Purpose: To study the dose distributions at the interface due to the presen
ce of a metal implant; to show the dose distributions in combined fields in
the presence of hip prostheses; and to demonstrate the capabilities and li
mitations of a conventional system.
Methods and Materials: Perturbations in the dose distribution caused by a h
ip prosthesis can result in unacceptable dose inhomogeneities within the ta
rget volume and in regions where tissues interface with implant. The Monte
Carlo technique and a conventional treatment planning system are used to ca
lculate the dose distributions.
Results: Dose increases of 15% in tissue are seen at the interface between
metal implant and tissue. Dose reductions of 5-25% or 10-45% are observed i
n the shadow of the hip prosthesis made of 0.5-3-cm-thick titanium or steel
alloy respectively. We compared predicted dose distribution between the Mo
nte Carlo simulation and a commercial treatment planning system (CADPLAN).
We found that CADPLAN underestimated the attenuation of hip prostheses. Thi
s has led to overestimation of the target dose by 14% for a typical four-fi
eld box technique.
Conclusions: An acceptable dose distribution can be achieved with a proper
lateral beam weighting and compensation using an eight-field technique. The
beam compensation may be applied to achieve an adequate target dose. (C) 2
001 Elsevier Science Inc.