Dose perturbations from implanted helical gold markers in proton therapy of prostate cancer

Abstract

Abstract

Implanted gold fiducial markers are widely used in radiation therapy to improve targeting accuracy.  Recent investigations have revealed that metallic fiducial markers can cause severe perturbations in dose distributions for proton therapy, suggesting smaller markers should be considered.  This objective of this study was to estimate the dosimetric impact of small gold markers in patients receiving proton therapy for prostate cancer.  Small, medium, and large helical wire markers of diameter 0.04 mm, 0.25 mm and 0.5 mm, respectively, and length 10 mm were implanted in an anthropomorphic phantom.  Radiographic visibility was confirmed using a kilovoltage x-ray imaging system; the dose perturbations were predicted from Monte Carlo simulations and confirmed by measurements.  Monte Carlo simulations indicated that size of dose perturbation depended on marker size, orientation, and distance from the beam’s end of range.  Specifically, the perturbation of proton dose for the lateral-opposed-pair treatment technique was 31% for large markers and 23% for medium markers in a typical orientation.  Consequently, these markers are not well suited for use in patients receiving proton therapy for prostate cancer.  Dose perturbation was not observed for the small markers, but these markers were deemed too fragile for transrectal implantation in the prostate.