Modulated electron beam therapy (MERT) using photon multi-leaf collimators (pMLC)
is an emerging technique. In this study characterization of electron beams collimted by
an Elekta Precise machine pMLC for MERT applications was done. The objectives of
the study were: a) to model the Elekta Precise machine using the EGSnrc MC codes to
generate electron energy spectra that replicate the machine. b) study the physical characteristics
of electron beams collimated by the pMLC at different source skin distances
(SSDs) and field sizes and to c) apply the findings in the treatment of scalp with electron
beam.
For objective (a) the EGSnrc/BEAMnrc MC codes were used to extract the electron energy
spectra from simulated PDD data. These spectra were used as input sources in the
MC code. Benchmarking against measurements in water in terms of percentage depth
dose and beam profiles were performed for 4â15 MeV over different applicators sizes.
Physical characteristics of the electron beams collimated by the pMLC using the generated
energy spectra were calculated. The SSDs ranged from 60â100 cm, field sizes
ranged from 1 Ã 1 up to 20 Ã 20 cm2. An anthropomorphic phantom for total scalp
treatment scanned using CT. Eight fields were incident on the scalp from different angles
for a 4 MeV electron beam.
The results showed that the generated electron energy spectra can be assumed to be a
realistic approximation of the linac. Penumbra data indicated that 60 cm SSD was the most favorable treatment distance for MERT. At this distance the field size is conserved.
The output factors were much higher compared to applicator collimated electron beams.
This will accelerate the MERT based dose delivery. No detectable leakage through the
pMLC was observed. The penumbra for single large fields can be improved by using
weighted abutted smaller fields. The virtual source position was found to be at 5 cm
below the exit window. The scalp treatment showed excellent dose distribution and optimal
dose coverage of the target while sparing distal organs at risk as quantified by a
dose volume historgam.
This study domenstrated that the MERT technique can be implemented on an Elekta
Precise. MC techniques showed to be valuable tools for doing forward optimization
and MERT driven dose calculations.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-11192010-152203 |
| Date | 19 November 2010 |
| Creators | Ali, Omer A |
| Contributors | Prof CA Willemse, Dr FCP du Plessis |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-11192010-152203/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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