Endoscopic sequestrectomy for skull base osteoradionecrosis in nasopharyngeal carcinoma patients: a 10­year experience.

BACKGROUND: Skull base osteoradionecrosis is a devastating post-irradiation complication in nasopharyngeal carcinoma patients. We conducted a retrospective analysis to assess the long-term survival and prognostic factors of patients with skull base osteoradionecrosis treated with endoscopic sequestrectomy. METHODS: We enrolled 59 nasopharyngeal carcinoma patients with skull base osteoradionecrosis who underwent endoscopic nasopharyngectomy. The clinical characteristics and outcome at the last follow-up visit were collected. The survival curve and univariate and multivariate survival analysis were analyzed by Kaplan-Meier and Cox proportional hazards model to analyze the potential prognostic factors of overall survival, including age, gender, number of radiation, number of operations, extension of disease (local or extensive), whether the ICA is exposed to the procedure (yes or no) and the hypha status (yes or no) at postoperative pathological examination. RESULTS: The predilection sites of skull base osteoradionecrosis in osteoradionecrosis patients are as follows: the base of the sphenoid bone and sphenoid sinus region, the clivus and petrous apex region including the internal carotid canal and the pterygoid process region (including its medial and lateral pterygoid plates). After surgery, clinical symptoms were alleviated in most patients to varying degrees. By the last follow-up visit, 26 patients had died. Most deaths (24) in the study occurred during the first 2 years. Most patients (24) died of sudden severe hemorrhage. The follow-up period ranged from 1 to 108 months, with a median of 27 months. The 2-year overall survival rate was 54.2%. Multivariate Cox regression analysis showed that the number of radiation (P = 0.026) and age (P = 0.002) were independent risk factors for the overall survival. CONCLUSIONS: Endoscopic sequestrectomy with minimal complications and clear vision is a valuable option for the therapy of skull base osteoradionecrosis in nasopharyngeal carcinoma patients.

Proton beam therapy for bone sarcomas of the skull base and spine: A retrospective nationwide multicenter study in Japan.

We conducted a retrospective, nationwide multicenter study to evaluate the clinical outcomes of proton beam therapy for bone sarcomas of the skull base and spine in Japan. Eligibility criteria included: (i) histologically proven bone sarcomas of the skull base or spine; (ii) no metastases; (iii) ≥20 years of age; and (iv) no prior treatment with radiotherapy. Of the 103 patients treated between January 2004 and January 2012, we retrospectively analyzed data from 96 patients who were followed-up for >6 months or had died within 6 months. Seventy-two patients (75.0%) had chordoma, 20 patients (20.8%) had chondrosarcoma, and four patients (7.2%) had osteosarcoma. The most frequent tumor locations included the skull base in 68 patients (70.8%) and the sacral spine in 13 patients (13.5%). Patients received a median total dose of 70.0 Gy (relative biological effectiveness). The median follow-up was 52.6 (range, 6.3-131.9) months. The 5-year overall survival, progression-free survival, and local control rates were 75.3%, 49.6%, and 71.1%, respectively. Performance status was a significant factor for overall survival and progression-free survival, whilst sex was a significant factor for local control. Acute Grade 3 and late toxicities of ≥Grade 3 were observed in nine patients (9.4%) each (late Grade 4 toxicities [n = 3 patients; 3.1%]). No treatment-related deaths occurred. Proton beam therapy is safe and effective for the treatment of bone sarcomas of the skull base and spine in Japan. However, larger prospective studies with a longer follow-up are warranted.

Intravoxel incoherent motion MRI in differentiation between recurrent carcinoma and postchemoradiation fibrosis of the skull base in patients with nasopharyngeal carcinoma.

PURPOSE: To determine the capacity of intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) in differential diagnosis between recurrent carcinoma and postchemoradiation fibrosis of skull base in patients with nasopharyngeal carcinoma (NPC). MATERIALS AND METHODS: Eleven patients with recurrent NPC and 21 patients with postchemoradiation fibrosis in the skull base were enrolled. All the diagnoses were proved by endoscopic biopsy or imaging follow-up. IVIM MRI was performed to obtain quantitative parameters including D (pure diffusion), f (perfusion fraction), and D* (pseudodiffusion). D, f, and D* were compared between two groups; the diagnostic performances of D and f were evaluated using the receiver operating characteristic (ROC) analysis. RESULTS: D and f values were significantly lower in recurrent carcinoma than that in fibrosis (P < 0.001; P = 0.001). No significant difference was found in D* values between recurrent carcinoma and fibrosis (P = 0.229). ROC curve analysis showed that the area under the curve of D and f values were 0.996 and 0.838, respectively. Respective cutoff values with sensitivity, specificity, and accuracy were: D = 1.161 × 10-3 mm2 /s (sensitivity 100.0%, specificity 95.2%, accuracy 96.9%), f = 0.109 (sensitivity 81.8%, specificity 71.4%, accuracy 75.0%). CONCLUSION: Recurrent NPC and postchemoradiation fibrosis in the skull base have distinctive D and f values. IVIM MRI could be used to differentiate between recurrent carcinoma and postchemoradiation fibrosis in patients with NPC. J. Magn. Reson. Imaging 2016;44:1556-1564.

Radionecrosis of the frontal lobe as a consequence of malignant ethmoid tumor management: incidence, diagnosis, risk factors, prevention and management.

Malignant ethmoid tumors are treated by surgery followed by radiotherapy. This study aimed to evaluate the incidence, risk factors and outcome of radionecrosis of frontal lobe and determine preventive measures. Retrospective study of ethmoid malignancies treated from 2000 to 2011. All patients underwent surgery with/without anterior skull base resection using endoscopic or external approaches followed by irradiation (mean dose 64 Gy). Median follow-up was 50 months. Eight of 50 patients (16 %) presented with fronto-basal radionecrosis, connected to duraplasty, with a latent interval of 18.5 months. Although asymptomatic in six, radionecrosis triggered seizures and required surgery in two cases. Survival was not impacted. Risk factors included dyslipidemia, occurrence of epilepsy and dural resection. Radionecrosis may result from the combination of anterior skull base resection and radiotherapy for the treatment of ethmoid malignancies. Preventive measures rely on improving the duraplasty and optimization of the Gy-dose delivery.

Successful reconstruction of irradiated anterior skull base defect using the dual flap technique involving local pericranial flap and radial forearm free flap.

Skull base reconstruction presents a challenging therapeutic problem requiring a multispecialty surgical approach and close cooperation between the neurosurgeon, head and neck surgeon, as well as plastic and reconstructive surgeon during all stages of treatment. The principal goal of skull base reconstruction is to separate the intracranial space from the nasopharyngeal and oropharyngeal cavities, creating support for the brain and providing a water-tight barrier against cerebrospinal fluid leakage and ascending infection. We present a case involving a 58-year-old man with anterior skull base defects (2.5 cm × 3 cm) secondary to the removal of olfactory neuroblastoma. The patient received conventional radiation therapy at 6000 cGy in 30 fractions approximately a month before tumor removal. The patient had radiation therapy before surgery and was planned to have postoperative radiation therapy, which would lead to a higher complication rate of reconstruction. Artificial dura was used for the packing of the dural defect, which was also suspected to increase the complication rate of reconstruction. For these reasons, we chose to apply the dual flap technique, which uses both local pericranial flap and de-epithelized radial forearm free flap for anterior skull base defect to promote wound healing. During 28 months of follow-up after coverage of the anterior skull base defect, the dual flap survived completely, as confirmed through follow-up magnetic resonance imaging. The patient was free of cerebrospinal fluid leakage, meningitis, and abscess, and there was minimal donor-site morbidity of the radial forearm free flap. Reconstruction of anterior skull base defects using the dual flap technique is safe, reliable, and associated with low morbidity, and it is ideal for irradiated wounds and low-volume defects.

High-dose conformal proton therapy for clinical perineural invasion in cutaneous head and neck cancer.

Non-melanomatous skin cancer (NMSC) is the most common malignancy worldwide. Perineural invasion (PNI) is an uncommon (<5%), high-risk feature observed with NMSC more commonly seen in those with squamous cell carcinoma. One-third of these patients will have clinical PNI, which refers to tumor cell invasion extensive enough to cause clinically detectable deficits of the involved nerve. Uncontrolled disease within the skull base can be debilitating and, if not eradicated, fatal. The primary management options including radiotherapy with or without surgery, with local control rates exceeding 50%. Given the overwhelming influence of local control on disease control and survival, dose escalation and complication mitigation through hyperfractionated and high-dose conformal skull-base proton therapy are strategies to improving the therapeutic window in patients with cutaneous head and neck cancer with clinical PNI.

Osteoradionecrosis of the Skull Base in Nasopharyngeal Carcinoma: Incidence and Risk Factors.

PURPOSE: Nasopharyngeal carcinoma (NPC) is a type of malignancy with a high prevalence in southern China and Southeast Asia. The primary treatment modality is radiation therapy (RT). Osteoradionecrosis (ORN) of the skull base remains one of the most serious complications after RT, affecting survival time and quality of life. Thus far, skull base ORN has been seldom reported and can be difficult to distinguish and easy to misdiagnose. In this retrospective study, we report the incidence of skull base ORN and analyze its associated factors in an attempt to decrease the occurrence of ORN. METHODS AND MATERIALS: From January 2001 to December 2012, a total of 1348 patients who received diagnoses of NPC received 1 course of RT. Complete medical records were reviewed, and the patients were examined by magnetic resonance imaging and nasopharyngeal endoscopy during follow-up after primary treatment. Patients with other tumors of the head and neck, a history of RT, failure to complete RT, and those lost to follow-up were excluded. Treatment was delivered with external beam RT using standard linear accelerators. RESULTS: A total of 1348 patients with NPC were enrolled in this study after 1 course of RT; among these patients, 14 received diagnoses of skull base ORN. The incidence of skull base ORN was 1.04%. The average latency interval from the completion of RT to the diagnosis of skull base ORN was 45.57 months. Skull base ORN after 1 course of RT was associated with the T stage; total radiation dose to the nasopharynx, including the skull base in the radiation field; and anemia. CONCLUSIONS: The occurrence of skull base ORN was associated with primary tumors with advanced T stages, high doses of nasopharynx RT, and radiation fields that included the skull base. These factors may be used as predictors for the incidence of skull base ORN.

Intensity-modulated radiotherapy for paranasal sinuses and base of skull tumors.

Paranasal sinus and skull base tumors are rare aggressive head and neck cancers, and typically present in the locally advanced stages. As a result, achieving wide surgical resection with clear margins is a challenge for these tumors, and radiotherapy is thus usually indicated as an adjuvant modality following surgery to optimize local control. Given the integral role of radiotherapy in the management of this subgroup of head and neck tumors, the advent of intensity-modulated radiotherapy (IMRT) has led to substantial improvement of clinical outcomes for these patients. This is primarily driven by the improvement in radiation dosimetry with IMRT compared to conventional two dimensional (2D)- and 3D-techniques, in terms of ensuring dose intensity to the tumor target coupled with minimizing dose exposure to critical organs. Consequently, the evident clinical benefits of IMRT have been in reduction of normal tissue toxicities, ranging from critical neurological symptoms to less debilitating but bothersome symptoms of eye infections and radiation-induced skin changes. Another domain where IMRT has potential clinical utility is in the management of a subset of non-resectable T4 paranasal sinus and skull base tumors. For these inoperable lesions, the steep dose-gradient between tumor and normal tissue is even more advantageous, given the crucial need to maintain dose intensity to the tumor. Innovative strategies in this space also include the use of induction chemotherapy for patient selection. In this review, we summarized the data for the aforementioned topics, including specific discussions on the different histologic subtypes of paranasal sinus and skull base tumors.

Role of surgery in the treatment of osteoradionecrosis and its complications after radiotherapy for nasopharyngeal carcinoma.

BACKGROUND: The purpose of this study was to review the efficacy of surgery for patients with osteoradionecrosis (ORN) after radiotherapy for nasopharyngeal carcinoma (NPC). METHODS: Between 2000 and 2016, we identified 162 patients with skull base ORN, among which 58 patients required surgery. A retrospective medical chart review was performed and the indications and results of surgical interventions were recorded. RESULTS: All surgeries were performed for the treatment of secondary complications of ORN, including central nervous system (CNS) infection (48.4%), blowout bleeding (24.1%), and severe pain (17.2%). Endoscopic debridement was done in 12 patients, whereas the rest required either maxillary swing or mandibulotomy, depending on the location of the necrosis. The majority of the patients required free vastus lateralis flap (72.5%) for reconstruction. Surgery was effective in the control of infection, bleeding, and pain. Multivariate analysis identified reirradiation and bone exposure on MRI as the significant independent risk factors predicting the future need of surgery. CONCLUSION: Surgery is effective in the treatment of secondary complications of skull base ORN after previous radiotherapy for NPC.

Highly Conformal Craniospinal Radiotherapy Techniques Can Underdose the Cranial Clinical Target Volume if Leptomeningeal Extension through Skull Base Exit Foramina is not Contoured.

AIMS: Craniospinal irradiation (CSI) remains a crucial treatment for patients with medulloblastoma. There is uncertainty about how to manage meningeal surfaces and cerebrospinal fluid (CSF) that follows cranial nerves exiting skull base foramina. The purpose of this study was to assess plan quality and dose coverage of posterior cranial fossa foramina with both photon and proton therapy. MATERIALS AND METHODS: We analysed the radiotherapy plans of seven patients treated with CSI for medulloblastoma and primitive neuro-ectodermal tumours and three with ependymoma (total n = 10). Four had been treated with a field-based technique and six with TomoTherapy™. The internal acoustic meatus (IAM), jugular foramen (JF) and hypoglossal canal (HC) were contoured and added to the original treatment clinical target volume (Plan_CTV) to create a Test_CTV. This was grown to a test planning target volume (Test_PTV) for comparison with a Plan_PTV. Using Plan_CTV and Plan_PTV, proton plans were generated for all 10 cases. The following dosimetry data were recorded: conformity (dice similarity coefficient) and homogeneity index (D2 - D98/D50) as well as median and maximum dose (D2%) to Plan_PTV, V95% and minimum dose (D99.9%) to Plan_CTV and Test_CTV and Plan_PTV and Test_PTV, V95% and minimum dose (D98%) to foramina PTVs. RESULTS: Proton and TomoTherapy™ plans were more conformal (0.87, 0.86) and homogeneous (0.07, 0.04) than field-photon plans (0.79, 0.17). However, field-photon plans covered the IAM, JF and HC PTVs better than proton plans (P = 0.002, 0.004, 0.003, respectively). TomoTherapy™ plans covered the IAM and JF better than proton plans (P = 0.000, 0.002, respectively) but the result for the HC was not significant. Adding foramen CTVs/PTVs made no difference for field plans. The mean Dmin dropped 3.4% from Plan_PTV to Test_PTV for TomoTherapy™ (not significant) and 14.8% for protons (P = 0.001). CONCLUSIONS: Highly conformal CSI techniques may underdose meninges and CSF in the dural reflections of posterior fossa cranial nerves unless these structures are specifically included in the CTV.

The Role of Radiation Therapy in the Management of Sinonasal and Ventral Skull Base Malignancies.

Sinonasal and ventral skull base malignancies are rare tumors that arise in a complex anatomic location juxtaposed with critically important normal tissues. The standard treatment paradigm for most histologies has been surgery followed by postoperative radiation therapy. Because of their propensity to present at an advanced stage and the presence of nearby critical structures, patients are at risk for severe radiation-induced long-term toxicity. Recent advances in radiotherapy technique have improved the therapeutic ratio between tumor control and normal tissue toxicity. This article reviews issues pertinent to the use of radiotherapy in the management of these tumors.

[Endoscopic surgery and reconstruction for extensive osteoradionecrosis of skull base after radiotherapy for nasopharyngeal carcinoma].

Objective: To investigate the clinical efficacy of endoscopic surgery for extensive osteoradionecrosis (ORN) of skull base in patients with nasopharyngeal carcinoma (NPC) after radiotherapy. Methods: Seventeen patients diagnosed as ORN of skull base after radiotherapy for NPC and underwent endoscopic surgery were retrospectively studied with their clinic data. Results: Based on the CT and endoscopic examination, all patients had large skull base defects with bone defects averaged 7.02 cm2 (range, 3.60 - 14.19 cm2). Excepting for curetting the sequestra, endoscopic surgery was also used to repair the wound or to protect the internal carotid artery with flap in 12 patients. No bone reconstructions were conducted in all patients with the bone defects of skull base. CT examinations were taken after endoscopic surgery when required. The postoperative follow-up ranged from 8 months to 6 years (average, 14 months). Aside from 1 patient with delayed cerebrospinal fluid (CSF), others had no related complications. Conclusions: The patients with extensive ORN can be treated with endoscopic surgery to curette the necrotic bone of skull base, and endoscopic reconstruction provides an alternative technique. It may not be necessary to reconstruct the bone defects at skull base, however, the exposed important structures of skull base, such as internal carotid artery, need to repair with soft tissue such as flap.

Primary endovascular treatment of post-irradiated carotid pseudoaneurysm at the skull base with the Pipeline embolization device.

BACKGROUND: A post-irradiated carotid pseudoaneurysm at the skull base can cause life-threatening blowout syndrome. Conventional treatments include parent vessel occlusion, endovascular coiling or covered stenting. Use of the Pipeline embolization device (PED) for pseudoaneurysm exclusion at the skull base is not well described. OBJECTIVE: To report the clinical and angiographic outcome after using multiple PEDs to treat recently ruptured radiation-induced carotid pseudoaneurysms at the skull base. METHODS: Retrospective review of the clinical and angiographic records of patients who received PEDs as primary treatment for skull base carotid pseudoaneurysm between April 1, 2011 to March 31, 2013. RESULTS: Seven patients (five men, two women) with a mean age of 58 years (range 47-65) were treated in the study period. Primary treatment with the PED alone, with adjunct coil embolization in two patients, achieved immediate hemostasis in all patients, with no pseudoaneurysm rebleeding after a mean follow-up of 15.3 months (range 4-24 months). One patient had periprocedural cerebral infarction. Delayed internal carotid artery occlusion secondary to in-stent thrombosis occurred in three patients, one of whom had lacunar infarct and two remained asymptomatic. CONCLUSIONS: Endovascular treatment with the PED was effective in excluding skull base post-irradiated carotid pseudoaneurysms and preventing recurrent blowout. However, the risk of ischemic complications in this group of patients was high and our experience did not support the use of flow diverters as a first-line treatment for this condition.

Computed tomography findings of bony regeneration after radiotherapy for nasopharyngeal carcinoma with skull base destruction: implications for local control.

PURPOSE: To evaluate the response of bony destruction (BD) of the skull base following radiotherapy in nasopharyngeal carcinoma (NPC) and investigate the implications of bony regeneration (BR) on local control and its related factors. METHODS AND MATERIALS: Ninety patients with NPC with skull base destruction clearly demonstrated on computed tomography (CT) were reviewed. These patients have completed the prescribed treatment and received regular CT follow-up. A total of 338 sets of CT images of the head and neck were reviewed. The tumor response and the appearance of BR in the previous destructive part of the skull base were recorded and analyzed. The tumor response was divided into complete, partial, or no response. BR was defined as recalcification or sclerotic change with partial or complete healing in the previous osteolytic bony defect. Local failure was confirmed either by pathological or merely by imaging studies showing progression of tumor in consecutive radiological pictures. RESULTS: The distribution of specific sites of bony destruction (BD) in these patients included the sphenoid bone (68%), paracavernous sinus area (48%), petrous apex (47%), clivus (44%), pterygoid plates (20%), and others (7%). The CT showed 57 patients (63%) had BR. All were observed within 1 year after treatment. Sixty-two patients (69%) had complete tumor response after treatment. Analyzed by logistic regression method, tumor response after treatment was found to have a statistically significant correlation with BR (p = 0.0004). Most BR (55/57) was demonstrated in patients with complete tumor response. The 3-year actuarial local control rate was 54 % in these patients. The local control was quite different in the comparison of patients with BR versus those with persistent BD (77% vs. 21%, p < 0.0001). Multivariate analysis showed that patients with complete tumor response or with BR on imaging had statistically better local control than those without either of the two findings (p < 0.05). CONCLUSION: Appearance of BR at previous destructive skull base following radiotherapy for NPC patients could be clearly demonstrated on CT. Bony regeneration significantly correlated with treatment response and local control. Although the underlying significance of BR was unknown, to predict the outcome after treatment, the appearance of BR shown on CT may imply the complete eradication of tumor in this area.

Adult-onset acquired oculomotor nerve paresis with cyclic spasms: relationship to ocular neuromyotonia.

PURPOSE: To describe the characteristics and significance of acquired oculomotor nerve paresis with cyclic spasm. METHOD: Retrospective case series of two patients with a history of previous skull base irradiation for intracranial tumor who developed double vision and were found to have oculomotor nerve paresis with cyclic spasm. Both patients underwent a complete neuroophthalmologic assessment, including testing of eyelid position, pupillary size and reactivity, and ocular motility and alignment during both the paretic and spastic phases of the condition. RESULTS: Both patients developed unilateral lid retraction and ipsilateral esotropia with limitation of abduction during the spastic phase of the cycle, with ipsilateral ptosis, exotropia, and variable limitation of adduction during the paretic phase. The cycles were continuous and were not induced or altered by eccentric gaze. CONCLUSIONS: Cyclic oculomotor nerve paresis with spasms may occur years after irradiation of the skull base. This condition is different from the more common ocular motor disturbance that occurs in this setting-ocular neuromyotonia. However, in view of the similarity between these two disorders, it seems likely that they are caused by a similar peripheral mechanism.

Massive epistaxis related to petrous carotid artery pseudoaneurysm after radiation therapy: emergency treatment with covered stent in two cases.

Two patients had acute left carotid rupture from radiation therapy-induced pseudoaneurysms, resulting in hemodynamic collapse. Because the patients were semicomatose and in shock, an immediate salvage procedure was needed. Location of the pseudoaneurysm at the skull base made surgical treatment less possible. Endovascular therapy was the treatment of choice. Preserving patency of the carotid artery was a desirable option. The successful use of a covered stent in the emergency treatment of massive epistaxis due to active bleeding from pseudoaneurysm in the petrous internal carotid artery (ICA) is described.

Posttreatment imaging of the skull base.

Imaging the skull base after surgery can be challenging because anatomic structures may have been destroyed by an underlying process or removed at surgery. Foreign substances may be introduced to fill a void left by tumor resection, for hemostasis, and to repair dural defects. Previous imaging studies must be available for comparison to understand the characteristics of an underlying lesion. By following the progression of a lesion on subsequent imaging studies, the nature of treatment-related changes and residual or recurrent pathology is best realized.

Risk factors for brain injury after carbon ion radiotherapy for skull base tumors.

BACKGROUND AND PURPOSE: This study aimed to determine the risk factors for radiation-induced brain injury (RIBI) after carbon ion radiotherapy (CIRT) for treating skull base tumors. MATERIALS AND METHODS: Between April 1997 and January 2009, CIRT at a total dose of 48.0-60.8Gy equivalent (GyE) was administered in 16 fractions to 47 patients with skull base tumors. Of these patients, 39 who were followed up with magnetic resonance imaging (MRI) for more than 24months were analyzed. RIBI was assessed according to the MRI findings based on the Late Effects of Normal Tissue-Subjective, Objective, Management, Analytic criteria; clinical symptoms were assessed according to the Radiation Therapy Oncology Group/European Organisation for Research and Treatment of Cancer tables. The correlations of clinical and dosimetric parameters with incidence of ⩾grade 2 RIBI were retrospectively analyzed. RESULTS: The median follow-up period was 67months. The 5-year actuarial likelihoods of ⩾grade 2 RIBI and ⩾grade 2 clinical symptoms were 24.5% and 7.0%, respectively. Multivariate analysis demonstrated that the brain volume receiving more than 50GyE (V50) was a significant risk factor for the development of ⩾grade 2 RIBI (p=0.004). CONCLUSION: V50 was a significant risk factor for ⩾grade 2 RIBI after CIRT using a 16-fraction regimen.

Effective dose span of ten different cone beam CT devices.

OBJECTIVES: Evaluation and reduction of dose are important issues. Since cone beam CT (CBCT) has been established now not just in dentistry, the number of acquired examinations continues to rise. Unfortunately, it is very difficult to compare the doses of available devices on the market owing to different exposition parameters, volumes and geometries. The aim of this study was to evaluate the spans of effective doses (EDs) of ten different CBCT devices. METHODS: 48 thermoluminescent dosemeters were placed in 24 sites in a RANDO(®) head phantom. Protocols with lowest exposition parameters and protocols with highest exposition parameters were performed for each of the ten devices. The ED was calculated from the measured energy doses according to the International Commission on Radiological Protection 2007 recommendations for each protocol and device, and the statistical values were evaluated afterwards. RESULTS: The calculation of the ED resulted in values between 17.2 µSv and 396 µSv for the ten devices. The mean values for protocols with lowest and highest exposition parameters were 31.6 µSv and 209 µSv, respectively. CONCLUSIONS: It was not the aim of this study to evaluate the image quality depending on different exposition parameters but to define the spans of EDs in which different CBCT devices work. There is a wide span of ED for different CBCT devices depending on the selected exposition parameters, required spatial resolution and many other factors.

Effective doses from cone beam CT investigation of the jaws.

OBJECTIVES: The purpose of the study was to calculate the effective dose delivered to the patient undergoing cone beam (CB) CT of the jaws and maxillofacial complex using the i-CAT Next Generation CBCT scanner (Imaging Sciences International, Hatfield, PA). METHODS: A RANDO® phantom (The Phantom Laboratory, Salem, NY) containing thermoluminence dosemeters were scanned 10 times for each of the 6 imaging protocols. Effective doses for each protocol were calculated using the 1990 and approved 2007 International Commission on Radiological Protection (ICRP) recommended tissue weighting factors (E1990, E2007). RESULTS: The effective dose for E1990 and E2007, respectively, were: full field of view (FOV) of the head, 47 µSv and 78 µSv; 13 cm scan of the jaws, 44 µSv and 77 µSv; 6 cm standard mandible, 35 µSv and 58 µSv; 6 cm high resolution mandible, 69 µSv and 113 µSv; 6 cm standard maxilla, 18 µSv and 32 µSv; and 6 cm high resolution maxilla, 35 µSv and 60 µSv. CONCLUSIONS: Using the new generation of CBCT scanner, the effective dose is lower than the original generation machine for a similar FOV using the ICRP 2007 tissue weighting factors.