There are two types of quality assurance: system and patient-specific. “System quality assurance refers to the daily, weekly, monthly and yearly QA assessments we use to test each gantry and the overall machinery associated with proton therapy delivery,” says Roelf Slopsema, M.S., physicist at the University of Florida Proton Therapy Institute (UFPTI). “For example, the daily system quality assurance procedures we perform measure output — specifically, to ensure we have the same amount of dose at isocenter — and the alignment accuracy of patient to proton beam. “Patient-specific quality assurance concerns the measurement of treatment fields in a water phantom to ensure accurate dosage and treatment penetration depth, in addition to hardware quality,” Slopsema continues. Hardware QA procedures test the range compensator and aperture, two proton therapy components that ensure proper dose distribution.

Quality assurance procedures can be time-intensive, and UFPTI’s three gantry treatment rooms each undergo approximately 20 minutes of QA procedures daily, an additional 60 to 90 minutes weekly, and another 30 minutes on a monthly basis, in addition to extensive annual QA testing. As various fields are measured and the system remains stable, physicists rely on previous measurements as references for future QA assessments. Slopsema garnered much of his QA expertise during his tenure at Massachusetts General Hospital in Boston, Massachusetts. He’s applied this knowledge to his work at UFPTI and says this type of information sharing between proton therapy centers will help refine and improve future QA procedures. “With so few proton therapy facilities in operation today, there’s no real set of QA standards yet, so each center is developing its own set of standards,” says Slopsema. “As more proton therapy systems come online, the more streamlined quality assurance procedures will become.”

Though many alignment, setup and imaging learnings carry over from conventional radiation therapy, the transition to proton therapy requires equipment-specific training due to the increased complexity of proton therapy mechanisms. Teaming proton therapy with other radiotherapy modalities makes centers more flexible and allows to treat more patients, as a number receive a combined cancer therapy regimen of photons and protons.

The first goal of quality assurance is to deliver safe and accurate treatment to patients. “It is important for proton therapy professionals to understand the system they are working with,” says Slopsema. “Physicists need to be familiar with the process of proton generation, the proper dosing and all of the varying elements. Taken in total, these components define the quality assurance procedures necessary to run a safe and efficient operation. And patients expect safety when they walk through the door.”