RESUMEN
PURPOSE: This study examines the optimal angle for a dual-field Stanford technique for TSET at extended SSD (SSD= 1, 2, 3, 4, 5 m) to predict a readily available optimal angle for any SSD. METHODS: The optimal angle at various SSDs is found using detector array. The diode array consists of 9 diodes placed on a vertical board with a measured vertical scale with the origin placed at isocenter. The lateral distance ranges from -100 to +75 cm. A square 36×36 cm2 field is used to deliver dose in HDTSe- delivery mode with a dose rate 2500 MU/min from a Varian Clinic 2300IX linac. Several pairs of gantry angles for the dual field are used, with the first gantry being 70°-78° and the second being 110° -102°. These Result in a dual field of 90° ± θ (θ = 10° - 20°) to build a suitable flatness profile on the vertical axis for treatment. The best group is chosen to determine the optimal angle for each SSD considered. From these optimal angles, an algorithm is determined for any extended SSD treatment. RESULTS: It is found that the optimal angle for TSET does change as one varies the SSD. These angle groups are specific for each SSD giving definite markers for the algorithm. At an SSD of 5 m it has been shown that an optimal angle of θ = 106° produces the best flatness on the vertical axis. While at SSD of 4 m, 9 = 18° Conclusions: An algorithm can now be applied for any treatment center considering a dual- field Stanford technique for TSET simplifying the physics commissioning process for the center in consideration.
RESUMEN
PURPOSE: To commission and verify an Epson scanner for film dosimetry for total skin electron beam therapy (TSEB). METHODS: Use data from an IBA PPC40 parallel-plate ion chamber and Sun Nuclear QED skin diode detectors as standard; we have made comparisons to the film measurement using Kodak XV films. Hurter-Driffield (HD) curve are established for 6 MeV total skin electron beams at a source-to-surface distance (SSD) of 5 m. Also HD curves are built for 6 MeV at a 100 cm SSD. Dose profiles for a series of oblique incident large electron fields are measured using the film for approximately 80 cGy dose delivered at the peak. The film is then scanned using two scanners, an Epson expression 10000 XL and a Vidar VXR-16 Dosimetry Pro. The optimal scanning conditions (e.g., dot per pixel size, internal color correction scheme) are chosen for the Epson scanner. Matlab is then used to analyze the optical density (OD) of the scanned films. A transmission densitometer made by Tobias Associates transmission is used to analyze the films to give a classical standard. RESULTS: The analysis of the Epson scanner is presented in two forms: one with and one without the HD correction from the established HD curve. The error analysis gives an uncertainty of 5% without the HD correction. An improved result of approximately 3% is found when an HD correction is applied to the analysis. CONCLUSIONS: A simple Epson scanner satisfies the commissioning standards for TSEB when an HD curve correction is applied.