TITLE:
Dosimetric Evaluation of Heterogeneities in Small Circular Fields of 6 MV Photon Beams with EBT2 and EDR2 Films: Comparison with Monte Carlo Calculation
AUTHORS:
Ali Mohammad, Hassan A. Nedaie, Mehran YarAhmadi, Nooshin Banaee, Mansour Naderi, Zohre Tizmaghz
KEYWORDS:
Stereotactic Radiosurgery, Heterogeneities, Film Dosimetry, Monte Carlo Calculation
JOURNAL NAME:
Journal of Modern Physics,
Vol.5 No.16,
October
21,
2014
ABSTRACT: The influence
of dose variation due to heterogeneities in narrow photon beams used in stereotactic
radiosurgery has been investigated. Since the lateral electronic disequilibrium
and existence of steep dose gradients in small fields and the presence of heterogeneities
can intensify these problems, in this study the effects of heterogeneities on 6
MV small photon beams produced by circular cone collimators with 5, 10, 15, 20 and
30 mm diameters are investigated. The heterogeneities include 3 cm Cork with density
of 0.2 g/cm3 instead of lung and 3 cm Polytetrafluoroethylene (P.T.F.E)
with density of 2.2 g/cm3 as bone. The measurements were carried out
with EBT2 gafchromic and EDR2 radiographic films. Simulation was done by MCNP Monte
Carlo Code (MCNP5). The depth dose curves in heterogeneous phantom were compared
with homogeneous phantom. A good agreement was obtained within film and Monte Carlo
calculations in presence of low density heterogeneity and also in the presence of
high density heterogeneity. Monte Carlo results showed good agreement after stopping
power correction.