Which tolerance is defined as 1% for TBI and 1 mm PDD shift for TSET?

Which tolerance is defined as 1% for TBI and 1 mm PDD shift for TSET?

• A. 1% (TBI) or 1 mm PDD shift (TSET)
• B. 2% from baseline
• C. ±1% from baseline
• D. Functional

Answer: (A)

In TG-142 style QA, tolerances are tailored to the modality because different therapies have different dosimetric sensitivities. Total body irradiation requires extremely uniform dose delivery across a large volume, so the allowable variation from the reference dose is very small—1%. Total skin electron therapy, on the other hand, relies on the shape of the depth-dose curve; a shift in that curve by more than 1 millimeter would change the dose at the skin and near-surface regions, so the tolerance is a 1 mm PDD shift. These precise values are the standard criteria used to decide if the machine and plan meet the required dosimetric accuracy for these techniques. Other options don’t capture these modality-specific limits, and “Functional” isn’t a dosimetric tolerance.

In TG-142 style QA, tolerances are tailored to the modality because different therapies have different dosimetric sensitivities. Total body irradiation requires extremely uniform dose delivery across a large volume, so the allowable variation from the reference dose is very small—1%. Total skin electron therapy, on the other hand, relies on the shape of the depth-dose curve; a shift in that curve by more than 1 millimeter would change the dose at the skin and near-surface regions, so the tolerance is a 1 mm PDD shift. These precise values are the standard criteria used to decide if the machine and plan meet the required dosimetric accuracy for these techniques. Other options don’t capture these modality-specific limits, and “Functional” isn’t a dosimetric tolerance.