Original Knee Fixation Device as a Useful Fixation Method during Prostate Intensity-Modulated Radiation Therapy.

Purpose: The purpose of he study was to reduce setup errors during intensity-modulated radiation therapy (IMRT) with an original knee fixation device (KFD) and evaluate the clinical target volume (CTV) coverage. Methods: Participants were classified into two groups: knee flexion (KF) group (n = 16), wherein participants' knees were fixed in a flexed position using the proposed KFD during planning computed tomography, and knee extension group (KE; n = 15), wherein no KFD was used. We investigated the residual rotational errors and inter-fractional setup errors with or without KFD. Furthermore, inter-fractional margins were calculated using logistic regression analysis, and CTV coverage was evaluated. Results: The residual rotational errors in the yaw and roll directions (P < 0.02) and the inter-fractional error in the anterior-posterior (A-P) direction (P < 0.02) improved significantly in the KF group compared with the KE group. Repeatability was improved for the pitch direction. The inter-fractional margins were 6.68 mm and 4.87 mm in the A-P and superior-inferior (S-I) directions, respectively, in the KF group, representing reductions (mm) of 20.8% and 12.6% compared with the KE group, respectively. The odds ratios for CTV coverage in the KF group compared to the KE group were 2.76 (P < 0.001) and 1.74 (P < 0.05) in the A-P and S-I directions, respectively. Conclusions: The IMRT fixation method using an original KFD improved the residual rotational error in the three directions and the inter-fractional error in the A-P direction, reduced the interfractional margins in the A-P, and S-I directions and improved CTV coverage. Our original KFD may be a useful fixation method during prostate IMRT.

Evaluation of Absorbed Dose for CBCT in Image-guided Radiation Therapy: Comparison of Each Devices and Facilities.

Recently, intensity-modulated radiation therapy (IMRT) is used worldwide, highly accurate verification of the location using image-guided radiation therapy (IGRT) has become critical. However, the use of cone-beam computed tomography (CBCT) to ascertain the location each time raises concerns about its influence on radiotherapy dosage and increased radiation exposure. The purpose of this study was to measure the absorbed dose using nine kilovoltage (kV) devices and two megavoltage (MV) devices (total 11 devices) at eight facilities, compare the absorbed dose among the devices, and assess the characteristics of the respective devices to ensure optimal clinical operation. For the measurement of the absorbed dose, a farmer-type ionization chamber dosimeter, calibrated using a 60Co and an IMRT dose verification phantom manufactured from water-equivalent material RW3, was used to measure the absorbed dose at nine points in the phantom for two regions, the pelvic and cephalic region. The average absorbed dose of the pelvic region was 3.09±0.21 cGy in kV-CBCT (OBI), 1.16±0.16 cGy in kV-CBCT (XVI), 5.64±1.48 cGy in MV-CBCT (4 MV), and 6.33±1.54 cGy in MV-CBCT (6 MV). The average absorbed dose of the cephalic region was 0.38±0.03 cGy in kV-CBCT (OBI), 0.23±0.06 cGy in kV-CBCT (XVI), 4.02±0.72 cGy in MV-CBCT (4 MV), and 4.46±0.77 cGy in MV-CBCT (6 MV). There was a difference in the absorbed dose at the measured points as well as in the dose distribution in the phantom cross section. No major difference was observed in the absorbed dose among identical devices, but a difference was identified among the devices installed at multiple facilities. Therefore, the angle of rotation should be paid attention to when CBCT is taken, and the image-taking conditions should be determined. In addition, it is important to handle the devices only after ascertaining the absorbed dose of each device.

Feasibility of patient dose reduction based on various noise suppression filters for cone-beam computed tomography in an image-guided patient positioning system.

We investigated the feasibility of patient dose reduction based on six noise suppression filters for cone-beam computed tomography (CBCT) in an image-guided patient positioning (IGPP) system. A midpoint dose was employed as a patient dose index. First, a reference dose (RD) and low-dose (LD)-CBCT images were acquired with a reference dose and various low doses. Second, an automated rigid registration was performed for three axis translations to estimate patient setup errors between a planning CT image and the LD-CBCT images processed by six noise suppression filters (averaging filter, median filter, Gaussian filter, edge-preserving smoothing filter, bilateral filter, and adaptive partial median filter (AMF)). Third, residual errors representing the patient positioning accuracy were calculated as Euclidean distances between the setup error vectors estimated using the LD-CBCT and RD-CBCT images. Finally, the residual errors as a function of the patient dose index were estimated for LD-CBCT images processed by six noise suppression filters, and then the patient dose indices for the filtered LD-CBCT images were obtained at the same residual error as the RD-CBCT image. This approach was applied to an anthropomorphic phantom and four cancer patients. The patient dose for the LD-CBCT images was reduced to 19% of that for the RD-CBCT image for the phantom by using AMF, while keeping a same residual error of 0.47 mm as the RD-CBCT image by applying the noise suppression filters to the LD-CBCT images. The average patient dose was reduced to 31.1% for prostate cancer patients, and it was reduced to 82.5% for a lung cancer patient by applying the AMF. These preliminary results suggested that the proposed approach based on noise suppression filters could decrease the patient dose in IGPP systems.

Imaging saponin-induced structural changes in neural processes with atomic force microscopy.

Temporal changes in the structure of neuronal processes in the presence of saponin were studied by atomic force microscopy in a fluid medium. After saponin treatment, concavities were formed on the surface of some neurites and fibrous structures in other neurites were splayed. The vertical height of these splayed fibrils or fibrillar bundles ranged from 13 to 370 nm, and the horizontal width was less than 500 nm. These findings suggest that formation of concavities and separation of bundled fibrils occurred simultaneously in saponin-treated neurites.