FIZIKA B 10 (2001)  4, 255-268

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Clinic of Oncology and Radiotherapy, University Hospital Centre Rebro, Kišpatićeva 12, HR-10000 Zagreb, Croatia
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Dedicated to Professor Kseno Ilakovac on the occasion of his 70th birthday

Received 12 September 2001; revised manuscript received 21 January 2002
Accepted 21 January 2002        Online 6 April 2002

An in-vivo dosimetry procedure for direct patient dose reading can help to define deviations of the actually delivered dose from the prescribed one. It is routinely performed by the use of external measurements, i.e. entrance and and exit dose readings at certain locations in the body. This article presents a method for the absorbed dose determination of the patient situated in a large 60Co gamma field, as in total body irradiation (TBI), during in-vivo irradiation and the radiation field analysis at extended distance (in low dose rate conditions) prior to the actual in vivo treatment. The new approach consists of: (1) adjusting the real patient's anatomical data (anterior posterior thickness at a number of points) to the theoretical model of an anthropomorphic phantom of a shape of an elliptical cylinder, and (2) using a n-type silicon field detector with increased sensitivity for the purpose of radiation-field analysis prior to the actual in vivo TBI treatment. Namely, the standard p type field detector, as commercially available for routine radiation field analysis at short distances and high dose rates, was not suitable for radiation field analysis under TBI conditions, because the signal was too weak. Dependence of the calibration factor of the silicon detector, exposed to different dose rates in standard and large field irradiation conditions, was investigated. The detector was found to be suitable for TBI measurements. This was confirmed, among others, in a depth dose curve's behaviour as compared to the results obtained by the standard p-type silicon detector at extended distances.

PACS numbers: 87.53.-j, 87.53.Dq
UDC 539.122

Keywords: in-vivo dosimetry, silicon detector, total body irradiation

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