Using PET for image-guided proton therapy

por John W. Mitchell, Senior Correspondent | June 10, 2015
CT Rad Oncology Proton Therapy X-Ray
Using PET imaging within a few minutes of proton therapy may have great potential benefits to patients, but requires some reconfiguring of current technology.

Research led by Dr. Georges El Fakhri at Massachusetts General Hospital (MGH), and published in the June issue of the International Journal of Radiation Oncology Biology Physics, demonstrates that PET is an effective tool to determine if the radiation dose is delivered to the intended cancer site.

“Proton therapy is very promising in targeting cancer, and has a lot of promise in delivering dose where it is needed and sparing other healthy tissues, but its curse resides in the fact that a small error in planning can result in a major dose to organs at risk near the tumor,” El Fakhri, Director of the Center for Advanced Medical Imaging Sciences at MGH and one of 11 members on the research team, told DOTmed News. “The modality is very promising but can be very unforgiving.”
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He said the research has been conducted on rabbits and a small number of human subjects. He said the next step is to extend the research to a larger sub-group of patients. Because humans receive up to 30 treatments as part of their therapy, a measurement taken after one treatment helps enlighten future treatments and ensure that the dose is delivered to its intended target, especially as the vascularity and consistency of the tumor changes over time in response to treatment.

The trick in combining PET and proton therapy is being able to take a measurement scan within two minutes of the proton therapy being administered. This allows for capture with PET of the two-minute physiological decay of radioactive water created in the patient during treatment(known as the “washout factor”).

“In order to scan a patient after treatment at our radiology facilities, it would take us, at best, 18 minutes” said Dr El Fakhri. “So the answer is to develop a portable set-up with the proton and PET in the same room with a rotating patient table.” Such image guidance systems exist for modulated radiation therapy, but are only beginning with proton therapy.

The team at MGH is working with Photo Diagnostic System Inc., which states on its website that it has developed the first portable PET/CT imaging system, to meet the need for clinical and pre-clinical research.

“Even though we’re in the early stages of research, this work is not lost on the proton therapy industry. Several companies are working on the next onboard imaging and guidance systems. I hope PET proton monitoring will become standard and contribute to improving therapy outcomes,” said El Fakhri.

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