Implementation, uptime, and safety of a pulsed dose rate afterloading machine.

Abstract

To review the routine use of pulsed dose rate brachytherapy (PDR) for replacement of low dose rate manual afterloading using classical dose rates and hourly pulses. Uptime (actual treatement time vs. planned time) and safety (dose to personnel, machine safety) of 110 implants in 101 patients were evaluated during the period from August 10, 1993 to December 27, 1994. This study includes 80 implants in gynecological tumors; 12 for sarcoma and 6 each for bronchus, gastrointestinal, and head and neck tumors. Thirty-seven of these implants were in 14 patients with a recurrence in previously irradiated areas. In 15 patients brachytherapy was the only treatment. All pulses were given hourly, and the median dose rate at specification points was 0.6 Gy (0.4 to 3 Gy). The total number of pulses per treatment varied from 3 to 120. After an initial period of machine-related problems, all treatments were supported well in all but one patient and could generally be given within 5 min of the planned time although the room was entered at a mean interval of 79 min. Whenever a problem that could interfere with proper machine function is detected, a message (status code) is generated. A median of one status code (range: 0 to 24) occurred during a single implant. Status codes were caused by an open door when a pulse had to be given (44%) or related to difficulty of movement of the check cable/source through plastic tubes (34%); the remaining status codes were due to a variety of causes. The dose received by the personnel decreased almost ninefold as compared to the period when permanent implants were used. We find PDR at hourly pulses to be feasible, safe, and both staff- and patient-friendly. For evaluation of the clinical results longer follow-up is needed.