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An isotope activity monitor (for radiotherapy)
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1975 Phys. Med. Biol. 20 142 (http://iopscience.iop.org/0031-9155/20/1/014) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 129.96.252.188 This content was downloaded on 03/10/2015 at 20:53
Please note that terms and conditions apply.
PHYS. MED. BIOL.,
1975, VOL. 20, NO. 1, 142-143. 0 1975
Instrumentab Note
An Isotope Activity Monitor D. L. HASKARD Anti-Cancer Foundation, University of Adelaide, South Australia Received 8 July 1974
1. Introduction
When intracavitary gynaecological applicatorsare used inradiotherapy, the associated dosimetry calculation can predict patient dosage with reasonable accuracy. An unknown error, however, could arise from incorrect choice of the caesium or cobalt tubes, because the identification code may be relatively faint or hard to distinguish. This means that the person responsible for the assembly of the applicator can be subject to considerable exposure due t o the time involved in reading and checking the source strength. As a result, an isotope activity monitor has been developed for use in this work. The caesium tube is placed in an indentation on a stainless steel sheet, above an ion chamber, and the source activity is displayed in digital form on the monitor panel meter. The monitor is calibrated for I3’Cs (up to 200 mCi for our monitor) although 6oCosources can also be checked as the equivalent values are printed on the monthly source strength tables by the computer. General description of monitor The monitor consists of a semi-cylindrical ion chamber sealed in a perspex box 7 5 x 75 x 50 mm, as shown in fig. 1. This type of chamber was chosen rather than a well chamber, due to the ease with which the sources could be placed for measurement. The collector consists of an 18 mm diameter cylinder by a rod made from 0.05 mm brass shim, which is supported along its axis attached to the BNC connector at the side of the chamber. The outer shield of 2.
,Leod shielding 25 mm thick
‘Brass shim 0.25 m m Fig. 1. Construction of monitor. All measurements given are in mm.
An Isotope Activity Monitor
143
the BNC connector is earthed (providing a guard ring) and the brass shim plate attached t o the top of the chamber is also earthed. This plate is necessary to shift the active volume of the chamber away from the source in order to reduce the inversesquare law errors due to sources of different diameters. The high tension (HT) plate consists of a 0.25 mm brass shim bent in a semicylindrical shape, with ends attached. The whole chamber is then mounted in a 25 mm thick lead shield. The ion chamber current is amplified and then Meter (DPM) model displayedon an Analog Devices 34 digitDigitalPanel AD2010/E. The monitor (component cost approximately Australian $150) has been in operation for six months, and has proved a valuable asset in the checking of the sources while loadingorunloading theintracavitary gynaecological applicators. Details of circuits can be obtained from the author on request. 3.
Summary
An instrument for monitoringthe activityof clinical gamma radiationsources used in intracavitary gynaecological applicators is described. This device is used routinelyfor checking the sources on loading and unloading of the applicators, and has proved a valuable asset in minimizing personnel radiation exposure and detecting possible errors in tube activity.
Search
Collections
Journals
About
Contact us
My IOPscience
An isotope activity monitor (for radiotherapy)
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1975 Phys. Med. Biol. 20 142 (http://iopscience.iop.org/0031-9155/20/1/014) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 129.96.252.188 This content was downloaded on 03/10/2015 at 20:53
Please note that terms and conditions apply.
PHYS. MED. BIOL.,
1975, VOL. 20, NO. 1, 142-143. 0 1975
Instrumentab Note
An Isotope Activity Monitor D. L. HASKARD Anti-Cancer Foundation, University of Adelaide, South Australia Received 8 July 1974
1. Introduction
When intracavitary gynaecological applicatorsare used inradiotherapy, the associated dosimetry calculation can predict patient dosage with reasonable accuracy. An unknown error, however, could arise from incorrect choice of the caesium or cobalt tubes, because the identification code may be relatively faint or hard to distinguish. This means that the person responsible for the assembly of the applicator can be subject to considerable exposure due t o the time involved in reading and checking the source strength. As a result, an isotope activity monitor has been developed for use in this work. The caesium tube is placed in an indentation on a stainless steel sheet, above an ion chamber, and the source activity is displayed in digital form on the monitor panel meter. The monitor is calibrated for I3’Cs (up to 200 mCi for our monitor) although 6oCosources can also be checked as the equivalent values are printed on the monthly source strength tables by the computer. General description of monitor The monitor consists of a semi-cylindrical ion chamber sealed in a perspex box 7 5 x 75 x 50 mm, as shown in fig. 1. This type of chamber was chosen rather than a well chamber, due to the ease with which the sources could be placed for measurement. The collector consists of an 18 mm diameter cylinder by a rod made from 0.05 mm brass shim, which is supported along its axis attached to the BNC connector at the side of the chamber. The outer shield of 2.
,Leod shielding 25 mm thick
‘Brass shim 0.25 m m Fig. 1. Construction of monitor. All measurements given are in mm.
An Isotope Activity Monitor
143
the BNC connector is earthed (providing a guard ring) and the brass shim plate attached t o the top of the chamber is also earthed. This plate is necessary to shift the active volume of the chamber away from the source in order to reduce the inversesquare law errors due to sources of different diameters. The high tension (HT) plate consists of a 0.25 mm brass shim bent in a semicylindrical shape, with ends attached. The whole chamber is then mounted in a 25 mm thick lead shield. The ion chamber current is amplified and then Meter (DPM) model displayedon an Analog Devices 34 digitDigitalPanel AD2010/E. The monitor (component cost approximately Australian $150) has been in operation for six months, and has proved a valuable asset in the checking of the sources while loadingorunloading theintracavitary gynaecological applicators. Details of circuits can be obtained from the author on request. 3.
Summary
An instrument for monitoringthe activityof clinical gamma radiationsources used in intracavitary gynaecological applicators is described. This device is used routinelyfor checking the sources on loading and unloading of the applicators, and has proved a valuable asset in minimizing personnel radiation exposure and detecting possible errors in tube activity.
