Earnshaw Medal
Earnshaw 2008 Nominees: Anna Linehan
A comparison of TLDs vs diodes for in-vivo patient dosimetry
In vivo dosimetry involves measuring the dose delivered to a particular point on a patient during radiation therapy. The aim of this study was to directly compare the use of semiconductor diode detectors and thermolurninescent detectors for this purpose. The diode was found to have a far superior reproducibility with a standard deviation of 0.9% compared to 2.5% for the TLDs (both for beam energy of 6MV). The TLD was found to possess a larger angular range up to 60°, with the diode only accurate to 40°. However its response was unpredictable with changing field size and SSDs while the diode had a linear response. The diode's response on energy, dose rate and temperature were also measured, as TLDs are independent of these factors, and found to have linear dependences which can be corrected for. Based on these factors, the diode was found to be more suited to point dose measurements for in vivo dosimetry. The possibility of using diodes for TB! was also examined by measuring the effect of placing a spoiler in the beam path on the diode reading as well as the dependence on surface-spoiler distance. While more tests must be performed in order to validate diodes for this purpose, our experiments indicate that diodes could provide a convenient, accurate and efficient alternative to TLDs for TB!.
Supervisor: Dr. Eric Finch (TCD), Dr. Kelly (St. Luke’s Hospital Dublin)
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