Evaluation of methods for red marrow dosimetry based on patients undergoing radioimmunotherapy

Figures & data

Table I.  Abbreviations.

Abbreviation	Explanation
ARM(t)	Activity in red marrow at time t after administration of the radiopharmaceutical
[ÃBL]	Cumulated activity calculated from the activity concentration in blood
[ÃPL]	Cumulated activity calculated from the activity concentration in plasma
ÃRB	Cumulated activity in the remainder of the body, ÃRB=ÃTB–ÃRM
ÃRM	Cumulated activity in the red marrow
ÃTB	Cumulated activity in the total body
CAP,sacrum	Number of counts in sacrum corrected for background, anterior [cps]
CPA,sacrum	Number of counts in sacrum corrected for background, posterior [cps]
DRM	Total mean absorbed dose in red marrow, DRM=DRM←RM+DRM←RB
DTB	Mean absorbed dose in the total body
DRM←RB	Mean absorbed dose in red marrow from activity in remainder of body
DRM←RM	Mean self-absorbed dose in red marrow
fsacrum	Fraction of total red marrow that is present in sacrum (fsacrum=0.099)
HCTpat	Haematocrit
k	Correction factor for camera sensitivity [cps/MBq]
µ	Effective attenuation coefficient (µ = 0.0983 cm^−1)
mTB,ph	Weight of total body for the phantom
mTB,pat	Weight of total body for the patient
mRM,ph	Weight of red marrow in the phantom
mRM,pat	Weight of red marrow in the patient
mRB,ph	Weight of remainder of body in the phantom
mRB,pat	Weight of remainder of body in the patient
RMBLR	Ratio of activity concentration in red marrow to blood
RMECFF	Ratio of activity concentration in red marrow to extracellular fluid (RMECFF = 0.19)
SRM←RB	Mean absorbed dose to the red marrow per unit cumulated activity in the remainder of the body
SRM←TB	Mean absorbed dose to the red marrow per unit cumulated activity in the total body
SRM←RM	Mean absorbed dose to the red marrow per unit cumulated activity in the red marrow, scaled for the weight of the red marrow of the patient
SRM←RM,ph	Mean absorbed dose to the red marrow per unit cumulated activity in the red marrow for the phantom
STB←TB	Mean absorbed dose to the total body per unit cumulated activity in the total body
T	Patient thickness over the sacrum region

Table II.  A summary of the methods used for calculating the absorbed dose and the median, minimum and maximum of the absorbed dose per unit of injected activity for all ad of the radiopharmaceutical (¹³¹I-LL2).

Abbreviation	Method	Characteristics
BL1	Blood method	Based on activity in blood; RMBLR = 0.36
BL2	Blood method	Based on activity in blood; RMBLR = 1
BL3	Blood method	Based on activity in blood; RMBLR = RMECFF/(1-HCT)
BL4	Blood method	Based on activity in plasma; RMECFF = 0.19
IM	Sacrum method	Scintillation camera images
TB1	Total body approximation	Handheld rate meter
TB2	Total body approximation	Scintillation camera images

Figure 1. Whole-body images (left: anterior, right: posterior) 24 hours after administration for patient:treatment number 6:1. The total body ROI, the sacrum ROI and the ROI for background correction are shown.

Figure 2. The CT scan of the sacral region for patient:treatment 6:1. Since the sacroiliac joint moves sagittally oblique the distance between the ventral and dorsal measurements differs. The mean of the ventral and dorsal measures was used when determining the width of the sacrum in order to correct for this difference.

Figure 3. The percent of injected activity per millilitre of a) blood and b) plasma as a function of time for all the patients. (Please note that the x-axes are shortened to make the data in the figures clearer.)

Figure 4. The percent of injected activity that is present in sacrum as a function of time for all the patients. The activity was determined from scintillation camera images by the geometric mean method.

Figure 5. The percent of injected activity in whole body as a function of time after administration for all the patients. The data was determined from a) single probe measurements and b) scintillation camera whole body-scans.

Figure 6. Interpatient variability: Absorbed dose to bone marrow per unit injected activity calculated with the four variations of the blood method (BL1–BL4) and the imaging method (IM) and absorbed dose to the total body per unit injected activity, calculated based on either external probe measurements (TB1) or the total body counts in scintillation camera images (TB2). The order of the patients is the same for all methods.

Table IIIa.  Absorbed dose to red marrow per unit administered activity for all patients and RIT treatments using the blood methods and the sacrum imaging method.

	DRM/A0 [mGy/MBq]
Patient: Treatment	BL1	BL2	BL3	BL4	IM	Max:Min
1:1	0.32	0.68	0.32	0.32	0.48	2.1
2:1	0.54	1.19	0.58	0.58	0.73	2.2
2:2	0.27	0.55	0.27	0.27	0.39	2.0
3:1	0.28	0.57	0.25	0.25	0.50	2.3
4:1	0.53	1.27	0.53	0.49	0.62	2.6
4:2	0.60	1.46	0.52	0.52	0.52	2.8
4:3	0.63	1.42	0.55	0.55	0.55	2.6
5:1	0.18	0.36	0.18	0.18	0.25	2.0
5:2	0.28	0.60	0.28	0.28	0.46	2.1
6:1	0.29	0.52	0.29	0.29	0.52	1.8
6:2	0.31	0.63	0.39	0.39	0.63	2.0
7:1	0.26	0.44	0.26	0.33	0.51	2.0
8:1	0.28	0.64	0.28	0.28	0.64	2.3
9:1	0.44	1.01	0.48	0.48	0.56	2.3
9:2	0.50	1.09	0.55	0.59	0.59	2.2
10:1	0.36	0.75	0.40	0.40	0.59	2.1
10:2	0.39	0.78	0.47	0.43	0.55	2.0
11:1	0.39	0.86	0.50	0.43	0.61	2.2
Median	0.34	0.72	0.40	0.40	0.55
Min.	0.18	0.36	0.18	0.18	0.25
Max.	0.63	1.46	0.58	0.59	0.73

Table IIIb.  Absorbed dose to total body per unit administered activity for all patients and RIT treatments using the total body approximation methods.

	DTB/A0 [mGy/MBq]
Patient:Treatment	TB1	TB2	Max:Min
1:1	0.19	0.24	1.3
2:1	0.28	0.26	1.1
2:2	0.15	0.14	1.1
3:1	0.15	0.16	1.1
4:1	0.23	0.26	1.1
4:2	0.19	0.25	1.3
4:3	0.35	0.23	1.5
5:1	0.09	0.09	1.0
5:2	0.15	0.23	1.5
6:1	0.20	0.21	1.1
6:2	0.24	0.24	1.0
7:1	0.20	0.22	1.1
8:1	0.19	0.20	1.1
9:1	0.21	0.23	1.1
9:2	0.23	0.29	1.3
10:1	0.19	0.31	1.6
10:2	0.25	0.29	1.2
11:1	0.16	0.25	1.6
Median	0.20		0.24
Min.	0.09		0.09
Max.	0.35		0.31

Table IV.  Fraction of self-absorbed dose to the total absorbed dose to the red marrow (D_RM←RM/D_RM).

	Fraction of self-absorbed dose
Patient:Treatment	BL1	BL2	BL3	BL4	IM
1:1	0.63	0.82	0.60	0.56	0.65
2:1	0.69	0.87	0.67	0.67	0.77
2:2	0.63	0.87	0.72	0.70	0.77
3:1	0.61	0.81	0.57	0.56	0.76
4:1	0.77	0.91	0.71	0.71	0.73
4:2	0.83	0.95	0.83	0.75	0.75
4:3	0.70	0.87	0.68	0.64	0.78
5:1	0.61	0.83	0.57	0.56	0.76
5:2	0.64	0.83	0.58	0.64	0.63
6:1	0.45	0.71	0.58	0.55	0.67
6:2	0.55	0.76	0.50	0.49	0.78
7:1	0.38	0.66	0.42	0.61	0.71
8:1	0.71	0.84	0.63	0.61	0.88
9:1	0.73	0.87	0.77	0.75	0.75
9:2	0.70	0.90	0.75	0.75	0.71
10:1	0.61	0.81	0.68	0.65	0.66
10:2	0.59	0.81	0.59	0.63	0.65
11:1	0.69	0.86	0.76	0.77	0.70
Median	0.64	0.84	0.65	0.64	0.74
Min.	0.38	0.66	0.42	0.49	0.63
Max.	0.83	0.95	0.83	0.77	0.88

Table V.  Variation of HCT_pat and the calculated RMBLR for all patients and RIT treatments. (RMBLR = 0.19/(1-HCT_pat))

Patient: Treatment	HCTpat [%]	RMBLR
1:1	44	0.34
2:1	50	0.38
2:2	54	0.41
3:1	39	0.31
4:1	43	0.33
4:2	38	0.31
4:3	37	0.30
5:1	46	0.35
5:2	42	0.33
6:1	59	0.46
6:2	54	0.41
7:1	50	0.38
8:1	43	0.33
9:1	54	0.42
9:2	55	0.42
10:1	58	0.45
10:2	57	0.44
11:1	63	0.51
Median	50	0.38
Min	37	0.30
Max	63	0.51

Table VI.  The correlation coefficients of the absorbed dose per unit injected activity for all the methods investigated for red marrow dosimetry.

	TB1	TB2	BL1	BL2	BL3	BL4	IM
TB1	1
TB2	0.57	1
BL1	0.73	0.58	1
BL2	0.66	0.53	0.99	1
BL3	0.71	0.72	0.93	0.90	1
BL4	0.75	0.72	0.93	0.89	0.97	1
IM	0.64	0.73	0.54	0.51	0.68	0.67	1

Table VII.  The correlation coefficients of the absorbed dose and the maximum drop in number of platelets and the absorbed dose and the time to nadir.

	Drop in platelets	Time to nadir
TB1	−0.58	0.31
TB2	−0.53	0.24
BL1	−0.53	0.26
BL2	−0.54	0.32
BL3	−0.56	0.12
BL4	−0.56	0.48
IM	−0.54	0.30