Sumarium 153 Therapy for Metastatic Hormone-Refractory Prostate Cancer
Aaron Scott
Medical
Rufus Poole, CNMT
Brief history:
Severe metastatic prostate cancer with diffuse involvement of the skeletal system including thoracic, lumbar, and sacral spine; right sternoclavicular area; right clavicle; several right ribs; and left femur.
Full History:
Patient is a 78 year-old male with painful bone metastases from prostate cancer with multiple bone lesions. He underwent evaluation for Samarium-153 therapy. Previous bone scan done 5 ½ months ago showed cancer affecting entire skeleton except skull. The patient has received Zometa and would like to see several changes in the uptake of MDP.
Radiopharmaceutical:
98.7 mCi of Quadramet Samarium-153 was administered
by slow intravenous drip. The typical dose of Samarium is 70 mCi, but due
to patient’s weight, dosage had to be increased. Samarium-153 is a
therapeutic agent, used to relieve pain from cancer, rather than a
diagnostic agent. It is very similar in function to Strontium-89. Both
decay by beta emission, but Samarium-153 differs because it shows
excellent biolocalization characteristics similar to Technetium-99m MDP.
|
|
Strontium-89 |
|
|
Emissions |
Avg. 233
keV beta |
Avg. 583
keV beta |
|
Excretion |
100% urinary |
2/3 urinary, 1/3 fecal |
|
Penetration |
1.7
mm in bone (avg.) |
8 mm in tissue (max.) |
Physical Characteristics: Samarium-153 is produced in high yield and purity by neutron irradiation of isotopically enriched samarium Sm 152 oxide (152Sm2O3). It emits both medium-energy beta particles and a gamma photon, and has a physical half-life of 46.3 hours (1.93 days). Samarium-153 has average and maximum beta particle ranges in water of 0.5 mm and 3.0 mm, respectively. The primary radiation emissions of samarium-153 are shown in Table A.
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Table A - SAMARIUM-153 PRINCIPAL RADIATION EMISSION DATA |
||
|
|
Radiation Energy (KeV)* |
Abundance |
|
Beta |
640 |
30% |
|
Beta |
710 |
50% |
|
Beta |
810 |
20% |
|
Gamma |
103 |
29% |
* Maximum energies are listed for the beta emissions; the average beta particle energy is 233 keV.
External Radiation: The specific gamma-ray constant for samarium-153 is 0.46 R/mCi-hr at 1 cm (1.24x10-5 mSv/MBq- hr at 1 Meter). The half-value thickness of lead (Pb) for samarium-153 is approximately 0.10 mm. The use of 1 mm of lead will decrease the external radiation exposure by a factor of approximately 1,000. Quadramet should be stored in a lead-shielded container and frozen until use.
Radioactive decay factors to be applied to the stated value for radioactive concentration at calibration are given in Table B. All radioactivity is calibrated to the reference date and time on the vial.
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Table B - SAMARIUM-153 PHYSICA L DECAY CHART, HALF-LIFE 46.3 HOURS (1.93 DAYS) |
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|
Time (hour)* |
Factor |
Time (hour)* |
Factor |
|
-48.0 |
2.05 |
+1.0 |
0.99 |
|
-36.0 |
1.71 |
+2.0 |
0.97 |
|
-24.0 |
1.43 |
+3.0 |
0.96 |
|
-20.0 |
1.35 |
+4.0 |
0.94 |
|
-16.0 |
1.27 |
+6.0 |
0.91 |
|
-12.0 |
1.20 |
+8.0 |
0.89 |
|
-8.0 |
1.13 |
+12.0 |
0.84 |
|
-6.0 |
1.09 |
+16.0 |
0.80 |
|
-4.0 |
1.06 |
+20.0 |
0.74 |
|
-3.0 |
1.05 |
+24.0 |
0.70 |
|
-2.0 |
1.03 |
+36.0 |
0.58 |
|
-1.0 |
1.02 |
+48.0 |
0.49 |
|
*Time = hours before (-) or after (+) calibration |
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