Measurement of absorbed doses near metal and dental material interfaces irradiated by X- and gamma-ray therapy beams

Abstract

Soft-tissue damage adjacent to dental restorations is a deleterious side effect of radiation therapy which is associated with low-energy electron scatter from dental materials of high electron density. This study was designed to investigate the enhancement of dose to soft tissue (or water) close to high electron-density materials and to measure the detailed lateral and depth-dose profiles in soft-tissue-simulating polymer adjacent to planar interfaces of several higher atomic-number materials: 18-carat gold dental casting alloy; Ag-Hg dental amalgam alloy; Ni-Cr dental casting alloy; and natural human tooth structure. Interleaved stacks of calibrated thin radiochromic dosimeter films and tissue-simulating polymer were used for these measurements. Assemblies of these polymer-dosimeter stacks on both sides of the dental materials were irradiated in one fixed direction by collimated 60Co gamma-ray or 10 MV x-ray beams directed perpendicularly to the material interfaces. In another test, designed to simulate more closely therapeutic treatment conditions, a phantom constructed on both sides of a row of restored and unrestored whole teeth (restoration materials: gold alloy crown; Ni-Cr alloy crown; Ag-Hg mesial-occlusal-distal (MOD) amalgam filling; unrestored tooth) was irradiated in one fixed direction by the collimated photon beams. Results indicate that the dose-enhancement in 'tissue' is as great as a factor of 2 on the backscatter side adjacent to gold and a factor of 1.2 adjacent to tooth tissue, but is insignificant on the forward-scatter side because of the predominant effect of attenuation by the high-density, high atomic-number absorbing material.

Backscattered Dose Perturbation Effects at Metallic Interfaces Irradiated by High-Energy X- and Gamma-Ray Therapeutic Beams

“…When a patient is treated with high atomic number metallic inhomogeneities embedded in body tissues, the dose at the metal-tissue interface increases significantly [9,10,30,33,35]. The metallic interfaces within the patient are formed by metallic prosthesis, metal tubes and pins placed after surgery, permanent metal implants, and the dental materials in teeth.…”

Effects of implantable biomaterials on radiation dosimetry

“…6 Other studies explain intuitive or anecdotal evidence of soft or hard tissue complications from radiation-dose enhancement proximal to metallic materials, such as gold dental crowns. 1,3,[7][8][9][10] Although the use of parallelopposed treatment fields minimizes these effects, the development of three-dimensional conformal techniques for treatment is reducing the prevalence of opposed fields, thus increasing the dose variances across interfaces between implants and normal tissue.…”

Feasibility of optimizing intensity‐modulated radiation therapy plans based on measured mucosal dose adjacent to dental fillings and toxicity outcomes

“…A number of previous studies have revealed the need for more accurate dose calculation techniques, such as Monte Carlo algorithm, especially when the structure is very close to the metallic implants and the local dose gradient is high, for example the abutting buccal or lingual mucosa as being studied here 14, 15, 16. Novel dose distributions generated by varying beam intensity and geometry within the IMRT software may explain the discrepancy in the trend of dose perturbations between this study and previous studies17, 18 most of which were done based on conventional RT techniques.…”