Mika Kortesniemi

Dosimetry and image quality of four dental cone beam computed tomography scanners compared with multislice computed tomography scanners

OBJECTIVES The aim of this study was to evaluate the radiation dose and image quality of four dental cone beam CT (CBCT) scanners, and to compare them with those of two multislice CT (MSCT) scanners. METHODS Tissue doses were measured using a tissue-equivalent anthropomorphic RANDO Head Phantom((R)) with thermoluminescence dosemeters (TLD). An RSVP Head Phantom(TM) with a specially designed cylindrical insert was used for comparison of image quality and absorbed dose. Image quality was evaluated in the form of contrast-to-noise ratio (CNR) and modulation transfer function (MTF). RESULTS Using standard imaging parameters, the effective doses varied between 14 microSv and 269 microSv (International Commission on Radiation Protection (ICRP) 1990) and 27 microSv and 674 microSv (ICRP 2008) with the CBCT scanners, and between 350 microSv and 742 microSv (ICRP 1990) and 685 microSv and 1410 microSv (ICRP 2008) with the MSCT scanners. The CNR of the CBCT and MSCT scanners were 8.2-18.8 and 13.6-20.7, respectively. Low-dose MSCT protocols provided CNRs comparable with those from CBCT scanners. The 10% MTF of the CBCT scanners varied between 0.1 mm(-1) and 0.8 mm(-1), and was 0.5 mm(-1) for all the MSCT protocols examined. CONCLUSIONS CBCT scanners provide adequate image quality for dentomaxillofacial examinations while delivering considerably smaller effective doses to the patient. Large variations in patient dose and image quality emphasize the importance of optimizing imaging parameters in both CBCT and MSCT examinations.

Accuracy of linear measurements using dental cone beam and conventional multislice computed tomography

OBJECTIVES The aim of this study was to evaluate the accuracy of linear measurements obtained with dental cone beam CT (CBCT) and multislice CT (MSCT) by altering radiation doses using pre-operative planning of the placement of oral implants as a model. METHODS A human cadaver mandible was examined in two edentulous areas and one dentate area using CBCT and MSCT. The mandible was examined both dry and immersed in sucrose solution isointense with soft tissue. Two readers measured four linear distances twice from each section. The mandible was cut into 4 mm thick slices at three marked places. These slices were microradiographed and used as the gold standard for measurements from each section. RESULTS The intraclass correlations between the intra- and interobserver readings obtained with the different methods showed almost perfect matches. The measurement error (ME) showed significant differences between the methods studied (P = 0.022): the mean ME was 4.7% for CBCT and 8.8% for MSCT of the dry mandible, 2.3% and 6.6%, respectively, for the mandible immersed in sucrose solution and 5.4% for low-dose MSCT. Lowering the MSCT radiation dose to less than a quarter of its conventional original value did not significantly affect the ME. CONCLUSIONS CBCT is a reliable tool for implant-planning measurements when compared with MSCT. In this study, a considerable radiation dose reduction could be achieved with low-dose MSCT examinations without a major loss of measurement accuracy.

Boron neutron capture therapy of brain tumors: clinical trials at the Finnish facility using boronophenylalanine

SummaryTwo clinical trials are currently running at the Finnish dedicated boron neutron capture therapy (BNCT) facility. Between May 1999 and December 2001, 18 patients with supratentorial glioblastoma were treated with boronophenylalanine (BPA)-based BNCT within a context of a prospective clinical trial (protocol P-01). All patients underwent prior surgery, but none had received conventional radiotherapy or cancer chemotherapy before BNCT. BPA-fructose was given as 2-h infusion at BPA-dosages ranging from 290 to 400 mg/kg prior to neutron beam irradiation, which was given as a single fraction from two fields. The average planning target volume dose ranged from 30 to 61 Gy (W), and the average normal brain dose from 3 to 6 Gy (W). The treatment was generally well tolerated, and none of the patients have died during the first months following BNCT. The estimated 1-year overall survival is 61%. In another trial (protocol P-03), three patients with recurring or progressing glioblastoma following surgery and conventional cranial radiotherapy to 50–60 Gy, were treated with BPA-based BNCT using the BPA dosage of 290 mg/kg. The average planning target dose in these patients was 25–29 Gy (W), and the average whole brain dose 2–3 Gy (W). All three patients tolerated brain reirradiation with BNCT, and none died during the first three months following BNCT. We conclude that BPA-based BNCT has been relatively well tolerated both in previously irradiated and unirradiated glioblastoma patients. Efficacy comparisons with conventional photo radiation are difficult due to patient selection and confounding factors such as other treatments given, but the results support continuation of clinical research on BPA-based BNCT.

Boron Neutron Capture Therapy in the Treatment of Locally Recurred Head-and-Neck Cancer: Final Analysis of a Phase I/II Trial

PURPOSE To investigate the efficacy and safety of boron neutron capture therapy (BNCT) in the treatment of inoperable head-and-neck cancers that recur locally after conventional photon radiation therapy. METHODS AND MATERIALS In this prospective, single-center Phase I/II study, 30 patients with inoperable, locally recurred head-and-neck cancer (29 carcinomas and 1 sarcoma) were treated with BNCT. Prior treatments consisted of surgery and conventionally fractionated photon irradiation to a cumulative dose of 50 to 98 Gy administered with or without concomitant chemotherapy. Tumor responses were assessed by use of the RECIST (Response Evaluation Criteria in Solid Tumors) and adverse effects by use of the National Cancer Institute common terminology criteria version 3.0. Intravenously administered L-boronophenylalanine-fructose (400 mg/kg) was administered as the boron carrier. Each patient was scheduled to be treated twice with BNCT. RESULTS Twenty-six patients received BNCT twice; four were treated once. Of the 29 evaluable patients, 22 (76%) responded to BNCT, 6 (21%) had tumor growth stabilization for 5.1 and 20.3 months, and 1 (3%) progressed. The median progression-free survival time was 7.5 months (95% confidence interval, 5.4-9.6 months). Two-year progression-free survival and overall survival were 20% and 30%, respectively, and 27% of the patients survived for 2 years without locoregional recurrence. The most common acute Grade 3 adverse effects were mucositis (54% of patients), oral pain (54%), and fatigue (32%). Three patients were diagnosed with osteoradionecrosis (each Grade 3) and one patient with soft-tissue necrosis (Grade 4). Late Grade 3 xerostomia was present in 3 of the 15 evaluable patients (20%). CONCLUSIONS Most patients who have inoperable, locally advanced head-and-neck carcinoma that has recurred at a previously irradiated site respond to boronophenylalanine-mediated BNCT, but cancer recurrence after BNCT remains frequent. Toxicity was acceptable. Further research on novel modifications of the method is warranted.

Limited Cone-Beam Computed Tomography Imaging of the Middle Ear: A Comparison with Multislice Helical Computed Tomography

Purpose: To determine the applicability of cone-beam computed tomography (CBCT) in otological imaging, and to compare its accuracy with the routinely used multislice helical CT (MSCT) for imaging of the middle- and inner-ear areas. Material and Methods: Thirteen unoperated human cadaver temporal bones were imaged with CBCT and MSCT. Sixteen landmarks of the middle and adjacent inner ear were evaluated and compared for their conspicuity according to a modified Likert scale. Total scores and scores for subgroups including landmarks of specific clinical interest were also compared. Results: No significant differences were found between the imaging techniques or subgroups when scores of individual structures were compared. While the middle ear itself was visible in all cases with CBCT, parts of the inner ear were “cut off” in four cases due to the limited field of view. For the same reason, the evaluation of the whole mastoid was not possible with CBCT. The cochlear and vestibular aqueducts were not visualized in either CT techniques. The contrast-to-noise ratio was more than 50% lower in CBCT than in MSCT, but still adequate for diagnostic task. Conclusion: CBCT proved to be at least as accurate as routinely used MSCT in revealing the clinically and surgically important middle-ear structures. The results show that high-quality imaging of the middle ear is possible with the current CBCT device.

L-BORONOPHENYLALANINE-MEDIATED BORON NEUTRON CAPTURE THERAPY FOR MALIGNANT GLIOMA PROGRESSING AFTER EXTERNAL BEAM RADIATION THERAPY: A PHASE I STUDY

PURPOSE To investigate the safety of boronophenylalanine-mediated boron neutron capture therapy (BNCT) in the treatment of malignant gliomas that progress after surgery and conventional external beam radiation therapy. METHODS AND MATERIALS Adult patients who had histologically confirmed malignant glioma that had progressed after surgery and external beam radiotherapy were eligible for this Phase I study, provided that >6 months had elapsed from the last date of radiation therapy. The first 10 patients received a fixed dose, 290 mg/kg, of L-boronophenylalanine-fructose (L-BPA-F) as a 2-hour infusion before neutron irradiation, and the remaining patients were treated with escalating doses of L-BPA-F, either 350 mg/kg, 400 mg/kg, or 450 mg/kg, using 3 patients on each dose level. Adverse effects were assessed using National Cancer Institute Common Toxicity Criteria version 2.0. RESULTS Twenty-two patients entered the study. Twenty subjects had glioblastoma, and 2 patients had anaplastic astrocytoma, and the median cumulative dose of prior external beam radiotherapy was 59.4 Gy. The maximally tolerated L-BPA-F dose was reached at the 450 mg/kg level, where 4 of 6 patients treated had a grade 3 adverse event. Patients who were given >290 mg/kg of L-BPA-F received a higher estimated average planning target volume dose than those who received 290 mg/kg (median, 36 vs. 31 Gy [W, i.e., a weighted dose]; p = 0.018). The median survival time following BNCT was 7 months. CONCLUSIONS BNCT administered with an l-BPA-F dose of up to 400 mg/kg as a 2-hour infusion is feasible in the treatment of malignant gliomas that recur after conventional radiation therapy.

Assessment of effective radiation dose of an extremity CBCT, MSCT and conventional X ray for knee area using MOSFET dosemeters.

The objective of this study was to assess and compare the organ and effective doses in the knee area resulting from different commercially available multislice computed tomography devices (MSCT), one cone beam computed tomography device (CBCT) and one conventional X-ray radiography device using MOSFET dosemeters and an anthropomorphic RANDO knee phantom. Measurements of the MSCT devices resulted in effective doses ranging between 27 and 48 µSv. The CBCT measurements resulted in an effective dose of 12.6 µSv. The effective doses attained using the conventional radiography device were 1.8 µSv for lateral and 1.2 µSv for anterior-posterior projections. The effective dose resulting from conventional radiography was considerably lower than those recorded for the CBCT and MSCT devices. The MSCT effective dose results were two to four times higher than those measured on the CBCT device. This study demonstrates that CBCT can be regarded as a potential low-dose 3D imaging technique for knee examinations.

Models for estimation of the 10B concentration after BPA-fructose complex infusion in patients during epithermal neutron irradiation in BNCT

PURPOSE To create simple and reliable models for clinical practice for estimating the blood (10)B time-concentration curve after p-boronophenylalanine fructose complex (BPA-F) infusion in patients during neutron irradiation in boron neutron capture therapy (BNCT). METHODS AND MATERIALS BPA-F (290 mg BPA/kg body weight) was infused i.v. during two hours to 10 glioblastoma multiforme patients. Blood samples were collected during and after the infusion. Compartmental models and bi-exponential function fit were constructed based on the (10)B blood time-concentration curve. The constructed models were tested with data from six additional patients who received various amounts of infused BPA-F and data from one patient who received a one-hour infusion of 170 mg BPA/kg body weight. RESULTS The resulting open two-compartment model and bi-exponential function estimate the clearance of (10)B after 290 mg BPA/kg body weight infusion from the blood with satisfactory accuracy during the first irradiation field (1 ppm, i.e., 7%). The accuracy of the two models in predicting the clearance of (10)B during the second irradiation field are for two-compartment model 1.0 ppm (8%) and 0.2 ppm (2%) for bi-exponential function. The models predict the average blood (10)B concentration with an increasing accuracy as more data points are available during the treatment. CONCLUSION By combining the two models, a robust and practical modeling tool is created for the estimation of the (10)B concentration in blood after BPA-F infusion.

Metamorphosis of a 35 Year-Old TRIGA Reactor into a Modern BNCT Facility

Using FiR 1, a 250kW TRIGA reactor as a neutron source for BNCT was screened as a viable option in 1990, as the future of the reactor was questioned. By the initiative of the medical radio isotope group at VTT the Finnish BNCT project started incorporating early on also the medical and medical physics sides.1,2 At first a thermal neutron source only was considered conceivable, but quite soon it was realized that using aluminum-aluminum fluoride moderator a high quality epithermal neutron source was quite feasible.3 After gaining support both from the medical community as well as from private and state financing sources a decision was made in 1994 to accomplish the necessary changes in the reactor and the reactor hall.

Assessment of radiation exposure in dental cone-beam computerized tomography with the use of metal-oxide semiconductor field-effect transistor (MOSFET) dosimeters and Monte Carlo simulations.

OBJECTIVES The aims of this study were to assess the organ and effective dose (International Commission on Radiological Protection (ICRP) 103) resulting from dental cone-beam computerized tomography (CBCT) imaging using a novel metal-oxide semiconductor field-effect transistor (MOSFET) dosimeter device, and to assess the reliability of the MOSFET measurements by comparing the results with Monte Carlo PCXMC simulations. STUDY DESIGN Organ dose measurements were performed using 20 MOSFET dosimeters that were embedded in the 8 most radiosensitive organs in the maxillofacial and neck area. The dose-area product (DAP) values attained from CBCT scans were used for PCXMC simulations. The acquired MOSFET doses were then compared with the Monte Carlo simulations. RESULTS The effective dose measurements using MOSFET dosimeters yielded, using 0.5-cm steps, a value of 153 μSv and the PCXMC simulations resulted in a value of 136 μSv. CONCLUSIONS The MOSFET dosimeters placed in a head phantom gave results similar to Monte Carlo simulations. Minor vertical changes in the positioning of the phantom had a substantial affect on the overall effective dose. Therefore, the MOSFET dosimeters constitute a feasible method for dose assessment of CBCT units in the maxillofacial region.