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FIZIKA B 10 (2001) 4, 255-268
 
TOTAL BODY IRRADIATION DOSIMETRY OF A LOW DOSE RATE 60Co
GAMMA FIELD
MLADEN VRTAR
Clinic of Oncology and Radiotherapy, University Hospital Centre
Rebro, Kišpatićeva 12, HR-10000 Zagreb, Croatia
E-mail addresses: mlvrtar@phy.hr
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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