Researchers Discover Benefits of Precision Radiation Therapy for Lung Cancer

AUSTIN: For patients with locally advanced, inoperable non-small cell lung cancer (NSCLC), experts now recommend using the more precise intensity-modulated radiation therapy (IMRT) instead of the older 3D-conformal radiation therapy (3D-CRT).

This recommendation comes from a recent study by researchers at The University of Texas MD Anderson Cancer Centre.

The study, published in JAMA Oncology, found that IMRT offers similar survival rates to 3D-CRT but with fewer side effects.

A detailed analysis of long-term outcomes from 483 patients in the Phase III NRG Oncology-RTOG 0617 randomized trial revealed that those treated with 3D-CRT were much more likely to suffer from severe pneumonitis, an inflammation of the lungs, compared to those treated with IMRT. The rates were 8.2% for 3D-CRT and 3.5% for IMRT.

Lead author Dr. Stephen Chun, an associate professor of Radiation Oncology, believes this study settles the long-standing debate over the best radiation technique for locally advanced NSCLC.

“3D-CRT is an old method that’s been used for over 50 years. Our research shows it’s time to switch to IMRT for lung cancer, just like we did for prostate, anal, and brain tumors years ago,” Chun said. “The better precision of IMRT provides real benefits for patients with advanced lung cancer.”

3D-CRT directs radiation in straight lines at tumors but can’t bend around complex shapes, leading to unnecessary radiation exposure to nearby organs. IMRT, developed in the 1990s, uses advanced computer methods to adjust multiple radiation beams to fit the shape of tumors. This allows for more precise radiation delivery and spares normal tissue. However, it also exposes a larger area to low-dose radiation, known as a low-dose radiation bath.

The long-term effects of this low-dose bath on the lungs have been a point of debate, despite evidence of IMRT’s other benefits. This study showed that the low-dose radiation bath did not lead to more secondary cancers, long-term toxicity, or affect survival with long-term follow-up.

Patients treated with IMRT had slightly better five-year overall survival rates (30.8%) compared to those treated with 3D-CRT (26.6%), and similar progression-free survival rates (16.5% vs. 14.6%). These results favored IMRT, even though patients in the IMRT group had larger and more challenging tumors near the heart.

The study also emphasized the importance of using IMRT to reduce radiation exposure to the heart. While past concerns focused on lung exposure, this study showed that the amount of the heart exposed to 40 Gy of radiation independently predicted survival. Patients with less than 20% of their heart exposed to 40 Gy had a median survival of 2.4 years, compared to 1.7 years for those with more than 20% exposure.

Dr. Chun stated that these findings support efforts to limit the heart’s exposure to 40 Gy, aiming for less than 20% as a new radiation planning goal.

“With many patients now surviving long-term with advanced lung cancer, we can’t ignore cardiac exposure,” Chun said. “We need to focus on maximizing radiation precision to reduce exposure to the heart and lungs and move past old concerns about the low-dose bath.”