Proton therapy offers great benefits as a treatment modality in radiation oncology for a variety of hard to treat tumors. While physicians manage the treatment of people, behind the scenes, proton physicists play a crucial role, providing support and guidelines for treatment planning for calculation of dose distributions, measurements of radiation delivery, measurements of proton beam data, quality assurance of all measuring equipment and of the proton accelerator, and calibration of proton beams, all essential to successful treatment outcomes.
Making the most of the characteristics of proton beams is the role of a team at M.D. Anderson Cancer Center using a proton machine for treatment of cancerous tumors. Proton therapy is a preferred method of treatment where limited radiation dose to critical organs is crucial, an option that may not be feasible to achieve in some instances when people are treated with high energy photon radiation. This is especially valuable in cases such as craniospinal irradiation for pediatric Central Nervous System tumors or in the treatment of people with lung cancer where dose can be restricted to the tumor without affecting nearby tissue and organs.
Currently two techniques are used for delivering proton beams. Passively scattered proton beams deliver uniform dose to the tumor and a small region of adjacent tissue and are shaped laterally by apertures and distally by compensators to reduce the dose to healthy tissue. M.D. Anderson Cancer Center has pioneered a second technique in North America that uses a pencil beam to focus the dose. The pencil beam delivers dose to the tumor at many different spots and multiple layers within the tumor, dramatically reducing the dose to healthy tissue as compared to passively scattered proton beams. The technique does not use apertures and compensators but instead restricts the dose by selecting the spots confined within the tumor. The dose calculation and the accuracy of delivery of these pencil beams is a complex process, but offers great advantages for sparing healthy tissue.
While proton therapy is improving both treatment and quality of life for people with tumors, there is still a great deal to be learned in order to maximize the benefits of this treatment modality. Dose delivery in an inhomogeneous media such as the human body needs to be further understood and investigated in order to assure more accurate dose calculation for optimal dose delivery to the tumor while sparing surrounding tissue, a major advantage offered by proton therapy. The M.D. Anderson team is hoping that their work will benefit others in the field. Dr. Bijan Arjomandy, a physicist at the M.D. Anderson Proton Therapy Center in Houston explains, "We hope that by sharing our experiences in developing such a QA program, we will provide an insight for new proton therapy facilities just establishing their programs," he says.
The research was described in the talk, "An Overview of Comprehensive Proton Machine Quality Assurance at the University of Texas M.D. Anderson Cancer Center," presented July 31, 2008 at the 50th meeting of the American Association of Physicists in Medicine.
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