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Identifying ‘cold spots’ may minimize adverse effects of radiotherapy
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Finding “cold spots,” or areas with potentially less active tumor cells, using fluorodeoxyglucose PET scans may improve control of cancer while exposing patients to lower doses of radiation.
“The only problem in radiotherapy is minimizing the side effects,” Christian Siedschlag, PhD, of the department of radiotherapy at the Dutch Cancer Institute, Amsterdam, said in a press release.
“If one could hit the tumor with arbitrarily high doses without having to worry about complications, all tumor cells could be killed with 100% certainty. Unfortunately, this is not the case; therefore, one must take every chance to administer no more dose than is absolutely necessary,” Siedschlag said.
Dutch researchers enrolled 61 patients with operable non–small cell lung cancer and used FDG-PET to examine whether certain areas in a tumor might not need irradiation, which would reduce the overall dose and minimize damage.
The glucose metabolism of a tumor was determined after an injection of “radioactive sugar” helped measure where the radioactivity is absorbed in the body. The increased metabolism of tumors typically makes lung tumors visible on PET scans as a bright sphere, with the highest intensity in the middle.
Sometimes, though, the shape is more irregular; for instance, doughnut-shaped with a cold spot in the middle or boomerang-shaped with a cold area on one side, according to Siedschlag. The researchers were motivated by whether or not they could give less radiation to these cold spots.
“If it turned out that these cold areas show less signal on a PET scan because there are less active tumor cells, then the answer would be yes. However, it could also have been that the radioactive sugar doesn’t reach the cold spots for other reasons,” he said.
Preliminary findings demonstrated that, in most cases, the cold spots consisted of dead tumor cells. Cold spots were observed on PET scans in seven patients. The cold spots were dead cells in five of these patients.
“By decreasing the doses given to the cold spots, one might be able to increase the dose given to the rest of the tumor while keeping the normal tissue dose constant, or one could keep the dose given to the rest of the tumor constant, which would lead to less side effects with an identical therapeutic result,” Siedschlag said.
We have known for several years that decreased uptake on PET scans may represent areas of cancer that are responding to treatment or possibly less aggressive. It would be very useful if we can partner this technology with the recent advances in improved targeting of radiation therapy to decrease the chance of damage to the surrounding tissues. Radiation is very effective at killing cancer cells, but limiting collateral damage to the areas not involved with cancer has always been the key. In the future, highly targeted radiation will increasingly be an alternative to surgery in lung cancer, and identifying precisely where the cancer is will be critical to the successful application of these technologies.
– Robert A. Kratzke, MD
Associate Professor, Department of Medicine, Masonic Cancer Center, University of Minnesota
For more information:
- Siedschlag C. #181O.