Independent dose per monitor unit review of eight U.S.A. proton treatment facilities

Purpose: Compare the dose per monitor unit at different proton treatment facilities using three different dosimetry methods. Methods: Measurements of dose per monitor unit were performed by a single group at eight facilities using 11 test beams and up to six different clinical portal treatment sites. These measurements were compared to the facility reported dose per monitor unit values. Results: Agreement between the measured and reported doses was similar using any of the three dosimetry methods. Use of the ICRU 59 N_D,w based method gave results approximately 3 higher than both the ICRU 59 N _X and ICRU 78 (TRS-398) N_D,w based methods. Conclusions: Any single dosimetry method could be used for multi-institution trials with similar conformity between facilities. A multi-institutional trial could support facilities using both the ICRU 59 N_X based and ICRU 78 (TRS-398) N_D,w based methods but use of the ICRU 59 N_D,w based method should not be allowed simultaneously with the other two until the difference is resolved.