The incidence of the different sources of noise on the uncertainty in radiochromic film dosimetry using single channel and multichannel methods

Abstract

The influence of the various sources of noise on the uncertainty in radiochromic film (RCF) dosimetry using single channel and multichannel methods is investigated in this work. These sources of noise are extracted from pixel value (PV) readings and dose maps. Pieces of an RCF were each irradiated to different uniform doses, ranging from 0 to 1092 cGy. Then, the pieces were read at two resolutions (72 and 150 ppp) with two flatbed scanners: Epson 10000XL and Epson V800, representing two states of technology. Noise was extracted as described in ISO 15739 (2013), separating its distinct constituents: random noise and fixed pattern (FP) noise. Regarding the PV maps, FP noise is the main source of noise for both models of digitizer. Also, the standard deviation of the random noise in the 10000XL model is almost twice that of the V800 model. In the dose maps, the FP noise is smaller in the multichannel method than in the single channel ones. However, random noise is higher in this method, throughout the dose range. In the multichannel method, FP noise is reduced, as a consequence of this method's ability to eliminate channel independent perturbations. However, the random noise increases, because the dose is calculated as a linear combination of the doses obtained by the single channel methods. The values of the coefficients of this linear combination are obtained in the present study, and the root of the sum of their squares is shown to range between [Formula: see text] and [Formula: see text] over the dose range studied. These results indicate the random noise to play a fundamental role in the uncertainty of RCF dosimetry: low levels of random noise are required in the digitizer to fully exploit the advantages of the multichannel dosimetry method. This is particularly important for measuring high doses at high spatial resolutions.

A protocol for accurate radiochromic film dosimetry using Radiochromic.com

“… 15 , 18 The signal of the scanner have noise. 14 , 28 , 29 The scanner lamp should warm-up before use. 30 , 31 And other minor sources of uncertainty of the scanner include grid patterns and positional inaccuracies.…”

“…While for treatments using small fields 100–150 dpi (0.25–0.17 mm) may be necessary. In this protocol, higher resolutions are discouraged because they produce larger noise 14 , 15 and slow down film scanning and analysis. Figure 2 depicts scanner settings for a calibration and a treatment using small fields.…”

“…Epson Expression 10000-12000XL are favored because they are less affected by the lateral artifact. [13][14][15][16][17][18][19][20] Epson scanners can be controlled with the associated Epson Scan software or with alternatives such as VueScan (Hamrick Software, Phoenix, AZ, USA).…”