The thermal characteristics of different diodes on in vivo patient dosimetry.
Diode sensitivity variations with temperature (SVWT) have been reported to vary from small negative values up to 0.6% per degrees C. Thus it is possible for diode calibration factors established at room temperature (approximately 20 degrees C) to yield errors in the range of -1% to +9% when diodes are placed on a patient's skin (approximately 30 degrees C) for in vivo entrance dose measurements. In this study we simulated several skin temperatures using a temperature-controlled aluminum surface in contact with a section of Bolus. The internal temperatures of several diodes with different buildup thickness were monitored as a function of time when placed in contact with the heated bolus. Our results indicate that for different combinations of room temperature (18 degrees C-23 degrees C) and patient skin temperature (28 degrees C-34 degrees C) diodes reached 90% of their equilibrium temperature within 3-5 min. In addition, the range of typical skin temperatures was determined by measurements performed on a number of actual patients under clinical conditions. Based on the results of our experiments a protocol was developed to minimize the temperature based errors for in vivo dosimetry.
Welsh
K T
KT
Department of Radiation Oncology, The State University of New York at Stony Brook, 11794-7028, USA.
Reinstein
L E
LE
D006358:Hot Temperature; D006801:Humans; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods*; D012867:Skin / Q000528:radiation effects; D013696:Temperature; D013997:Time Factors