Calibration of EBT2 film using a red‐channel PDD method in combination with a modified three‐channel technique

Abstract

Spatial homogeneity was significantly improved via the calibration method described here. This technique is both convenient and time-efficient because it does not require cutting the film, and only two exposures are necessary.

A novel film calibration method, applied to stereotactic cone commissioning

“…It is remarkable that even with a much higher than experimentally observed level of noise added, the 95% confi dence level for the absolute mean/max variation is below 1.6% / 2.8% for the 4 patterns case, and below 1.3% / 2.5% for the 5 or 6 patterns case if the analysis includes the primary, secondary and tertiary calibration points. These uncertainty levels are similar or smaller (especially for the realistic case 1 noise) compared to the 1.1% to 2.1% range reported by Papaconstadopoulos, et al, [22], or with the 2% 2mm gamma criteria used by Chang, et al, [15]. The 95% confi dence level for the simulated dose profi les for the absolute mean and maximum difference between the original dose profi le and those generated from the simulated "noisy data".…”

“…DOI: https://dx.doi.org/10.17352/ijrro.000033 20 to 300 cGy, generating several calibration points. A PDD (Percentage Depth Dose) method for fi lm calibration [15,16], was also proposed. Both methods use radiation patterns on sheets of fi lm to generate a calibration curve for the entire batch of fi lm and are affected by inaccuracies due to post-irradiation time dependence [15][16][17][18], light sensitivity [9][10][11][12][13][14][15][16][17][18][19], inter-sheet non-uniformity, and variations in scanning conditions.…”

Calibration of gafchromic EBT film using the Microtek ScanMaker 9800XL plus flatbed scanner with a modified one red-channel after three-channel method

“…The film was also oriented parallel to the central beam axis and the upper edge of the film was parallel to the gantry rotation axis, which is conventionally the Y-axis in the literature. [1426272833] To measure the reference dose, a 0.6 cc Farmer chamber was located at a depth of 31 cm, 10 cm thick backup plates were placed under the entire 30 cm × 30 cm × 30 cm phantom, and the source-surface-distance was set to 100 cm. The reference dose measurement using the chamber at depth 31 cm may not be necessary if the monthly dosimetry calibration was performed just before the film-dose calibration.…”

“…However, equation (1) must be modified with a template matrix, T U , because the IT values do not correspond to a rational fitting form (equation 4) and the calibration cannot be correctly performed, as shown in Figure 1. Therefore, it is not possible to use the three-channel method[26] if T U is not used. Multiplying I U by the template matrix, the modified IT, N U , is written as:…”

“…To reduce the calibration uncertainties, a power-function fitting process using only the red channel OD was used for the three-channel technique. [26]…”