Physicists Provide ‘Guiding Hands' for Proton Therapeutic Applications

While physicians manage the treatment of people, behind the scenes, proton physicists play a vital 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 necessary for effective treatment outcomes.

Getting the most of the characteristics of proton beams is the role of a team at M.D. Anderson Cancer Center (Houston, TX, USA) 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 in some instances when people are treated with high-energy photon radiation. This is particularly beneficial in cases such as craniospinal irradiation for pediatric central nervous system tumors or in the treatment of individuals 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 neighboring 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 utilizes 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, drastically 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 targets 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 individuals with tumors, there is still much to be learned to maximize the benefits of this treatment modality. Dose delivery in an inhomogeneous media such as the human body needs to be additionally understood and studied to assure more accurate dose calculation for optimal dose delivery to the tumor while sparing surrounding tissue, a key 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, TX, USA, explained, "We hope that by sharing our experiences in developing such a QA [quality assurance] program, we will provide an insight for new proton therapy facilities just establishing their programs,” he remarked.

The study's findings were presented at the University of Texas M.D. Anderson Cancer Center, on July 31, 2008, at the 50th meeting of the American Association of Physicists in Medicine.

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M.D. Anderson Cancer Center