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Depth absorbed dose distributions for electrons
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1976 Phys. Med. Biol. 21 453 (http://iopscience.iop.org/0031-9155/21/3/015) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 128.111.121.42 This content was downloaded on 22/11/2014 at 00:43
Please note that terms and conditions apply.
PHYS. MED. BIOL.,
1976, VOL. 21, NO. 3, 453-454 @ 1976
CORRESPONDENCE Depth Absorbed Dose Distributions for Electrons THE EDITOR, Sir, We should like to comment on the reply to our letter (Atherton andColeman 1975) by Dr. Brahme and Dr. Svensson regarding their comparisons of microtron and linear accelerator electron beam central axis depth dose distributions (Brahme, Hult6n and Svensson 1975, Brahme and Svensson 1976). Our measurementsof dose in the build-up region were made withthe multiple plate sealed ion chamber capsule in position. This assembly, with its upper and lower covers of the capsule, provides most of the scattering which is required a t 10 MeV to produce an adequate beam area. It isthereforeincorrectfor Brahme and Svensson to describe it as 'a beam of little clinical use'. Furthermore, since they accept the diode detector as satisfactory for measurements beyond the dose maximum we feel that our comparisons for this part of the depth dose distribution are valid. We note their objection to the use of the semiconductordetectorin the build-up region and have now received data relating to the sL75-20 beams measured in the build-up region with a liquid ion chamber, and in the fall-off region with anordinary ionizationchamber, which have been supplied by Professor Kotter and Dr. Lindskoug of Sahlgrenska Sjukhuset, Gothenburg.
'OFT EIeclr001 I0H.V IO x IOtm.
Lsquld
90 0
-
l
D
B
,on chamber
5L75.20 LlnaF Hicrotron
~
""~
O
1 2 3 L Depth tn water ( c m )
Fig. 1.
5
6
454
Correspondence
We are grateful to them for permission to make use of this information. I n fig. 1 the results of the foil scattered and collimated 10 MeV electron beam measured with a liquid ion chamber are presented together with the measurements made on a microtron with a foil scatterer, which were given by Brahme and Svensson in fig. 2 of their paper. Allowing for the differences in the nominal it is apparent that the beamenergy as determined byextrapolatedrange fall-off characteristics as judged by the 85, 50 and 30% values are virtually identical. It is also interesting to note that in the fall-off region this normal clinical beam agrees exactly with the distribution given in our previous letter even though this was attained without added scatterer or collimator. In the build-up region the liquid ion chamber results for both machines are similar. Although the surface dose for the microtron is some 5% lower, the 80% doses are within 1.5 mm and the 85% values within 2.5 mm. While the differences may be of scientific interest, we submit that for clinical purposes they are not significant. our conclusion that when measurementsaretaken Theseresultssupport undersimilarconditions the claim that the narrowenergy spectrum, clean geometryand small amount of scatteringin the microtronproducebeams significantly different from those obtained from linear accelerators cannot be justified. L.ATHERTON, Particle Accelerator Division, M.E.L. Equipment Company Ltd, Manor Royal, Crawley, West Sussex RH10 2PZ, 26 February 1976 U.K. REFERENCES ATHERTON,L., and COLEMAN,F. J., 1975, Phys. M e d . Biol., 20, 658. BRAHME, A., HULTEN, G., and SVENSSON,H., 1975, Phys. M e d . Biol., 20, 39. BRAHME, A., and SVENSSON,H., 1976, Phys. M e d . Biol., 21, 304.
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About
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My IOPscience
Depth absorbed dose distributions for electrons
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1976 Phys. Med. Biol. 21 453 (http://iopscience.iop.org/0031-9155/21/3/015) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 128.111.121.42 This content was downloaded on 22/11/2014 at 00:43
Please note that terms and conditions apply.
PHYS. MED. BIOL.,
1976, VOL. 21, NO. 3, 453-454 @ 1976
CORRESPONDENCE Depth Absorbed Dose Distributions for Electrons THE EDITOR, Sir, We should like to comment on the reply to our letter (Atherton andColeman 1975) by Dr. Brahme and Dr. Svensson regarding their comparisons of microtron and linear accelerator electron beam central axis depth dose distributions (Brahme, Hult6n and Svensson 1975, Brahme and Svensson 1976). Our measurementsof dose in the build-up region were made withthe multiple plate sealed ion chamber capsule in position. This assembly, with its upper and lower covers of the capsule, provides most of the scattering which is required a t 10 MeV to produce an adequate beam area. It isthereforeincorrectfor Brahme and Svensson to describe it as 'a beam of little clinical use'. Furthermore, since they accept the diode detector as satisfactory for measurements beyond the dose maximum we feel that our comparisons for this part of the depth dose distribution are valid. We note their objection to the use of the semiconductordetectorin the build-up region and have now received data relating to the sL75-20 beams measured in the build-up region with a liquid ion chamber, and in the fall-off region with anordinary ionizationchamber, which have been supplied by Professor Kotter and Dr. Lindskoug of Sahlgrenska Sjukhuset, Gothenburg.
'OFT EIeclr001 I0H.V IO x IOtm.
Lsquld
90 0
-
l
D
B
,on chamber
5L75.20 LlnaF Hicrotron
~
""~
O
1 2 3 L Depth tn water ( c m )
Fig. 1.
5
6
454
Correspondence
We are grateful to them for permission to make use of this information. I n fig. 1 the results of the foil scattered and collimated 10 MeV electron beam measured with a liquid ion chamber are presented together with the measurements made on a microtron with a foil scatterer, which were given by Brahme and Svensson in fig. 2 of their paper. Allowing for the differences in the nominal it is apparent that the beamenergy as determined byextrapolatedrange fall-off characteristics as judged by the 85, 50 and 30% values are virtually identical. It is also interesting to note that in the fall-off region this normal clinical beam agrees exactly with the distribution given in our previous letter even though this was attained without added scatterer or collimator. In the build-up region the liquid ion chamber results for both machines are similar. Although the surface dose for the microtron is some 5% lower, the 80% doses are within 1.5 mm and the 85% values within 2.5 mm. While the differences may be of scientific interest, we submit that for clinical purposes they are not significant. our conclusion that when measurementsaretaken Theseresultssupport undersimilarconditions the claim that the narrowenergy spectrum, clean geometryand small amount of scatteringin the microtronproducebeams significantly different from those obtained from linear accelerators cannot be justified. L.ATHERTON, Particle Accelerator Division, M.E.L. Equipment Company Ltd, Manor Royal, Crawley, West Sussex RH10 2PZ, 26 February 1976 U.K. REFERENCES ATHERTON,L., and COLEMAN,F. J., 1975, Phys. M e d . Biol., 20, 658. BRAHME, A., HULTEN, G., and SVENSSON,H., 1975, Phys. M e d . Biol., 20, 39. BRAHME, A., and SVENSSON,H., 1976, Phys. M e d . Biol., 21, 304.
