Thomas Merchant, DO, PhD

Thomas Merchant, DO, PhD



3D Radiation -- Preserving Brain Function

Radiation is one of the most effective treatments for children with brain tumors, yet the threat of its side effects on cognitive development, growth, and academic performance has for decades dissuaded many parents and physicians from using this therapy.

But at St. Jude, a three-dimensional approach to treating brain tumors with radiation is challenging the general consensus that radiation treatment for brain cancer is inevitably a tradeoff of life for a loss of cognitive function and normal growth.

Dr. Thomas Merchant, a physician in St. Jude’s Department of Radiation Oncology, has made that tradeoff obsolete for many children with brain tumors. We can now give them more effective radiation therapy for brain tumors while preserving their cognitive and physical development.

Dr. Merchant left Memorial Sloan-Kettering Cancer Center in New York City to work at St. Jude. Only St. Jude, with its broad and generous policy for accepting children regardless of ability to pay for treatment, transportation, or room and board, could offer him the opportunity to explore the potential of conformal radiation therapy for pediatric tumors. That’s because at St. Jude could he find the resources and enough young patients to conduct his studies. And while “time-is-money” limitations constrain many research physicians elsewhere, at St. Jude Dr. Merchant is able to spend the many hours needed to prepare for each treatment, without regard to cost and personnel time.

The technique combines CAT scans and MRI to create pictures that a computer then turns into three-dimensional images of the tumor exactly as it appears in the brain. By combining these images with computer-controlled radiation beams and meticulous positioning of the treatment table on which the patient lies, radiation hits the tumor from precisely calculated angles and to precisely calculated depths, obliterating the cancer and sparing healthy tissue.

This work represents the adaptation of a radiation therapy technique used for prostate and other adult cancers in order to treat a very limited volume of brain tissue in children. Key to Dr. Merchant’s success was showing how to define the target, how much normal tissue to include or exclude in order to ensure full treatment with minimal damage to healthy tissue, and defining the limits of this technique.

Conformal radiation therapy is demanding. It requires many hours of preparation time to define the area to be treated, create the three-dimensional treatment plan, and prepare the radiation equipment (linear accelerator) so the child receives highly targeted treatment. But the extra time and expense pays off.

Now, as patients are returning for their examinations up to five years post-treatment, to undergo special cognitive testing and physical evaluation, Dr. Merchant is finding they retain cognitive functioning and normal growth patterns.

 

 


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