Effect of calculation method on kidney dosimetry in ¹⁷⁷Lu-octreotate treatment

Figures & data

Figure 1. Correlations of the absorbed kidney doses (Gy/GBq) for the whole kidney and the small volume methods.

Figure 2. Absorbed doses (Gy/GBq) for patients who had received the intended activity of 7.4 GBq (78 treatments, mean 0.43 Gy/GBq black squares) compared to those who had lower activities (18 treatments, mean 0.49 Gy/GB black triangles) in their ¹⁷⁷Lu-octreotate treatments. Method: whole kidney method.

Table 1. Absorbed doses measured by the whole kidney and by the small volume methods and their ratios among the 24 consecutive patients who received four ¹⁷⁷Lu-octreotate treatments at eight-week intervals.

Patients	Total	Whole kidney volume			Small volume
	GBq	Gy/GBq	Range	T½ (h)	Gy/GBq	Range	T½ (h)
1	15.3	0.64	0.45–0.80	35.5	1.09	0.81–1.39	38.6
2	15.7	0.34	0.27–0.46	52.4	0.60	0.50–0.79	57.7
3	21.0	0.38	0.33–0.42	41.5	0.64	0.61–0.69	41.5
4	22.2	0.45	0.37–0.53	47.5	0.71	0.59–0.88	47.1
5	23.6	0.89	0.65–1.06	45.7	1.64	1.12–1.91	48.4
6	27.1	0.32	0.25–0.47	38.4	0.53	0.40–0.82	37.8
7	27.1	0.35	0.22–0.45	45.3	0.63	0.37–0.83	49.2
8	29.9	0.32	0.31–0.36	47.0	0.49	0.44–0.57	43.7
9	30.1	0.61	0.54–0.72	53.1	1.03	0.86–1.29	48.6
10	30.4	0.59	0.52–0.67	40.4	0.95	0.79–1.06	41.4
11	30.5	0.43	0.37–0.49	41.2	0.72	0.65–0.80	41.6
12	30.9	0.40	0.36–0.48	46.3	0.61	0.51–0.70	45.0
13	31.0	0.55	0.51–0.66	39.7	0.84	0.70–0.96	44.4
14	31.1	0.39	0.37–0.41	46.7	0.69	0.66–0.71	52.7
15	31.1	0.42	0.33–0.52	51.3	0.71	0.59–0.83	48.5
16	31.2	0.26	0.24–0.29	37.5	0.41	0.36–0.46	41.2
17	31.2	0.46	0.40–0.50	52.3	0.82	0.71–0.90	54.8
18	31.3	0.34	0.27–0.38	39.3	0.46	0.38–0.52	41.1
19	31.3	0.35	0.34–0.37	42.4	0.64	0.63–0.67	43.8
20	31.4	0.42	0.36–0.46	58.9	0.71	0.59–0.80	56.8
21	31.7	0.43	0.41–0.47	43.4	0.74	0.67–0.78	44.2
22	31.8	0.46	0.36–0.54	46.3	0.74	0.61–0.81	43.2
23	32.5	0.42	0.33–0.54	52.1	0.80	0.71–0.89	53.7
24	33.0	0.33	0.30–0.37	42.1	0.59	0.54–0.66	43.6
Mean	28.5	0.44		45.3	0.74		46.2

Table 2. A comparison of the whole kidney and the small volume methods for determining the mean absorbed kidney doses (Gy/GBq) and their ratios for right and left kidneys for 24 patients given four successive treatment cycles of ¹⁷⁷Lu-octreotate at eight-week intervals.

^177Lu	Whole kidney volume method (Gy/GBq)		Small volume method (Gy/GBq)		Ratio
Cycle	Right kidney	Left kidney	Right kidney	Left kidney	Mean	Range
1	0.46 (0.26–1.09)	0.46 (0.24–1.02)	0.74 (0.40–2.08)	0.76 (0.40–1.74)	1.66	1.33–2.23
2	0.41 (0.22–0.65)	0.40 (0.23–0.65)	0.67 (0.33–1.12)	0.67 (0.38–1.12)	1.66	1.49–1.99
3	0.46 (0.24–0.93)	0.44 (0.24–0.83)	0.78 (0.37–1.82)	0.76 (0.43–1.48)	1.71	1.46–1.96
4	0.46 (0.22–1.09)	0.44 (0.23–1.02)	0.79 (0.33–2.08)	0.76 (0.38–1.74)	1.73	1.61–1.90

Figure 3. (a) Calculated kidney doses (Gy) for the whole kidney method based on the OLINDA calculation with three time points correlated with the new equation for activities measured at 24 and 168 h after the ¹⁷⁷Lu-octreotate treatment including individual kidney volumes. (b) Calculated kidney doses (Gy) for the small volume method based on the OLINDA calculation at three time points (dots) and the new equation for two time points at 24 and 168 h (line) after the ¹⁷⁷Lu-octreotate treatment.

Figure 4. Calculated medulla and cortex doses for the small volume method based on the two time points calculation method and Equation 1.

Table 3. Correlation coefficients R² between the calculated kidney doses (Gy) and those given by the OLINDA method for three time points when the radiation dose calculations are based on a single SPECT/CT scan for different time points (a, b, c), and for two time points, 24 and 168 h from treatment (d) and when kidney volume is included to our current analysis (e).

	Parameters in the model	Correlation coefficient R^2
a	counts 24 h SPECT/CT, C24	0.4897
b	counts 72 h SPECT/CT, C72	0.4666
c	counts 168 h SPECT/CT, C168	0.5078
d	T½ * C24	0.5604
e	T½ * C24/kidney volume, Vk	0.9061