Commissioning of a fluoroscopic-based real-time markerless tumor tracking system in a superconducting rotating gantry for carbon-ion pencil beam scanning treatment.

PURPOSE: To perform the final quality assurance of our fluoroscopic-based markerless tumor tracking for gated carbon-ion pencil beam scanning (C-PBS) radiotherapy using a rotating gantry system, we evaluated the geometrical accuracy and tumor tracking accuracy using a moving chest phantom with simulated respiration. METHODS: The positions of the dynamic flat panel detector (DFPD) and x-ray tube are subject to changes due to gantry sag. To compensate for this, we generated a geometrical calibration table (gantry flex map) in 15° gantry angle steps by the bundle adjustment method. We evaluated five metrics: (a) Geometrical calibration was evaluated by calculating chest phantom positional error using 2D/3D registration software for each 5° step of the gantry angle. (b) Moving phantom displacement accuracy was measured (±10 mm in 1-mm steps) with a laser sensor. (c) Tracking accuracy was evaluated with machine learning (ML) and multi-template matching (MTM) algorithms, which used fluoroscopic images and digitally reconstructed radiographic (DRR) images as training data. The chest phantom was continuously moved ±10 mm in a sinusoidal path with a moving cycle of 4 s and respiration was simulated with ±5 mm expansion/contraction with a cycle of 2 s. This was performed with the gantry angle set at 0°, 45°, 120°, and 240°. (d) Four types of interlock function were evaluated: tumor velocity, DFPD image brightness variation, tracking anomaly detection, and tracking positional inconsistency in between the two corresponding rays. (e) Gate on/off latency, gating control system latency, and beam irradiation latency were measured using a laser sensor and an oscilloscope. RESULTS: By applying the gantry flex map, phantom positional accuracy was improved from 1.03 mm/0.33° to <0.45 mm/0.27° for all gantry angles. The moving phantom displacement error was 0.1 mm. Due to long computation time, the tracking accuracy achieved with ML was <0.49 mm (=95% confidence interval [CI]) for imaging rates of 15 and 7.5 fps; those at 30 fps were decreased to 1.84 mm (95% CI: 1.79 mm-1.92 mm). The tracking positional accuracy with MTM was <0.52 mm (=95% CI) for all gantry angles and imaging frame rates. The tumor velocity interlock signal delay time was 44.7 ms (=1.3 frame). DFPD image brightness interlock latency was 34 ms (=1.0 frame). The tracking positional error was improved from 2.27 ± 2.67 mm to 0.25 ± 0.24 mm by the tracking anomaly detection interlock function. Tracking positional inconsistency interlock signal was output within 5.0 ms. The gate on/off latency was <82.7 ± 7.6 ms. The gating control system latency was <3.1 ± 1.0 ms. The beam irradiation latency was <8.7 ± 1.2 ms. CONCLUSIONS: Our markerless tracking system is now ready for clinical use. We hope to shorten the computation time needed by the ML algorithm at 30 fps in the future.

Cross-sectional online survey of research productivity in young Japanese nursing faculty.

AIM: To investigate the factors affecting the research productivity of young nursing faculty in Japan. METHODS: An online survey targeting young nursing scholars (aged ≤ 39 years) who were members of the Japan Academy of Nursing Science was conducted from October to November 2012. Of 1634 potential respondents, 648 completed the survey (39.7%), and 400 full-time faculty of a baccalaureate degree program were selected for the analysis. The numbers of English-language and Japanese publications in the past 3 years were regressed onto personal characteristics, such as academic degree and type of university. RESULTS: The mean numbers of publications in English and Japanese in the past 3 years were 0.41 and 1.63, respectively. Holding a doctoral degree was significantly related to a higher number of publications in English and Japanese (e(ß) = 5.78 and e(ß) = 1.89, respectively). Working at a national university (e(ß) = 2.15), having a research assistant (e(ß) = 2.05), and the ability to read research articles in English (e(ß) = 2.27) were significantly related to more English-language publications. Having the confidence to conduct quantitative research (e(ß) = 1.67) was related to a larger number of Japanese publications. The lack of mentoring (e(ß) = 0.97) and university workload (e(ß) = 0.96) were associated with a lesser number of Japanese publications. CONCLUSION: The research productivity of young nursing faculty appeared to be quite low. Strategies to enhance research productivity in young nursing faculty, such as encouraging the achievement of a doctoral degree or enrichment of research resources, should be undertaken.