Practical kidney dosimetry in peptide receptor radionuclide therapy using [177Lu]Lu-DOTATOC and [177Lu]Lu-DOTATATE with focus on uncertainty estimates

EJNMMI Physics

Table 2 Uncertainty budget for the dosimetry procedure

Section in paper	Source	Uncertainty estimate
Dose calibrator calibration and activity measurement	Calibration source^a	3%
	Calibration of dose calibrators^a	1%
	Dose calibrator stability	1%
Quantitative SPECT (QSPECT)	Scanner calibration	2% + 1%
	Reproduction of activity	6%
	Scanner stability	2%
	Deadtime correction^b	1%
Kidney delineation and partial volume correction	Kidney delineation	3%
Kidney delineation and partial volume correction	Partial volume correction	7%
Time-activity curve and absorbed dose	Single exponential model	1% + 1%
	Fitting uncertainty	Individual value from fit (normally 1–10%)
	Assumption of equal effective half-life^c	12%
	1-SPECT AUC calculation^c	Individual value dependent on 3-SPECT fit
	Dose factor	1% + 1%
	*Total (3-SPECT—example)*^d	*13%*^e
	*Total (1-SPECT—example)*^d	*19%*^e

^aFor calculations of specific absorbed dose (Gy/GBq) this error cancels out, as it enters in both dose (Gy) measured through scanner calibration and activity (GBq) measured through dose calibrator calibration
^bIf the deadtime correction factor was applied
^cOnly relevant for 1-SPECT fractions
^dTaking 6% standard uncertainty on AUC as in Fig. 6b. 1-SPECT example: Assuming effective half-life of 2.2 d, scan performed 24 h after injection and 9% standard uncertainty on λ (see Eq. (4))
^eThe stated total uncertainty was obtained by adding the uncertainty components in quadrature and is thus valid for independent error sources. The value was rounded up