A light field-based method to adjust rounded leaf end MLC position for split shape dose calculation correction in a radiation therapy treatment planning system.

We present an analytical and experimental study of split shape dose calculation correction by adjusting the position of the round leaf end position in an intensity-modulated radiation therapy treatment planning system. The precise light field edge position (Xtang.p ) was derived from 50% of the central axis dose created by nominal light field using geometry and mathematical methods. Leaf position (Xmlc.p), defined in the treatment planning system for monitor unit calculation, could be derived from Xtang.p. Offset (correction) could be obtained by the position corresponding to 50% of the central axis dose minus the Xmlc.p position. For SSD from 90 cm to 120 cm at 6 MV and 10 MV, the 50% dose position was located outside of Xmlc,p in the MLC leaf position range of +8 cm to -8 cm, where the offset correction positively increased, whereas the offset correction negatively increased when the MLC leaf position was in the range of -12 cm to -8 cm and +20 cm to +8 cm when the 50% position was located inside Xmlc,p. The monitor unit calculation could provide underdosage or overdosage of 7.5% per mm without offset correction. Calibration could be performed at a certain SSD to fit all SSD offset corrections. With careful measurement and an accurate offset correction, it is possible to achieve the dose calculation with 0.5% error for the adjusted MLC leaf edge location in the treatment planning system.

Analyzing coronary artery disease in patients with low CAC scores by 64-slice MDCT.

PURPOSE: Coronary artery calcification (CAC) scores are widely used to determine risk for Coronary Artery Disease (CAD). A CAC score does not have the diagnostic accuracy needed for CAD. This work uses a novel efficient approach to predict CAD in patients with low CAC scores. MATERIALS AND METHODS: The study group comprised 86 subjects who underwent a screening health examination, including laboratory testing, CAC scanning, and cardiac angiography by 64-slice multidetector computed tomographic angiography. Eleven physiological variables and three personal parameters were investigated in proposed model. Logistic regression was applied to assess the sensitivity, specificity, and accuracy of when using individual variables and CAC score. Meta-analysis combined physiological and personal parameters by logistic regression. RESULTS: The diagnostic sensitivity of the CAC score was 14.3% when the CAC score was ≤30. Sensitivity increased to 57.13% using the proposed model. The statistically significant variables, based on beta values and P values, were family history, LDL-c, blood pressure, HDL-c, age, triglyceride, and cholesterol. CONCLUSIONS: The CAC score has low negative predictive value for CAD. This work applied a novel prediction method that uses patient information, including physiological and society parameters. The proposed method increases the accuracy of CAC score for predicting CAD.

Dose verification in intensity modulation radiation therapy: a fractal dimension characteristics study.

PURPOSE: This study describes how to identify the coincidence of desired planning isodose curves with film experimental results by using a mathematical fractal dimension characteristic method to avoid the errors caused by visual inspection in the intensity modulation radiation therapy (IMRT). METHODS AND MATERIALS: The isodose curves of the films delivered by linear accelerator according to Plato treatment planning system were acquired using Osiris software to aim directly at a single interested dose curve for fractal characteristic analysis. The results were compared with the corresponding planning desired isodose curves for fractal dimension analysis in order to determine the acceptable confidence level between the planning and the measurement. RESULTS: The film measured isodose curves and computer planning curves were deemed identical in dose distribution if their fractal dimensions are within some criteria which suggested that the fractal dimension is a unique fingerprint of a curve in checking the planning and film measurement results. The dose measured results of the film were presumed to be the same if their fractal dimension was within 1%. CONCLUSIONS: This quantitative rather than qualitative comparison done by fractal dimension numerical analysis helps to decrease the quality assurance errors in IMRT dosimetry verification.