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May 6, 2013
By Dr. Anita Mahajan
Precise targeting of a tumor that limits radiation exposure in normal tissues is critical when treating pediatric cancer patients with radiation. Since its outset, nearly seven years ago when the MD Anderson Proton Therapy Center treated the first pediatric patient, the aim has always been to maximize this benefit and provide a viable cancer treatment option with fewer short and long-term side effects for children who are still growing and developing. Intensity-modulated proton therapy with multi-field optimization (IMPT) provides a way to do just that.
MPT, considered one of the most sophisticated treatment options by many radiation oncologists, relies on complex treatment planning systems and an intricate network of magnets within the treatment gantry to focus and aim a narrow proton beam and essentially "paint" the radiation onto the tumor layer by layer. It is best used to deliver a potent and precise dose of protons to the most complicated tumors of the head and neck, spine or pelvis. IMPT enhances the ability of another advanced form of proton therapy - pencil beam - to treat a tumor from multiple angles, at various depths and degrees of intensity. While each treatment field generated in pencil beam covers the entire area of the tumor, true IMPT patches together fields that treat one portion of the target area at a time until the entire tumor is treated.
IMPT for Pediatric Patients
This distinction allows for more precise dose distribution in which very specific amounts of radiation can be sculpted to the peaks and valleys of a tumor. Increased dosing is calculated for regions that need it the most while areas that can be spared, such as those near critical structures like the brainstem, receive a lower dose. IMPT is particularly attractive for children with rhabdomyosarcoma, skull base chordoma and Ewing's sarcoma in which the unparalleled ability to shape the treatment beam and confine radiation to the high-dose areas can help limit serious long-term side effects. For example, one patient being treated with IMPT is a teen girl diagnosed with skull base chordoma. The location of her tumor, nestled in between the brainstem and spinal cord, was a deciding factor in providing IMPT as a treatment choice.
Experts expect IMPT to offer even more robust benefits as the technology matures, continuously adapting best practices for applying IMPT to the common cancers seen in children. In some pediatric cases, IMPT has been combined with passively scattered proton therapy or other forms of radiation therapy to offer the treatment option best suited for the particular way a tumor sits or the organs that surround it. To ensure IMPT is delivered as expected, additional safety and quality assurance steps are essential components of an IMPT pediatric case. Such safeguards confirm that the computer simulation in treatment planning is replicated in the actual treatment.
Future of the IMPT Technology
Research for other facets of IMPT, including learning how to calibrate the technology to account for so-called "moving targets" is also advancing. For example, a lung tumor which moves up and down as a patient breathes in and out presents a challenging tumor motion phenomenon that can limit the possible applications of IMPT. Another area of interest is to understand precisely how IMPT affects the low-dose area of child's treatment field.
Today, IMPT illustrates a multidisciplinary and comprehensive approach to helping parents and caregivers manage their child's cancer. This advanced form of treatment builds on decades of innovation in radiation and pediatric subspecialties. As treatment teams continue to extend proton therapy to benefit pediatric patients, the ultimate goal, as always, is to deploy technology to provide the patient with the best possible outcome against their cancer.
MD Anderson Proton Therapy Center continues the rapid evolution of proton technology as the first center in North America to treat young children and adults with IMPT.
By Anita Mahajan, M.D., medical director for the Proton Therapy Center and the director of Pediatric Radiation Oncology, Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center. Dr. Mahajan works primarily with pediatric patients at the MD Anderson Proton Therapy Center. The center treats over 120 children annually and has seen over 600 patients since opening in 2006.
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