High-presssure liquid chromatographic determination of methotrexate and its major metabolite, 7-hydroxymethotrexate, in human plasma.

Abstract

Background and purpose: It is estimated that one third of the institutes applying clinical beta sources does not perform\nindependent dosimetry. The Netherlands commission on radiation dosimetry (NCS) recently published recommended\nquality control procedures and detectors for the dosimetry of beta sources. The main issues of NCS Report 14 are\nsummarized here.\nMaterials and methods: A dosimetry survey was performed among 23 institutes in The Netherlands and Belgium. Well\nionization chambers, a plastic scintillator, plane-parallel ionization chamber, diode and radiochromic film were used for\ndetermination of source strength (dose rate at reference distance) and uniformity of intravascular and ophthalmic\nsources. The source strength of multiple sources of each type was measured and compared with the source strength\nspecified by the manufacturer.\nResults: The standard deviation of the difference between measured and specified source strength was mostly about\n3%, but varied between 0.8 and 15.8% depending on factors such as source type, detector, phantom and manufacturers\ncalibration. The average non-uniformity was about 7% for intravascular sources and 20% for ophthalmic sources. It is\nestimated that the total relative standard uncertainty can be kept below G4% (1s) with all detectors tested. Maximum\ndeviations in source strength of 10% and a non-uniformity below 10% (intravascular) and 30% (ophthalmic) are\nrecommended.\nConclusions: Dosimetric and non-dosimetric quality control procedures on beta sources are recommended. They enable\nstandardized measurements, including the determination of relative source strength and non-uniformity. Absolute\ncalibrations depend on the future introduction of primary standards for clinical beta sources.