Kimiya Noto

Chest CT Performed with 3D and z-Axis Automatic Tube Current Modulation Technique: Breast and Effective Doses

RATIONALE AND OBJECTIVES Chest computed tomographic (CT) scans are the most effective examinations for detecting lung cancer at an early stage. In chest CT examinations, it is important to consider the reduction of radiation dose, particularly to the mammary gland. The objective of this study was to assess breast doses and effective doses on chest CT examinations between three-dimensional and z-axis automatic tube current modulation (ATCM) techniques. MATERIALS AND METHODS Absorbed dose to the breast, lung, mediastinum, and skin was evaluated with an anthropomorphic phantom and radiophotoluminescence glass dosimeters using two different CT scanners. The dosimeters were placed inside and outside the phantom. The phantom was scanned using three-dimensional and z-axis ATCM techniques after scanning localizer radiographs from the horizontal and vertical directions. After scanning, each organ dose was calculated. Moreover, the dose-length product recorded in the dose reports was examined, and each effective dose was calculated. RESULTS Compared with z-axis ATCM, three-dimensional ATCM reduced breast dose by 0.7% to 18.6% and effective dose by 4.9% to 10.2%. In particular, three-dimensional ATCM reduced frontal breast dose. For other organs, three-dimensional ATCM reduced absorbed doses by 3.4% to 13.6% compared to z-axis ATCM. CONCLUSION Three-dimensional ATCM can reduce absorbed doses to the breast and other organs, in addition to reducing effective dose, compared to z-axis ATCM.

A head phantom study for intraocular dose evaluation of 64-slice multidetector CT examination in patients with suspected cranial trauma

PURPOSE In cases of suspected cranial trauma, cranial CT examinations should be performed to rule out pathology. There are some methods available for reducing intraocular doses; however, it is difficult for the operators to conduct the necessary measurements because of restrictions in time and patient mobility, especially in high-energy trauma cases. Therefore, we performed a head phantom study for intraocular dose evaluation of 64-slice multidetector CT examination in patients with suspected cranial trauma. MATERIALS AND METHODS Assuming that the orbitomeatal (OM) line and bed were vertical, a head phantom was tilted from 10 degrees caudally to 25 degrees cranially at 5-degree intervals. At each tilted position, the phantom was examined using a 64-section multidetector CT device using three acquisition protocols. Intraocular doses during each examination were measured using small dosimeters. RESULTS Assuming that the OM line and bed were vertical, intraocular doses varied between 52 and 140%, 17-138%, and 90-142% during helical, non-helical, and helical CT angiographic examinations, respectively. Intraocular doses increased when the phantom was tilted cranially. CONCLUSION If possible, the best way to reduce the intraocular dose is by angling the gantry cranially, tilting the head of each patient caudally and adopting a non-helical acquisition method. During procedure, the acquisition angle should be angled cranially more than 0 degrees based on the OM line. The estimation of intraocular dose using the acquisition angle and displayed volumetric CT dose index might be useful to evaluate the deterministic effect risks and to inform patients about the associated risks.

Estimation of organ-absorbed radiation doses during 64-detector CT coronary angiography using different acquisition techniques and heart rates: a phantom study.

Background Though appropriate image acquisition parameters allow an effective dose below 1 mSv for CT coronary angiography (CTCA) performed with the latest dual-source CT scanners, a single-source 64-detector CT procedure results in a significant radiation dose due to its technical limitations. Therefore, estimating the radiation doses absorbed by an organ during 64-detector CTCA is important. Purpose To estimate the radiation doses absorbed by organs located in the chest region during 64-detector CTCA using different acquisition techniques and heart rates. Material and Methods Absorbed doses for breast, heart, lung, red bone marrow, thymus, and skin were evaluated using an anthropomorphic phantom and radiophotoluminescence glass dosimeters (RPLDs). Electrocardiogram (ECG)-gated helical and ECG-triggered non-helical acquisitions were performed by applying a simulated heart rate of 60 beats per minute (bpm) and ECG-gated helical acquisitions using ECG modulation (ECGM) of the tube current were performed by applying simulated heart rates of 40, 60, and 90 bpm after placing RPLDs on the anatomic location of each organ. The absorbed dose for each organ was calculated by multiplying the calibrated mean dose values of RPLDs with the mass energy coefficient ratio. Results For all acquisitions, the highest absorbed dose was observed for the heart. When the helical and non-helical acquisitions were performed by applying a simulated heart rate of 60 bpm, the absorbed doses for heart were 215.5, 202.2, and 66.8 mGy for helical, helical with ECGM, and non-helical acquisitions, respectively. When the helical acquisitions using ECGM were performed by applying simulated heart rates of 40, 60, and 90 bpm, the absorbed doses for heart were 178.6, 139.1, and 159.3 mGy, respectively. Conclusion ECG-triggered non-helical acquisition is recommended to reduce the radiation dose. Also, controlling the patients’ heart rate appropriately during ECG-gated helical acquisition with ECGM is crucial.

Relationship between specific organ doses and volumetric CT dose indices in multidetector CT studies.

Organ doses are useful for estimating radiation doses to patients. However, it is impossible to determine specific organ doses for each patient. The aim of this study was to examine the relationship between specific organ doses and volumetric CT dose indices (CTDIvols) in multidetector CT studies to estimate specific organ doses in each patient. Radiophotoluminescent glass dosimeters were placed at locations corresponding to specific organs of an anthropomorphic phantom. Thereafter, the phantoms were examined with respect to various imaging ranges and protocols, including cranial, thoracic and abdominal acquisitions using a 64‐section multidetector CT. Concurrently, we recorded the mean CTDIvol for each acquisition range. In the cranial acquisition, the displayed mean CTDIvol was 69.0 mGy, and the absorbed doses for brain and intra‐ocular lenses were 57.2 ± 2.6 and 57.1 ± 3.0 mGy, respectively. In the thoracic acquisition, the displayed mean CTDIvol was 16.3 mGy, and the absorbed doses for breast and lung were 19.1 ± 6.4 and 31.7 ± 2.2 mGy, respectively. In the abdominal acquisition, the displayed mean CTDIvol was 21.6 mGy, and the absorbed doses for stomach and colon were 28.2 ± 6.1 and 28.0 ± 8.6 mGy, respectively. The displayed mean CTDIvols overestimated the specific organ doses in the cranial acquisition and underestimated them in the thoracic and abdominal acquisitions. However, the approximate specific organ doses may be estimated by multiplying the displayed mean CTDIvols with a conversion factor for each organ.

Accuracy of Dose Delivery in Multiple Breath-Hold Segmented Volumetric Modulated Arc Therapy: A Static Phantom Study

Purpose. Accuracy of dose delivery in multiple breath-hold segmented volumetric modulated arc therapy (VMAT) was evaluated in comparison to noninterrupted VMAT using a static phantom. Material and Methods. Five VMAT plans were evaluated. A Synergy linear accelerator (Elekta AB, Stockholm, Sweden) was employed. A VMAT delivery sequence was divided into multiple segments according to each of the predefined breath-hold periods (10, 15, 20, 30, and 40 seconds). The segmented VMAT delivery was compared to noninterrupted VMAT delivery in terms of the isocenter dose and pass rates of a dose difference of 1% with a dose threshold of 10% of the maximum dose on a central coronal plane using a two-dimensional dosimeter, MatriXX Evolution (IBA Dosimetry, Schwarzenbruck, Germany). Results. Means of the isocenter dose differences were 0.5%, 0.2%, 0.2%, 0.0%, and 0.0% for the beam-on-times between interrupts of 10, 15, 20, 30, and 40 seconds, respectively. Means of the pass rates were 85%, 99.9%, 100%, 100%, and 100% in the same order as the above. Conclusion. Our static phantom study indicated that the multiple breath-hold segmented VMAT maintains stable and accurate dose delivery when the beam-on-time between interrupts is 15 seconds or greater.

Evaluation of patient doses due to fluoroscopic exposures.

The present study measures entrance surface doses of radiation administered to patients during various fluoroscopic procedures using a dose-area product meter as well as the duration of each procedure. A conversion factor for entrance skin dose to patients was calculated. The average dose to patient during the insertion of intravenous hyperalimentation was 10.2 (maximum, 74.0) mGy, during a barium meal, 58.4 (maximum, 184.0) mGy, for endoscopic retrograde cholangio-pancreatography (ERCP), 97.3 (maximum, 376.0) mGy and for a barium enema, 86.1 (maximum, 271.0) mGy. Doses tended to increase in the abdominal domain and when patients undergo not only diagnostic evaluation but also treatment requiring procedures such as drainage. The management of radiation doses determined using a dose-area product meter is very important and that of individual patients is enabled using the Radiation Information System (RIS).

Evaluation of transmission data of diagnostic X rays through concrete using Monte Carlo simulation

The transmittance of diagnostic X-ray beams through concrete of two different densities were measured. Broad-beam X-ray transmissions were estimated using a Monte Carlo simulation at tube voltages of 50-150 kV and compared with National Council on Radiation Protection and Measurements (NCRP) data. The observed levels were higher than those predicted by the NCRP data; that is, the NCRP data underestimate the leakage radiation from widely used inverter systems. Some of the issues were resolved and new data were proposed.

Development of Optical Computed Tomography for Evaluation of the Absorbed Dose of the Dyed Gel Dosimeter

Optical computed tomography (optical CT) is a reading device of the dyed gel dosimeters. We are developing the optical CT for the evaluation of three dimensional radiation absorbed dose distribution in the dyed gel dosimeters. We made dyed gel with leuco crystal violet and the dyed gel will be contained in vials. The dyed gel dosimeters were irradiated with 10 MV X-ray beam at 100–2000 MU. The optical CT we developed was consists of a liquid crystal monitor VL-176SE (FUJITSU, Japan) as a light source and a camera uEye XS (iDS, Germany). The dyed gel dosimeter was rotated by a step of every 0.9° with the stepper motor ST-42BYH 1004-5013 (MERCURY MOTOR, China) in a water tank and be taken 400 projections per rotation. Volume data was reconstructed from the projection images with the image processing software Plastimatch. The correlation between the absorbed dose and signal values of the dyed gel dosimeters in the reconstructed image was analyzed. The developed optical CT could reconstructed the images of the dyed gel dosimeters and the signal values of the dyed gel dosimeters in the reconstructed images had linear response related to the dose up to 20 Gy.

Evaluation of Deformable Image Registration Between High Dose Rate Brachytherapy and Intensity Modulated Radiation Therapy for Prostate Cancer

High risk prostate cancer is treated with a combination of intensity-modulated radiation therapy (IMRT) and high dose rate brachytherapy (HDR-BT). Deformable image registration (DIR) techniques used for dose accumulation sums dose distributions. The accuracy of DIR would get worse when density of an organ in a pair of registering two images differs greatly each other. Needles and contrast medium are used in HDR-BT. In this study, the effect of needles and contrast medium for DIR accuracy was evaluated. Six patients with prostate cancer were enrolled, who were treated with the combination of HDR-BT and IMRT. In the HDR-BT plan, needleless image (NI) and needleless and no-contrast medium image (NCI) were created from the original HDR-BT plan image (OI) to investigate the influence of needles and contrast medium. Both DIR and rigid registration (RR) were performed on the OI, NIs and NCIs by using MIM Maestro ver. 6.7.6 (MIM software Inc, Cleveland, USA) and after that the dose distribution of HDR-BT (used as the reference image) and IMRT were accumulated. The Dice Similarity coefficient (DSC) between DIR and RR were analyzed and compared each other. The mean DSC values of the prostate with DIR on OI, NI and NCI were 0.51, 0.57 and 0.73, respectively. The DSC with DIR on NCI was higher than DSC with DIR on OI and NI. The DSC values improved by removing the contrast medium.

An uncertainty metric to evaluate deformation vector fields for dose accumulation in radiotherapy

Background and purpose In adaptive radiotherapy, deformable image registration (DIR) is used to propagate delineations of tumors and organs into a new therapy plan and to calculate the accumulated total dose. Many DIR accuracy metrics have been proposed. An alternative proposed here could be a local uncertainty (LU) metric for DIR results. Materials and methods The LU represented the uncertainty of each DIR position and was focused on deformation evaluation in uniformly-dense regions. Four cases demonstrated LU calculations: two head and neck cancer cases, a lung cancer case, and a prostate cancer case. Each underwent two CT examinations for radiotherapy planning. Results LU maps were calculated from each DIR of the clinical cases. Reduced fat regions had LUs of 4.6 ± 0.9 mm, 4.8 ± 1.0 mm, and 4.5 ± 0.7 mm, while the shrunken left parotid gland had a LU of 4.1 ± 0.8 mm and the shrunken lung tumor had a LU of 3.7 ± 0.7 mm. The bowels in the pelvic region had a LU of 10.2 ± 3.7 mm. LU histograms for the cases were similar and 99% of the voxels had a LU < 3 mm. Conclusions LU is a new uncertainty metric for DIR that was demonstrated for clinical cases. It had a tolerance of <3 mm.