TABLE 3.

Estimated uncertainty budget for EBT3 and EBT‐XD film measurements. One of the largest sources of uncertainty is associated with film position due to an initial dose fall‐off of approximately 10% per mm from isocenter. The uncertainty associated with the Task Group‐51 dose calibration for the linac¹⁷ is not included since it is a systematic error common to all dosimetric measurements and treatment planning calculations. The EBT‐XD film measurements were acquired over a time period of 6 months; a larger beam output uncertainty, relative to the EBT3 film measurement, was assigned to these measurements

Measurement uncertainties (k = 1) for EBT3 & EBT‐XD Film
Maximum dose uncertainties
Type of uncertainty	Source of uncertainty	Dose effect
Statistical	Film position	±3%
	Beam output	±0.25% (EBT3 film), ±0.5% (EBT‐XD Film)
Systematic	Film calibration and dose extraction from red (EBT3)/green (EBT‐XD) channel 28 , 29	±3%
	Correction for film image resolution and smoothing	±0.3%
Total		±4.3% (EBT3 film), ±4.3% (EBT‐XD film)

Dose width uncertainties
Type of uncertainty	Source of uncertainty	Width effect
Statistical	Film position	±1%
Systematic	Correction for film image resolution and smoothing	±1%
Total		±1.4%