SACM - Australia
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Item Restricted Evaluation Of The Radiodensity Of Prosthetic Dental Materials For Head And Neck Radiotherapy(Saudi Digital Library, 2025) Bahakam, Omar; Judge, Roy; Ungureanu, Elena; Sapkaroski, Daniel; Judge, RoyAbstract Background and Study Rationale: Head and neck cancers are among the most prevalent tumours worldwide, with more than 900,000 new cases reported each year. It is estimated that Australia records about 5000 new cases every year. Of the many choices of treatment, radiotherapy remains a viable option in managing tumours, as evidenced by the fact that around 78% of head and neck cancer patients received it1-3. Radiotherapy has also grown, and unlike three-dimensional conformal radiation therapy, radiation therapy now involve using intensity-modulated radiation therapy, volumetric-modulated arc therapy and proton therapy3. These advancements are made to improve the effectiveness of radiation and reduce its effects on other parts of the body and organs to reduce side effects. However, in patients with head and neck cancer, the problem with foreign bodies such as dental prostheses and restorations comes into play as they pose a challenge regarding radiation treatment planning and delivery owing to difficulties in dose distribution. Defining the image of a tumour and its relationship with the surrounding anatomical structures is difficult in the case of gold, amalgam, and zirconia dental restorations1-5. Improvements in imaging techniques and algorithms used in radiation therapy treatment planning are still insufficient to accurately calculate the exact needed radiation dose due to dental restoration artifacts. The purpose of this work is to compare the effects of various dental prosthetic materials on the radiation dose distribution and to discuss possible strategies for reducing these artefacts. As a result, the study aims at enhancing the effectiveness of radiation therapy for head and neck cancer patients with a view of increasing the chances of accurate treatment planning and enhanced prognoses. Study Aims and Objectives: This study, which was carried out in collaboration with the University of Melbourne and Peter MacCallum Cancer Centre, assesses the radiodensity of commonly used dental prostheses and restorations. Through conducting a detailed examination of the radiographic properties of common dental materials, the research aims to determine the effects of these materials on the accuracy of the radiation dose delivery and their effect on the treatment outcome. At the end of the study, the research will offer recommendations that would help to reduce the impact of dental prosthetic materials in radiation therapy planning for patients with head and neck cancer. The study has three primary objectives: 1) To create a jaw model that accurately represents the radiodensities of a human jaw, which will be used to investigate dental prostheses. 2) Measure the radiodensity of commonly used dental materials; their effect on radiation therapy treatment planning will be analyzed to develop dental prosthetic artefact tables. 3) To develop a clinical protocol to improve the current radiation therapy treatment planning for head and neck cancer patients. The study has been rigorously reviewed and approved by the Peter MacCallum Cancer Centre Low and Negligible Risk Research Ethical Review Committee (LNRR-ERC), under HREC Reference: HREC/80541/PMCC. Methodology: This work entailed developing a jaw model that is incorporated into an anthropomorphic phantom, and measuring the radiodensity of various dental prostheses to assess their impact on radiation therapy (RT) planning. A) Model Construction: The process started with the acquisition of a stone dental cast which was used to produce a digital jaw model. Then, oral hard tissues including enamel, dentin and bone were virtually sectioned and modeled with the aid of different CAD software. CBCT scans of patients treated at Peter MacCallum Cancer Centre were used to calibrate the radiodensity of the model to be as close as possible to real oral hard tissue. The physical model was then 3D printed using Iron PLA and PLA materials for the model’s construction. The dental prostheses of different types such as crowns and bridges were placed into the model for mimicing multiple clinical situations. B) Scanning and Data Collection: The second phase involved taking multiple CT scans with dental cone-beam CT (CBCT) and radiotherapy CT (RT CT). The scanning scenarios included scanning each prosthesis by itself and multiple prostheses together. Hounsfield Unit (HU) values were obtained in a very systematic manner to assess the effect of each prosthesis on image quality. Also, scans with and without laboratory putty were done to check the impact of laboratory putty on the image artifacts. Results: This study aims to know the effect of various dental prosthetic materials on the CT scan imaging quality between Radiation Therapy CT (RT CT) and Dental Cone Beam CT (CBCT). The outcomes are restricted to Hounsfield Unit (HU) values since they represent the image quality and the artifact severity in different materials and conditions. Gold Crown (#27):Gold crowns generated significantly higher artifacts in RT CT than Dental CBCT. Without other prostheses, RT CT recorded a mean HU of 20,265 compared to 15,980 in Dental CBCT, indicating a 21% reduction in artifacts for Dental CBCT (p < 0.001). With additional prostheses and the use of lab putty, the artifacts were further reduced by up to 64% in Dental CBCT compared to RT CT. Zirconia Crown (#26):RT CT generally produced higher HU values than Dental CBCT. In isolated scans, Dental CBCT recorded 33% higher values. However, in more complex scenarios, including multiple prostheses, the difference between RT CT and Dental CBCT became less significant, especially with the use of lab putty, which minimized the variance in HU values between the two imaging modalities. Amalgam Restoration (#25):Dental CBCT consistently yielded lower HU values, with a reduction of 59% in artifacts compared to RT CT. The use of putty further minimized artifacts, resulting in a 69% reduction in Dental CBCT compared to RT CT (p < 0.001). Lithium Disilicate Crown (#24):The difference in HU values between RT CT and Dental CBCT was relatively small for lithium disilicate crowns. The maximum recorded difference was approximately 8%, and no significant statistical difference was observed between the two modalities. PFM Crown (#23):PFM crowns consistently generated higher artifacts in RT CT compared to Dental CBCT. In the most complex scenarios, RT CT recorded 78% higher HU values than Dental CBCT (p < 0.001). Lab putty significantly reduced the artifacts in Dental CBCT scans. Implant (#22):The implant model showed consistently better image quality and fewer artifacts in Dental CBCT, with artifact reductions ranging from 33% to 51% across various scenarios. Dental CBCT scans were consistently superior to RT CT scans for imaging implants. Maryland Bridge (#21 & #11):Dental CBCT recorded significantly fewer artifacts for both the metal wedge and ceramic pontic parts of the Maryland bridge compared to RT CT. Artifact reduction ranged from 25% to 46%, depending on the complexity of the scanning scenario. Lithium Disilicate Veneer (#12) and Composite Restoration (#14):Both lithium disilicate veneers and composite restorations produced lower HU values in both imaging modalities, with no significant difference observed between RT CT and Dental CBCT scans. PFM Bridge (#15-17):RT CT scans consistently recorded higher HU values compared to Dental CBCT. Dental CBCT reduced artifacts by up to 50% when combined with the use of lab putty. Among the different dental materials, Dental CBCT generated lower HU values, which consequently means less artifacts, and therefore suitable for use in radiation therapy planning especially when dealing with dental prostheses. Conclusion: This study involved the development of a 3D jaw model that accurately represented the radiodensities of various oral hard tissues. Additionally, the study demonstrated that dental Cone Beam CT (CBCT) generated significantly fewer artefacts and lower Hounsfield Unit (HU) values compared to Radiation Therapy CT (RT CT) when imaging dental prosthetic materials. The reduction in artefacts was particularly pronounced in scenarios involving multiple prostheses. Specifically, prostheses such as gold crowns, amalgam restorations, and zirconia crowns produced markedly fewer artefacts in Dental CBCT, thereby enhancing image clarity and improving the accuracy of radiotherapy planning. Furthermore, the utilization of dental lab putty effectively reduced the number of artefacts in both imaging modalities, with the most substantial decrease observed in Dental CBCT scans.24 0