The brand-new version of gamma knife, Perfexion, is equipped with an automatic collimator arrangement system that does not require manual collimator exchange and a couch-traveling system that is approximately ten times faster than Model C, so treatment time with multiple shots is assumed to remain within a clinically acceptable range. In this study, the treatment plans for Model C and Perfexion were compared from the viewpoint of number of shots, coverage, selectivity, conformity, and gradient in planning target volume (PTV) coverage. We enrolled 187 and 89 patients with vestibular schwannomas treated by Model C and Perfexion in the study. Treatment planning was created on a Leksell GammaPlan workstation. The mean PTV was 5.2 ml (range 0.1–18.4 ml) in Model C and 4.1 ml (range 0.1–32.1 ml) in Perfexion. The mean shot number for Model C and Perfexion was 11 (range 2–27) and 16 (range 1–41) at the isodose contour of 40–60%, respectively. The mean PTV coverage was 94% (range 73–100%) and 98% (range 91–100%), and the mean PTV selectivity was 83% (range 46–98%) and 87% (range 63–97%) for Model C and Perfexion, respectively. The mean conformity index was 1.15 (range 0.81–2.02) and 1.14 (range 0.97–1.57), and the mean gradient index was 2.82 (range 2.37–3.35) and 2.91 (range 2.55–4.48) for Model C and Perfexion, respectively. In Perfexion, better PTV coverage and selectivity were achieved by using an excessively large number of shots. In addition, the use of a small collimator in Perfexion produced a steeper dose gradient. Our comparative research demonstrated the greater clinical usefulness of Perfexion.
The purpose of our study was to evaluate radiation dose and beam quality in photon-counting digital mammography (PCDM) and compare them with those in a full-field digital mammography (FFDM) unit. Dose variation in the X-ray tube axis direction, aluminum half-value layer, average glandular and skin doses, and contrast-to-noise ratio (CNR) were evaluated for the PCDM and FFDM units. In PCDM, the dose variation in the X-ray tube axis direction was greater than that in FFDM. At a tube voltage of 28 kV, the first half-value layers were 0.407 mmAl for PCDM, 0.357 mmAl for FFDM with a molybdenum target and molybdenum filter (Mo/Mo), and 0.579 mmAl for FFDM with a tungsten target and rhodium filter (W/Rh). The average glandular doses with 45-mm-equivalent breast thickness were 0.723 mGy for the PCDM, 1.55 mGy for the FFDM with Mo/Mo in low-dose mode, and 0.835 mGy for the FFDM with W/Rh in low-dose mode. In PCDM, the skin dose was equivalent to or lower than that in FFDM. The CNR was 2.65±0.04, 2.35±0.04, and 2.52±0.03 for the PCDM, FFDM with Mo/Mo, and that with W/Rh, respectively. The CNR for PCDM was significantly higher than that for FFDM (p<0.001). It is therefore possible to reduce the radiation dose to the patient by using a PCDM unit while maintaining a significantly higher CNR than with the FFDM unit.
The measurement of half-value layers (HVLs) and effective energy in X-ray computed tomography (CT) using conventional nonrotating methods is regarded as a highly challenging task, as it necessitates the use of a nonrotating X-ray tube and the assistance of service engineers. Several convenient methods have been proposed to circumvent this limitation; however, to the best of our knowledge, there are no reports that provide a comparative study on the accuracy of each method. This prompted us to compare the accuracy and practicality of each method. Effective energy was calculated using four methods: lead shielding, copper pipe, localization, and inner-metal center-air ratio (IMCAR). The accuracy of each method for the measurement of effective energy in X-ray CT was evaluated and compared with the conventional nonrotating method. The differences in the effective energy were 0.0 to 0.6 keV (0.0% to 1.1%) for lead shielding, −2.2 to −0.6 keV (1.4% to 4.3%) for copper pipe, 4.7 to 16.7 keV (9.9% to 31.4%) for localization, and −7.4 to −0.3 keV (0.6% to 17.5%) for the IMCAR method. The results indicate that the lead shielding method is the most accurate and practical method of estimating effective energy in X-ray CT.
Objectives: The goal of this study was to assess the diagnostic accuracy of Pixon-processed images in comparison with raw images for computer-assisted interpretation of bone scintigraphy (BONENAVI). Methods: Whole-body scans of 57 patients with prostate cancer who had undergone bone scintigraphy for suspected bone metastases were obtained approximately 3 h after intravenous injection of 740 MBq 99mTc-methylene diphosphonate. We obtained two image sets: raw images and images processed using the Pixon method. Artificial neural network (ANN) values, bone scan index (BSI), number of hotspots and regional ANN value of two images set were automatically calculated by the BONENAVI software. Areas under the receiver operator characteristic curves (AUC) were calculated in patient-based and lesion-based analyses. Results: In ten cases with bone metastases, ANN, BSI and number of hotspots for processed images were equivalent to those in the raw images. However, in 47 cases without bone metastases, ANN, BSI and number of hotspots for processed images showed significantly lower values than those for the raw images (p<0.05). Sensitivity, specificity and accuracy of the raw images were 90.2, 44.7 and 65.9%, and those of the processed images were 90.2, 57.4 and 72.7%, respectively. The AUC for processed images was equivalent to that for raw images. Conclusions: Specificity and accuracy in the detection of bone metastases showed the Pixon-processed images to have high diagnostic performance. We conclude that the precision of computer-assisted interpretation of bone scintigraphy can be enhanced by using Pixon processing.
The purpose of this study was to evaluate the accuracy of positional verification during overall radiation treatment periods in accelerated partial breast irradiation using one or more surgical clips. We first investigated the appropriate computed tomography (CT) slice thickness and detectability of clips for a matching criterion in a phantom study. Next, clinical investigations were carried on 12 patients with multiple clips positioned around the lumpectomy cavity. During radiation treatment planning, a 5-mm region of interest (5-mm ROI) was defined by adding a three dimentional (3D) margin of 5 mm to each clip. During treatment, the clips on two orthogonal kilovoltage X-ray images acquired were moved so as to be included in the corresponding 5-mm ROI on digitally reconstructed radiographs (DRRs). Positional accuracy was calculated using the displacement of each clip in the verification images. The displacements of each clip acquired in all setups were then calculated throughout the overall radiation treatment period and the factors affecting the displacement of clips were investigated. Positional accuracy was also investigated in setups using skin marks and in setups using the bone structure around the thorax. We demonstrated in a phantom study that a CT slice thickness of 2.5 mm was appropriate. In our clinical investigations, 91% of the clips were included in the 5-mm ROI. The interfractional displacement of clips was large, with a long distance between the isocenter and each clip at the time of radiation treatment planning.