Development and Accuracy Evaluation of Augmented Reality-based Patient Positioning System in Radiotherapy: A Phantom Study.

BACKGROUND/AIM: To develop and evaluate the accuracy of augmented reality (AR)-based patient positioning systems in radiotherapy. MATERIALS AND METHODS: AR head-mounted displays (AR-HMDs), which virtually superimpose a three-dimensional (3D) image generated by the digital imaging and communications in medicine (DICOM) data, have been developed. The AR-based positioning feasibility was evaluated. Then, the setup errors of three translational axes directions and rotation angles between the AR and the conventional laser-based positioning were compared. RESULTS: The AR-based pelvic phantom positioning was feasible. The setup errors of AR-based positioning were comparable to laser-based positioning in all translational axis directions and rotation angles. The time necessary for AR-based positioning was significantly longer than that for laser-based positioning (171.0 s vs. 47.5 s, p<0.001). CONCLUSION: AR-based positioning for radiotherapy was feasible, and showed comparable positioning errors to those of conventional line-based positioning; however, a markedly longer setup time was necessary.

[Characteristics of Monitor Chamber for Photon Energy Mounted on Linear Accelerators].

Radiotherapy linear accelerators are calibrated to deliver a specific dose under standard conditions following accepted protocols (for example, JSMP12 protocol). The linear accelerator output is calibrated to deliver 1.0 cGy per 1.0 monitor unit (MU) at the depth of maximum in tissue maximum ratio. Beams of photons or electrons pass through a monitor chamber located in the linear accelerators head, which turns off the beam once the prescribed MU is delivered. The clinical outcome of radiotherapy demands that the linear accelerators output do not deviate from the calibrated level by more than a few percent. The purpose of this study is to characterize and understand the long term behavior of the output, change of flatness and symmetry from megavoltage radiotherapy linear accelerators (TrueBeam, Varian Medical Systems). Output trends of beams from three linear accelerators in two institutions over a period of more than 3 years are reported and analyzed. Output taken once per month the basis of this study. The output is measured using ionization chamber with water phantom. These are calibrated by accredited dosimetry laboratory with Japanese traceability system. When the output variation was bounded ±1%, monitor chamber was re-calibrated. The results show that the output from Linac was constantly upward trend. The output of Linac increased up to 8.0% in 1st year. However, upward trend became plateau slowly after years. Beams of same energies from another Linac are correlated with a correlation coefficient. Symmetry and flatness from one Truebeam stabled within 1%. If these adjustments are artificially removed then there is an increase in output, it is important to check the output of linear accelerator periodically.

Improved error detection using a divided treatment plan in volume modulated arc therapy.

AIM: We sought to improve error detection ability during volume modulated arc therapy (VMAT) by dividing and evaluating the treatment plan. BACKGROUND: VMAT involves moving a beam source delivering radiation to tumor tissue through an arc, which significantly decreases treatment time. Treatment planning for VMAT involves many parameters. Quality assurance before treatment is a major focus of research. MATERIALS AND METHODS: We used an established VMAT prostate treatment plan and divided it into 12° × 30° sections. In all the sections, only image data that generated errors in one segment and those that were integrally acquired were evaluated by a gamma analysis. This was done with five different patient plans. RESULTS: The integrated image data resulting from errors in each section was 100% (tolerance 0.5 mm/0.5%) in the gamma analysis result in all image data. Division of the treatment plans produced a shift in the mean value of each gamma analysis in the cranial, left, and ventral directions of 94.59%, 98.83%, 96.58%, and the discrimination ability improved. CONCLUSION: The error discrimination ability was improved by dividing and verifying the portal imaging.

Utility of intraoral stents in external beam radiotherapy for head and neck cancer.

AIM: This study aimed to assess the utility and stability of intraoral stent during intensity-modulated radiation therapy (IMRT). BACKGROUND: The benefits of intraoral stents in radiotherapy are unclear. MATERIALS AND METHODS: We analyzed 386 setup errors in 12 patients who received IMRT for head and neck cancers without intraoral stents (intraoral stent [-]) and 183 setup errors in 6 patients who received IMRT with intraoral stents (intraoral stent [+]). All patients were matched according to the immobilization method (masks and boards). Setup errors were measured as the distance from the initial setup based on the marking on the skin and mask to the corrected position based on bone matching on cone beam computed tomography. RESULTS: The mean interfractional setup errors in the right-left, craniocaudal, anterior-posterior (AP), and three-dimensional (3D) directions were -0.33, 0.08, -0.25, and 2.75 mm in the intraoral stent (-) group and -0.37, 0.24, -0.63, and 2.42 mm in the intraoral stent (+) group, respectively (P = 0.50, 0.65, 0.01, and 0.02, respectively). The systematic errors for the same directions were 0.89, 1.46, 1.15, and 0.88 mm in the intraoral stent (-) group and 0.62, 1.69, 0.68, and 0.56 mm in the intraoral stents (+) group, respectively. The random errors were 1.43, 1.43, 1.44, and 1.22 mm in the intraoral stent (-) group and 1.06, 1.11, 1.05, and 0.92 mm in the intraoral stents (+) group, respectively. CONCLUSION: Setup errors can be significantly reduced in the AP and 3D-directions by using intraoral stents.

Polaprezinc protects normal intestinal epithelium against exposure to ionizing radiation in mice.

Polaprezinc (PZ), an antiulcer drug, has been reported to have antioxidant effects. The purpose of the present study was to assess the radioprotective effects of PZ in the normal intestine of C57BL/6J mice. PZ was orally administered at 100 mg/kg body weight in the drinking water. Firstly, the present study compared the survival of normal intestinal crypt epithelial cells with mice that received PZ prior to or following irradiation. Next, the present study examined the sequential changes of the incidence of apoptosis in the normal intestine of mice that received irradiation. The mice that received PZ prior to irradiation demonstrated a stronger protective effect on the normal intestine compared with those that received PZ after irradiation. The present study therefore administrated PZ 2 h before irradiation in the subsequent experiments. The mice receiving PZ developed fewer apoptotic cells in the duodenum, jejunum and ileum. Radiation-induced cell death occurred with a peak at position 10 or lower from the base of the crypt axis, and was subsequently reduced by PZ treatment. Pretreatment with PZ protected the normal intestinal tissues from radiation-induced apoptosis.