O9. Dosimetry effects caused by bilateral and unilateral hip prostheses: A Monte Carlo study in megavoltage photon radiotherapy. (September 2016)

• Record Type: Journal Article
• Authors: Mahuvava, C.
• Is Part Of: Physica medica. Volume 32(2016)Supplement 2
• Page Start: 143
• Publication Date: 2016-09
• Subjects: Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2016.07.017
• Languages: English
• ISSNs: 1120-1797

Abstract

Abstract : Introduction: Hip prostheses (HPs) are used in hip augmentation to replace diseased hip joints. However, high-density and high-atomic-number inserts may cause dose perturbations in the target volume and in tissue-HP interface regions. This study evaluates the dosimetric effect of various HPs during prostate radiotherapy using Monte Carlo (MC) simulations. Materials and Methods: BEAMnrc and DOSXYZnrc MC user-codes were respectively used to model an Elekta Precise linac head and to calculate absorbed dose distributions in a CT-based phantom. Unilateral and bilateral HP contours were delineated in the pelvis CT dataset using MCSHOW and then converted into stainless steel (SS316L), titanium (Ti6Al4V) and ultra-high-molecular-weight polyethylene (UHMWPE) using an IDL code. Four, five and six conformal photon field plans of 6, 10, 15 and 20 MV were used. Results: The dose within and beyond the metallic inhomogeneity drops significantly due to beam attenuation. For bilateral prostheses, the maximum isocenter dose reduction was 23%, 17% and <1% for SS316L, Ti6Al4V and UHMWPE, respectively. For unilateral HP, the respective dose reductions were 19%, 12% and <1%. The 6-field plan produced the best target coverage and least dose perturbation. Up to 38% dose enhancement was found at the bone-steel proximal interface due to radiation backscattered from the metal surface. Backscatter perturbation was more pronounced than forward scatter. Conclusions: Our software enabled the addition of HPs in the CT dataset of a patient without HPs, allowing simulations to be performed without metal artefacts. Plans with more oblique beam portals can compensate for dose attenuated in fields passing through HPs. Shadowing and interface effects are density-dependent and greatest for SS316L. The attenuation effect of metallic HPs can be minimized (to below 5%) by using a 6-field plan at high energies. However, non-coplanar beams may be necessary to avoid HPs whilst giving sufficient target dose.