Total Lung Damage from Radiation Therapy is Related to Regional Changes in Function
SAN ANTONIO, TX - Researchers from Duke University Medical Center report that radiation doses delivered during cancer treatment can be related to changes in total lung function, bringing them one step closer to improving this therapy.
By understanding how radiation distribution relates to lung damage, the researchers might be able to optimize the amount of radiation used to treat tumors near or in the lungs.
"If we can understand how the radiation doses damage normal tissue, it might let us further minimize damage to normal tissue and actually raise the dose we're able to give to the tumor," said principal investigator Dr. Lawrence Marks, associate professor of radiation oncology in the Duke Comprehensive Cancer Center.
The findings of the study are scheduled for presentation today (Nov. 1) at the annual meeting of the American Society for Therapeutic Radiology and Oncology.
While lung damage currently resulting from radiation treatment rarely affects patients' day-to-day abilities, such as climbing stairs or exercising, knowing exactly how radiation doses to certain parts of the lung affect total lung function might improve treatment for lung cancer, which is difficult to treat effectively if surgery is not an option.
Radiation kills cancerous cells by creating oxygen radicals, highly reactive atoms that damage the cell's DNA. Normal cells also are affected, but to a lesser degree because they are not replicating and therefore aren't duplicating their genetic material.
While careful high-tech analysis and planning can reduce exposure of normal tissue to radiation, physicians are not able to prevent such damage entirely. If the tumor is near or in the lung, chances are at least part of the healthy lung will suffer, limiting the radiation that can be delivered for therapy.
The Duke study, which included results from 96 patients, tested a model to predict how overall lung function would change based on regional lung changes and then relate that information to radiation distribution in the lung.
"We know the radiation dose distribution throughout the lung, and we can determine the regional lung function and the total lung function," explained Marks. "Right now we need all three, but eventually we want to predict the total changes in lung function just from the proposed radiation treatment plan."
To measure the radiation dose distribution, the researchers calculate how much energy is deposited in every region of the lung by using the physics of radiation and its interaction with tissue. The result is a map of radiation dose for different lung regions.
They then determine the function of each of those regions by imaging with Single Photon Emission Computed Tomography, or SPECT imaging, a non-invasive imaging technique that shows how well blood flows to different parts of the lungs. Using a computer program, researchers recreate the radiation dose regions on the pre- and post-treatment SPECT images and calculate the radiation-induced changes in each region.
For the function of the whole lung, the researchers rely on pulmonary function tests that provide information such as lung volume. Again, measurements taken before and after the patient receives radiation treatment let the researchers calculate the damage caused by the radiation.
For their predictive model, the scientists added the changes in regional function to get a predicted total change in lung function, which they compared to the actual change measured by the pulmonary function tests. They saw a relation between the two, but it wasn't a perfect match.
"The predicted whole lung injury was related to the actual lung damage that we saw," said Marks. "So we do know that this is a reasonable way to progress toward understanding and minimizing lung damage, but we're not there yet."
The researchers are adding more patients to the study, updating the computer model and evaluating their ability to predict lung damage. The study was funded in part by a grant from the National Cancer Institute.