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Volume 6, Issue 2 (9-2008) |
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The effect of electronic disequilibrium on the received dose by lung in small fields with photon beams: Measurements and Monte Carlo study
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A. Mesbahi   |
| , asgharmesbahi@yahoo.com |
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Abstract: (12444 Views) |
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Background: Prediction of the absorbed dose in
irradiated volume plays an important role in the
outcome of radiotherapy. Application of small fields
for radiotherapy of thorax makes the dose
calculation process inaccurate due to the existence
of electronic disequilibrium and intrinsic
deficiencies in dose calculation algorithms. To study
the lung absorbed dose in radiotherapy with small
fields, the central axis absorbed dose in heterogeneous
thorax phantom was measured by ionization
chamber and calculated for small fields by Monte
Carlo (MC) method. Materials and Methods: A solid
slab phantom consisting of unit and low density
materials was used for dose measurements. The 6
and 18 MV photon beams of Elekta SL25 linac were
simulated using MCNP4C MC Code. The model was
validated by comparing the calculated depth dose
and beam profiles with measurements in a water
phantom. The MC model was used to calculate the
depth doses in unit density and low density
materials resembling the soft tissue and lung,
respectively. Two small field sizes including 5×5 and
2×2 cm2 were used in this study. Results: The
measured depth dose values were in good
agreement with MC results and the difference less
than 2% was observed. A large dose reduction was
seen in lung for field size of 2×2 cm2 due to the
lateral electronic disequilibrium and it reached up to
16.2% and 33.3% for 6 and 18 MV beams,
respectively. Dose build up and down at material
interfaces was predicted by MC method. Conclusion:
Our study showed that the dose reductions with
small fields in lung and dose variations at interfaces
was very considerable, and inaccurate prediction of
absorbed dose in lung using small fields and photon
beams may lead to critical consequences for
patients. |
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| Keywords: Electronic disequilibrium, radiotherapy of lung, Monte Carlo method. |
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Full-Text [PDF 460 kb]
(4479 Downloads)
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Type of Study: Original Research |
Subject:
Radiation Biology
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Mesbahi A. The effect of electronic disequilibrium on the received dose by lung in small fields with photon beams: Measurements and Monte Carlo study. Int J Radiat Res 2008; 6 (2) :70-76 URL: http://ijrr.com/article-1-406-en.html
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