Pioneered at Memorial Sloan-Kettering to treat prostate cancer, a new treatment called Intensity Modulated Radiation Therapy (IMRT) is now making a dramatic difference for many children who until recently faced lifelong disabilities. Radiation therapy can successfully treat and cure some cancers, but it can also cause serious long-term side effects to normal tissue, especially in children. To address this problem, IMRT targets tumors so efficiently that it leaves healthy tissue unharmed even when the cancer is wrapped around a vital organ.
IMRT utilizes sophisticated computer programs to calculate variable doses and angles of radiation to target a tumor. Radiation is then delivered through multiple beams rather than a single, large, uniform beam. "IMRT allows us to get high doses of radiation into the tumor without giving too much radiation to the healthy tissues nearby; thereby avoiding or minimizing serious, permanent complications that kids can have after treatment with radiation," explained Center radiation oncologist Suzanne Wolden, who specializes in pediatrics.
The technology was designed with the idea of delivering higher doses of radiation to adult prostate cancer tumors and eventually to tumors of the breast and lung. It is now used to treat pediatric cancers that require high doses of radiation such as sarcomas, brain tumors and cancer of the head and neck, and up to 80 kids a year are treated with it at the Center.
Infants with Rhabdomyosarcoma, a tumor of the muscle, have poor cure rates because standard radiation causes such debilitating side effects that doctors or parents often decide not to treat them aggressively. IMRT is now enabling doctors to cure many of these children. Dr. Wolden recently treated a one year-old girl with a tumor sitting between her hip joints. Traditional radiation therapy would severely impair bone growth to the area and essentially cause the girl to grow up with the pelvis of a one year-old baby. "It's unimaginable. We probably would just not treat her, and then she would be at high risk of dying from her cancer," said Dr. Wolden. "But with IMRT we were able to design radiation fields that gave high doses to the tumor, and kept the dose to her hip joints very low. We don't anticipate problems with either normal growth or hip replacements down the line," added Dr. Wolden.
IMRT has also been critical in reducing the effects of cancers to the head and neck, where radiation therapy can cause severe neurocognitive problems and hearing loss. Medulloblastoma, a common pediatric brain tumor, leaves a large fraction of patients with extreme hearing loss due to inner ear damage from high doses of radiation and chemotherapy. "When children lose their hearing it's much more significant than when adults do, because it has a big impact on how they are able to learn and how they do in school," explained Dr. Wolden, who recently treated a six year-old girl with IMRT for a Medulloblastoma tumor. "With IMRT we were able to get the dose of radiation to her inner ears low enough that we don't expect hearing loss. So far, hearing tests after the treatment show her hearing has remained excellent."
The process of administering IMRT is labor intensive and requires a team of medical physicists, oncologists, and technicians. Initially the patient has a special CT scan, and the images from that scan are put into a computer where a three dimensional recreation of the patient's body is generated. The physician outlines the target tumor and identifies the healthy surrounding organs or tissue. Then the physician and the physicist work with the computer to plan the number of beams, dose variations, and angles from which to focus on the tumor. Finally, the team performs a dress rehearsal on the treatment machine to verify the data and to run quality assurance checks.
Memorial Sloan-Kettering has one of the largest volumes of pediatric oncology patients in the country, and is one of the few centers in the world to focus on the use of IMRT in pediatric patients. However, in some cases, tumors are still best treated with standard therapy when they are not wrapped around critical organs, or when a tumor requires low doses of radiation. Still, Dr. Wolden believes that pediatric patients as a group stand to benefit the most from IMRT.
Dr. Wolden looks forward to further advances of IMRT treatment. And future research may also reduce the labor behind the procedure, which when combined with a reduction in the long-term complications from traditional radiation therapy may lessen and/or outweigh the higher costs of the new procedure.
