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Title: The optimisation of an X-Ray fluorescence system for the in vivo measurement of platinum in head and neck tumours
Author: Bennett, C. A.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1998
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There is still much information to be gained on the pharmacokinetics of platinum based chemotherapy agents such as cisplatin, and its second generation analogue, carboplatin. A 99mTc based XRF system in backscatter geometry has been re-introduced in Swansea, for the in vivo measurement of platinum uptake in head and neck tumours. The minimum detection limit (MDL) was found to be 21 ppm for a tumour depth of 10 mm, increasing to 40 ppm for a depth of 20 mm, for a skin dose of 9 mGy. In vivo measurements were therefore limited to superficial tumours only. Eight patients underwent a total of fifteen measurements using the 99mTc system. The MDL was exceeded in five of these measurements. Replacing the 99m Tc source with 133Xe, and optimising the collimator-to-skin distance, improved the sensitivity of the system for tumour depths less than 15 mm. The MDL was reduced to 15 ppm at a depth of 10 mm, for the same skin dose. The sensitivity of the Swansea in vivo XRF system was significantly improved by the introduced of a polarised x-ray source. A clinical orthovoltage x-ray unit (Pantak DXT-300), which is routinely used for radiotherapy treatments, was adapted for this purpose. Experimental investigation into the effect of varying the operating voltage, polarising material and additional filtration on the system sensitivity, showed that the optimum combination consisted of a copper polariser, 0.25 mm of additional tin filtration in the primary beam and an operating voltage of 220 kV. The MDL at a depth of 20 mm was 8 ppm for the optimised system, with a corresponding skin dose of approximately 3 mGy. This represents more than an 80% reduction in the MDL compared to the 99mTc based system, enabling the measurement of deeper tumours, with increased sensitivity.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available