Based on data from California Cancer Registry, this study reported that of the 2,499,510 people with a cancer diagnosis during the study period, 578,632 (23%) received some type of RT, and of these, 8609 received PBT (1.5%). PBT was most often used to treat cancers of the prostate (41.3%), breast (14.0%), eye (11.7%), lung (6.1%), and brain (6.0%).

PBT use was highest in 2003-2004 and then declined over time. PBT use was significantly associated with being white or male, younger age, higher socioeconomic status, Medicare or dual Medicare-Medicaid insurance, uninsured/self-pay status, and proximity to treatment.