Comparative dosimetry of radiography device, MSCT device and two CBCT devices in the elbow region

The aim of the study was to estimate and to compare effective doses in the elbow region resulting from four different x-ray imaging modalities. Absorbed organ doses were measured using 11 metal oxide field effect transistor (MOSFET) dosimeters that were placed in a custom-made anthropomorphic elbow RANDO phantom. Examinations were performed using Shimadzu FH-21 HR radiography device, Siemens Sensation Open 24-slice MSCT-device, NewTom 5G CBCT device, and Planmed Verity CBCT device, and the effective doses were calculated according to ICRP 103 recommendations. The effective dose for the conventional radiographic device was 1.5 µSv. The effective dose for the NewTom 5G CBCT ranged between 2.0 and 6.7 µSv, for the Planmed Verity CBCT device 2.6 µSv and for the Siemens Sensation MSCT device 37.4 µSv. Compared with conventional 2D radiography, this study demonstrated a 1.4-4.6 fold increase in effective dose for CBCT and 25-fold dose for standard MSCT protocols. When compared with 3D CBCT protocols, the study showed a 6-19 fold increase in effective dose using a standard MSCT protocol. CBCT devices offer a feasible low-dose alternative for elbow 3D imaging when compared to MSCT.

A Deep Learning-Based Automated CT Segmentation of Prostate Cancer Anatomy for Radiation Therapy Planning-A Retrospective Multicenter Study

A commercial deep learning (DL)-based automated segmentation tool (AST) for computed tomography (CT) is evaluated for accuracy and efficiency gain within prostate cancer patients. Thirty patients from six clinics were reviewed with manual- (MC), automated- (AC) and automated and edited (AEC) contouring methods. In the AEC group, created contours (prostate, seminal vesicles, bladder, rectum, femoral heads and penile bulb) were edited, whereas the MC group included empty datasets for MC. In one clinic, lymph node CTV delineations were evaluated for interobserver variability. Compared to MC, the mean time saved using the AST was 12 min for the whole data set (46%) and 12 min for the lymph node CTV (60%), respectively. The delineation consistency between MC and AEC groups according to the Dice similarity coefficient (DSC) improved from 0.78 to 0.94 for the whole data set and from 0.76 to 0.91 for the lymph nodes. The mean DSCs between MC and AC for all six clinics were 0.82 for prostate, 0.72 for seminal vesicles, 0.93 for bladder, 0.84 for rectum, 0.69 for femoral heads and 0.51 for penile bulb. This study proves that using a general DL-based AST for CT images saves time and improves consistency.

Effective Radiation Dose in the Wrist Resulting from a Radiographic Device, Two CBCT Devices and One MSCT Device: A Comparative Study

The objective of the present study was to assess and compare the effective doses in the wrist region resulting from conventional radiography device, multislice computed tomography (MSCT) device and two cone beam computed tomography (CBCT) devices using MOSFET dosemeters and a custom made anthropomorphic RANDO phantom according to the ICRP 103 recommendation. The effective dose for the conventional radiography was 1.0 μSv. The effective doses for the NewTom 5 G CBCT ranged between 0.7 μSv and 1.6 μSv, for the Planmed Verity CBCT 2.4 μSv and for the MSCT 8.6 μSv. When compared with the effective dose for AP- and LAT projections of a conventional radiographic device, this study showed an 8.6-fold effective dose for standard MSCT protocol and between 0.7 and 2.4-fold effective dose for standard CBCT protocols. When compared to the MSCT device, the CBCT devices offer a 3D view of the wrist at significantly lower effective doses.

Accuracy and precision of patient positioning for pelvic MR-only radiation therapy using digitally reconstructed radiographs

BACKGROUND AND PURPOSE

Magnetic resonance imaging (MRI) has in recent years emerged as an imaging modality to drive precise contouring of targets and organs at risk in external beam radiation therapy. Moreover, recent advances in MRI enable treatment of cancer without computed tomography (CT) simulation. A commercially available MR-only solution, MRCAT, offers a single-modality approach that provides density information for dose calculation and generation of positioning reference images. We evaluated the accuracy of patient positioning based on MRCAT digitally reconstructed radiographs (DRRs) by comparing to standard CT based workflow.

MATERIALS AND METHODS

Twenty consecutive prostate cancer patients being treated with external beam radiation therapy were included in the study. DRRs were generated for each patient based on the planning CT and MRCAT. The accuracy assessment was performed by manually registering the DRR images to planar kV setup images using bony landmarks. A Bayesian linear mixed effects model was used to separate systematic and random components (inter- and intra-observer variation) in the assessment. In addition, method agreement was assessed using a Bland-Altman analysis.

RESULTS

The systematic difference between MRCAT and CT based patient positioning, averaged over the study population, were found to be (mean [95% CI])  -0.49 [-0.85 to  -0.13] mm, 0.11 [-0.33 to  +0.57] mm and  -0.05 [-0.23 to  +0.36] mm in vertical, longitudinal and lateral directions, respectively. The increases in total random uncertainty were estimated to be below 0.5 mm for all directions, when using MR-only workflow instead of CT.

CONCLUSIONS

The MRCAT pseudo-CT method provides clinically acceptable accuracy and precision for patient positioning for pelvic radiation therapy based on planar DRR images. Furthermore, due to the reduction of geometric uncertainty, compared to dual-modality workflow, the approach is likely to improve the total geometric accuracy of pelvic radiation therapy.

LOW-DOSE CT PROTOCOL OPTIMIZATION FOR THE ASSESSMENT OF ACUTE APPENDICITIS: THE OPTICAP PHANTOM STUDY

The aim was to evaluate effects of voltage, noise input (NI) and iterative reconstruction (IR) on radiation dose and image quality in order to establish a contrast enhanced low-dose protocol for assessment of acute appendicitis. An anthropomorphic abdominal phantom mimicking contrast enhanced abdomen was scanned with 80, 100 and 120 kV, standard and strong IR and 11 NIs (66 protocols). A total of 14 test tubes of increasing iodine dilutions and one tube with an appendicolith were evaluated within the phantom. The dose, HUs, noise, contrast-to-noise ratio (CNR) and figure of merit (FOM) were determined. Visual quality scores were assessed by two readers. A clinically used voltage-IR combination (120 kV, standard IR) was used as a reference. Overall, 100 kV with standard IR (p = 0.002) and 80 kV with both IRs (p < 0.001) showed higher CNR than the reference, but noise was most pronounced at 80 kV (p < 0.001). The highest FOM was found in the 100 kV protocols (p < 0.001). The reference and 100 kV with standard IR had highest image quality scores, where the 100 kV protocol enabled a distinct dose reduction. Lowering the voltage seems to be a more favorable tool than IR changes in optimizing the dose in contrast enhanced abdominal CT.

TRIAL REGISTRATION

ClinicalTrials.gov number, NCT01022567.

Dose monitoring in pediatric and young adult head and cervical spine CT studies at two emergency duty departments

PURPOSE

As the number of pediatric computed tomography (CT) imaging is increasing, there is a need for real-time radiation dose monitoring and evaluation of the imaging protocols. The aim of this study was to present the imaging data, patient doses, and observations of pediatric and young adult trauma-and routine head CT and cervical spine CT collected by a dose monitoring software.

METHODS

Patient age, study date, imaging parameters, and patient dose as volume CT dose index (CTDI_vol) and dose length product (DLP) were collected from two emergency departments' CT scanners for 2-year period. The patients were divided into four age groups (0-5, 6-10, 11-15, and 16-20 years) for statistical analysis and effective dose determination. The 75th percentile doses were evaluated to be used as local diagnostic reference levels (DRLs).

RESULTS

Six hundred fifteen trauma head, 318 routine head, and 592 trauma cervical spine CT studies were assessed. All mean CTDI_vol values were statistically lower in hospital B (40.3 ± 12.3, 30.03 ± 11.1, and 6.9 ± 3.1 mGy, respectively) than in hospital A (53.0 ± 12.9, 43.2 ± 8.7, and 18.3 ± 7.3 mGy, respectively). Statistically significant differences were observed on scanning length between hospitals and between CTDI_vol values when protocol was updated. The 75th percentiles of trauma cervical spine in hospital B can be used as local DRL. Non-optimized protocols were also revealed in hospital A.

CONCLUSION

Dose monitoring software offers a valuable tool for evaluating the imaging practices and finding non-optimized protocols.

Third-line treatment and 177Lu-PSMA radioligand therapy of metastatic castration-resistant prostate cancer: a systematic review

Aims

There is a controversy as to the relative efficacy of ¹⁷⁷Lu prostate specific membrane antigen (PSMA) radioligand therapy (RLT) and third-line treatment for patients with metastatic castration-resistant prostate cancer (mCRPC). The aim of our systematic review was to elucidate whether ¹⁷⁷Lu-PSMA RLT and third-line treatment have similar effects and adverse effects (PROSPERO ID CRD42017067743).

Methods

The review followed Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Searches in Pubmed and Embase selected articles up to September 2017. A search in ClinicalTrials.gov indicated ongoing studies. The meta-analysis used the random-effects model.

Results

Twelve studies including 669 patients reported ¹⁷⁷Lu-PSMA RLT. Overall, 43% of the patients had a maximum decline of PSA of ≥50% following treatment with ¹⁷⁷Lu-PSMA RLT. The treatment with ¹⁷⁷Lu-PSMA-617 and ¹⁷⁷Lu-PSMA for imaging and therapy (I&T) had mainly transient adverse effects. Sixteen studies including 1338 patients reported third-line treatment. Overall, 21% of the patients had a best decline of PSA of ≥50% following third-line treatment. After third-line treatment with enzalutamide and cabazitaxel, adverse effects caused discontinuation of treatment for 10% to 23% of the patients. ¹⁷⁷Lu-PSMA RLT gave a best PSA decline ≥50% more often than third-line treatment (mean 44% versus 22%, p = 0.0002, t test). ¹⁷⁷Lu-PSMA RLT gave objective remission more often than third-line treatment (overall 31 of 109 patients versus 43 of 275 patients, p = 0.004, χ² test). Median survival was longer after ¹⁷⁷Lu-PSMA RLT than after third-line treatment, but the difference was not statistically significant (mean 14 months versus 12 months, p = 0.32, t test). Adverse effects caused discontinuation of treatment more often for third-line treatment than for ¹⁷⁷Lu-PSMA RLT (22 of 66 patients versus 0 of 469 patients, p < 0.001, χ² test).

Conclusions

As for patients with mCRPC, treatment with ¹⁷⁷Lu-PSMA-617 RTL and ¹⁷⁷Lu-PSMA I&T gave better effects and caused fewer adverse effects than third-line treatment.

177Lu-PSMA-617 radioligand therapy for a patient with lymph node metastatic prostate cancer

Prostate specific membrane antigen (PSMA) is expressed in unfavorable prostate cancer. PSMA is basis for new diagnostics and theranostics. PET/CT using PSMA is more sensitive than choline PET/CT. ¹⁷⁷Lu-PSMA radioligand therapy is mainly used for patients with end-stage prostate cancer. This report describes a patient with a third recurrence in lymph nodes. The recurrence was treated with ¹⁷⁷Lu-PSMA radioligand therapy instead of chemotherapy with docetaxel. The effect was in part evaluated relative to that of two established salvage treatments. Prior salvage radiotherapy and abiraterone of the first and second recurrence in lymph nodes had given only a partial reduction of PSA. Nevertheless within five months of follow-up, ¹⁷⁷Lu-PSMA radioligand therapy of the third recurrence in lymph nodes reduced PSA for a period to unmeasurable levels. ¹⁷⁷Lu-PSMA radioligand therapy gave only mild adverse effects. In conclusion, for a patient with lymph node metastatic prostate cancer, ¹⁷⁷Lu-PSMA-617 radioligand therapy had an attractive therapeutic profile. A follow-up study of similar patients is being planned.

Comparison of Effective Dose and Image Quality for Newborn Imaging on Seven Commonly Used CT Scanners

This study compares the image quality and the patient doses on seven different computed tomography (CT) scanners for newborn chest imaging. The dose was measured by using an anthropomorphic newborn phantom and thermoluminescence dosemeters (TLDs). The effective dose was estimated separately based on a dose-length-product display, TLD measurements and the ImPACT CT dose calculation software. The image quality was assessed using a signal-to-noise ratio and a contrast-to-noise ratio (CNR). In order to compare the different scanners, a figure of merit (FOM) based on the rate of CNR2 and computed tomography dose index (CTDIvol) was calculated. The organ doses within the scan area ranged between 0.3 and 2.9 mGy and they depended on the organ and used scanner. The highest effective dose (1.1 mSv) was observed on Aquilion 32 and the lowest effective dose was observed on the Aquilion One (0.22 mSv). The lowest organ doses and highest FOM were observed on the Optima 660. With the Aquilion One and the Definition Dual Flash the examination was 71-90% faster when compared with other scanners. Newer devices equipped with novel dose-saving methods provide a lower dose, as well as take better advantage of the radiation in the image formation.

Planning of External Beam Radiotherapy for Prostate Cancer Guided by PET/CT

In this paper, we give an overview of articles on non-choline tracers for PET/CT for patients with prostate cancer and planning of radiotherapy guided by PET/CT. Nineteen articles described (11)C-Acetate PET/CT. Of 629 patients 483 (77%, 95% CI 74% - 80%) had positive (11)C-Acetate PET/CT scans. Five articles described (18)F-FACBC PET/CT. Of 174 patients, 127 (73%, 95% CI 68% - 78%) had positive scans. Both tracers detected local lesions, lesions in regional lymph nodes, and distant organs. Ten articles described (18)F-NaF PET/CT and found that 1289 of 3918 patients (33%) had positive reactive lesions in bones. PET/CT scan can guide external beam radiotherapy (EBRT) planning for patients with loco-regional prostate cancer. In six studies with 178 patients with localized prostate cancer, PET/CT pointed out dominant intraprostatic lesions (DIL). Oncologists gave EBRT to the whole prostate and a simultaneously integrated boost to the DIL. Four studies with 254 patients described planning of EBRT for patients with PETpositive lymph nodes. After the EBRT, 15 of 29 node-positive patients remained in remission for median 28 months (range 14 to 50 months). Most articles describe (11)C- and (18)F-Choline PET/CT. However, (11)C-Acetate and (18)F-FACBC may also be useful tracers for PET/CT. Planning of radiotherapy guided by MRI or PET/CT is an investigational method for localized prostate cancer. Current clinical controlled trials evaluate whether the method improves overall survival.

Dental cone beam CT: A review

For the maxillofacial region, there are various indications that cannot be interpreted from 2D images and will benefit from multiplanar viewing. Dental cone beam CT (CBCT) utilises a cone- or pyramid-shaped X-ray beam using mostly flat-panel detectors for 3D image reconstruction with high spatial resolution. The vast increase in availability and amount of these CBCT devices offers many clinical benefits, and their ongoing development has potential to bring various new clinical applications for medical imaging. Additionally, there is also a need for high quality research and education. European guidelines promote the use of a medical physics expert for advice on radiation protection, patient dose optimisation, and equipment testing. In this review article, we perform a comparison of technical equipment based on manufacturer data, including scanner specific X-ray spectra, and describe issues concerning CBCT image reconstruction and image quality, and also address radiation dose issues, dosimetry, and optimisation. We also discuss clinical needs and what type of education users should have in order to operate CBCT systems safely. We will also take a look into the future and discuss the issues that still need to be solved.

Characterization of MOSFET dosimeters for low-dose measurements in maxillofacial anthropomorphic phantoms

The aims of this study were to characterize reinforced metal‐oxide‐semiconductor field‐effect transistor (MOSFET) dosimeters to assess the measurement uncertainty, single exposure low‐dose limit with acceptable accuracy, and the number of exposures required to attain the corresponding limit of the thermoluminescent dosimeters (TLD). The second aim was to characterize MOSFET dosimeter sensitivities for two dental photon energy ranges, dose dependency, dose rate dependency, and accumulated dose dependency. A further aim was to compare the performance of MOSFETs with those of TLDs in an anthropomorphic phantom head using a dentomaxillofacial CBCT device. The uncertainty was assessed by exposing 20 MOSFETs and a Barracuda MPD reference dosimeter. The MOSFET dosimeter sensitivities were evaluated for two photon energy ranges (50–90 kVp) using a constant dose and polymethylmethacrylate backscatter material. MOSFET and TLD comparative point‐dose measurements were performed on an anthropomorphic phantom that was exposed with a clinical CBCT protocol. The MOSFET single exposure low dose limit (25% uncertainty, k=2) was 1.69 mGy. An averaging of eight MOSFET exposures was required to attain the corresponding TLD (0.3 mGy) low‐dose limit. The sensitivity was 3.09±0.13 mV/mGy independently of the photon energy used. The MOSFET dosimeters did not present dose or dose rate sensitivity but, however, presented a 1% decrease of sensitivity per 1000 mV for accumulated threshold voltages between 8300 mV and 17500 mV. The point doses in an anthropomorphic phantom ranged for MOSFETs between 0.24 mGy and 2.29 mGy and for TLDs between 0.25 and 2.09 mGy, respectively. The mean difference was −8%. The MOSFET dosimeters presented statistically insignificant energy dependency. By averaging multiple exposures, the MOSFET dosimeters can achieve a TLD‐comparable low‐dose limit and constitute a feasible method for diagnostic dosimetry using anthropomorphic phantoms. However, for single in vivo measurements (<1.7 mGy) the sensitivity is too low.

PACS number: 87.50.wj

VMAT technique enables concomitant radiotherapy of prostate cancer and pelvic bone metastases

BACKGROUND

Prostate cancer (PCa) patients with metastatic disease often suffer from skeletal pain and urinary retention impairing their quality of life. Prophylactic radiotherapy to bone metastases planned concomitantly with primary PCa radiotherapy could enable more precise control of combined dose in healthy tissues when compared to sequential palliative treatment.

MATERIALS AND METHODS

Volumetric modulated arc therapy (VMAT) was planned for 14 PCa patients with primary bone metastases. The bone planning target volume (PTVbone) was contoured together with the PTVs of prostate (pr), pelvic lymph nodes (ln) and seminal vesicles (sv). Another virtual plan was calculated excluding PTVbone for dose volume histogram (DVH) comparison. DVHs were additionally compared to a set of actual VMAT treatment plans of a control cohort of 13 high risk PCa patients treated with PTVpr, PTVsv and PTVln. The prescribed doses varied between 42 and 76 Gy for PTVbone.

RESULTS

Recommended healthy tissue tolerances (Quantec) were not exceeded except for one patient's rectum V50Gy value. Rectum doses did not increase significantly due to the inclusion of PTVbone. For bladder, there was a slight increase for V65Gy and V50Gy (2.7% and 7.4%). The DVHs of metastatic and non-metastatic patients were comparable. There were no differences in the PTVpr DVH parameters, while mean PTVln dose increased by 3.7 Gy-4.4 Gy due to the increased treatment volume related to PTVbone. All side effects were <grade 3 during the mean follow-up duration of 25 months.

CONCLUSIONS

VMAT offers a good optimization tool for adding extra PTVs to the radiotherapy plan. Radiotherapy of bone metastases concomitantly with irradiation of the primary prostate tumor is a safe and well-tolerated approach and deserves to be studied in a randomized setting.

Effective radiation dose of a MSCT, two CBCT and one conventional radiography device in the ankle region

BACKGROUND

The aim of this study was to assess and compare the effective doses (ICRP 103) in the ankle region of X-ray imaging resulting from a multi slice computed tomography (MSCT) device, two cone beam CT (CBCT) devices and one conventional x-ray device.

METHODS

Organ dose measurements were performed using 20 metal oxide field effect transistor (MOSFET) dosimeters that were placed in a custom made anthropomorphic RANDO ankle phantom. The following scanners were assessed in this study: Siemens Sensation Open 24-slice MSCT-scanner (120 kVp, 54 mAs), NewTom 5G CBCT scanner (110 kVp, 2.3 - 59 mAs), Planmed Verity CBCT-scanner (90 kVp, 48 mAs), Shimadzu FH-21 HR direct radiography equipment (AP + LAT), (57 kVp, 16 mAs).

RESULTS

Measurements of the MSCT device resulted in 21.4 μSv effective dose. The effective doses of CBCTs were between 1.9 μSv and 14.3 μSv for NewTom 5G and 6.0 μSv for Planmed Verity. Effective doses for the Shimadzu FH-21 HR conventional radiography were 1.0 μSv (LAT) and 0.5 μSv (AP), respectively.

CONCLUSIONS

Compared with a conventional 2D radiographic device, this study showed a 14-fold effective dose for standard MSCT and 1.3 -10 fold effective dose for standard CBCT protocols. CBCT devices offers a 3D view of ankle imaging and exhibited lower effective doses compared with MSCT.

Volumetric-modulated arc therapy for a pelvic lymph node metastasis from prostate cancer: a case report

A 50-year-old patient had an early biochemical recurrence after radical prostatectomy and androgen deprivation therapy and castration. An anti-1-amino-3-[¹⁸F] fluorocyclobutane-1-carboxylic acid positron emission tomography/computed tomography scan showed a single pelvic lymph node metastasis. The patient was given volume-modulated arc therapy with a cumulative dose of 50 Gy for the volume with pelvic lymph nodes and 78 Gy to the boost volume for the lymph node metastasis. He experienced only a transitory mild toxicity from the rectum and the urinary bladder and had a partial remission for 16 months.

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.

Characterization of MOSFET dosimeter angular dependence in three rotational axes measured free-in-air and in soft-tissue equivalent material

When performing dose measurements on an X-ray device with multiple angles of irradiation, it is necessary to take the angular dependence of metal-oxide-semiconductor field-effect transistor (MOSFET) dosimeters into account. The objective of this study was to investigate the angular sensitivity dependence of MOSFET dosimeters in three rotational axes measured free-in-air and in soft-tissue equivalent material using dental photon energy. Free-in-air dose measurements were performed with three MOSFET dosimeters attached to a carbon fibre holder. Soft tissue measurements were performed with three MOSFET dosimeters placed in a polymethylmethacrylate (PMMA) phantom. All measurements were made in the isocenter of a dental cone-beam computed tomography (CBCT) scanner using 5º angular increments in the three rotational axes: axial, normal-to-axial and tangent-to-axial. The measurements were referenced to a RADCAL 1015 dosimeter. The angular sensitivity free-in-air (1 SD) was 3.7 ± 0.5 mV/mGy for axial, 3.8 ± 0.6 mV/mGy for normal-to-axial and 3.6 ± 0.6 mV/mGy for tangent-to-axial rotation. The angular sensitivity in the PMMA phantom was 3.1 ± 0.1 mV/mGy for axial, 3.3 ± 0.2 mV/mGy for normal-to-axial and 3.4 ± 0.2 mV/mGy for tangent-to-axial rotation. The angular sensitivity variations are considerably smaller in PMMA due to the smoothing effect of the scattered radiation. The largest decreases from the isotropic response were observed free-in-air at 90° (distal tip) and 270° (wire base) in the normal-to-axial and tangent-to-axial rotations, respectively. MOSFET dosimeters provide us with a versatile dosimetric method for dental radiology. However, due to the observed variation in angular sensitivity, MOSFET dosimeters should always be calibrated in the actual clinical settings for the beam geometry and angular range of the CBCT exposure.

Volumetric-Modulated arc Therapy for a Pelvic Lymph Node Metastasis from Prostate Cancer: A Case Report

A 50-year-old patient had an early biochemical recurrence after radical prostatectomy and androgen deprivation therapy and castration. An anti-1-amino-3-[18F] fluorocyclobutane-1-carboxylic acid positron emission tomography/computed tomography scan showed a single pelvic lymph node metastasis. The patient was given volume-modulated arc therapy with a cumulative dose of 50 Gy for the volume with pelvic lymph nodes and 78 Gy to the boost volume for the lymph node metastasis. He experienced only a transitory mild toxicity from the rectum and the urinary bladder and had a partial remission for 16 months.

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.

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.

Organ doses and effective doses in pediatric radiography: patient-dose survey in Finland

BACKGROUND

Use of the effective dose in diagnostic radiology permits the radiation exposure of diverse diagnostic procedures to be quantified. Fundamental knowledge of patient doses enhances the implementation of the "as low as reasonably achievable" (ALARA) principle.

PURPOSE

To provide comparative information on pediatric examination protocols and patient doses in skull, sinus, chest, abdominal, and pelvic radiography examinations.

MATERIAL AND METHODS

24 Finnish hospitals were asked to register pediatric examination data, including patient information and examination parameters and specifications. The total number of examinations in the study was 1916 (1426 chest, 228 sinus, 96 abdominal, 94 skull, and 72 pelvic examinations). Entrance surface dose (ESD) and dose-area products (DAP) were calculated retrospectively or DAP meters were used. Organ doses and effective doses were determined using a Monte Carlo program (PCXMC).

RESULTS

There was considerable variation in examination protocols between different hospitals, indicating large variations in patient doses. Mean effective doses of different age groups ranged from 5 microSv to 14 microSv in skull and sinus examinations, from 25 microSv to 483 microSv in abdominal examinations, and from 6 microSv to 48 microSv in chest examinations.

CONCLUSION

In chest and sinus examinations, the amount of data was extensive, allowing national pediatric diagnostic reference levels to be defined. Parameter selection in pediatric examination protocols should be harmonized in order to reduce patient doses and improve optimization.

Results of a European survey on patient doses in paediatric radiology

Paediatric patients represent a very specific group within the radiology department. Compared to adult patients, they are more sensitive to radiation. As they are sometimes submitted to several radiology procedures, dose and image quality should be well balanced. Nowadays, only a few centres specialize in paediatric imaging, and knowledge of paediatric patient doses is, therefore, very scattered. The effect of the introduction of digital technology on paediatric patient doses remains largely undocumented. Data collected in the present survey illustrate that there is a clear need for standardisation in this domain. The proposal of a European diagnostic reference level (DRL) is quite difficult. Preliminary DRLs, based on typically 5-7 radiology centres per examination are proposed. The 'effective dose' may or may not be a very rigorous parameter, but it still remains useful nowadays to calculate a parameter that summarises the possible radiation-induced detriment to these young patients. However, conversion factors for calculation of the effective dose should be harmonised. Future studies should include an image quality evaluation study, using criteria that account for digital equipment. Data collection would be straightforward and could be performed in a systematic and automatic way if DICOM headers of digital images would include appropriate as well as relevant information for the particular case of paediatric examinations.

Diagnostic reference levels for thorax X-ray examinations of paediatric patients

Based on the Medical Exposure Directive of the European Commission, 97/43/Euratom, The Radiation and Nuclear Safety Authority (STUK) in Finland has the responsibility for setting national diagnostic reference levels (DRLs) for the most common radiological examinations. Paediatric patients deserve special attention because of the higher radiation risk compared with adults. The purpose of this paper is to present a method that takes into account patient size when setting DRLs in paediatric patients. The overall data consisted of patient doses collected from six hospitals during the years 1994-2001, and new measurements in two hospitals in 2004. In total, there were 700 chest examinations. The method established by the National Radiological Protection Board (UK) for setting DRLs was not considered feasible in Finnish practice. Patient doses correlated exponentially with the projection thickness, which was measured directly for each patient. Since 1 January 2006, paediatric DRLs for conventional chest examinations have been specified in Finland as a DRL curve by using both dose quantities (entrance surface doses (ESD) and dose-area product (DAP)) as a function of patient projection thickness.

Ultrafast dynamics of halogens in rare gas solids

We perform time resolved pump-probe spectroscopy on small halogen molecules ClF, Cl2, Br2, and I2 embedded in rare gas solids (RGS). We find that dissociation, angular depolarization, and the decoherence of the molecule is strongly influenced by the cage structure. The well ordered crystalline environment facilitates the modelling of the experimental angular distribution of the molecular axis after the collision with the rare gas cage. The observation of many subsequent vibrational wave packet oscillations allows the construction of anharmonic potentials and indicate a long vibrational coherence time. We control the vibrational wave packet revivals, thereby gaining information about the vibrational decoherence. The coherence times are remarkable larger when compared to the liquid or high pressure gas phase. This fact is attributed to the highly symmetric molecular environment of the RGS. The decoherence and energy relaxation data agree well with a perturbative model for moderate vibrational excitation and follow a classical model in the strong excitation limit. Furthermore, a wave packet interferometry scheme is applied to deduce electronic coherence times. The positions of those cage atoms, excited by the molecular electronic transitions are modulated by long living coherent phonons of the RGS, which we can probe via the molecular charge transfer states.

Radiation exposure in body computed tomography examinations of trauma patients

Multi-slice CT provides an efficient imaging modality for trauma imaging. The purpose of this study was to provide absorbed and effective dose data from CT taking into account the patient size and compare such doses with the standard CT dose quantities based on standard geometry. The CT examination data from abdominal and thoracic scan series were collected from 36 trauma patients. The CTDI(vol), DLP(w) and effective dose were determined, and the influence of patient size was applied as a correction factor to calculated doses. The patient size was estimated from the patient weight as the effective radius based on the analysis from the axial images of abdominal and thoracic regions. The calculated mean CTDI(vol), DLP(w) and effective dose were 15.2 mGy, 431 mGy cm and 6.5 mSv for the thorax scan, and 18.5 mGy, 893 mGy cm and 14.8 mSv for the abdomen scan, respectively. The doses in the thorax and abdomen scans taking the patient size into account were 34% and 9% larger than the standard dose quantities, respectively. The use of patient size in dose estimation is recommended in order to provide realistic data for evaluation of the radiation exposure in CT, especially for paediatric patients and smaller adults.