Using GafChromic film to estimate the effective dose from dental cone beam CT and panoramic radiography

OBJECTIVES

To demonstrate the feasibility of GafChromic(®) XR-QA2 (ISP Corp., Wayne, NJ) as a dosemeter when performing measurements of the effective dose from three cone beam CT (CBCT) units and to compare the doses from examinations of three common dental clinical situations. A second aim was to compare the radiation doses for three digital panoramic units with the doses for the CBCT units.

METHODS

The CBCT units used were Veraviewepocs 3De(®) (J Morita MFG Corp., Kyoto, Japan), ProMax(®) 3D (Planmeca, Helsinki, Finland) and NewTom VGi(®) (Quantitative Radiology, Verona, Italy). GafChromic XR-QA2 films were placed between the selected layers of the head and neck of a tissue-equivalent human skull (RANDO(®) phantom; The Phantom Laboratory, Salem, NY). The exposure parameters were set using the automatic exposure control function of the units. Depending on the availability, medium and smaller field of view (FOV) scanning modes were used. The effective dose was estimated using the 2007 International Commission on Radiological Protection formalism.

RESULTS

The lowest effective dose of a CBCT unit was observed for ProMax 3D, FOV 4 × 5 cm (10 μSv), the highest for NewTom VGi, FOV 8 × 8 cm-high resolution (129 μSv). The range of effective doses for digital panoramic machines measured was 8-14 μSv.

CONCLUSIONS

This study demonstrates the feasibility of using radiochromic films for dental CBCT and panoramic dosimetry.

Raman spectroscopy demonstrates Amifostine induced preservation of bone mineralization patterns in the irradiated murine mandible

PURPOSE

Adjuvant radiotherapy in the management of head and neck cancer remains severely debilitating. Fortunately, newly developed agents aimed at decreasing radiation-induced damage have shown great promise. Amifostine (AMF) is a compound, which confers radio-protection to the exposed normal tissues, such as bone. Our intent is to utilize Raman spectroscopy to demonstrate how AMF preserves the mineral composition of the murine mandible following human equivalent radiation.

METHODS

Sprague Dawley rats were randomized into 3 experimental groups: control (n=5), XRT (n=5), and AMF-XRT (n=5). Both XRT and AMF groups underwent bioequivalent radiation of 70Gy in 5 fractions to the left hemimandible. AMF-XRT received Amifostine prior to radiation. Fifty-six days post-radiation, the hemimandibles were harvested, and Raman spectra were taken in the region of interest spanning 2mm behind the last molar. Bone mineral and matrix-specific Raman bands were analyzed using one-way ANOVA, with statistical significance at p<0.05.

RESULTS

The full-width at half-maximum of the primary phosphate band (FWHM) and the ratio of carbonate/phosphate intensities demonstrated significant differences between AMF-XRT versus XRT (p<0.01) and XRT versus control (p<0.01). There was no difference between AMF-XRT and control (p>0.05) in both Raman metrics. Computer-aided spectral subtraction further confirmed these results where AMF-XRT was spectrally similar to the control. Interestingly, the collagen cross-link ratio did not differ between XRT and AMF-XRT (p<0.01) but was significantly different from the control (p<0.01).

CONCLUSION

Our novel findings demonstrate that AMF prophylaxis maintains and protects bone mineral quality in the setting of radiation. Raman spectroscopy is an emerging and exceptionally attractive clinical translational technology to investigate and monitor both the destructive effects of radiation and the therapeutic remediation of AMF on the structural, physical and chemical qualities of bone.

[Retromolar mandibular anesthesia. Radiological and topographical study of an additional method of lower teeth anesthesia]

The aim of the study was to estimate the clinical efficacy of mandibular third molars anesthesia with various combinations of local anesthesia methods. Anatomical, radiological and morphological methods were used in the study. The topographic features of retromolar triangle were thoroughly examined. The neurovascular bundle revealed its relationship with retromolar area structures. According to the results of the clinical study the most effective combinations of mandibular third molars analgesia were selected.

Hyperbaric oxygen therapy and delayed radiation injuries (soft tissue and bony necrosis): 2012 update

Informal surveys at CME meetings have shown that approximately one-third of patients in the United States receive hyperbaric oxygen (HBO2) for delayed radiation injury. More than 600,000 patients receive radiation for malignancy in our country annually, and about one-half will be long-term survivors. Serious radiation complications occur in 5-10% of survivors. A large population of patients is therefore at risk for radiation injury. HBO2 has been applied to treat patients with radiation injury since the mid-1970s. Published results are consistently positive, but the level of evidence for individual publications is usually not high level, consisting mostly of case series and case reports. Only a rare randomized controlled trial has been accomplished. Radiation injury is one of the UHMS "approved" indications, and third-party payors will usually reimburse for this application. This updated review summarizes the publications available reporting results in treating radiation-injured patients. Mechanisms of HBO2 in radiation injury are discussed briefly. Outcome is reported on a mostly anatomic basis though due to the nature of the injury a positive outcome at one anatomic site is supportive of HBO2 at other sites. The potential benefit of prophylactic HBO2 before frank damage is also discussed in high-risk patients. The concerns of HBO2 enhancing growth of or precipitating recurrence of malignancy is discussed and largely refuted.

Treatment of irradiated mandibles with mesenchymal stem cells transfected with bone morphogenetic protein 2/7

PURPOSE

The study aimed to evaluate whether mesenchymal stem cells transfected with bone morphogenetic protein (BMP) 2/7 could increase bone regeneration after radiotherapy using a rabbit model of mandibular distraction osteogenesis.

MATERIALS AND METHODS

Twelve rabbits were randomly assigned to the sham control, radiotherapy control, nontransfected mesenchymal stem cells (MSCs), and MSCs transfected with BMP-2/7 groups. All rabbits, except those in the sham control group, received preoperative radiation of 9 Gy for 5 fractions. One month after radiotherapy, all rabbits underwent unilateral mandibular distraction at a rate of 0.9 mm/d for 11 days. At the end of active distraction, MSCs combined with bovine collagen were injected into the distraction zone. After 4 weeks of consolidation, the mandibular samples were collected and subjected to radiographic, microcomputed tomographic, and histologic examinations.

RESULTS

By radiographic examination, animals injected with nontransfected MSCs or MSCs encoding BMP-2/7 exhibited more bone formation than the control groups. Histologic examination showed that the group with MSCs encoding BMP-2/7 had a more mature medullary cavity than the nontransfected MSCs group.

CONCLUSIONS

MSCs encoding BMP-2/7 can increase bone healing in irradiated mandibular bone.

Deferoxamine reverses radiation induced hypovascularity during bone regeneration and repair in the murine mandible

BACKGROUND

Deferoxamine (DFO) is an iron-chelating agent that has also been shown to increase angiogenesis. We hypothesize that the angiogenic properties of DFO will improve bone regeneration in distraction osteogenesis (DO) after x-ray radiation therapy (XRT) by restoring the vascularity around the distraction site.

MATERIAL AND METHODS

Three groups of Sprague-Dawley rats underwent distraction of the left mandible. Two groups received pre-operative fractionated XRT, and one of these groups was treated with DFO during distraction. After consolidation, the animals were perfused and imaged with micro-CT to calculate vascular radiomorphometrics.

RESULTS

Radiation inflicted a severe diminution in the vascular metrics of the distracted regenerate and consequently led to poor clinical outcome. The DFO treated group revealed improved DO bone regeneration with a substantial restoration and proliferation of vascularity.

CONCLUSIONS

This set of experiments quantitatively demonstrates the ability of DFO to temper the anti-angiogenic effect of XRT in mandibular DO. These exciting results suggest that DFO may be a viable treatment option aimed at mitigating the damaging effects of XRT on new bone formation.

Characterization of optically stimulated luminescence dosemeters to measure organ doses in diagnostic radiology

OBJECTIVE

The aim of this study was to assess the characteristics of an optically stimulated luminescence dosemeter (OSLD) for use in diagnostic radiology and to apply the OSLD in measuring the organ doses by panoramic radiography.

METHODS

The dose linearity, energy dependency and angular dependency of aluminium oxide-based OSLDs were examined using an X-ray generator to simulate various exposure settings in diagnostic radiology. The organ doses were then measured by inserting the dosemeters into an anthropomorphic phantom while using three panoramic machines.

RESULTS

The dosemeters demonstrated consistent dose linearity (coefficient of variation<1.5%) and no significant energy dependency (coefficient of variation<1.5%) under the applied exposure conditions. They also exhibited negligible angular dependency (≤ 10%). The organ doses of the X-ray as a result of panoramic imaging by three machines were calculated using the dosemeters.

CONCLUSION

OSLDs can be utilized to measure the organ doses in diagnostic radiology. The availability of these dosemeters in strip form proves to be reliably advantageous.

HDR brachytherapy irradiation of the jaw - as a new experimental model of radiogenic bone damage

INTRODUCTION

Hitherto, no suitable experimental model exists to test new treatments for radiogenic bone damage, such as new step from knowledge about bone growth factors or angiogenesis factors. The goal of this investigation was to establish such a standardised experimental model.

MATERIAL AND METHODS

Twenty-four rats were used in this study. In 12 rats a plastic tube was implanted along the right half of the mandible and treated with a single dose of 20 Gy at a high-dose-rate (HDR) using an afterloading machine, the remainder served as control (n=12). One hundred days after irradiation both sides of the mandible were examined using paraffin embedding and non-decalcified histology.

RESULTS

All HDR irradiated rats developed localised alopecia within 2 weeks of radiotherapy. In the irradiated group, a clear growth reduction of the ipsilateral incisor was observed. Paraffin histology revealed minimal damage of the bone structure with slightly increased signs of regeneration. The bone apposition rate was significantly reduced on the irradiated right side, compared with the left side (p=0.028). The average diameter of the mandibular condyles on the irradiated right sides was significantly reduced when compared with the left sides (p=0.023).

CONCLUSIONS

It is possible to induce radiogenic damage of the mandible by using HDR brachytherapy with a single dose of 20 Gy comparable to 45 x 2 Gy of conventional irradiation. This new model is easy and predictable and appears to be suitable for the testing of new treatment modalities. It is advantageous for the testing of bone growth and angiogenesis factors that the contralateral side exhibits completely normal bone apposition characteristics enabling a split-mouth design for future experiments.

Assessment of vascularity in irradiated and nonirradiated maxillary and mandibular minipig alveolar bone using laser doppler flowmetry

PURPOSE

The purpose of this animal study was to confirm that laser Doppler flowmetry (LDF) is a reproducible method for the assessment of maxillary and mandibular alveolar bone vascularity and that there is less vascularity in irradiated mandibular and maxillary bone compared to nonirradiated bone.

MATERIALS AND METHODS

All maxillary and mandibular premolars and molars of 6 Göttingen minipigs were extracted. After a 3-month healing period, 3 minipigs received irradiation at a total dose of 24 Gy. Three months after irradiation, 5 holes were drilled in the residual alveolar ridge of each edentulous site in each minipig. Local microvascular blood flow around all 120 holes was recorded by LDF prior to implant placement. In 1 irradiated and 1 nonirradiated minipig, an additional hole was drilled in a right maxillary site to enable repeated LDF recordings.

RESULTS

The alveolar bone appeared less vascularized in irradiated than in nonirradiated minipigs. The effect of radiation appeared more pronounced in the mandible than in the maxilla. LDF was demonstrated to be a reproducible method for assessing alveolar bone vascularity. However, recordings varied by edentulous site as well as by minipig.

CONCLUSION

The authors' hypotheses regarding LDF and vascularity were supported. Further research validating the use of LDF in human beings, especially in those who have undergone radiation therapy for head and neck cancer, is necessary.

The effect of radiation in distraction osteogenesis for reconstruction of mandibular segmental defects

Distraction osteogenesis is useful in the reconstruction of mandibular segmental defects. The effects of radiotherapy on distracted bone after resection of squamous cell carcinoma of the oral cavity are still unknown. We report the outcome in six patients who had distraction osteogenesis after postoperative radiotherapy. Distraction was by a unidirectional semi-buried device and panoramic radiographs were taken monthly during the distraction and consolidation periods to monitor the progress of the distraction. Follow-up ranged from 15 to 45 months (mean 33). The dose of radiation ranged from 60 to 70Gy. In one patient the bone was completely exposed and all the screws were loosened. There was no calcification and the gap remained radiolucent in the panoramic radiographs. The other five patients had excellent or good quality of bone. We conclude that radiotherapy may not interfere substantially with distraction osteogenesis although larger series the necessary.

Immediate placement of implants and appliance in an irradiated patient: a case study

PURPOSE

The purpose of this study was to evaluate the immediate placement of implants and appliance using hyperbaric oxygenation on a 45-year-old male with a history of squamous cell carcinoma of the floor of the mouth.

MATERIALS

Five Nobel Biocare implants between the mental foamina were used along with a course of pre- and postsurgical hyperbaric oxygenation.

RESULTS

After 39 months, the patient is symptom free and shows no signs of rejection. Conclusion Using an accepted hyperbaric oxygenation protocol when placing and restoring immediate implants in this patient resulted in a successful treatment outcome.

Bone tissue microscopic findings related to the use of diode laser (830etam) in ovine mandible submitted to distraction osteogenesis

PURPOSE: To analyze the microscopic characteristics of the effect of Gallium-Aluminum Arsenid diode laser (GaAlAs - 830etam) applied during the activation and consolidation period to ovine mandibles submitted to distraction osteogenesis. METHODS: Eighteen sheep underwent surgery in order to have bone distractors implanted in the left side of the jaw area. They were divided into three groups: 1 - Control; 2 - Laser irradiation during the activation period; 3 - Laser irradiation during the fixation period. The irradiation was carried out in five sessions, on every other day, with 4,0J/cm² doses applied to four pre-established areas, totaling 16J per session. After four days of latency under post-operative care, ten days of distractor activation (at 1mm/day) and twenty-one days of fixation the animals were sacrificed and the devices removed for microscopic analysis. RESULTS: The groups that received laser irradiation (GaAlAs) presented a greater amount of mineralized bone trabeculae when compared to the Control Group. Despite that, cartilaginous tissues were also found in Group 2. CONCLUSION: The laser has been more favorable when used in the consolidation period, after bone elongation.

[Mandibular swing procedure for surgical resection of advanced oropharyngeal carcinoma]

OBJECTIVE

To explore a better approach to resect the advanced oropharyngeal carcinoma.

METHODS

From 1995 to 2005, 17 patients underwent mandibular swing procedure for excision of advanced oropharyngeal carcinoma including: 13 tonsillar cancers, 2 soft palate carcinomas and 2 lingual root cancers. Surgical procedure was selected according to the lesion. All tumors were resected through the mandibular swing approach or its combined approaches. Immediate reconstruction of the surgical defect was done using tongue flap, pectoralis major myocutaneous flap, sternohyoid myofascial flap, temporalis myofascial flap and forehead flap, respectively. After surgical resection of the tumors, all patients received postoperative radiotherapy.

RESULTS

All patients' advanced oropharyngeal carcinoma were successfully resected as planned through the mandibular swing procedure or its combined procedures without severe complications. Functions of deglutition, respiration and speech were well restored. The 3- and 5-year survival rate was 54. 5% and 40%, respectively.

CONCLUSION

The mandibular swing procedure and its combined approach is safe and effective in the surgical resection of the advanced oropharyngeal carcinoma, which can provide a good exposure for the oropharynx, supraglottic region, hypopharynx, the parapharyngeal space and the base of the skull.

A mobilization regimen to prevent mandibular hypomobility in irradiated patients: an analysis and comparison of two techniques

Radiotherapy, when used in head and neck cancer treatment, can produce side effects in the patients, such as decreased salivary production, xerostomia, opportunistic infections, radiation caries, dysphagia, local discomfort and the limitation of mouth opening. The aim of this study was to evaluate the amplitude of mouth opening in patients before and immediately after the completion of radiotherapy, comparing the effectiveness of two physiotherapy exercises. The irradiated sites included the masticatory muscles. The results demonstrated that there were no statistically significant differences between the two instituted exercises; however there was a trend towards better clinical results in group 2. The amplitude of mouth opening showed a trend towards reduction, but this was not statistically significant. When the pterygoid and sternocleidomatoid muscles were included in the irriated field, patients were observed to have more morbidity. This indicates the great importance of these muscles in mouth opening. Based on the results obtained within this study, it is not possible to conclude that physiotherapy exercies are efficacious in preventing trismus. Future longitudinal studies are required to verify the onset of trismus in radiotherapy patients.

Quality of interstitial PDR-brachytherapy-implants of head-and-neck-cancers: predictive factors for local control and late toxicity?

BACKGROUND AND PURPOSE

Parameters and indices related to the implant geometry in use for describing the quality of volume implants in interstitial brachytherapy were developed on the basis of LDR-brachytherapy. The aim of our study was to evaluate their usefulness for predicting late toxicity and local control in the PDR-brachytherapy of head-and-neck-tumors.

PATIENTS AND METHODS

Between January 2000 and October 2004, 210 patients were treated with PDR-brachytherapy which was administered either postoperatively or as definitive treatment. Brachytherapy was used as sole treatment in some cases while in others a combination with EBRT was used. For assessment of quality of implants we analyzed the following indices and parameters using the univariate chi2 test and multivariate logistic regression analysis: V85, V120 and V150 (volume enclosed by the surface of the 85%-, 120%- and 150%-isodose), UI (uniformity index), QI (quality index), HI (homogeneity index), VGR (volume gradient ratio), DNR (dose non-uniformity ratio), LD (low dose), HD (high dose), PD (peak dose) and the intersource spacing.

RESULTS

After a median follow-up of 24 months (4-50) the rate of - usually transient - soft tissue necrosis (STN) was 11%, osteoradionecrosis (ORN) was seen in 7.6% of cases and local relapse occurred in 7% of cases. Univariate analysis shows a significant influence on the development of soft tissue necrosis for V85, and on osteoradionecrosis for HD and PD. In the multivariate analysis a correlation between soft tissue necrosis and QI was found. For local control a correlation with QI, VGR and minimal tube distance was found using univariate analysis.

CONCLUSIONS

Using interstitial PDR-brachytherapy in head-and-neck-tumors the probability of local control and of the development of soft tissue necrosis or osteoradionecrosis is dependent on dose and volume parameter like the volume of the reference isodose, the high and peak dose values, on the homogeneity of the dose distribution, quantified by the quality index or the volume gradient ratio as well on the minimal tube distance.

Choosing an intensity-modulated radiation therapy technique in the treatment of head-and-neck cancer

PURPOSE

With the emerging use of intensity-modulated radiation therapy (IMRT) in the treatment of head-and-neck cancer, selection of technique becomes a critical issue. The purpose of this article is to establish IMRT guidelines for head-and-neck cancer at a given institution.

METHODS AND MATERIALS

Six common head-and-neck cancer cases were chosen to illustrate the points that must be considered when choosing between split-field (SF) IMRT, in which the low anterior neck (LAN) is treated with an anterior field, and the extended whole-field (EWF) IMRT in which the LAN is included with the IMRT fields. For each case, the gross tumor, clinical target, and planning target volumes and the surrounding critical normal tissues were delineated. Subsequently, the SF and EWF IMRT plans were compared using dosimetric parameters from dose-volume histograms.

RESULTS

Target coverage and doses delivered to the critical normal structures were similar between the two different techniques. Cancer involving the nasopharynx and oropharynx are best treated with the SF IMRT technique to minimize the glottic larynx dose. The EWF IMRT technique is preferred in situations in which the glottic larynx is considered as a target, i.e., cancer of the larynx, hypopharynx, and unknown head-and-neck primary. When the gross disease extends inferiorly and close to the glottic larynx, EWF IMRT technique is also preferred.

CONCLUSION

Depending on the clinical scenario, different IMRT techniques and guidelines are suggested to determine a preferred IMRT technique. We found that having this treatment guideline when treating these tumors ensures a smoother flow for the busy clinic.

Retrieved Implants from Irradiated Sites in Humans: A Histologic/Histomorphometric Investigation of Oral and Craniofacial Implants

PURPOSE

The aim of this report was to quantitatively and qualitatively evaluate the tissue response to bone-anchored implants retrieved from irradiated sites in patients.

MATERIALS AND METHODS

The material consists of 23 consecutively received Brånemark implants (Nobel Biocare AB, Göteborg, Sweden) placed in pre- or postoperatively irradiated sites. Twenty-two of the 23 implants were suitable for histologic evaluation of undecalcified sections in the light microscope.

RESULTS

The oral implants with shorter time in situ demonstrated sparse bone to implant contact with mainly dense connective tissue in the interface. However, for implants with longer time in situ, high amounts of bone-implant contact and bone fill of threads were noted. The mean values of bone-implant contact and bone area within the thread were calculated to 40% (16-94) and 70% (13-96), respectively. The craniofacial implants, with the exception of two implants lined with a capsular formation, demonstrated mature and newly formed bone at the bone-implant interface. The mean value for bone-metal contact was calculated to 45 and 53% for two specimens. The mean value for bone area within the thread ranged from 65 to 88% for three specimens. CONCLUSION; The possibility to achieve bone anchorage of implants in irradiated tissue was supported by the findings in this study. However, due to limited material, conclusions with regard to radiation dose and bone tissue response to implants cannot be stated.

Implant survival in mandibles of irradiated oral cancer patients

OBJECTIVE

The aim of this study was to analyze long-term implant survival in the mandible after radiotherapy and radical surgery in oral cancer patients.

STUDY DESIGN

Between 1990 and 2003, 71 patients (15 females, 56 males; average age 57.8 years, range 16-84.1 years) were treated with dental implants after radiochemotherapy and ablative surgery of oral cancer. Radiation therapy was delivered in daily fractions of 2 Gy given on 25 days (total dose of 50 Gy). Oral defects were reconstructed microsurgically with jejunal, iliac crest or radial forearm grafts. Thereafter 316 dental implants were placed in the non-irradiated residual bone (84; 27%), irradiated residual bone (154; 49%) or grafted bone (78; 25%) at various intervals (mean interval 1.41 (+/- 1.01) years, range 0.34-6.35 years).

RESULTS

The mean follow-up time after implant insertion was 5.42 (+/- 3.21) years (range 0.3-13.61 years). The overall 2-, 3-, 5-, and 8-year survival rates of all implants were 95%, 94%, 91% and 75%. Forty-four implants were lost in 21 patients during the observation period. Irradiation of the mandibular bone showed significantly (P = 0.0028) lower implant survival compared with non-irradiated mandibular bone. The 8-year survival rate in the non-irradiated residual bone (two loss), irradiated residual bone (29 loss) or grafted bone (13 loss) were 95%, 72% and 54%, respectively. Time of implantation after irradiation showed no statistically significant influence. Implant brand, length or diameter or the incidence of resective surgery on the mandible and gender of patients had no statistically significant influence on implant survival.

CONCLUSION

Radiation therapy with 50 Gy was significantly related to shorter implant survival in mandibular bone. Survival was lowest in grafted bone. Time of implant placement had no statistically significant influence on survival under the conditions of this study. Although implant survival is lower in irradiated mandibles, implants significantly facilitate prosthodontic treatment and enhance outcome of oral rehabilitation in cancer patients.

Effekte der Hyperbaren Sauerstofftherapie (HBO) bei der Behandlung infizierter freier Knochentransplantate

BACKGROUND

Hyperbaric oxygen therapy (HBO) leads to a significant increase of oxygen supply in poorly perfused tissue. Several physiological mechanisms of this treatment modality are suitable for having a positive effect on infected large autologous free bone transplants.

CASE REPORT

In a 49-year-old male with a metastasized squamous cell carcinoma of the floor of the mouth radical tumour surgery with subsequent radiation was performed. Nine years later an infected osteoradionecrosis of the mandible emerged which required a continuity-resection with simultaneously performed reconstruction of the mandible using an autologous free transplanted iliac bone graft. Four days post surgery wide intraoral dehiscence with complete denuding of the bone graft occurred. For this reason initiation of an adjuvant hyperbaric oxygen therapy in addition to high dose antibiotic therapy and local wound care. Combined therapy led to granulation tissue on the surface of the transplanted bone with subsequent epithelization. Complete incorporation and conversion of the bone transplant with full rehabilitation concerning function and aesthetics was noted.

DISCUSSION

Without HBO treatment the large volume infected autologous free bone transplant would have been lost. Beside other capabilities of HBO the induction of rapid neovascularisation and increasing oxygen diffusion radius are the reasons that the infected transplant was saved. Only under these conditions it was possible to erradicate the bacterial infection effectively with antibiotics.

Effects of irradiation on bone remodelling around mandibular implants: an experimental study in dogs

This research focuses on the effects of radiotherapy on bone remodelling around mandibular implants in dogs. After bilateral extraction of the mandibular premolars and first 2 molars, each of 11 beagles received 8 mandibular implants. Four animals were irradiated 4 weeks after implantation and 4 others 8 weeks before implantation; the remaining 3 did not receive radiotherapy. Irradiation consisted of 10 daily fractions of 4.3Gy (60)Co. Fluorochromes were given at implantation and irradiation to allow the measurement of bone apposition. The dogs were killed 6 months after implantation. Each hemi-mandible was processed according to bone-specific histological techniques. New bone formation was visible around 85 of the 88 implants. Stimulated mandibular remodelling was attested in both irradiated groups by increased porosity and numerous labelled osteons. Resorption was more pronounced in the group irradiated after implantation, but osteon formation appeared unvarying. Osseointegration was thus shown to be compatible with bone irradiation as bone turnover activities were maintained throughout the experiment. As the apposition stage of the remodelling cycle appears crucial to achieve optimal osseointegration, its normal completion should be taken into account in clinical practice by respecting a 6-month period between irradiation and implantation.

Osteoradionecrosis of the Mandible

BACKGROUND AND PURPOSE

Osteoradionecrosis (ON) of the mandible is a serious late complication of high-dose radiation therapy for tumors of the oropharynx and oral cavity. After doses between 60 and 72 Gy using standard fractionation, an incidence of ON between 5% and 15% is reported in a review from 1989, whereas in more recent publications using moderately accelerated or hyperfractionated irradiation and doses between 69 and 81 Gy, the incidence of ON is between < 1% and ~ 6%. Intensity-modulated radiation therapy (IMRT) is expected to translate into a further important reduction of ON. The aim of this descriptive study was to assess absolute and relative bone volumes exposed to high IMRT doses, related to observed bone tolerance.

PATIENTS AND METHODS

Between December 2001 and November 2004, 73 of 123 patients treated with IMRT were identified as subgroup "at risk" for ON (> 60 Gy for oropharyngeal or oral cavity cancer). 21/73 patients were treated in a postoperative setting, 52 patients underwent primary definitive irradiation. In 56 patients concomitant cisplatin-based chemotherapy was applied. Mean follow-up time was 22 months (12-46 months). Oral cavity including the mandible bone outside the planning target volume was contoured and dose-volume constraints were defined in order to spare bone tissue. Dose-volume histograms were obtained from contoured mandible in each patient and were analyzed and related to clinical mandible bone tolerance.

RESULTS

Using IMRT with doses between 60 and 75 Gy (mean 67 Gy), on average 7.8, 4.8, 0.9, and 0.3 cm(3) were exposed to doses > 60, 65, 70, and 75 Gy, respectively. These values are substantially lower than when using three-dimensional conformal radiotherapy. The difference has been approximately quantified by comparison with a historic series. Additional ON risk factors of the patients were also analyzed. Only one grade 3 ON of the lingual horizontal branch, treated with lingual decortication, was observed.

CONCLUSION

Using IMRT, only very small partial volumes of the mandibular bone are exposed to high radiation doses. This is expected to translate into a further reduction of ON and improved osseointegration of dental implants.

Distraction Osteogenesis in Irradiated Rabbit Mandibles With Adjunctive Hyperbaric Oxygen Therapy

PURPOSE

The purpose of this study was to evaluate the effect of hyperbaric oxygen therapy on bone regeneration during distraction of irradiated rabbit mandibles.

MATERIALS AND METHODS

Twenty New Zealand white rabbits were randomly sub-divided into 4 groups. Group 1 served as control, group 2 received preoperative radiation therapy, group 3 received pre- and postoperative hyperbaric oxygen (HBO) therapy, and group 4 received preoperative radiation therapy and pre- and postoperative HBO therapy. All rabbits underwent a corticotomy of the left body of the mandible after placement of a distraction device. Distraction, at a rate of 1 mm/day and a rhythm of 1 turn/day, began after a 3-day latency period for 14 days. Thirty days after completion of the distraction protocol, the animals were euthanized, and histomorphometric and radiographic data of the distraction segments were obtained.

RESULTS

Histomorphometric analysis of new bone fill was greatest in the non-irradiated groups compared to groups receiving radiation therapy, regardless of HBO therapy (P = .03). Pre-corticotomy bone density measurements showed a significant increase in bone density over time (P = .0007). This resulted in a significant relationship between HBO therapy, radiation therapy, and time (P = .0050).

CONCLUSIONS

The results of the study support the use of HBO therapy during distraction osteogenesis. Any additional therapeutic benefit of HBO therapy in irradiated bone would require additional investigation.

Distraction osteogenesis in the irradiated rabbit mandible

PURPOSE

The potential use of distraction osteogenesis in mandibular reconstruction has been limited by its questionable efficacy in previously radiated bone. The purpose of this study was to evaluate the effects of irradiation on mandibular distraction osteogenesis (DO).

MATERIALS AND METHODS

Six rabbits received a unilateral irradiation (group R) in the mandible with a total dose of 27.0 Gy in five 5.4 Gy fractions (equivalent to 50 Gy/25 fractions). The contralateral side served as control (group C). Bilateral osteotomy was made 3 months after completion of irradiation. After a 1-week latency period bone distraction was activated at a rate of 0.5 mm twice daily for 8 days, followed by a consolidation phase of 6 weeks. New bone underwent radiographic, densitometric, histological and histomorphometric analysis.

RESULTS

Two rabbits were excluded from the study, one due to infection on both sides and death in another animal. After 6 weeks of consolidation, the irradiation group had no significantly lower BMD than control group. No difference was found between the percent area of new bone in both groups. New bone was more mature and organised of group C than in groups R. Larger chondroid islands were found evident in distracted bone of group R than group C.

CONCLUSIONS

It seems that DO can be feasible in previously irradiated rabbit mandible.

Evaluation of scatter dose of dental titanium implants exposed to photon beams of different energies and irradiation angles in head and neck radiotherapy

OBJECTIVES

In this study, quantification of backscatter doses between scattering titanium dental implant and the thermoluminescent dosimeter (TLD(100)) radiation detector at axial beam irradiation-angle range of 0-90 degrees in head and neck radiotherapy is done to evaluate irradiation angle dependency of dose enhancement contributing to osteoradionecrosis.

METHODS

A cylindrical titanium dental implant with diameter of 4 mm and length of 9 mm was implanted into a specially-designed human mandible phantom with a TLD100 chip placed on the buccal site and irradiated with 6 MV X, 25 MV X and Co-60 gamma sources at 19 different irradiation angles.

RESULTS

Dose enhancement on a buccal site of the titanium implant depends on the incident beam angle. At angles of 65 degrees, 60 degrees and 40 degrees the maximum detected scatter doses over the titanium implant are 36%, 32% and 23% for Co-60 gamma, 6 MV X-ray and 25 MV X-ray, respectively. The dose enhancement at different beam angles was less pronounced in 25 MV X and more pronounced in Co-60 gamma irradiation.

CONCLUSIONS

For the different radiation beams studied, the irradiation angle between scattering titanium dental implants and the central axis does not significantly affect the total dose that may lead to osteoradionecrosis of the mandible.

Distraction osteogenesis assisted by tissue engineering in an irradiated mandible: a case report

Distraction osteogenesis (DO) can provide predictable bone regeneration without grafting procedures but requires long treatment time and forms less bone transverse to the direction of distraction. To promote 3-dimensional bone formation and shorten the consolidation period, tissue-engineered osteogenic material (injectable bone) was applied in a patient who was being treated with vertical DO with an osteocutaneous fibular flap to reconstruct the mandible. The material, which comprised autologous mesenchymal stem cells culture-expanded then induced to be osteogenic in character and platelet-rich plasma (PRP) activated with thrombin and calcium chloride, was infiltrated into the distracted tissue at the end of distraction and injected into a space created labially with a titanium mesh at implant placement. The infiltration contributed to full consolidation of the regenerate for 3 months, and the injection thickened the regenerated ridge and bridged a gap between the native mandible and distracted fibula. The reconstructed mandible was expanded from 10 mm to 25 mm in height despite a lacerated and opened labial periosteum in the distracted area. Six implants 18 mm in length were placed and subsequently achieved osseointegration. The cutaneous flap covering the implants was trimmed, and the palatal mucosa was transplanted to the regenerated ridge for vestibuloplasty. These raw surfaces were covered with PRP; within 3 weeks, they had attained an epithelium. The implants have supported a fixed prosthesis with adequate surrounding bone and attached mucosa. DO was assisted by tissue engineering and became effective in restoring the compromised mandible.