BACKGROUND.
Ambulatory infusion pumps are used to deliver concurrent chemotherapy with pelvic radiation therapy for patients with rectal carcinoma. The pump is worn around the waist and may be exposed to direct as well as scattered radiation, possibly leading to a complete malfunction, requiring a new pump, and/or changes in the pump timing, with clinically significant reductions in chemotherapy administration.
METHODS.
Two new ambulatory chemotherapy pumps were irradiated using a 6-megavolt linear accelerator. The first pump received gradually increasing doses to determine whether a complete malfunction were possible and the approximate dose. The second pump was irradiated with a single large dose of 20 Gray (Gy) followed by smaller doses of 2 Gy to characterize the dose better. After each dose of radiation was given to both pumps, an internal self-diagnostic test and an independent assessment of the pump timing were performed.
RESULTS. The first
pump malfunctioned completely at a cumulative dose of 38.6 Gy after receiving an individual dose of 20 Gy. The second pump tolerated the single dose of 20 Gy without difficulty and completely malfunctioned at doses of 40 -42 Gy. The second pump exhibited a reduction in pump timing by 25% at a cumulative dose of 40 Gy, which resolved spontaneously by approximately 2 hours.
CONCLUSIONS.
Even if removed from the direct radiation beam, an individual pump could accumulate enough radiation for complete failure during the treatment of fewer than 20 patients. Prior to a complete malfunction, the flow rate of chemotherapy may decrease by 25% for a number of hours without detection. Additional work will be necessary to define further the nature of the reduction in pump timing observed.