Epidemiological analysis of patients with prostate cancer treated with proton beams at LLUMC

The James M. Slater, M.D. Proton Therapy Treatment and Research Center of the Loma Linda University Medical Center (LLUMC) has treated more than 15,000 patients with proton beams since its inception in 1990, and it is responsible for the majority of patients treated with protons in a hospital setting. Moreover, it is one of only a few institutions with approval by the Federal Drug Administration to treat patients with dynamically scanned proton beams with such beams available presently for experimentation at LLUMC. These features place LLUMC in a unique position for determining improved estimates of outcomes and risks associated with proton therapy including more precise risk estimates for second cancers in patients treated with active or passive proton delivery systems An ancillary benefit in the context of establishing the risks of doses in medical applications is that it would provide a much more solid basis for the estimation of effective doses and the application of microdosimetric spectral analyses to such risk estimations. Such results are important as both the number of institutions treating with protons and the number of patients treated with protons will be increasing rapidly over the next few years. The LLUMC prostate cancer group is the largest and most homogeneously treated proton patient group at the facility and has the potential for yielding risk estimates of secondary cancers with reasonable uncertainty, as will be discussed in this presentation. The total dose and dose per fraction for all patients treated to date have a relatively restricted range from 74 Gy to 81 Gy. In addition, the primary treatment planning and delivery technique (opposing laterals with one field treated per day, proton energy range 225-250 MeV) has not been changed from inception. In particular, this group represents a single-institution homogeneous cohort in terms of treatment parameters important for, for example, secondary neutron dose outside the treatment volume. The potential clinical and epidemiological benefit from such treatments has provided the impetus for the development of a comprehensive patient database. A projected accrual has been calculated based upon the current number of proton patients already being followed, their observed survival, and the censoring rate because of loss to follow-up. The analysis is presented and discussed for a patient population restricted to those treated with protons only, i.e., not including those who received combined proton and X-ray treatments.