Radiation exposure from handling alpha emitting radiopharmaceutical radium-223 dichloride with and without syringe shield

Objectives Radium-223 dichloride (Xofigo) is a new alpha-emitting radiopharmaceutical approved by FDA for treatment of castration resistant prostate cancer bone metastases. An experiment was carried out to determine the exposure associated with handling of radium-223 dichloride radiopharmaceutical with and without the use of a syringe shield. Of the total decay of radium-223, 95.3% are alpha, 3.6% beta and 1.1% gamma.

Methods A syringe containing 106 microcuries of radium-223 dichloride was placed on a stand unshielded and exposure measurements were made at 1 cm, 30 cm, and 100 cm with a calibrated ionization survey meter, Victoreen model 451. This process was repeated with radium-223 dichloride syringe covered with a lead syringe shield and then by covering the radium-223 syringe with a plastic beta shield. Reading was also obtained with an alpha probe, Ludlum model 43-92 attached to Ludlum model 3 survey meter with a calibrated efficiency of 5 percent for alpha particles only.

Results Results from this experiment for radiation exposure of radium-223 dichloride syringe unshielded, were 5.8 mR/hr at 1 cm, 0.21 mR/hr at 30 cm, and 0.01 mR/hr at 100 cm, the latter being background radiation. Exposures obtained from radium-223 dichloride syringe shielded with a lead syringe shied was 1.2 mR/hr at 1 cm, 0.08 mR/hr at 30 cm, and 0.01 mR/hr at 100 cm. Exposure when the radium-223 chloride syringe was covered with plastic beta shield was 3.3 mR/hr at 1 cm, 0.13 mR/hr at 30 cm, and 0.01 mR/hr at 100 cm. Exposure from alpha radiation measured with alpha detector probe measured less than 10 cpm at 1 cm.

Conclusions Even though all alpha radiations are shielded by the syringe, beta and gamma radiations escaping from the syringe warrant the use of syringe shield to minimize the exposure from handling radium-223 dichloride dosages. Standard radiation safety practice established in Nuclear Medicine Department in the use of syringe shield should be adequate for radiation protection.