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O n March 27, the first patient benefited from a novel advancement in BWH’s arsenal of radiation treatments used for brain tumor and head and neck cancer patients. The new technology—intensity modulated radiation therapy (IMRT)—allows radiation oncologists to modulate radiation therapy between tumors and healthy tissue in ways not yet possible until now.
Specifically, IMRT reduces the risk to patients of radiation-related injury to normal structures. For example, in tumors close to the optic nerve, IMRT permits precise shaping of the radiation dose with a sharp decrease in dose beyond the margins of the tumor. This reduces exposure to the optic nerve and therefore lowers the potential risk of vision loss.
As members of the Radiation Oncology Department recently reviewed a particularly complex patient case, one in which it would have been extremely difficult to achieve desired clinical objectives through conventional external beam techniques, it was decided that IMRT could be the solution.
IMRT offers a striking improvement over conventional radiation therapy, according to Naren Ramakrishna, MD, PhD, director of the Adult Central Nervous System Radiotherapy program in the Department of Radiation Oncology at BWH. With conventional radiation therapy, the total dose administered to tumors in close proximity to or growing into a critical structure such as the optic nerve or the brain stem are often limited by the radiation tolerance of the normal structures. As a result, conventional radiation treatment may be compromised as higher, more effective doses can’t be delivered to the tumor out of the need to spare critical structures.
“Many brain and head and neck tumors are established adjacent to or grow into vital structures within the skull, as in this patient’s case. IMRT was the logical solution as it allowed us to administer a higher dose of radiation to the cancerous tumor while protecting the critical structures and other healthy tissue in the skull with a lower dosage,” said Ramakrishna.
Using the Novalis machine and planning software, physicists and physicians within the Department of Radiation Oncology were able to manipulate radiation distribution in the radiation field to appropriately treat the patient’s complex tumor.
Much of the work associated with this highly advanced technology takes place behind the scenes in a planning lab prior to patient treatment. Fred Hacker, PhD and Piotr Zygmanski, PhD are the two physicists most closely involved with IMRT patient cases, which typically calls for considerably more planning time than conventional stereotactic planning for tumor treatment.
“IMRT is an evolution that builds on all the techniques we’ve been using up to this point. It adds one more layer and makes our treatment much more precise,” said Hacker.
IMRT planning begins with careful mapping of tumor and critical structures by the physician. Hacker and others then plan for the treatment, by applying physics to designate varying doses of radiation in the various radiation fields that are applied to the tumor during treatments. To test the desired results, the physicists used a model head with films to confirm the radiation results. The films indicated desired results and the patient’s radiation therapy, using Ramakrishna’s input and Hacker’s planning, then began.
“Although the patient’s treatments are ongoing, the results look promising,” said Ramakrishna, who forecasts that BWH will soon be able to treat several patients each month using IMRT. In addition to treating patients with complex tumors, Ramakrishna explains that IMRT will be well-suited for treating pediatric tumors since the effects of radiation on young patients can have more of a damaging effect on their critical structures, which are still in development.