Not too long ago, radiation prescribed for cancer treatment was calculated by physical measurement and mathematic formulas worked out by hand.
Now computers do much of that detail work, but the job of a dosimetrist is as important as ever in making sure patients receive the right dose of radiation in exactly the right place. And thanks to advancements in the field—the development of proton therapy and advanced application technologies such as pencil-beam scanning, sophisticated software modeling platforms and high tech imaging capabilities—patients receive precise, customized therapy that’s the best in the world.
Kevin Kirby is one of six dosimetrists who work at Provision Center for Proton Therapy. These experts in the delivery of radiation for treatment of cancer work with radiation oncologist and physicists to determine the best treatment plan and then ensure its successful delivery, says Kirby, who spoke recently at a patient chat, held each Wednesday at the proton therapy center. The talks provide information on a variety of topics of interest to patients and their families.
“Our job is to create (proton therapy) dosage that focuses just in the tumor,” Kirby says. “We figure out the best way to position the patient so we can minimize any radiation to excess tissue.”
With the pencil beam application ability, calculations must be made to determine the direction and length of path for the protons being channeled to the tumor. In some cases, treatment can be made challenging by the location of the tumor, on the lung, for instance, in which radiation must be administered while the patient is breathing.
“We are able to predict the motion of the lungs by using four-dimensional CT scans to develop the treatment plans,” he says.
A laundry list of equipment and programs are involved in coming up with the unique plan for each patient. In the case of the lung cancer patient, for example, a respiratory device helps plan for treatment between breaths. Medcam marries patient x-rays with CT scans to aid dosimetrists, physicians and physicists in creating the treatment protocol. A software package called “Matrix” serves as quality assurance for treatment before it starts, even sending protons into the nozzle through which they’ll be delivered to the patient. Treatment planning software serves as a “flight simulator, which also allows for changes in the treatment plan based on shifts inside a patients body during the course of therapy. Another program, Mosaiq, records the treatment itself, creating a unique therapy chart for every patient.
Among the team of caregivers, physicians prescribe and monitor treatment, physicists manage the entire process on both the equipment and treatment delivery side and therapists interact directly with patients who are receiving therapy. Dosimetrists, says Kirby, focus specifically on the way radiation—in this case, proton therapy—targets the cancer in the patient’s body.
“We take the prescription the doctor gives and determine how to deliver it,” he says.