Answer to Question #4091 Submitted to "Ask the Experts"

I am a nuclear medicine technologist and my hospital just started offering a therapy for liver cancer involving ⁹⁰Y. I have drawn numerous doses of ^99mTc and ²⁰¹Tl but nothing as "powerful" as a ⁹⁰Y dose. The vial contains approximately 87 mCi and I draw on average 20 mCi to be given to one patient. With a maximum energy of 2.2 MeV that can travel approximately 30 feet in air, should I be concerned about my exposure? I use as much radiation protection equipment as possible during the drawing procedure. Given that, do you think I get any deep dose from the beta? I have drawn 17 doses in the last two months and have not received the dosimetry on my ring badge yet. I am not too worried about my hands. What if I stick myself with a contaminated needle? What kind of exposure are we talking about then (whole body and local)? The material I am referring to is a ⁹⁰Y-labeled microsphere.

Therapeutic administrations involving ⁹⁰Y do indeed bring a number of important concerns for radiological protection. As you note, the beta emitted by ⁹⁰Y is of high energy (~2.3 MeV maximum, 0.93 MeV average) and can penetrate the outer protective (dead) layer of skin and irradiate the epidermis and dermis. It will not, however, penetrate more than about 1 cm into the body, and thus will not irradiate deep organs, like a gamma emitter will. Handling of the ⁹⁰Y should be minimized, and therapeutic quantities should be shielded as much as possible (with acrylic—not lead—in storage areas, around syringes, etc.).

Minimize the time in contact with such materials, and keep them at a distance from your person and hands as much as possible. Obviously, be careful to avoid an internal contamination, as you note. If this should occur, the quantities will probably be small, and the consequences will not be serious—but the situation should be treated seriously, with a careful assessment of dose by a health physicist. You should spend some time talking with the health physics staff at your institution about the specific procedures that you are using and all of these concerns. I'm a bit surprised that this was not done with all of your staff before these procedures were started.

Any therapeutic use of a radiopharmaceutical needs to be well planned and carefully treated. As you say, the more routine diagnostic procedures, while they should not be treated flippantly, are of lower concern. Many centers are using ⁹⁰Y microspheres, radiolabeled antibodies, and other therapeutic agents, so we have good experience with these compounds. In any specific application, knowledge of good health physics principles and this experience of others needs to be brought to bear, to ensure that radiation doses are kept as low as reasonably achievable while delivering the required therapy to the patients.

Michael G. Stabin, PhD, CHP