Researchers find how precise radiation treatment helps treat lung cancer

AustinFor patients with locally advanced, unresectable non-small cell lung cancer (NSCLC), the standard use of more precise intensity-modulated radiation therapy (IMRT) is recommended compared with the alternative 3D-conformal radiation therapy (3D-CRT).

This conclusion is based on the findings of a recent study conducted by researchers at the University of Texas MD Anderson Cancer Center.

The research, recently published in JAMA Oncology, showed that IMRT has comparable survival rates and fewer side effects.

A prospective secondary analysis of long-term outcomes of 483 patients in the phase III NRG Oncology-RTOG 0617 randomized trial showed that patients treated with 3D-CRT were significantly more likely to experience severe pneumonitis — inflammation of the lungs — than patients treated with IMRT, at 8.2 percent and 3.5 percent, respectively.

According to lead author Stephen Chun, M.D., associate professor of radiation oncology, this study will bring final conclusion to the long-standing debate over the optimal radiation technique for locally advanced NSCLC.

“3D-CRT is a rudimentary technology that has been used for more than 50 years. Our findings suggest that it is time to routinely adopt IMRT over 3D-CRT for lung cancer, just as we did decades ago for prostate, rectal and brain tumors,” Chun said. “The improved accuracy of IMRT translates into real benefits for patients with locally advanced lung cancer.”

3D-CRT targets and shapes radiation in straight lines directed at the tumor, but lacks the ability to bend and twist into complex shapes, resulting in unnecessary radiation exposure to nearby organs. IMRT, developed in the 1990s, uses advanced computational methods to dynamically modulate multiple radiation beams to mold radiation according to the shape of the tumor. While this can deliver radiation more precisely and spare normal tissue, bringing radiation from multiple directions can also create a larger area exposed to low-dose radiation less than 5 Grays (Gy), known as a low-dose radiation bath.

The unknown, long-term effects on the lungs of this low-dose bath have fueled historical debate over IMRT and 3D-CRT in lung cancer, despite significant evidence of other benefits of IMRT. In this study, researchers showed that the low-dose radiation bath had no association with additional secondary cancers, long-term toxicity, or survival with long-term follow-up.

Patients had a numerically better but statistically similar five-year overall survival rate for IMRT (30.8 percent) compared with 3D-CRT (26.6 percent), as well as a progression-free survival rate (16.5 percent vs. 14.6 percent). Overall, these results favored IMRT, even though patients in the IMRT arm had significantly larger tumors and more tumors in unfavorable locations near the heart.

These findings also highlight the importance of using IMRT to reduce the cardiac risk of doses of 20 to 60 Gy. Historical concern has focused primarily on lung risk, but this study demonstrated that the volume of the heart exposed to 40 Gy independently predicted survival in multivariate analysis. Specifically, patients whose heart was exposed to less than 20 percent of 40 Gy had a median survival of 2.4 years, whereas patients whose heart was exposed to more than 20 percent of 40 Gy had a median survival of 1.7 years.

According to Chun, these data validate efforts to limit the volume the heart receives to 40 Gy, and to aim for less than 20% as a new radiation planning objective.

“With substantial numbers of patients achieving long-term survival for locally advanced lung cancer, cardiovascular risk is no longer a consideration,” Chun said. “It is time for us to focus on maximizing radiation precision and conformity to minimize cardiopulmonary risk and abandon historical concerns over low-dose baths.”

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