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

Annelise Giebeler,George Ciangaru,Wayne Newhauser,Jonas Fontenot,Peter Balter,Ronald Zhu

doi:10.1120/jacmp.v10i1.2875

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. The 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 with lengths of 10 mm and helix diameters of 0.35 mm, 0.75 mm, and 1.15 mm, respectively, were implanted in an anthropomorphic phantom. Radiographic visibility was confirmed using a kilovoltage x‐ray imaging system, and 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 oblique orientation. Results for perpendicular and parallel orientations were respectively lower and higher. 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.PACS number: 87.53.Pb

Highlights

The full potential of external beam radiation therapy can only be realized if the radiation field is accurately targeted on diseased tissue
64 Giebeler A. et al.: Helical gold markers in proton prostate therapy therapeutic proton dose which, in the case of gold fiducial markers, can cause dose to be reduced by as much as 85% from the prescribed amount.[11,12] A fiducial marker’s size, composition, location, and orientation are key factors that should be considered when determining the appropriateness of a marker’s use in patients receiving proton therapy. This was illustrated in a recent study by Newhauser et al[11] in which proton dose perturbations caused by solid cylindrical markers made of gold, stainless steel, and titanium were compared using Monte Carlo simulations
Our results indicate that proton dose perturbations caused by the medium and large helical gold markers exceeded 10%

Summary

Introduction

The full potential of external beam radiation therapy can only be realized if the radiation field is accurately targeted on diseased tissue. 64 Giebeler A. et al.: Helical gold markers in proton prostate therapy therapeutic proton dose which, in the case of gold fiducial markers, can cause dose to be reduced by as much as 85% from the prescribed amount.[11,12] A fiducial marker’s size, composition, location, and orientation are key factors that should be considered when determining the appropriateness of a marker’s use in patients receiving proton therapy This was illustrated in a recent study by Newhauser et al[11] in which proton dose perturbations caused by solid cylindrical markers made of gold, stainless steel, and titanium were compared using Monte Carlo simulations. Study results suggested that gold markers with a smaller mass may provide an acceptable solution

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Conclusion