Dosimetric evaluation of the effect of dental implants in head and neck radiotherapy

doi:10.1016/j.tripleo.2004.11.048

Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology

Volume 99, Issue 6, June 2005, Pages 743-747

https://doi.org/10.1016/j.tripleo.2004.11.048 Get rights and content

Objective

The aim of the study was to examine the dose enhancement from scattered radiation at bone-dental implant interfaces during simulated head and neck radiotherapy.

Study design

Four cylindrical titanium dental implants with 3 different sizes and lengths were implanted into a human mandible in 4 different positions. Ionization measurements for 6 MV X, 25 MV X, and Co-60 gamma rays were done. Thermoluminescent dosimeter (TLD₁₀₀) chips were used to measure radiation dose enhancement due to the scattered electrons from titanium and electronic disequilibrium at the tissue-metal interface.

Results

The results showed that for Co-60, there is a 21% maximum increase in dose to alveolar mandibular bone at the close proximity to the titanium. For 6-MV x-rays the dose enhancement increase was almost the same or slightly lower than for Co-60, while for 25-MV high-energy x-rays, dose enhancement was lower than that of others. This increase in dose enhancement fell off rapidly and became insignificant at 2 mm from the interface.

Conclusion

Total dose that may lead to osteoradionecrosis risk of the mandible is slightly but not significantly affected by the scattered dose of the dental implants of lower jaw in the radiation field exposed to 3 different radiation beams.

Section snippets

Material and methods

A special phantom, actual human cadaver mandible (effective Z = 7.8) surrounded with water establishing soft tissue density (effective Z = 7.4), was used for measurements (Fig 1). A Co-60 teletherapy machine (Theratron 780, Nordion, Ontario, Canada) and a dual energy linear accelerator (Philips SL-25, Philips Medical Systems, Crawley, UK) were sources for irradiation. Four pure titanium (Z = 22) root-form cylindrical implants of 3 different sizes with diameters of 3, 3.5, and 4 mm and lengths of 11,

Results

Scatter factor measurement results for 3 different sizes of titanium for each energy are given in Table I. The percentage of scatter factor for 6-MV X and Co-60 gamma was higher than 25-MV x-ray, while the difference was negligible between 6 MV X and Co-60 gamma. Scattered dose decreased sharply relating to the distance between implant and TLD₁₀₀. Scatter factor, which is the ratio of measured scatter dose with implant to measurement without implant, was used to establish the dose enhancement.

Discussion

The interaction of high-energy x- and gamma rays with matter is the result of the Compton effect, in which the photon collides with electrons in the material to produce a broad spectrum of secondary electrons by inelastic collision processes and by Pair production in which the photon is absorbed and a positron-electron pair is produced. The degree of Compton and high-energy electron dose enhancement at an interface depends primarily on electron scattering differences at the bone-titanium

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Titanium alloys have been frequently used for medical implants. However, their presence can cause variability in radiation dose during radiotherapy, leading to potential complications. Herein, this work aims to explore the impact of 3D printed Ti6Al4V implants on the dose of 6MV X-ray in radiotherapy, through direct measurement in the ionization chamber. The findings indicate that the absorption effect of titanium alloy implants lowers the dose behind the implants, while the backscattering effect increases the dose in front of the implants. It is demonstrated that the size, thickness, and mesh density of the titanium alloy implant show no significant effect on the dose in front of the implants. Nonetheless, it is found that the dose behind the implants increases with mesh density and decreases with implant thickness. Laser polishing is implemented as a surface modification technique for titanium implants, resulting in significantly improved implant surface smoothness, a reduction of the surface roughness, a decrease in defects and an alteration in the elemental composition percentage. Furthermore, the reduction in surface roughness leads to a transition towards a hydrophilic implant surface, which also leads to the enhancement of specular reflection and the reduction of diffuse scattering on the implant surface, thus producing a complex influence on the radiation dose. It is also revealed that at a constant X-ray irradiation energy, the dose values in front of and behind the implant both exhibit a declining trend as the irradiation field size increases. Finally, the existence of a dose compensation effect of scattered radiation on the primary radiation during radiotherapy is confirmed. This work provides important reference for clinical practice, aiding medical professionals in formulating precise treatment plans, optimizing the efficacy of radiotherapy, and minimizing side effects.
Impact of different fixed dental prostheses on radiation dose in helical tomotherapy as measured with metal oxide semiconductor field-effect transistor dosimetry
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This ex vivo study evaluated the effects of different fixed dental prostheses and protective materials on scattered radiation during radiation therapy (RT).
Natural teeth (group NT) and 4 types of prostheses (group BL: bilayer lithium disilicate glass-ceramic; group MZ: monolithic zirconia ceramic; group BZ: bilayer zirconia-based all ceramic; and group BM: bilayer metal-ceramic restorations) were examined in maxillary and mandibular arch phantoms. All groups were divided into 3 subgroups: (1) without protective material over the prostheses; (2) protected with a soft acrylic night guard; and (3) protected with polyvinylsiloxane putty. All groups were irradiated with helical RT at 2 Gy and 6 MV photon energy. Doses were measured internally and externally 3 times on each phantom. Results were significant at P < .05.
No statistically significant differences in doses were found between groups NT and BL in either phantom, but these groups were different from the others. The differences between groups BZ and MZ were insignificant. Doses in group BM were significantly larger than all other groups. No significant differences existed between doses with and without protective material.
Doses increased significantly due to scattered radiation from the prostheses with increasing material density. Protective materials had no significant effect on dose.
Dose distrubution evaluation of different dental implants on a real human dry-skull model for head and neck cancer radiotherapy
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In this case, the back scattering from high-density and high-atomic (Z) dental implant materials can damage the surrounding tissues, with soft and hard tissue complications in the oral cavity (Reitemeier et al., 2004; Beyzadeoğlu et al., 2006). In the planning of head and neck radiotherapy, dental implants in the irradiated area may increase the risk of mucosal complications such as mucositis and osteoradionecrosis due to scattered radiation (Chin et al., 2009; Ozen et al., 2005). Treatment Planning Systems (TPS) only consider electron densities in inhomogeneous regions; they don't consider chemical compositions of dental implant materials.
In this study, the effect of different dental implant materials on dose distribution in head and neck cancer radiotherapy planning was investigated in a real human dry-skull taken from cadaver.
The effect of Root-shaped Yttrium (Y) stabilized tetragonal Zr polycrystalline (Y-TZP), Titanium (Ti), Alumina (Al₂O₃) and polyether ether ketone (PEEK) dental implants on dose distribution was investigated by three different methods; Monte Carlo (MC) simulation, Eclipse Treatment Planning System's (TPS) Pencil Beam Convolution (PBC) algorithm and Thermoluminescence Dosimeter (TLD). The 6 MV photon beam simulation was performed for the Varian 2300 C/D linear accelerator using the EGSnrc based BEAMnrc MC Code. To perform MC simulation on skull phantom, phantom CT images with extended CT scale were imported to BEAMnrc/EGSnrc MC code via CTCREATE code.
According to the dose distribution measurement in dry skull, the calculated dose differences between PBC and MC algorithms were in the range of 0.6–4.5% whereas the dose difference between MC and TLD were in the range of 1,1–14.6% range depending on implant material. The PBC calculated dose increase difference range confirmed with TLD measurements was between 1.7% and 19.8%. The PBC algorithm could not fully determine the dose due to backscattering caused by dental implants. This is probably due to the limitations and shortcomings of the PBC algorithm.
The maximum dose increase was observed for the Y-TZP dental implant material, which has the highest physical density. No significant dose increase was observed for the PEEK implant probably due to the low physical density of implants close to the physical density of water.
Rehabilitation post maxillary and mandibular reconstruction: Current status and future approaches
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Results revealed a 16% reduction in radiation dose behind the implant and an 8% increase in dose in the areas immediately in front of and adjacent to the implant [32]. Hence, implants appeared to affect the scatter of radiation and may increase the risk of osteoradionecrosis [33]. Secondly, with immediate implant placement, there is the risk of poor implant positioning.
Rehabilitation post reconstruction in head and neck cancer surgery is a vital component to improving quality of life. In this paper we discuss the current approaches to reconstruction of the maxilla and mandible and how they pertain to rehabilitation. There is a detailed discussion of dental rehabilitative challenges with different composite flaps and ways to solve those challenges. We conclude with a discussion about future approaches to reconstruction and how they will impact on improving rehabilitative outcomes and ultimately improve the quality of life of our patients.
Overdentures on primary mandibular implants in patients with oral cancer: A follow-up study over 14 years
2014, British Journal of Oral and Maxillofacial Surgery
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Comparison, however, is difficult as most studies have reported implants placed after radiotherapy.15 Primary implants can cause backscattering of radiation, which results in an increased dose of radiation in the surrounding bone in front of and next to the implants of 10%-21%.23,24 Whether this locally increased dose of radiation can be the explanation for the increased loss of implants in irradiated bone or a higher risk of developing ORN is not yet known but presumably, even when this risk is increased, it will still be lower than for implants placed after radiotherapy.
We aimed to assess oral functioning, patients’ satisfaction, condition of peri-implant tissues, and survival of implants up to 14 years after their insertion in patients with oral cancer who had had mandibular overdentures placed over primary implants. Endosseous dental implants were inserted prospectively in the interforaminal region of the mandible during resection of the tumour in 164/180 patients with oral cancer. All 58 patients were evaluated by questionnaires and clinical assessments during a final assessment in 2012. Implant-retained mandibular overdentures were inserted, and prosthetic rehabilitation and oral functioning were not associated with primary site or stage of the tumour, number or type of implants inserted, or the type of reconstruction. Over time the peri-implant mucosa was usually free of inflammation. More implants were lost in patients treated by radiotherapy (27/318, 8.5%) than in those not so treated (1/206, 0.5%). Patients who had been treated by irradiation reported more problems in oral functioning and less satisfaction than those who had not. Patients with an implant-retained mandibular overdenture reported fewer problems in oral functioning than patients without an overdenture.
Primary insertion of an implant should be routinely incorporated in the surgical planning for patients with oral cancer, as oral functioning in those wearing mandibular overdentures improved considerably and peri-implant health was at least reasonable.
Dosimetric distribution of the surroundings of different dental crowns and implants during LINAC photon irradiation
2014, Radiation Physics and Chemistry
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The dosimetric effects of dental materials on the surrounding tissues have been studied, with focus on the effects of dental metallic crowns (or the known geometry and chemical compositions were used to simulate dental crowns) on the mucosa (by Shimozato et al., 2011; Reitemeier et al., 2002; Farahani et al., 1990; Farman et al., 1985). Several studies reported on the scatter effect of dental implants on bone or soft tissues ( by Friedrich et al., 2010; Binger et al., 2008; Beyzadeoglu et al., 2006; Ozen et al., 2005) and some used other dental materials (metals, metallic alloys, amalgam, synthetic materials) to investigate the effects on soft tissues and bone ( by Chin et al., 2009; Spirydovich et al., 2006; Fuller et al., 2004; Thilmann et al., 1996). The previously mentioned research utilizing various metallic materials and phantom geometries allowed for the refinement of the current research.
In radiotherapy of the head and neck, metal dentures or implants will increase the risk of complications such as mucositis and osteoradionecrosis. The aim of this study is to explore the back scatter effect of commercially available dental metal alloys on the mucosa and bone under 6 MV LINAC irradiation. The Monte Carlo method has been employed to calculate the dose distribution in the heterogeneous media of the designed oral phantom based on the oral cavity geometry.
Backscatter dose increases up to a maximum of 53%, and is primarily dependent on the physical density and electron density of the metal crown alloy. Ceramic metal crowns have been quantified to increase backscatter dose up to 10% on mucosa. Ceramic serves as an inherent shield of mucosa. The backscatter dose will be greater for a small field size if the tumor is located at a deeper region. Titanium implants will increase the backscatter dose by 13% to bone but will not affect the mucosa. QC-20 (polystyrene resin) is recommended as a shield material (3 mm) to eliminate the backscatter dose on mucosa due to the high density metals.

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Oral and Maxillofacial RadiologyDosimetric evaluation of the effect of dental implants in head and neck radiotherapy

Objective

Study design

Results

Conclusion

Section snippets

Material and methods

Results

Discussion

J Prosthet Dent

J Prosthet Dent

Oral Sur Oral Med Oral Pathol

J Oral Maxillofac Surg

J Prosthet Dent

Oral Sur Oral Med Oral Pathol

Tumors of the head and neck. In clinical and pathological considerations

Cancer statistics

CA Cancer J Clin

The problem of reduction of residual ridges

Metal selection and surface characteristics

A clinical evaluation of implants in irradiated oral cancer patients

J Dent Res

Dosimetry at interfaces for high energy X and gamma rays

Br J Radiology

Oral and Maxillofacial Radiology
Dosimetric evaluation of the effect of dental implants in head and neck radiotherapy