRIC of 6.1 Gy (range, 2.5-10).
In multivariate analyses, EDRIC appeared independently associated with OS (HR = 1.17; P = .03), local PFS (HR = 1.17; P = .02) and DFS (HR = 1.15; P = .04).
Median OS for patients with an EDRIC above 7.3 Gy was 14.3 months, whereas median OS for patients with an EDRIC below 5.1 Gy was 28.2 months.
A higher EDRIC correlated with a greater risk for grade 3 or higher lymphopenia (P = .004).
Study limitations included its retrospective nature, as well as the fact that all patients were from the same institution.
“The estimated dose of radiation to immune cells is an important predictor of tumor control and survival. In fact, it ends up being one of the most important predictors,” Nath said in the release. “Now that we have ways to estimate this radiation dose, we can look at sparing the immune system as an organ-at-risk.” – by John DeRosier
Disclosures: The authors’ report no relevant financial disclosures.