Real-time MRI Adaptive Radiation Therapy for Oncology Applications

ART is intended to provide more precisely targeted treatment to spare healthy organs at risk of developing radiation-induced comorbidities as a side effect of therapy. Real-time intrafraction MRI guidance integrated into the treatment delivery system is a recent advance in ART intended to improve accuracy and precision, specifically related to tissue motion. Real-time MRI ART is designed to particularly address tumor or organ movement during treatment.

Dosimetrists planning RT consider tumor location, prescribed dosing at the tumor site, and the radiation beam pathway through the body. Between planning and treatment phases, changes can occur that influence RT considerations, including patients losing weight, tumors shrinking, and tumors or organs naturally moving, particularly in regions where movement is related to function (e.g., lungs, stomach, bowels).1-3 Careful planning can account for some of these changes, but larger planning margins—extending the treatment volume beyond known tumor boundaries—are utilized to ensure the prescribed dose is achieved for the whole tumor, including imperfectly defined edges. When margins are enlarged, patients receive unnecessary radiation to healthy tissues. Real-time plan adjustments potentially address these changes without extending margins; however, they require complex computations that are infeasible without specialized software. Novel treatment adaptation algorithms incorporating tumor changes visible with real-time MRI can reportedly make fast computations that allow clinicians to pause treatment, alter the treatment path, adjust dosing, and change patient positioning without major delays.4

Real-time MRI ART combines two existing technologies to work concurrently without interfering with the other's function. MRI cannot be easily used with linear accelerators (linacs) used for RT delivery as typically configured because the magnetic field, radiofrequency field, and x-rays would interfere with one another. However, novel construction and shielding between the components can reportedly mitigate these effects, allowing MRI and RT to occur simultaneously.5 RT using 60Co radiation sources can also be compatibly configured with MRI because 60Co produces gamma rays instead of x-rays and does not create magnetic interference. Technologic advances, regardless of whether a linac or 60Co radiation source is used, potentially allow...