ajor organs were calculated based on clinical biodistribution data in five patients with castration-resistant prostate cancer. Calculations of absorbed radiation doses were performed using OLINDA/EXM (Organ Level INternal Dose Assessment/EXponential Modeling), a software program based on the Medical Internal Radiation Dose (MIRD) algorithm, which is widely used for established beta and gamma emitting radionuclides. For radium-223, which is primarily an alpha particle-emitter, assumptions were made for intestine, red marrow and bone/osteogenic cells to provide the best possible absorbed radiation dose calculations for Xofigo, considering its observed biodistribution and specific characteristics.
The calculated absorbed radiation doses to different organs are listed in Table 2. The organs with highest absorbed radiation doses were bone (osteogenic cells), red marrow, upper large intestine wall, and lower large intestine wall. The calculated absorbed doses to other organs are lower.
Table 2: Calculated Absorbed Radiation Doses to Organs Target Organ Mean
(Gy/MBq) Mean
(rad/mCi) Coefficient of Variation
(%)
*
LLI: lower large intestine
†
ULI: upper large intestine
Adrenals
0.00012
0.44
56
Brain
0.00010
0.37
80
Breasts
0.00005
0.18
120
Gallbladder wall
0.00023
0.85
14
LLI* wall
0.04645
171.88
83
Small intestine wall
0.00726
26.87
45
Stomach wall
0.00014
0.51
22
ULI† wall
0.03232
119.58
50
Heart wall
0.00173
6.40
42
Kidneys
0.00320
11.86
36
Liver
0.00298
11.01
36
Lungs
0.00007
0.27
90
Muscle
0.00012
0.44
41
Ovaries
0.00049
1.80
40
Pancreas
0.00011
0.41
43
Red marrow
0.13879
513.51
41
Osteogenic cells
1.15206
4262.60
41
Skin
0.00007
0.27
79
Spleen
0.00009
0.33
54
Testes
0.00008
0.31
59
Thymus
0.00006
0.21
109
Thyroid
0.00007
0.26
96
Urinary bladder wall
0.00403
14.90
63
Uterus
0.00026
0.94
28
Whole body
0.02311
85.50
16
ULI: upper large intestine
Adrenals
0.00012
0.44
56
Brain
0.00010
0.37
80
Breasts
0.00005
0.18
120
Gallbladder wall
0.00023
0.85
14
LLI* wall
0.04645
171.88
83
Small intestine wall
0.00726
26.87
45
Stomac
