Dosimetry of beta-ray ophthalmic applicators: Comparison of different measurement methods

An international intercomparison of the dosimetry of three beta particle em itting ophthalmic applicators was performed, which involved measurements wi th radiochromic film, thermoluminescence dosimeters (TLDs), alanine pellets , plastic scintillators, extrapolation ionization chambers, a small fixed-v olume ionization chambers, a diode detector and a diamond detector. The sou rces studied were planar applicators of Sr-90-Y-90 and Ru-106-Rh-106, and a concave applicator of Ru-106-Rh-106. Comparisons were made of absolute dos imetry determined at 1 mm from the source surface in water or water-equival ent plastic, and relative dosimetry along and perpendicular to the source a xes. The results of the intercomparison indicate that the various methods y ield consistent absolute dosimetry results at the level of 10%-14% (one sta ndard deviation) depending on the source. For relative dosimetry along the source axis at depths of 5 mm or less, the agreement was 3%-9% (one standar d deviation) depending on the source and the depth. Crucial to the proper i nterpretation of the measurement results is an accurate knowledge of the de tector geometry, i.e., sensitive volume and amount of insensitive covering material. From the results of these measurements, functions which describe the relative dose rate along and perpendicular to the source axes are sugge sted. (C) 2001 American Association of Physicists in Medicine.