Affiliations: Department of Biomedical Sciences and of Morphologic
and Functional Imaging, University of Messina, Messina, Italy | Radiotherapy Unit, University Hospital "G. Martino", Messina, Italy
Note: [] Corresponding author: Ernesto Amato, Department of Biomedical
Sciences and of Morphologic and Functional Imaging, University of Messina, via
Consolare Valeria, 1 – Pad. E, I-98125 Messina, Italy. Tel.: +39 090 2212942;
Fax: +39 090 2212843; E-mail: eamato@unime.it
Abstract: OBJECTIVE: Purpose of this work was to study the
dose perturbation within the target volume of a external MV radiation therapy
when using metal fiducials. METHODS: We developed a Monte
Carlo simulation in Geant4 of a cylindrical fiducial made either of gold or of
steel and simulated the photon irradiation beam originating from a medical
Linac operating at 6, 10 or 15 MV. For each energy, two different irradiation
schemes were simulated: a single 5 × 5-cm square field in the -x
direction, and five 5 × 5-cm fields at 0°, 80°,
165°, 195° and 280°. RESULTS: In a single beam irradiation scheme, we observed a dose reduction behind fiducials
varying from −20% for gold at 6 MV to −5% for steel at 15 MV, and a
dose increment in front of the fiducial ranging from +33% for gold at
15 MV to +10% for steel at 6 MV. When five beams were employed, a dose
increment ranging from +28% to +46% has been found around gold.
Around a steel fiducial, an average increment of +17% was found,
irrespective of the photon energy. CONCLUSIONS: When using a
single beam, the decrement of dose behind both steel and gold markers increases
with the photon energy. This effect vanishes when a multifield treatment is
delivered; in this instance there is a dose increment around fiducials,
according to both fiducial material and photon energy, with lower values for
steel and 6 MV. This energy represents the best choice when fiducial markers
are present inside the irradiated volume.
Keywords: Radiotherapy, Monte Carlo, dose, fiducial marker x-rays
