title: Evaluation of a 3D diode array dosimeter for helical tomotherapy delivery QA.
abstract: The Delta4 biplanar diode array dosimeter was validated for helical tomotherapy delivery QA. The basic detector characteristics were found to be satisfactory in terms of short-term reproducibility (0.1%), linearity (<0.1%), dose rate dependence (0.4%), and absolute calibration accuracy (0.4% in the center of the phantom compared with the independently calibrated diode). Relative calibration of the arrays was verified by comparison with film and by rotating the detector 180°. The dosimeter response to rotational irradiation changed by no more than 0.2% when one of the detector boards was replaced by the homogeneous phantom material. The daily output correction factor can be derived from a Delta4 measurement in a uniform cylindrical field. The γ(3%, 3 mm) passing rate (absolute dose) was above 90% for all 9 evaluated clinical plans, and above 96% for all but one. The mean passing rate was 97 ± 2.7%. The plans varied in modulation factor, pitch, and calculation grid size. For best results, the phantom needs to be aligned carefully, preferably by megavoltage computed tomography imaging.
authors.affiliation: Moffitt Cancer Center, Tampa, FL, USA. vladimir.feygelman@moffitt.org
authors.forename: Vladimir
authors.initials: V
authors.lastname: Feygelman
authors.forename: D
authors.initials: D
authors.lastname: Opp
authors.forename: K
authors.initials: K
authors.lastname: Javedan
authors.forename: A J
authors.initials: AJ
authors.lastname: Saini
authors.forename: G
authors.initials: G
authors.lastname: Zhang
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000295:instrumentation*; D015203:Reproducibility of Results; D012666:Semiconductors; D012680:Sensitivity and Specificity