Digital volume tomography: radiologic examinations of the temporal bone

OBJECTIVE: We evaluated the clinical applicability and the value of digital volume tomography for visualization of the lateral skull base using temporal bone specimens. MATERIALS AND METHODS: Twelve temporal bone specimens were used to evaluate digital volume tomography on the lateral skull base. Aside from the initial examination of the temporal bones, radiologic control examinations were performed after insertion of titanium, gold, and platinum middle-ear implants and a cochlear implant. RESULTS: With high-resolution and almost artifact-free visualization of alloplastic middle-ear implants of titanium, gold, or platinum, it was possible to define the smallest bone structures or position of the prosthesis with high precision. Furthermore, the examination proved that digital volume tomography is useful in assessing the normal position of a cochlear implant. CONCLUSION: Digital volume tomography expands the application of diagnostic possibilities in the lateral skull base. Therefore, we believe improved preoperative diagnosis can be achieved along with more accurate planning of the surgical procedure. Digital volume tomography delivers a small radiation dose and a high resolution coupled with a low purchase price for the equipment.     

Radiographic imaging of the mastoid process with conventional tomography: a novel positioning technique

The Scanora (Soredex, Helsinki, Finland) is a multimodal unit for maxillofacial imaging combining narrow beam radiography and pluridirectional spiral tomography. We describe a novel technique for imaging the mastoid process based on a modification of the program for coronal tomography of the ear. This technique is of potential clinical value for implant planning and postoperative evaluation in the temporal bone.     

Use of computed tomography for a three-dimensional treatment planning system

Computed tomography (CT) can generate a set of serial contiguous slices which form a volume of medical image data. We have developed new techniques for creating computer synthesized 3-D images directly from a volume encoded as a three-dimensional array. The operator can place the eye anywhere in object space to selectively view a portion of the volume from any angle. A set of volume processing tools have been recently developed to allow interactive manipulation of image data within the volume. These tools allow the system to be used for surgical planning, and craniofacial implant design.     

Computed tomography for dental implants: the influence of the gantry angle and mandibular positioning on the bone height and width

OBJECTIVES: To investigate the effect of deviation of mandibular positioning, by changing the gantry angle, on the measured height and width of dental implant sites in reformatted cross-sectional computed tomography (CT) scans. METHODS: CT images of ten human dry mandibles were made in three gantry positions to simulate changes in patient positioning: (1) parallel to the lower base of the mandible (standard); (2) with a gantry inclination of +19 degrees ; and (3) with an inclination of -19 degrees . One examiner measured the bone height and width at selected sites in the images at three different times. Results were compared with a paired test in SAS 8.02. RESULTS: In relation to bone height, when the jaws were inclined to the inferior direction (gantry angle +19 degrees ), there was no statistically significant difference for any region studied. There was a statistically significant difference for the incisor region when the jaws were inclined to the superior direction (gantry angle -19 degrees ). With respect to the width of the bone rim, there was a statistically significant difference only for the region of the molars when the jaw was inclined to the inferior direction and for the region of the canine, when the inclination was to the superior direction. CONCLUSIONS: Errors in mandibular positioning of 19 degrees produced image discrepancies with regard to bone height and width which were not excessive. Thus, examinations do not have to be repeated owing to variation of mandibular positioning because the differences were lower than 10% of the value found for the standard position.     

Predictability of reformatted computed tomography for pre-operative planning of endosseous implants

OBJECTIVES: To determine the reliability of reformatted 2D-CT for pre-operative planning of implant placement. METHODS: One hundred consecutive partially or fully edentate patients underwent 2-D reformatted CT pre-operative planning and subsequent implant placement. The number, site and size of the implants, the available bone height and anatomical complications were recorded. The pre-operative planning and the outcome at surgery were compared statistically using a percentage agreement and Kendall's correlation coefficient. RESULTS: Agreement between the pre- and intra-operative data was good for the number of implants (60%) and the selected sites (70%). From a total of 416 implants planned, 21 implants could not be placed because of intra-operative findings. Agreement was relatively poor for implant size (44%) and anatomical complications (46%). Kendall's correlation coefficient was highest for the number of implants (0.80) and implant sites (0.81). It was much lower for implant sizes (0.51) and did not reach significance for anatomical complications (0.09). CONCLUSIONS: Reformatted 2D-CT is reliable for the pre-operative assessment of the number and sites of implants in the jaws. It is less predictable for the implant size needed and poor for anatomical complications.     

Computed tomography in dental implantology: medico-legal implications

Diagnostic imaging plays an important role in both the planning of dental implants and the follow-up evaluation of the procedure. It is widely known that computed tomography (CT) together with Dentascan software is the most accurate imaging technique in the planning of implant treatment. Unlike conventional radiological techniques, CT enables the three-dimensional evaluation of the bone without the overlapping of adjacent structures, as well as a precise measurement of the bone tissue available in the future implant site, contributing in this way to a significant reduction in unsuccessful treatment. CT also enables a qualitative evaluation of the bone structure together with a precise definition of the adjacent anatomical structures and possible associated pathologies. Finally, given the wealth of information provided by CT, it is clear that the technique can also be used for judging in retrospect the correctness of a dental implant procedure. The present paper describes the CT findings that are most relevant to the medicolegal assessment of professional liability in implantology.     

CT-image-based conformal brachytherapy of breast cancer. The significance of semi-3-D and 3-D treatment planning.

PURPOSE: To compare the conventional 2-D, the simulator-guided semi-3-D and the recently developed CT-guided 3-D brachytherapy treatment planning in the interstitial radiotherapy of breast cancer. PATIENTS AND METHODS: In 103 patients with T1-2, N0-1 breast cancer the tumor bed was clipped during breast conserving surgery. Fifty-two of them received boost brachytherapy after 46 to 50 Gy teletherapy and 51 patients were treated with brachytherapy alone via flexible implant tubes. Single, double and triple plane implant was used in 6, 89 and 8 cases, respectively. The dose of boost brachytherapy and sole brachytherapy prescribed to dose reference points was 3 times 4.75 Gy and 7 times 5.2 Gy, respectively. The positions of dose reference points varied according to the level (2-D, semi-3-D and 3-D) of treatment planning performed. The treatment planning was based on the 3-D reconstruction of the surgical clips, implant tubes and skin points. In all cases the implantations were planned with a semi-3-D technique aided by simulator. In 10 cases a recently developed CT-guided 3-D planning system was used. The semi-3-D and 3-D treatment plans were compared to hypothetical 2-D plans using dose-volume histograms and dose non-uniformity ratios. The values of mean central dose, mean skin dose, minimal clip dose, proportion of underdosaged clips and mean target surface dose were evaluated. The accuracy of tumor bed localization and the conformity of planning target volume and treated volume were also analyzed in each technique. RESULTS: With the help of conformal semi-3-D and 3-D brachytherapy planning we could define reference dose points, active source positions and dwell times individually. This technique decreased the mean skin dose with 22.2% and reduced the possibility of geographical miss. We could achieve the best conformity between the planning target volume and the treated volume with the CT-image based 3-D treatment planning, at the cost of worse dose homogeneity. The mean treated volume was reduced by 25.1% with semi-3-D planning, however, it was increased by 16.2% with 3-D planning, compared to the 2-D planning. CONCLUSION: The application of clips into the tumor bed and the conformal (semi-3-D and 3-D) planning help to avoid geographical miss. CT is suitable for 3-D brachytherapy planning. Better local control with less side effects might be achieved with these new techniques. Conformal 3-D brachytherapy calls for new treatment planning concepts, taking the irregular 3-D shape of the target volume into account. The routine clinical application of image-based 3-D brachytherapy is a real aim in the very close future.     

Design, analysis and simulation for development of the first clinical micro-CT scanner

In this article, we propose to develop the first clinical micro-CT (CMCT) system for human temporal bone imaging in vivo. This CMCT system consists of medical CT and micro-CT scanners either as separate components or in a combination, a cross-modality registration mechanism such as a facial surface scanner, and associated software. This system integrates the strengths of state-of-the-art medical CT and micro-CT techniques to achieve a spatial resolution that is much higher than currently available for inner ear imaging at acceptable dose levels. Our design, analysis, and simulation results demonstrate that the CMCT system is feasible for inner ear imaging and other clinical applications. For example, the CMCT system has the potential to improve the safety of guiding cochlear implant electrodes within the inner ear and assist the placement of inner ear microcatheters for delivery of gene modification therapy or administration of neurotrophic factors. Imaging of microarchitectures of the cancellous bone would be also an important application.     

Clinical commissioning of Laitinen Stereoadapter for fractionated stereotactic radiotherapy

The Laitinen Stereoadapter 5000 from Sandstroem Trade and Technology was acceptance tested and commissioned for clinical use in a Fractionated Stereotactic Radiotherapy Program at our facility. The frame was implemented to function as a localization device for target delineation rather than as an immobilization device. The frame is of non-invasive nature utilizing ear plugs and a nasion bridge adapter as the connecting points with the patient’s head. The reproducibility of the head frame position with respect to external skull reference points was tested. CT and MRI imaging studies were performed on a patient phantom with the stereoadapter in place. The target was delineated and target coordinates were calculated for two implanted targets. The phantom was positioned according to the target coordinates on a Siemens MXE Linear Accelerator by aid of the target positioning lasers. Radiographic port film images were taken with the circular fields typically used in stereotactic radiosurgery. A complete treatment isodose plan was performed and dosimetric accuracy was tested by positioning a small volume ionization chamber at the center of the target volume in the head phantom. The results of these tests were found to be clinically acceptable.     

Clinical commissioning of Laitinen Stereoadapter for fractionated stereotactic radiotherapy

The Laitinen Stereoadapter 5000 from Sandstroem Trade and Technology was acceptance tested and commissioned for clinical use in a Fractionated Stereotactic Radiotherapy Program at our facility. The frame was implemented to function as a localization device for target delineation rather than as an immobilization device. The frame is of non-invasive nature utilizing ear plugs and a nasion bridge adapter as the connecting points with the patient’s head. The reproducibility of the head frame position with respect to external skull reference points was tested. CT and MRI imaging studies were performed on a patient phantom with the stereoadapter in place. The target was delineated and target coordinates were calculated for two implanted targets. The phantom was positioned according to the target coordinates on a Siemens MXE Linear Accelerator by aid of the target positioning lasers. Radiographic port film images were taken with the circular fields typically used in stereotactic radiosurgery. A complete treatment isodose plan was performed and dosimetric accuracy was tested by positioning a small volume ionization chamber at the center of the target volume in the head phantom. The results of these tests were found to be clinically acceptable.     

CAD/CAM and rapid prototyped scaffold construction for bone regenerative medicine and surgical transfer of virtual planning: A pilot study

We developed a model to test new bone constructs to replace spare skeletal segments originating from new generation scaffolds for bone marrow-derived mesenchymal stem cells. Using computed tomography (CT) data, scaffolds were defined using computer-aided design/computer-aided manufacturing (CAD/CAM) for rapid prototyping by three-dimensional (3D) printing. A bone defect was created in pig mandible ramus by condyle resection for CT and CAD/CAM elaboration of bone volume for cutting and scaffold restoration. The protocol produced a perfect-fitting bone substitute model for rapid prototyped hydroxyapatite (HA) scaffolds. A surgical guide system was developed to accurately reproduce virtually planned bone sectioning procedures in animal models to obtain a perfect fit during surgery.     

CT-Based Interstitial HDR Brachytherapy

PURPOSE: Development, application and evaluation of a CT-guided implantation technique and a fully CT-based treatment planning procedure for brachytherapy. METHODS AND MATERIALS: A brachytherapy procedure based on CT-guided implantation technique and CT-based treatment planning has been developed and clinical evaluated. For this purpose a software system (PROMETHEUS) for the 3D reconstruction of brachytherapy catheters and patient anatomy using only CT scans has been developed. An interface for the Nucletron PLATO BPS treatment planning system for optimization and calculation of dose distribution has been devised. The planning target volume(s) are defined as sets of points using contouring tools and are used for optimization of the 3D dose distribution. Dose-volume histogram based analysis of the dose distribution (COIN analysis) enables a clinically realistic evaluation of the brachytherapy application to be made. The CT-guided implantation of catheters and the CT-based treatment planning procedure has been performed for interstitial brachytherapy and for different tumor sites in 197 patients between 1996 and 1997. RESULTS: The accuracy of the CT reconstruction was tested using first a quality assurance phantom and second, a simulated interstitial implant of 12 needles. These were compared with the results of reconstruction using radiographs. Both methods gave comparable results with regard to accuracy, but the CT based reconstruction was faster. Clinical feasibility was proved in pre-irradiated recurrences of brain tumors, in pretreated recurrences or metastatic disease, and in breast carcinomas. The tumor volumes treated were in the range 5.1 to 2,741 cm3. Analysis of implant quality showed a slightly significant lower COIN value for the bone implants, but no differences with respect to the planning target volume. CONCLUSIONS: The Offenbach system, incorporating the PROMETHEUS software for interstitial HDR brachytherapy has proved to be extremely valuable in routine clinical practice for many tumor sites. Our CT-guided implantation technique together with a fully CT-based planning system has enabled conformal brachytherapy treatment to become routine.     

Application of three-dimensional orthogonal neural network to craniomaxillary reconstruction

The purpose of this investigation is to establish a practical method to predict and create surface a profile of bone defects by a well-trained 3-D orthogonal neural network. First, the coordinates of the skeletal positions around the boundary of bone defects are input into the 3-D orthogonal neural network to train it to learn the scattering characteristic. The 3-D orthogonal neural network avoids local minima and converges rapidly. After the neural network has been well trained, the mathematic model of the bone defect surface is generated, and the pixel positions are derived. Herein, to verify its performance the proposed method is applied on a patient with a craniofacial defect.     

An interactive data preparation procedure for three-dimensional interstitial and intracavitary dose calculation programs.

A computer system has been developed to assist in preparing data for interstitial and intracavitary calculations. This approach used graphic and interactive techniques, and removes all the format problems which led to errors in data preparation. The program reconstructs the implant and rotates it about X, Y and Z axes to allow close examination of the positions of the radiation sources. The site of the dose calculation can be selected by positioning a frame representing the calculation plane in the reconstructed implant. The output of the program is the three-dimensional data of the source and plane co-ordinates, together with the co-ordinates to define the area on the plane where the calculation is to be performed.     

Treatment planning considerations for permanent breast seed implant

PurposeTo determine an optimal planning strategy for permanent breast seed implant that minimizes dose heterogeneity without degrading coverage and conformity.Methods and MaterialsA simple model was developed to investigate planning strategies incorporating a range of ¹⁰³Pd seed activities, needle and seed spacings, and implants in which seed positions are either restricted to or permitted outside of spherical planning target volumes (PTVs). To address more realistic target geometries, model parameters were used to retrospectively replan a 10-patient cohort in MIM Symphony.ResultsWe confirm that the current clinical modified uniform implantation pattern provides the most favorable dose distributions, given the resolution of the template grid and spacer length. We show that needle and seed counts for replans with seed placement permitted 0.3 cm outside of the PTV are most comparable to clinical preplans, but offer a 13 ± 11% average reduction in the V_PTV150%. Replans produced with seed placement 0.5 cm outside of the PTV provide the largest improvement in dose homogeneity, at the cost of a slight increase in irradiated volume and an increase in the number of needles and seeds.ConclusionsImplanting seeds beyond the PTV within a 0.3–0.5 cm margin, and optimizing seed activity on a per patient basis, allows for improvement in dose homogeneity. However, these plans require higher needle and seed counts and result in a small increase in irradiated volume. Before planning recommendations can be made, the implications of these changes must be investigated in the context of clinical outcome for permanent breast seed implant.     

Three-dimensional endoluminal ultrasound-guided interstitial brachytherapy in patients with anal cancer

Background: New techniques using image guidance other than computed tomography (CT) and traditional two-dimensional (2D) endosonography might improve interstitial brachytherapy in patients with anal cancer.

Purpose: To investigate a new technique guided by three-dimensional (3D) endosonography used in our institution.

Material and Methods: Seventeen patients with anal carcinoma were referred to interstitial brachytherapy under 3D endosonographic guidance after external radiotherapy. The procedure was initiated by anal endosonography performed with a 10-MHz rotating endoprobe. Cross-sectional images of the anal sphincters were stored on a 3D system during retraction of the endoprobe through the anal canal. Afterward, any projection could be reconstructed. From this scanning, the optimal positioning of the needles was determined. The needles were inserted through holes in an externally fixated anal template. A repeated endosonography assured that optimal tumor coverage could be obtained by adjusting the number, dwell positions, and/or position of the needles.

Results: In all patients, endosonography was able to visualize the extension of the tumors and the position of each needle in 3D.

Conclusion: 3D endosonography guidance of interstitial brachytherapy in anal carcinoma seems to optimize the implant procedure and offer better information for dose planning.     

Comparison of interpolated vs. calculated micromultileaf settings in dynamic conformal arc treatment.

Stereotactic radiosurgery has developed into a technique where patient positioning and treatment delivery can be performed with submillimeter precision. Achievement of this level of precision has allowed margins to be significantly reduced, and in some cases, removed altogether. Joined with these reductions in treatment margin has come a desire to shape the radiation beam, further limiting dose to normal tissues. Initial applications of shaped radiosurgery fields utilized circular blocking apertures in an attempt to shape the beam to these small volumes. The resultant dose distributions conformed well to spherical treatment volumes but were inadequate for situations where the volume of interest was irregular in shape. Other techniques, such as applying these circular apertures through multiple isocenter positions to a single volume, have been investigated as possible ways to better conform dose distributions to these irregularly-shaped volumes. Recent technological advances allow the use of micromultileaf collimators which dynamically shape the beam by adjustment of individual leaves as the gantry rotates through the are. With margins potentially so tight, accurate evaluation of these dynamically adjusting treatment parameters becomes critical. Our current treatment planning software evaluates adjustments of the leaf positions in increments of 10 degrees and then does a linear interpolation between increments. Treatment delivery, however, is performed with adjustment in leaf position more consistent with a 1 degree increment. This paper compares the individual position of each leaf as determined for the 10 degrees interpolation to required changes in leaf position when the calculation is performed at increments of less than 10 degrees. Our data suggest that there are instances where improvements can be seen when corrections in leaf positions are made at these smaller increments.     

Arthroscopic reconstruction of the posterior cruciate ligament. Magnetic resonance study for bone tunnel positioning and comparison with clinical results]

INTRODUCTION: The success of arthroscopic cruciate ligament reconstruction depends on several factors, such as patient selection, correct surgical execution, and postoperative rehabilitation. Technical considerations include graft choice, positioning, fixation, intercondylar notch enlargement, and new ligament tensioning. Graft acceptance is effected by all these factors. Tunnel position is of great importance both for biomechanical reasons and optimal function of the new ligament, and to avoid stress, friction, abnormal strain, and/or damage to the reconstructed ligament. Many orthopedic and radiographic literature studies discuss the exact site of anterior cruciate ligament insertion for the best possible anatomical reconstruction. In contrast, the debate over insertional area and anatomical landmarks is open for the posterior cruciate ligament (PCL), because of the difficult execution of this type of reconstruction and the smaller number of candidates. MATERIAL AND METHODS: Fifty patients with a healthy PCL underwent MRI of the knee for other diagnostic reasons and we measured the position of PCL insertion at the tibial and femoral condyles. We also examined with MRI 20 surgical patients with a reconstructed PCL. Graft position was assessed with the same method and the results compared with physical findings of joint stability and the IKDC form score. RESULTS: Three main landmarks were found on standard axial, coronal and sagittal MR images: T1 on the tibia, and F1 and F2 on the femur. These points refer to the fibrous ligament center and designate the medial, middle and lateral portion of the tibial plateau, as well as the anterior/posterior and high/low positions on the roof of the intercondylar notch and anteromedial side of the medial condyle, respectively. According to these data, the midline position, whether slightly medial or lateral, of tibial insertion, was clinically less important. On the contrary, correct femoral tunnel positioning was found to effect subsequent joint stability and prompt rehabilitation. CONCLUSIONS: This method for MR measurement is easy and repeatable, and can be used for surgical planning and patient follow-up. We found it extremely useful for the correct positioning of bone tunnels, particularly the femoral condyle, in all cases.     

Impact of CT information on the treatment planning for lung tumors

With CT information available today, the prevailing, though strong, argument for not applying lung corrections is that all clinical experience gathered so far applies to doses that were prescribed for uniform density throughout the treated volume. To ease the transition from not correcting, to the state of accounting for increased lung transmission, we have planned 10 patients: (a) in the conventional way with a wire contour obtained at simulation; target volume and critical structures were drawn in by the physician utilizing information gathered from diagnostic CT scans and X-ray films; no lung correction was applied for treatment planning. (b) For the same patients, a CT scan was obtained in treatment position and the target volume was outlined on the CT film utilizing the same information as in (a); a relative lung density of 0.3 was assigned for treatment planning. The geometric accuracy of patient outline and target volume obtained in both planning modalities is analyzed, and the intended and actually delivered tumor doses are compared when optimized treatment plans from either planning modality are selected for treatment.