A study on beams passing through hip prosthesis for pelvic radiation treatment.
OBJECTIVE
To study the dose distributions at the interface due to the presence of a metal implant; to show the dose distributions in combined fields in the presence of hip prostheses; and to demonstrate the capabilities and limitations of a conventional system.


METHODS
Perturbations in the dose distribution caused by a hip prosthesis can result in unacceptable dose inhomogeneities within the target volume and in regions where tissues interface with implant. The Monte Carlo technique and a conventional treatment planning system are used to calculate 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 in 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 Monte Carlo simulation and a commercial treatment planning system (CADPLAN). We found that CADPLAN underestimated the attenuation of hip prostheses. This has led to overestimation of the target dose by 14% for a typical four-field 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.
Ding
G X
GX
Department of Medical Physics, Fraser Valley Cancer Centre, British Columbia Cancer Agency, Surrey, BC, Canada. gding@bccancer.bc.ca
Yu
C W
CW
D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D013232:Steel; D014057:Tomography, X-Ray Computed
D013232:Steel