Fully automated searching for the optimal VMAT jaw settings based on Eclipse Scripting Application Programming Interface (ESAPI) and RapidPlan knowledge-based planning.

PURPOSE: Eclipse treatment planning system has not been able to optimize the jaw positions for Volumetric Modulated Arc Therapy (VMAT). The arbitrary and planner-dependent jaw placements define the maximum field size within which multi-leaf-collimator (MLC) sequences can be optimized to modulate the beam. Considering the mechanical constraints of MLC transitional speed and range, suboptimal X jaw settings may impede the optimization or undermine the deliverability. This work searches optimal VMAT jaw settings automatically based on Eclipse Scripting Application Programming Interface (ESAPI) and RapidPlan knowledge-based planning. METHODS AND MATERIALS: Using an ESAPI script, the X jaws of rectal VMAT plans were initially set to conform the planning-target-volume (PTV), and were gradually extended toward the isocenter (PTV center) in 5-7 mm increments. Using these jaw pairs, 592 plans were automatically created for 10 patients and quantitatively evaluated using a comprehensive scoring function. A published RapidPlan model was evoked by ESAPI to generate patient-specific optimization objectives without manual intervention. All candidate plans were first stored as text files to save storage space, and only the best, worst, and conformal plans were consequently recreated for comparison. RESULTS: Although RapidPlan estimates dose-volume histogram (DVH) based on individual anatomy, the geometry-based expected dose (GED) algorithm does not recognize different jaw settings but uses PTV-conformal jaws as default; hence, identical DVHs were observed regardless of planner-defined jaws. Therefore, ESAPI finalized dose-volume calculation and eliminated the plans with unacceptable hotspots before comparison. The plan quality varied dramatically with different jaw settings. Trade-offs among different organs-at-risk (OARs) were collectively considered by the proposed scoring method, which identified the best and worst plans correctly. The plans using conformal jaws were neither the best nor the worst of all candidates. CONCLUSIONS: VMAT plans using optimal jaw locations can be created automatically using ESAPI and RapidPlan. Conformal jaws are not the optimal choice.

Influence of Class II Elastics on Centric Relation and Centric Occlusion Discrepancy after Orthodontic Treatment / Influencia de los Elásticos de Clase II sobre la Discrepancia de Relación Céntrica para la Oclusión Céntrica Después del Tratamiento Ortodóncico

ABSTRACT: The objective of this study was to verify the influence of the use of Class II intermaxillary elastics on centric relation (CR) to centric occlusion (CO) occlusal discrepancy. A total of 30 patients had been at the contention stage for at least three months were divided in two groups: G1 - 15 had been submitted to intramaxillary orthodontic mechanics only, and G2 - 15 had used Class II intermaxillary elastics. Distances of horizontal and vertical overlap and the distance or coincidence of the mandibular dental midline in relation to the maxillary midline were measured in CR and CO positions. Intergroup comparisons were performed using the Mann-Whitney test. No statistically significant differences (P>0.05) were found between G1 and G2. Both in the horizontal and vertical directions, these discrepancies were smaller than or equal to 1mm in 96.66 % of the patients. In the transverse plane, there was no discrepancy in 63.33 % of the patients, and in 33.33 % these discrepancies were equal to 0.5 mm. The use of Class II elastic didn't be capable of increasing the occlusal discrepancies between CR and CO.

RESUMEN: El objetivo de este estudio fue verificar la influencia del uso de los elásticos intermaxilares Clase II en la discrepancia oclusal entre la relación céntrica (RC) y la oclusión céntrica (OC). Un total de 30 pacientes que permanecieron en la fase de contención durante al menos tres meses se dividieron en dos grupos: G1 - 15 fueron sometidos solamente a la mecánica ortodóncica intramaxilar, y G2 - 15 habían utilizado elásticos de clase II intermaxilar. Se midieron las distancias de traslapo horizontal y vertical y la distancia o coincidencia de la línea mediana dentaria mandibular con respecto a la línea mediana maxilar en las posiciones RC y OC. Las comparaciones entre grupos se realizaron mediante la prueba de Mann-Whitney. No se encontraron diferencias estadísticamente significativas (P> 0.05) entre G1 y G2. Tanto en las direcciones horizontal como vertical, estas discrepancias fueron menores o iguales a 1 mm en el 96,66 % de los pacientes. En el plano transversal, no hubo discrepancia en el 63,33 % de los pacientes, y en un 33,33 % estas discrepancias fueron iguales a 0,5 mm. El uso de la clase II elástica no logró aumentar las discrepancias entre RC y OC.

A comparative study of identical VMAT plans with and without jaw tracking technique.

The unwanted radiation transmission through the multileaf collimators could be reduced by the jaw tracking technique which is commercially available on Varian TrueBeam accelerators. On the basis of identical plans, this study aims to investigate the dosimetric impact of jaw tracking on the volumetric-modulated arc therapy (VMAT) plans. Using Eclipse treatment planning system (TPS), 40 jaw-tracking VMAT plans with various tumor volumes and shapes were optimized. Fixed jaw plans were created by editing the jaw coordinates of the jaw-tracking plans while other parameters were identical. The deliverability of this artificial modification was verified using COMPASS system via three-dimentional gamma analysis between the measurement-based reconstruction and the TPS-calculated dose distribution. Dosimetric parameters of dose-volume histogram (DVH) were compared to assess the improvement of dose sparing for organs at risk (OARs) in jaw-tracking plans. COMPASS measurements demonstrated that over 96.9% of structure volumes achieved gamma values less than 1.00 at criteria of 3 mm/3%. The reduction magnitudes of maximum and mean dose to various OARs ranged between 0.06% ~ 6.76% (0.04 ~ 7.29 Gy) and 0.09% ~ 7.81% (0.02 ~ 2.78 Gy), respectively, using jaw tracking, agreeing with the disparities of radiological characteristics between MLC and jaws. Jaw tracking does not change the delivery efficiency and total monitor units. The dosimetric comparison of VMAT plans with and without jaw tracking confirms the physics hypotheses that reduced transmission through tracking jaws will reduce doses to OARs without sacrificing the target dose coverage because it is meant to be covered by radiation beams going through the opening.

The Effect of a Radiation Positioning Stent (RPS) in the Reduction of Radiation Dosage to the Opposing Jaw and Maintenance of Mouth opening after Radiation Therapy.

The effect of a radiation positioning stent (RPS) in radiation dosage reduction to the opposing jaw and maintenance of mouth opening was audited. 55 Head and Neck cancer patients who received radiotherapy were reviewed. Radiation dosages at similar points in the primary/opposing jaws were measured along with the mouth opening. Results showed a significant reduction in the radiation dosage to the opposing jaw in patients given the RPS. Mouth opening was generally maintained in patients given the RPS (77.7% improvement in mouth opening) compared to patients without RPS. Patients undergoing radiotherapy who had an RPS showed a significant reduction in radiation dosage to the opposing jaw and maintained their mouth opening in the short-term.

A modified occlusal wafer for managing partially dentate orthognathic patients--a case series.

A multidisciplinary approach is essential in orthognathic surgery to achieve stable and successful outcomes. The model surgery planning is an important aspect in achieving the desired aims. An occlusal wafer used at the time of surgery aids the surgeon during correct placement of the jaws. When dealing with partially dentate patients, the design of the occlusal wafer requires modification to appropriately position the jaw. Two cases with partially dentate jaws are presented in which the occlusal wafer has been modified to provide stability at the time of surgery.

Dosimetric comparison between jaw tracking and static jaw techniques in intensity-modulated radiotherapy.

PURPOSE: To compare the dosimetric differences between jaw tracking technique (JTT) and static jaw technique (SJT) in dynamic intensity-modulated radiotherapy (d-IMRT) and assess the potential advantages of jaw tracking technique. METHODS: Two techniques, jaw tracking and static jaw, were used respectively to develop the d-IMRT plans for 28 cancer patients with various lesion sites: head and neck, lungs, esophageal, abdominal, prostate, rectal and cervical. The dose volume histograms (DVH) and selected dosimetric indexes for the whole body and for organs at risk (OARs) were compared. A two dimensional ionization chamber Array Seven29 (PTW, Freiburg, Germany) and OCTAVIUS Octagonal phantom (PTW, Freiburg, Germany) were used to verify all the plans. RESULTS: For all patients, the treatment plans using both techniques met the clinical requirements. The V5, V10, V20, V30, V40 (volumes receiving 5, 10, 20, 30 and 40 Gy at least, respectively), mean dose (Dmean) for the whole body and V5, V10, V20, Dmean for lungs in the JTT d-IMRT plans were significantly less than the corresponding values of the SJT d-IMRT plans (p < 0.001). The JTT d-IMRT plans deposited lower maximum dose (Dmax) to the lens, eyes, brainstem, spinal cord, and right optic nerve, the doses reductions for these OARs ranged from 2.2% to 28.6%. The JTT d-IMRT plans deposited significantly lower Dmean to various OARs (all p values < 0.05), the mean doses reductions for these OARs ranged from 1.1% to 31.0%, and the value reductions depend on the volume and the location of the OARs. The γ evaluation method showed an excellent agreement between calculation and measurement for all techniques with criteria of 3%/3 mm. CONCLUSIONS: Both jaw tracking and static jaw d-IMRT plans can achieve comparable target dose coverage. JTT displays superior OARs sparing than SJT plans. These results are of clinical importance, especially for the patients with large and complex targets but close to some highly radio-sensitive organs to spare, and for patients with local recurrent or secondary primary malignant lesion within a previously irradiated area.

Simplified edentulous treatment technique for edentulous hemimaxillectomy patients: case history report.

Technical difficulties in the construction of hard palate obturators following oncologic surgery are due to the recording limitations of the entire defect area, plus prosthesis base instability during recording of maxillomandibular relationships. This article describes a time-saving technique that ensures stable and precise recording bases. A light-polymerizing acrylic resin layer is used for making the first impression of the defect, while simultaneously obtaining an acrylic resin impression tray and base for recording maxillomandibular relationships. Adhesive paper copies are used for the arrangement of the anterior teeth.

Comparison of the accuracy of a 3-dimensional virtual method and the conventional method for transferring the maxillary cast to a virtual articulator.

STATEMENT OF PROBLEM: The currently available virtual articulators fail to locate the digitized maxillary cast at the exact position in the virtual environment. Some locate the casts on a mechanical articulator with a facebow, and this position is then digitized for the virtual environment. PURPOSE: The purpose of this study was to compare the location of the maxillary cast on an articulator by using 2 different procedures: the conventional method and a virtual method. MATERIAL AND METHODS: With the conventional procedure, the kinematic axis of the participant was determined with an axiograph. The location of the maxillary cast in reference to this axis was then physically transferred to a Panadent mechanical articulator. By a virtual procedure, the same kinematic axis and the maxillary cast were transferred directly from the participant to the Panadent virtual articulator by means of reverse engineering devices. The locations obtained with both procedures were compared in a virtual environment with an optical scanner. By calculating the deviation at every point of the occlusal surface, the results obtained with this procedure were then compared with those of the conventional method. RESULTS: The mean deviation on the occlusal surface was 0.752 mm, and the standard deviation was 0.456 mm. CONCLUSIONS: The deviation between the procedures was sufficiently small to allow the methodology for orthodontic purposes. However, the accuracy of the virtual procedure should be improved so as to extend its use to other fields, such as orthognathic surgery or dental restorations, in which the clinical technique requires an articulator.

An advanced navigational surgery system for dental implants completed in a single visit: an in vitro study.

In this study, we have developed an advanced navigational implant surgery system to overcome some disadvantages of the conventional method and have evaluated the accuracy of the system under in vitro environment. The patient splint for registration and tracking was improvised using a bite splint without laboratory work and the offset of an exchanged drill was calibrated directly without pivoting during surgery. The mean target registration errors (TRE) were 0.35 ± 0.11 mm using the registration body, 0.34 ± 0.18 mm for the registration method with prerecorded fiducials, and 0.35 ± 0.16 mm for the direct calibration of a drill offset. The mean positional deviations between the planned and placed implants in 110 implant surgeries were 0.41 ± 0.12 mm at the center point of the platform and 0.56 ± 0.14 mm at the center point of the apex. The mean angular deviation was 2.64°± 1.31 for the long axis of the implant. In conclusion, the developed system exhibited high accuracy, and the improved tools and simplified procedures increased the convenience and availability. With this advanced approach, it will be possible to complete dental implant surgery during a single visit at local clinics using a navigational guidance involving cone-beam computed tomographic images.

An integrated orthognathic surgery system for virtual planning and image-guided transfer without intermediate splint.

Accurate surgical planning and transfer of the planning in orthognathic surgery are very important in achieving a successful surgical outcome with appropriate improvement. Conventionally, the paper surgery is performed based on a 2D cephalometric radiograph, and the results are expressed using cast models and an articulator. We developed an integrated orthognathic surgery system with 3D virtual planning and image-guided transfer. The maxillary surgery of orthognathic patients was planned virtually, and the planning results were transferred to the cast model by image guidance. During virtual planning, the displacement of the reference points was confirmed by the displacement from conventional paper surgery at each procedure. The results of virtual surgery were transferred to the physical cast models directly through image guidance. The root mean square (RMS) difference between virtual surgery and conventional model surgery was 0.75 ± 0.51 mm for 12 patients. The RMS difference between virtual surgery and image-guidance results was 0.78 ± 0.52 mm, which showed no significant difference from the difference of conventional model surgery. The image-guided orthognathic surgery system integrated with virtual planning will replace physical model surgical planning and enable transfer of the virtual planning directly without the need for an intermediate splint.

Thickness and marking quality of different occlusal contact registration strips

Objectives Evaluate the thickness and the marking quality of different occlusal contact registration strips (OCRS) and a possible correlation between them. Material and Methods The following OCRS were selected: Accufilm II, BK20, BK21, BK22, BK23, BK28, and BK31. The thickness was measured in three points of the OCRS with an electronic measuring device (TESA), and the mean was calculated. To produce the marks on the strips, composite resin specimens were adapted to a universal testing machine (Versat 2000) with 40 kgf load cell at a speed of 1.0 mm/min. The mark images were photographed with a stereoscopic microscope (Stemi SV11) and processed and analyzed by the 550-Leica Qwin® analyzer. Results Values (μm) found in the 1st and 2nd thickness measurements were: Accufilm II - 16.4 and 14.2; BK20 - 10.0 and 8.1; BK21 - 9.5 and 8.0; BK22 - 9.7 and 8.7; BK23 - 9.8 and 7.9; BK28 - 12.8 and 10.0; and BK31 - 8.4 and 8.0, respectively. The mean (mm2) values found in the mark areas were: Accufilm II - 0.078; BK20 - 0.035; BK21 - 0.045; BK22 - 0.012; BK23 - 0.022; BK28 - 0.024; and BK31 - 0.024. The results were submitted to the Kruskal-Wallis (p<0.05) and Pearson’s correlation tests. Conclusions Only in the 2nd measurement, the OCRS thickness observed was similar to the value indicated by the manufacturers; the Accufilm II and the BK28 strips showed the better marks; and no correlation was found between the thickness and the marking area. .

Dental image replacement on cone beam computed tomography with three-dimensional optical scanning of a dental cast, occlusal bite, or bite tray impression.

The goal of the present study was to compare the accuracy of dental image replacement on a cone beam computed tomography (CBCT) image using digital image data from three-dimensional (3D) optical scanning of a dental cast, occlusal bite, and bite tray impression. A Bracket Typodont dental model was used. CBCT of the dental model was performed and the data were converted to stereolithography (STL) format. Three experimental materials, a dental cast, occlusal bite, and bite tray impression, were optically scanned in 3D. STL files converted from the CBCT of the Typodont model and the 3D optical-scanned STL files of the study materials were image-registered. The error range of each methodology was measured and compared with a 3D optical scan of the Typodont. For the three materials, the smallest error observed was 0.099±0.114mm (mean error±standard deviation) for registering the 3D optical scan image of the dental cast onto the CBCT dental image. Although producing a dental cast can be laborious, the study results indicate that it is the preferred method. In addition, an occlusal bite is recommended when bite impression materials are used.

How accurate are rapid prototyped (RP) final orthognathic surgical wafers? A pilot study.

Computer packages have been introduced to simulate the movements of the jaw in three dimensions to facilitate planning of treatment. After final 3-dimensional virtual planning, a rapid prototype wafer can be manufactured and used in theatre. Our aim was to assess the accuracy of rapid prototyping of virtual wafers derived from laser scanned dental models using CAD/CAM software. Upper and lower plaster models from 10 orthognathic patients, the articulated models, and the conventional wafers were scanned. The virtual wafers were made from CAD/CAM software, and printed on a stereolithographic printer. We also scanned the articulated models with rapid prototype wafers in place. The validity of the final rapid prototype wafer was measured by the accuracy with which upper and lower models related to one another. The absolute mean error of the rapid prototype wafer when aligned with the dental models was 0.94 (0.09) mm. The absolute distance of the 2 models articulated by conventional and rapid prototype wafers ranged from 0.04 - 1.73mm. The rapid prototype wafers were able to orientate the upper and lower dental models with an absolute mean error of 0.94 (0.09) mm, but it ranged from 0.04-1.73mm.

Proporção divina em indivíduos oclusões classes I, II e III esqueléticas em radiografias cefalométricas laterais / Proporción divina en pacientes con oclusión clases I, II y III esqueléticas en radiografías cefalométricas laterales / Divine proportion in patients with skeletal occlusion classes I, II and III on lateral cephalometric radiographs

Introdução: o conceito inicial de beleza remete a um conjunto que engloba harmonia e equilíbrio das proporções faciais estabelecidas pelas estruturas esqueléticas, dentárias e de tecidos moles. Objetivo: o objetivo deste estudo foi analisara proporção divina em radiografias cefalométricas laterais de 93 indivíduos brasileiros adultos, acima de 18 anos, de ambos os gêneros, com classes I, II e III esqueléticas, não submetidos a tratamento ortodôntico, por meio do software de cefalometria Aurea Ceph. Métodos: para análise estatística, foi aplicada a análise de variância ANOVA, teste Tukey e T de Studentem nível de significância de 5 porcento. Resultados: das sete razões estudadas, quando se avaliou as classes, evidenciou-se diferença estatisticamente significante entre a relação (N-Ena/V1S-DM16) nas classes I e III eas relações (A-Pog/V1-C1MS e A-Pog/V1S-MD16) nas classes II e III. Quando se comparou as razões nas diferentes classes em relação ao número áureo (1 618) houve diferença estatisticamente significante na classe I para as razões (N-Ena/V1S-DM16, V1S-C1MS/C1MS-DM16 e Ena-Me/AB); na classe II para as razões (A-Pog/V1-C1MS e A-Pog/V1S-MD16); e na classe III para as razões (N-Ena/V1S-DM16, Ena-Enp/V1S-C1MS, V1S-C1MS/C1MS-DM16 e Ena-Me/AB). Conclusões: de acordo com a metodologia empregada e os resultados obtidos, concluiu-se que das sete razões analisadas, a classe I apresentou três razões divinas, a classe II duas e a classe III quatro. O grupo classe II apresentou razões divinas com componente dentário e medidas verticais, sugerindo que a magnitude do erro sagital é importante no conceito da estética facial(AU)

Introducción: el concepto inicial de la belleza se refiere a un conjunto con la armonía y el equilibrio de las proporciones faciales establecidos por el tejido óseo, dental y suave. Objetivo: el objetivo de este estudio fue analizar la divina proporción en las radiografías cefalométricas de 93 individuos brasileños adultos, de 18 años, de uno y otro géneros, con las clases I, II y III del esqueleto, y no sometidos a un tratamiento de ortodoncia por medio de software de cefalometría Áurea Ceph". Métodos: el análisis estadístico se aplicó al análisis de varianza ANOVA, prueba de Tukey y prueba t de Student. El nivel de significación fue de 5 por ciento. Resultados: de los siete ratios estudiados, hubo una diferencia estadísticamente significativa entre las proporciones al comparar las clases en (N-Ena/V1S-DM16) clases I y III y (A-Pog/V1-C1MS, A-Pog/V1S-MD16) clases II y III. Cuando se comparó con las proporciones en las diferentes clases en relación con el número de oro (1 618), hubo diferencia estadísticamente significativa en la clase I para las (N-Ena/V1S-DM16, razones V1S-C1MS/C1MS-DM16, Ena-Me/AB), y en clase II de (A-Pog/V1-C1MS razones, A-Pog/V1S-MD16) y clase III para los (N-Ena/V1S-DM16 razones, Ena-Enp/V1S-C1MS, V1S-C1MS/C1MS-DM16, Ena-Me/AB). Conclusiones: de acuerdo con la metodología utilizada y los resultados obtenidos, se concluyó que en siete de las razones expuestas, la clase que tenía tres razones áureas se observó en dos y cuatro, clase II a clase III. El grupo de clase II fueron razones áureas con componente dental y horizontal, lo que sugiere que la magnitud del error es importante en el concepto de estética facial sagital. El grupo de clase II fueron razones áureas con componente dental y medidas verticales, y también sugiere que la magnitud del error es importante en el concepto de estética facial sagital(AU)

Introduction: the original concept of beauty refers to a set of harmony and balance features determined by bone, dental and soft tissue. Objective: the purpose of this study was to analyze divine proportion as reflected on cephalometric radiographs of 93 Brazilian subjects of both sexes aged 18 with skeletal classes I, II and III, not undergoing orthodontic treatment. The analysis was based on cephalometric software Aurea Ceph. Methods: statistical analysis was performed with ANOVA, Tukey's test and Student's t test. The significance level was 5 percent. Results: the seven ratios studied showed a statistically significant difference between proportions when comparing (N-Ena/V1S-DM16) classes I and III, and (A-Pog/V1-C1MS, A-Pog/V1S-MD16) classes II and III. When proportions in the different classes were compared with the golden number (1 618), a statistically significant difference was found in class I for (N-Ena/V1S-DM16, V1S-C1MS/C1MS-DM16, Ena-Me/AB), in class II for (A-Pog/V1-C1MS, A-Pog/V1S-MD16) and in class III for (N-Ena/V1S-DM16, Ena-Enp/V1S-C1MS, V1S-C1MS/C1MS-DM16, Ena-Me/AB). Conclusions: based on the methodology used and the results obtained, it was concluded that in seven of the ratios presented, the class with three golden ratios was found in two and four, class II to class III. The class II group were golden ratios with a dental and horizontal component, suggesting that the magnitude of the error is relevant to the concept of sagittal facial aesthetics. The class II group were golden ratios with a dental component and vertical measurements, also suggesting that the magnitude of the error is relevant to the concept of sagittal facial aesthetics(AU)

Use of the matching optimal symmetry plane method in planning surgical correction of facial asymmetry--a preliminary report of 20 patients.

PURPOSE: A voxel-based median plane (optimal symmetry plane [OSP]) was developed to assess facial bone asymmetry. The purpose of the present study was to introduce a new method of planning surgical correction of facial asymmetry using the OSPs as guides and test its effectiveness. PATIENTS AND METHODS: A retrospective study was conducted of 20 facial asymmetry patients with a mandibular deviation of 4 mm or greater or 4° or more that required surgical correction. In the test group (n = 8), the plans for asymmetry correction were formulated using the matching OSP method, in which the OSPs of the facial bones are tracked and matched during the model surgery setup. In the control group (n = 12), traditional planning was conducted. The traditional plans were cross-checked for symmetry through tracking and revised as needed. The symmetry results of the plans were compared between the 2 groups and within the control group. The outcome measures were the deviation distances between the OSPs of the midface and mandible at the anterior or posterior mandible, the occlusal plane cant, and the angle formed by the 2 OSPs. Surgery was performed in accordance with the final plans, and the results were assessed for symmetry. RESULTS: The traditional plans left a major mandibular deviation in 5 of the 12 control subjects compared with none in the test group. The test group did significantly better than the control group. The revised plans were significantly better than the initial plans. Postoperatively, significant improvements in symmetry were observed. CONCLUSION: The new method resulted in surgical plans that brought about significantly less postoperative mandibular deviation while maintaining a reasonable occlusion.

Measurement and Monte Carlo simulation for energy- and intensity-modulated electron radiotherapy delivered by a computer-controlled electron multileaf collimator.

The dosimetric advantage of modulated electron radiotherapy (MERT) has been explored by many investigators and is considered to be an advanced radiation therapy technique in the utilization of electrons. A computer-controlled electron multileaf collimator (MLC) prototype, newly designed to be added onto a Varian linac to deliver MERT, was investigated both experimentally and by Monte Carlo simulations. Four different electron energies, 6, 9, 12, and 15 MeV, were employed for this investigation. To ensure that this device was capable of delivering the electron beams properly, measurements were performed to examine the electron MLC (eMLC) leaf leakage and to determine the appropriate jaw positioning for an eMLC-shaped field in order to eliminate a secondary radiation peak that could otherwise appear outside of an intended radiation field in the case of inappropriate jaw positioning due to insufficient radiation blockage from the jaws. Phase space data were obtained by Monte Carlo (MC) simulation and recorded at the plane just above the jaws for each of the energies (6, 9, 12, and 15 MeV). As an input source, phase space data were used in MC dose calculations for various sizes of the eMLC shaped field (10 × 10 cm2, 3.4 × 3.4 cm2, and 2 × 2 cm2) with respect to a water phantom at source-to-surface distance (SSD) = 94 cm, while the jaws, eMLC leaves, and some accessories associated with the eMLC assembly as well were modeled as modifiers in the calculations. The calculated results were then compared with measurements from a water scanning system. The results showed that jaw settings with 5 mm margins beyond the field shaped by the eMLC were appropriate to eliminate the secondary radiation peak while not widening the beam penumbra; the eMLC leaf leakage measurements ranged from 0.3% to 1.8% for different energies based on in-phantom measurements, which should be quite acceptable for MERT. Comparisons between MC dose calculations and measurements showed agreement within 1%/1 mm based on percentage depth doses (PDDs) and off-axis dose profiles for a range of field sizes for each of the electron energies. Our current work has demonstrated that the eMLC and other relevant components in the linac were correctly modeled and simulated via our in-house MC codes, and the eMLC is capable of accurately delivering electron beams for various eMLC-shaped field sizes with appropriate jaw settings. In the next stage, patient-specific verification with a full MERT plan should be performed.

Evaluation of two dental registration-splint techniques for surgical navigation in cranio-maxillofacial surgery.

BACKGROUND: Surgical navigation requires precise registration of the pre-operative image dataset to the patient in the operation theatre. Different marker-based and marker-free registration techniques are available, each of them with advantages and disadvantages regarding precision and clinical handling. In this model study, the precision of two dental splint techniques for marker-based registration is analyzed. MATERIALS AND METHODS: A synthetic full-size human skull was registered with its cone beam computed tomography dataset using (a) a dentally-mounted "rapid" occlusal splint with five titanium screws directly attached to the splint, (b) an "extender", a dentally-mounted occlusal splint with similar fiducials fixed to an extension of the splint. The target registration error was measured for 170 landmarks distributed over the viscero- and neurocranium in 10 repeats per splint type using the Vector Vision2 (BrainLAB AG, Heimstetten, Germany) navigation system. Statistical and graphical evaluations were performed per anatomical region. RESULTS: In the periorbital region, the rapid splint, with an average deviation of 1.50 mm (SD = 0.439) showed greater accuracy than the extender with 1.76 mm (SD = 0.525). The viscerocranial results for both splints were similar (extender 1.84 mm, SD = 0.559, rapid occlusal splint 1.86 mm, SD = 0.686). In the cranial vault region, registration with the extender (2.33 mm, SD = 0.685) proved to be more precise than with the rapid splint (2.86 mm, SD = 0.929). CONCLUSIONS: Due to the more compact dimension of the rapid occlusal splint, errors close to the splint were smaller compared to the extender technique. The advantage of greater distances between the registration fiducials on the extender is particularly important in areas such as the orbital roof, the cranial vault, and the lateral skull base.