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In this paper, we described and characterized a novel biplanar diode array, and demonstrated its applicability to dosimetric QA of the step-and-shoot IMRT. It is the first commercially available device of its kind specifically designed for measurements at varying gantry angles. The detector consists of a cylindrical PMMA phantom with two orthogonal detector boards. There are a total of 1069 p-type 1 mm wide diode detectors covering the measurement area of 20 x 20 cm2 in each of the measurement planes. The orthogonal detector arrays ensure that the dose modulation information is not lost regardless of the beam incidence angle. For absolute calibration, the dose to the reference detector is calculated at the appropriate SSD and radiological depth by the treatment planning system and is scaled by the measured accelerator output. The directly measured rotational response on the central axis shows the maximum variation of approximately +/-3% in the narrow +/-1 degree angular intervals centered on the detector boards. This variation is reduced to less than +/- 2% outside of the four similarly centered +/-5 degrees angular intervals. For all detectors, the difference between the measured and calculated dose for a plan with twelve equally spaced beams is -0.2+/-0.9%. Of eleven IMRT plans, ten passed the gamma(3%,3mm) criterion at or above 95%, while one passed at 92%. Delta4 is a useful tool for IMRT QA, allowing for essentially instantaneous on-line analysis of absolute dose errors in 3D.

We conducted a comprehensive evaluation of the clinical accuracy of an image-guided frameless intracranial radiosurgery system. All links in the process chain were tested. Using healthy volunteers, we evaluated a novel method to prospectively quantify the range of target motion for optimal determination of the planning target volume (PTV) margin. The overall system isocentric accuracy was tested using a rigid anthropomorphic phantom containing a hidden target. Intrafraction motion was simulated in 5 healthy volunteers. Reinforced head-and-shoulders thermoplastic masks were used for immobilization. The subjects were placed in a treatment position for 15 minutes (the maximum expected time between repeated isocenter localizations) and the six-degrees-of-freedom target displacements were recorded with high frequency by tracking infrared markers. The markers were placed on a customized piece of thermoplastic secured to the head independently of the immobilization mask. Additional data were collected with the subjects holding their breath, talking, and deliberately moving. As compared with fiducial matching, the automatic registration algorithm did not introduce clinically significant errors (<0.3 mm difference). The hidden target test confirmed overall system isocentric accuracy of < or =1 mm (total three-dimensional displacement). The subjects exhibited various patterns and ranges of head motion during the mock treatment. The total displacement vector encompassing 95% of the positional points varied from 0.4 mm to 2.9 mm. Pre-planning motion simulation with optical tracking was tested on volunteers and appears promising for determination of patient-specific PTV margins. Further patient study is necessary and is planned. In the meantime, system accuracy is sufficient for confident clinical use with 3 mm PTV margins.