In radiation therapy, the goal is always to maximize the dose on the tumor and minimize radiation going to normal tissues. One way to do this is to use bolus material for tumors that are near the surface of the body and skin. Boluses act as an artificial tissue that absorb radiation doses. A bolus can be made of many types of materials— water-soaked gauze, a modeling compound like Play-Doh, or prefabricated sheets of artificial “skin.” None of these are ideal because they do not mold directly to the surface, are not the same density as the tissue, and can leave air gaps where the body surface changes shapes. These air gaps interfere with the radiation dose. For example, a flat sheet cannot completely cover a curved part of a body, such as over the nose.
After a patient has a CT scan of the area to be treated, a bolus can be “drawn” on the surface. This can then be imported into other software which allows for the creation of a three-dimensional (3D) structure which can be printed using a rubbery material that exactly conforms to the patient and is placed on them before each treatment. Each bolus takes between six and 12 hours to print, depending on the thickness and size.
“The 3D printer allows oncologists to make a bolus that is the exact shape as the contour of the patient,” said Dr. Michael Kent, radiation oncologist and director of the Center for Companion Animal Health. “This eliminates air gaps and helps change how the dose distributes to the tissue.”
To see a timelapse version of the printer in action, please see the “UC Davis 3D Printer Timelapse” video on YouTube.
Bob and Lori Pryt brought their dog Enzo to the veterinary hospital in 2012 for treatment of a jaw cancer. After several surgeries and a course of radiation therapy, Enzo remains happy and cancer free. Last year, the Pryts asked Dr. Kent about equipment needs at the center. Dr. Kent mentioned how 3D printing could improve radiation treatments.
The Pryts supported the purchase of the 3D printer and the needed computer equipment to provide the best care possible for each patient. After researching the best type of material with which to print (one that would closely replicate tissue), the radiation oncology specialists began printing custom boluses for each patient that needs one.
Because of the Pryts’ gift and support of the research to bring this technology to the veterinary hospital, boluses can be printed for just a few dollars each, allowing the service to implement this new technology without increasing costs.
“This is a great example of how practical translational research can quickly be brought to the clinic and impact our patients,” said Dr. Kent.
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