Radiation absorbed doses from Co-57- and Co-55 bleomycin

Area of Science:

• Nuclear medicine
• Medical physics
• Radiopharmaceutical dosimetry

Background:

• Bleomycin is a chemotherapy agent used in cancer treatment.
• Radiolabeled bleomycin has been investigated for diagnostic and therapeutic applications.
• Accurate dosimetry is essential for evaluating the safety and efficacy of radiopharmaceuticals.

Purpose of the Study:

• To calculate organ radiation doses in adult patients following intravenous administration of Cobalt-57 (Co-57) and Cobalt-55 (Co-55) bleomycin.
• To derive somatically effective total-body doses for these radiopharmaceuticals.
• To discuss the impact of impurities and daughter products on radiation dose calculations.

Main Methods:

• Organ radiation doses were calculated using the Medical Internal Radiation Dose (MIRD) methodology.
• Residence times (cumulated activity per unit injected radioactivity) were determined for source organs (bladder, kidney, liver, remainder of body).
• Data were derived from Co-57 bleomycin clearance measurements in a limited patient cohort.

Main Results:

• The somatically effective doses were calculated as 0.26 ± 0.03 rad/mCi (70 ± 9 μGy/MBq) for Co-57 bleomycin and 0.63 ± 0.09 rad/mCi (171 ± 23 μGy/MBq) for Co-55 bleomycin.
• Key source organs contributing to the dose were identified as the bladder, kidney, and liver.
• The study considered the influence of Co-56 impurity in Co-55 and the Fe-55 daughter product.

Conclusions:

• The calculated somatically effective doses provide essential data for risk-benefit assessments of Co-57 and Co-55 bleomycin.
• Understanding radiation dose distribution is critical for optimizing the use of these radiopharmaceuticals in patient care.
• Further investigation into the dosimetric impact of impurities and daughter products is warranted.