Dental Artifacts Research Articles

Feasibility and Incremental Benefit of Puffed-Cheek 18F-FDG PET/CT on Oral Cancer Patients

The complexity of small oral cavity and intimate apposition of the oral cavity mucosal surfaces make CT identification of obvious masses difficult. Puffed-cheek CT improves the evaluation of oral cavity lesions. We used the puffed-cheek maneuver with 18F-FDG PET/CT scans to determine the feasibility and accuracy in clinical practice and to identify any benefits. Twenty-two patients with oral cancer were included. They were instructed to perform the puffed-cheek maneuver after a conventional 18F-FDG PET/CT scan. Two physicians reviewed the puffed-cheek and conventional 18F-FDG PET/CT images and achieved consensus about the cancer extent, location, and dental artifacts before classifying and grading the oral cancers. Dichotomous results of localized or extended cancer and artifact grading scores from the puffed-cheek and conventional 18F-FDG PET/CT methods were compared using McNemar test and the Wilcoxon signed-rank test. P < 0.05 was considered significant. The puffed-cheek maneuver with 18F-FDG PET/CT was practical and had incremental benefits. The conventional 18F-FDG PET/CT classified 12 patients correctly as having localized or extended cancer, and the puffed-cheek 18F-FDG PET/CT classified 21 patients correctly. Puffed-cheek 18F-FDG PET/CT found a synchronous skip cancer and provided detailed cancer delineation. This method might reduce the effects of dental artifacts without undesirable muscular FDG uptake. Puffed-cheek PET/CT is feasible in the current clinical setting and can improve the delineation of oral cancer extent and location, with a potential benefit of reducing dental artifacts.

TU‐E‐141‐06: Estimation of Dose Distributions with the Dental Artifact Correction in Radiation Treatment Plans for Head‐And‐Neck Cancers

Purpose: Metal artifacts generated by dental implants cause dose discrepancy in intensity‐modulated radiation therapy (IMRT) of head‐and‐neck cancer cases due to the inaccurate predicted doses. To determine the effective metal artifact reduction (MAR) method presenting minimum dose errors with delivered dose, dosimetric impact of different MAR methods were evaluated in radiation treatment plans. Methods: MAR was implemented using Euler elastic and curvature based sinogram inpainting (EECSI) algorithm, volume clustering with Hounsfield unit (HU) overriding (VCU), and multimodal image‐based correction (MIC). When delivered doses were calculated on the corrected computed tomography (CT) images by employing the same plan parameters in the reference IMRT plan (Planref), dose errors were analyzed with dose‐volume histograms (DVHs), monitor unit, and dose conformity of target volumes. Dosimetric impacts were also estimated using the biophysical evaluation parameters in three oropharyngeal patients. Results: Optimized fluence in the Planref resulted in overdose up to 5% in the salivary glands and spinal cords on the corrected CT images, while the overdose in target volumes increased tumor control probability of 3–7%. Target doses in peripheral regions affected by the surrounded dark pixels were deformed and decreased conformity. The DVHs of organs at risk (OAR) and target volumes also showed the 5–8% volume gap in the prescription dose range. As the efficient MAR is employed into the head‐and‐neck IMRT plans, more accurate predicted doses of primary structures would be achieved, even if the dose differences of each MAR method are small less than 2–3%. Conclusion: EEECSI and VCU were useful methods to reduce the metal artifacts and to predict more accurate delivered doses. Since dental artifacts cause dose variation in peripheral region of target volumes and OAR, dose calculation on corrected CT images using efficient MAR techniques and dose verification would be encouraged in head‐and‐neck IMRT plans.

Feasibility of clinical Magnetoencephalography (MEG) functional mapping in the presence of dental artefacts

ObjectiveTo evaluate the viability of MEG source reconstruction in the presence of large interference due to orthodontic material. MethodsWe recorded the magnetic fields following a simple hand movement and following electrical stimulation of the median nerve (somatosensory evoked field –SEF). These two tasks were performed twice, once with and once without artificial dental artefacts. Temporal Signal Space Separation (tSSS) was applied to spatially filter the data and source reconstruction was performed according to standard procedures for pre-surgical mapping of eloquent cortex, applying dipole fitting to the SEF data and beamforming to the hand movement data. ResultsComparing the data with braces to the data without braces, the observed distances between the activations following hand movement in the two conditions were on average 6.4 and 4.5mm for the left and right hand, respectively, whereas the dipole localisation errors for the SEF were 4.1 and 5.4mm, respectively. Without tSSS it was generally not possible to obtain reliable dipole fit or beamforming results when wearing braces. ConclusionWe confirm that tSSS is a required and effective pre-processing step for data recorded with the Elekta-MEG system. Moreover, we have shown that even the presence of large interference from orthodontic material does not significantly alter the results from dipole localisation or beamformer analysis, provided the data are spatially filtered by tSSS. SignificanceState-of-the-art signal processing techniques enable the use of MEG for pre-surgical evaluation in a much larger clinical population than previously thought possible.

Simultaneous PET/MR imaging in a human brain PET/MR system in 50 patients—Current state of image quality

ObjectivesThe present work illustrates the current state of image quality and diagnostic accuracy in a new hybrid BrainPET/MR. Materials and methods50 patients with intracranial masses, head and upper neck tumors or neurodegenerative diseases were examined with a hybrid BrainPET/MR consisting of a conventional 3T MR system and an MR-compatible PET insert. Directly before PET/MR, all patients underwent a PET/CT examination with either [18F]-FDG, [11C]-methionine or [68Ga]-DOTATOC. In addition to anatomical MR scans, functional sequences were performed including diffusion tensor imaging (DTI), arterial spin labeling (ASL) and proton-spectroscopy. Image quality score of MR imaging was evaluated using a 4-point-scale. PET data quality was assessed by evaluating FDG-uptake and tumor delineation with [11C]-methionine and [68Ga]-DOTATOC. FDG uptake quantification accuracy was evaluated by means of ROI analysis (right and left frontal and temporo-occipital lobes). The asymmetry indices and ratios between frontal and occipital ROIs were compared. ResultsIn 45/50 patients, PET/MR examination was successful. Visual analysis revealed a diagnostic image quality of anatomical MR imaging (mean quality score T2 FSE: 1.27±0.54; FLAIR: 1.38±0.61). ASL and proton-spectroscopy was possible in all cases. In DTI, dental artifacts lead to one non-diagnostic dataset (mean quality score DTI: 1.32±0.69; ASL: 1.10±0.31). PET datasets of PET/MR and PET/CT offered comparable tumor delineation with [11C]-methionine; additional lesions were found in 2/8 [68Ga]-DOTATOC-PET in the PET/MR. Mean asymmetry index revealed a high accordance between PET/MR and PET/CT (1.5±2.2% vs. 0.9±3.6%; mean ratio (frontal/parieto-occipital) 0.93±0.08 vs. 0.96±0.05), respectively. ConclusionsThe hybrid BrainPET/MR allows for molecular, anatomical and functional imaging with uncompromised MR image quality and a high accordance of PET results between PET/MR and PET/CT. These results justify the application of this technique in further clinical studies and may contribute to the transfer into whole-body PET/MR systems.

Reduction of dental filling metallic artifacts in CT‐based attenuation correction of PET data using weighted virtual sinograms optimized by a genetic algorithm

The presence of metallic dental fillings is prevalent in head and neck PET/CT imaging and generates bright and dark streaking artifacts in reconstructed CT images. The resulting artifacts would propagate to the corresponding PET images following CT-based attenuation correction (CTAC). This would cause over- and/or underestimation of tracer uptake in corresponding regions thus leading to inaccurate quantification of tracer uptake. The purpose of this study is to improve our recently proposed metal artifact reduction (MAR) approach and to assess its performance in a clinical setting. The proposed MAR algorithm is performed in the virtual sinogram space to overcome the challenges associated with manipulating raw CT data. The corresponding bins of the virtual sinogram affected by metallic objects are obtained by forward projection of segmented metallic objects in the original CT image. These bins are then substituted by weighted values of three estimates: the affected bins in the original sinogram, the bins in the corrected sinogram using spline interpolation, and the sinogram bins in the neighboring column of the sinogram matrix. The optimized weighting factors (alpha, beta, and gamma) were estimated using a genetic algorithm (GA). The optimized combination of weighting coefficients was obtained using the GA applied to 24 clinical CT data sets. The proposed MAR method was then applied to 12 clinical head and neck PET/CT data sets containing dental artifacts. Analysis of the results was performed using Bland and Altman plots and a method allowing analysis in the absence of gold standard called regression without truth (RWT). The proposed method was also compared to an image-based MAR method. Optimization of the weighting coefficients using the GA resulted in an optimum combination of parameters of alpha=0.26, beta=0.67, and gamma=0.07. According to Bland and Altman plots generated for both CT and PET images of the clinical data, the proposed MAR algorithm is efficient for reduction of streak artifacts in CT images and such reduce the over- and/or underestimation o tracer uptake. The RWT method also confirmed the effectiveness of the proposed MAR method. The obtained figures of merit revealed that attenuation corrected PET data corrected using CTAC after applying the MAR algorithm are more similar to the assumed gold standard. Comparison with the knowledge-based method revealed that the proposed method mainly corrects the artifactual regions without modifying the unaffected regions. The knowledge-based method globally modifies the images including those that do not include metallic artifacts. The proposed MAR algorithm improves the quality and quantitative accuracy of clinical head and neck PET/CT images and could be easily integrated in clinical setting.

Inter-observer and Intra-observer Target Volume Delineation Variability in Oropharyngeal Cancer Patients with Significant Dental Artifact on CT

Inter-observer and Intra-observer Target Volume Delineation Variability in Oropharyngeal Cancer Patients with Significant Dental Artifact on CT

Dental Hardware Complicating Diagnosis in Refractory Gelastic Epilepsy Secondary to Hypothalamic Hamartoma

Hypothalamic hamartomas (HH) are developmental malformations of the hypothalamus associated with a potentially treatable epileptic encephalopathy, characterized by early onset gelastic seizures, the later development of multiple seizure types and progressive cognitive and behavioral decline. Surgical treatment of HH can lead to seizure control and improvement in the cognitive-behavioral syndrome. Video-EEG telemetry (VET) is often necessary to characterize the semiology of the seizures, but there are no specific interictal or ictal EEG pattems that will confirm the diagnosis. Magnetic resonance imaging (MRI) can identify HH and define their anatomy, but the imaging findings may be subtle and susceptible to artifactual contamination. We present a patient with intractable gelastic epilepsy in whom the diagnosis of HH was initially missed due to failure to recognize the clinical syndrome and contamination of the MRI images with dental hardware artifact. VET confirmed the clinical diagnosis and the HH was identified on MRI after the dental hardware was removed. VET should be performed to confirm seizure semiology in patients with suspected gelastic epilepsy. Establishing this diagnosis can subsequently direct the appropriate neuroradiological evaluation for HH and surgical treatment of these lesions.

Influence of dental metallic artifact from multislice CT in the assessment of simulated mandibular lesions

ObjectiveThis study evaluated the influence of metallic dental artifacts on the accuracy of simulated mandibular lesion detection by using multislice technology.Material and MethodsFifteen macerated mandibles were used. Perforations were done simulating bone lesions and the mandibles were subjected to axial 16 rows multislice CT images using 0.5 mm of slice thickness with 0.3 mm interval of reconstruction. Metallic dental restorations were done and the mandibles were subjected again to CT in the same protocol. The images were analyzed to detect simulated lesions in the mandibles, verifying the loci number and if there was any cortical perforation exposing medullar bone. The analysis was performed by two independent examiners using e-film software.ResultsThe samples without artifacts presented better results compared to the gold standard (dried mandible with perforations). In the samples without artifacts, all cortical perforation were identified and 46 loci were detected (of 51) in loci number analysis. Among the samples with artifacts, 12 lesions out of 14 were recognized regarding medullar invasion, and 40 out of 51 concerning loci number. The sensitivity in samples without artifacts was 90% and 100% regarding loci number and medullar invasion, respectively. In samples with artifacts, these values dropped to 78% and 86%, respectively. The presence of metallic restorations affected the sensitivity values of the method, but the difference was not significant (p>0.05).ConclusionAlthough there were differences in the results of samples with and without artifacts, the presence of metallic restoration did not lead to misinterpretation of the final diagnosis. However, the validity of multislice CT imaging in this study was established for detection of simulated mandibular bone lesions.

Evaluation of the impact of dental artefacts on intensity-modulated radiotherapy planning for the head and neck

Background and purpose High density materials create severe artefacts in the computed tomography (CT) scans used for radiotherapy dose calculations. Increased use of intensity-modulated radiotherapy (IMRT) to treat oropharyngeal cancers raises concerns over the accuracy of the resulting dose calculation. This work quantifies their impact and evaluates a simple corrective technique. Materials and methods Fifteen oropharyngeal patients with severe artefacts were retrospectively planned with IMRT using two different CT/density look-up tables. Each plan was recalculated using a corrected CT dataset to evaluate the dose distribution delivered to the patient. Plan quality in the absence of dental artefacts was similarly assessed. A range of dosimetric and radiobiological parameters were compared pre- and post-correction. Results Plans using a standard CT/density look-up table (density ⩽1.8 g/cm 3) revealed inconsistent inter-patient errors, mostly within clinical acceptance, although potentially significantly reducing target coverage for individual patients. Using an extended CT/density look-up table (density ⩽10.0 g/cm 3) greatly reduced the errors for 13/15 patients. In 2/15 patients with residual errors the CTV extended into the severely affected region and could be corrected by applying a simple manual correction. Conclusions Use of an extended CT/density look-up table together with a simple manual bulk density correction reduces the impact of dental artefacts on head and neck IMRT planning to acceptable levels.

Utility of Megavoltage Fan-Beam CT for Treatment Planning in a Head-And-Neck Cancer Patient with Extensive Dental Fillings Undergoing Helical Tomotherapy

The purpose of this study was to demonstrate the potential utility of megavoltage fan-beam computed tomography (MV-FBCT) for treatment planning in a patient undergoing helical tomotherapy for nasopharyngeal carcinoma in the presence of extensive dental artifact. A 28-year-old female with locally advanced nasopharyngeal carcinoma presented for radiation therapy. Due to the extensiveness of the dental artifact present in the oral cavity kV-CT scan acquired at simulation, which made treatment planning impossible on tomotherapy planning system, MV-FBCT imaging was obtained using the HI-ART tomotherapy treatment machine, with the patient in the treatment position, and this information was registered with her original kV-CT scan for the purposes of structure delineation, dose calculation, and treatment planning. To validate the feasibility of the MV-FBCT-generated treatment plan, an electron density CT phantom (model 465, Gammex Inc., Middleton, WI) was scanned using MV-FBCT to obtain CT number to density table. Additionally, both a “cheese” phantom (which came with the tomotherapy treatment machine) with 2 inserted ion chambers and a generic phantom called Quasar phantom (Modus Medical Devices Inc., London, ON, Canada) with one inserted chamber were used to confirm dosimetric accuracy. The MV-FBCT could be used to clearly visualize anatomy in the region of the dental artifact and provide sufficient soft-tissue contrast to assist in the delineation of normal tissue structures and fat planes. With the elimination of the dental artifact, the MV-FBCT images allowed more accurate dose calculation by the tomotherapy system. It was confirmed that the phantom material density was determined correctly by the tomotherapy MV-FBCT number to density table. The ion chamber measurements agreed with the calculations from the MV-FBCT generated phantom plan within 2%. MV-FBCT may be useful in radiation treatment planning for nasopharyngeal cancer patients in the setting of extensive dental artifacts.

Image Quality Analysis to Reduce Dental Artifacts in Head and Neck Imaging with Dual-Source Computed Tomography

Important oropharyngeal structures can be superimposed by metallic artifacts due to dental implants. The aim of this study was to compare the image quality of multiplanar reconstructions and an angulated spiral in dual-source computed tomography (DSCT) of the neck. Sixty-two patients were included for neck imaging with DSCT. MPRs from an axial dataset and an additional short spiral parallel to the mouth floor were acquired. Leading anatomical structures were then evaluated with respect to the extent to which they were affected by dental artifacts using a visual scale, ranging from 1 (least artifacts) to 4 (most artifacts). In MPR, 87.1 % of anatomical structures had significant artifacts (3.12 +/- 0.86), while in angulated slices leading anatomical structures of the oropharynx showed negligible artifacts (1.28 +/- 0.46). The diagnostic growth due to primarily angulated slices concerning artifact severity was significant (p < 0.01). MPRs are not capable of reducing dental artifacts sufficiently. In patients with dental artifacts overlying the anatomical structures of the oropharynx, an additional short angulated spiral parallel to the floor of the mouth is recommended and should be applied for daily routine. As a result of the static gantry design of DSCT, the use of a flexible head holder is essential.

Tumor Volume Assessment by18F-FDG PET/CT in Patients with Oral Cavity Cancer with Dental Artifacts on CT or MR Images

The purpose of this study was to investigate the clinical usefulness of PET/CT or CT-attenuated PET in the evaluation of patients with oral cavity cancer (OCC) in whom dental artifacts distorted the conventional CT or MR images of the oral cavity. A PET/CT scan, in addition to a CT or MRI scan, was performed in 69 patients with OCC who had dentures or dental implants. A total of 64 PET/CT, 64 CT, and 27 MR images were analyzed including images from scans performed on 40 patients with OCC without dental artifacts on the conventional images; these were used for comparison. The CT-attenuated PET scan for the detection of primary tumors was compared with the CT or MRI scan. We also evaluated the correlation between the PET/CT volume and the pathologic volume using a regression analysis. In addition, subgroup analysis was performed to determine what proportion of subjects benefited most from the PET/CT. CT-attenuated PET detected more primary tumors than did CT in patients with OCC with dental artifacts (95.3% vs. 75.0%, respectively; P=0.0016). PET/CT volume with a standardized uptake value (SUV) cutoff point of 3.5 predicted the pathologic volume more accurately than did the other cutoff points in patients with OCC with or without artifacts. After comparing pathologic volume and PET/CT(SUV 3.5) volume, the following regression equation was developed: log (pathologic volume)=0.6 x log (PET/CT(SUV 3.5) volume) + 1.3 (R(2) = 0.42, P<0.0001). Subgroup analysis showed that the prediction of the pathologic volume from the PET/CT images was more reliable for tumors that were more than 2 cm in depth (R(2)=0.72). For patients with OCC with dental artifacts on the conventional imaging, PET/CT could provide useful clinical information about the primary tumors, particularly in cases with advanced tumors.

Diagnostic accuracy of cone-beam CT in the assessment of mandibular invasion of lower gingival carcinoma: Comparison with conventional panoramic radiography

Purpose To evaluate the diagnostic accuracy of cone-beam CT in assessing mandibular invasion by lower gingival carcinoma and compare it with that of panoramic radiography. Patients and methods Fifty patients with squamous cell carcinoma of the lower gingiva who were examined by both panoramic radiography and cone-beam CT before surgery were included in this study. Five radiologists used a 6-point rating scale to independently evaluate cone-beam CT and panoramic images for the presence or absence of alveolar bone and mandibular canal involvement by tumor. Using the histopathogical findings as the gold standard, we calculated and compared the area under the receiver operating characteristic curve (Az value) and the sensitivity and specificity of the two imaging modalities. Results In evaluations of both alveolar bone and mandibular canal involvement, the mean Az value for cone-beam CT (0.918 and 0.977, respectively) was significantly higher than that for panoramic radiography (0.793 and 0.872, respectively). The mean sensitivity for cone-beam CT (89% and 99%, respectively) was significantly higher than that for panoramic radiography (73% and 56%, respectively). There was no significant difference in the mean specificity. While cone-beam CT could provide high-resolution three-dimensional images, the image quality around the alveolar crest was often hampered by severe dental artifacts and image noise, resulting in difficulties in detecting subtle alveolar invasion. Conclusion Cone-beam CT was significantly superior to panoramic radiography in evaluating mandibular invasion by lower gingival carcinoma. Its diagnostic value in detecting subtle alveolar invasion, however, may be limited by severe dental artifacts and image noise.

The Effect of Dental Artifacts, Contrast Media, and Experience on Interobserver Contouring Variations in Head and Neck Anatomy

To investigate interobserver variability in the delineation of head-and-neck (H&N) anatomic structures on CT images, including the effects of image artifacts and observer experience. Nine observers (7 radiation oncologists, 1 surgeon, and 1 physician assistant) with varying levels of H&N delineation experience independently contoured H&N gross tumor volumes and critical structures on radiation therapy treatment planning CT images alongside reference diagnostic CT images for 4 patients with oropharynx cancer. Image artifacts from dental fillings partially obstructed 3 images. Differences in the structure volumes, center-of-volume positions, and boundary positions (1 SD) were measured. In-house software created three-dimensional overlap distributions, including all observers. The effects of dental artifacts and observer experience on contouring precision were investigated, and the need for contrast media was assessed. In the absence of artifacts, all 9 participants achieved reasonable precision (1 SD < or =3 mm all boundaries). The structures obscured by dental image artifacts had larger variations when measured by the 3 metrics (1 SD = 8 mm cranial/caudal boundary). Experience improved the interobserver consistency of contouring for structures obscured by artifacts (1 SD = 2 mm cranial/caudal boundary). Interobserver contouring variability for anatomic H&N structures, specifically oropharyngeal gross tumor volumes and parotid glands, was acceptable in the absence of artifacts. Dental artifacts increased the contouring variability, but experienced participants achieved reasonable precision even with artifacts present. With a staging contrast CT image as a reference, delineation on a noncontrast treatment planning CT image can achieve acceptable precision.

Reliability of CT-based tumor volumetry after intraarterial chemotherapy in patients with small carcinoma of the oral cavity and the oropharynx

The aim of the study was to evaluate the feasibility and consistency of CT-based tumor volumetry in patients with early carcinoma of the oral cavity and the oropharynx before and after intraarterial (IA) chemotherapy, comparing these data with clinical remission rates. Included in the study were 61 patients (mean age 59.3 years; 47 men) with histologically proven small carcinoma of the oral cavity or the oropharynx (local tumor stages T1/2). Patients received IA chemotherapy with high-dose cisplatin as part of a multimodal therapeutic regimen and underwent both clinical and radiological examination before and 4 weeks after local chemotherapy. Clinical evaluation of tumor response was possible in all patients (61/61). Radiological assessment of tumor volume was feasible in 42 of 61 patients (69%), but failed in 19 (31%) due to the absence of deep tumoral spread, lack of contrast enhancement or severe dental artifacts. Patients in whom evaluation was possible according to volumetric and clinical criteria revealed comparable remission rates: overall response 54.8% versus 52.4%, stable disease 40.4% versus 47.6%, and tumor progression 4.8% versus 0.0%. Because volume calculation was not feasible in approximately one-third of the patients, it cannot be recommended as a reliable indicator for treatment response in patients with small carcinoma of the oral cavity.

Imaging for evaluation of suspected cervical spine trauma: A 2-year analysis

To examine the role of radiography in screening trauma patients with suspected injury to the cervical spine. Over a period of 2 years, 5172 people were admitted to our trauma service and 297 (5.4%) were found to have cervical fractures. The radiographic and CT films and reports of 245 of these 297 patients were reviewed. The 245 subjects had sustained 309 distinct individual injuries. Radiography detected injuries in 108 cases (44.1%) and CT detected injuries in 243 cases (99.2%). The two fractures missed by CT occurred at C2; one fracture was obscured by dental artefacts and the other was in the horizontal plane of the scan. Both fractures were detected on lateral radiographs of the region. CT is superior to radiography for identification of cervical spine fractures. The fractures most likely to be missed by CT occur at C2. We recommend that CT be used as the primary screening method for people with suspected cervical injury, together with a single lateral view of the cervical spine to include the C2 region.

Moderne Bildgebung der Nasennebenhöhlen

Depending on the problems, CT or MRI should be used in the differential diagnosis of conditions affecting the nasal sinuses. In particular, when chronic sinusitis is present, computed tomography should be performed before surgery to ascertain the condition of the bones. In most cases spiral CT with a decidedly lowered tube voltage and power (MAS product) is now used for this purpose. This means that the patient is exposed to about 70% less radiation than in other CT investigations. To avoid artefacts attributable to dental fillings, whenever possible the spiral should be tilted in such a way that the dental artefacts are not within the mass imaged. When an isotropic voxel is selected secondary reformatting is possible with no loss of quality. Diagnostic MRI should include both T1- and T2-weighted sequences before and after the administration of contrast agent. For the differential diagnosis of a space-occupying tumour coronal cuts about 2 mm apart are advised, whether the spiral or the conventional technique is used. A T2-weighted and fat-suppressed sequence or a STIR (short tau inversion recovery) sequence can also be helpful in the recognition and visualization of lymph nodes. If orbital involvement seems possible it is advisable to use a T1-weighted and fat-suppressed sequence in the coronal plane in addition to check this.

402 Dosimetric impact of dental metal artifact present in head and neck CT data sets on IMRT dose distributions

402 Dosimetric impact of dental metal artifact present in head and neck CT data sets on IMRT dose distributions

A method of eliminating streak artifacts from metallic dental restorations in CTs of head and neck cancer patients.

The purpose of this report was to develop a method to reduce streak artifacts derived from dental restorations in CT-imaging of the head and neck region. We selected six patients who were being treated for head and neck cancer and who had metal-derived artifacts on their CT that limited pre- or post-surgical visualization. The metal restorations were removed and replaced with non-metallic composite resin restorations. The CT was repeated as required on completion of the procedures. The streak artifacts were completely eliminated in patients in whom radiolucent composite materials were used. Patients have been followed for 6-26 months with no complications or breakdown of the restorations. The substitution of radiolucent for metallic restorations in special cases should be considered as a solution to CT dental artifact problems.

Variability of tumor volumes in T3-staged head and neck tumors.

The Tumor Node Metastasis (TNM) classification system describes head and neck tumors using anatomic or unidimensional criteria and may therefore fail to define the actual three-dimensional tumor bulk. To investigate this we measured variability of tumor volumes (Vvol) in T3-staged head and neck tumors. Patient material consisted of pretreatment computerized tomography (CT) scans of 71 patients, seen between 1990 and 1995, with T3 head and neck carcinoma involving different subsites. Computerized tomographic scans of 42 patients displayed distinct tumor boundaries and were free of motion and/or dental artifacts. Using these scans, tumor volumes were measured using the summation-of-areas technique, and Vvol was determined. Following are the tumor-volume measurements: T3 larynx carcinoma (n = 12) Vvol, 1.7-17.0 mL (median 3.7 mL); T3 oropharynx carcinoma (n = 13) Vvol, 10.0-41.2 mL (median 18.3 mL); T3 hypopharynx carcinoma (n = 10) Vvol, 8.9-67.8 mL (median 17.4 mL); T3 nasopharynx carcinoma (n = 3) Vvol, 3.7-30.1 mL; T3 maxillary sinus carcinoma (n = 4) Vvol, 56.0-103.1 mL. T3-Staged tumors of the head and neck show considerable variability of tumor volumes. Incorporation of tumor volume data may further refine the TNM staging system.