Calculation of doses to the public in contact with patients underwent radiopharmaceutical therapy with 177Lu: model multi-factor study
Authors: Chipiga L. A. , Likhacheva A. V. , Zvonova I. A. , Vodovatov A. V. , Toskin O. Yu. , Sapelnikov A. A. , Velichkina K. S. , Terenteva A. S. , Stanzhevsky A. A. , Ryzhkova D. V. 
Published: February 2025

INTRODUCTION: Associated with the development of radiopharmaceutical therapy with 177Lu (177Lu-DOTA-TATE, 177Lu-PSMA-617), the issue of radiation protection of the public becomes important. Nowadays, national regulatory and methodological documents on radiation safety do not contain release criteria of patients after radiopharmaceutical therapy with 177Lu. Existing approaches to determining the release criteria after radiopharmaceutical therapy do not consider radiation exposure from the patient during long-term contact with the patient (up to several days in a confined space) and possible of generation of biological waste containing 177Lu in public transport during the first hours and days after release. In order to choose an optimal approach to determine release criteria, it is necessary to assess the radiation exposure from the patient on different categories of people from the public.

OBJECTIVE: Estimation of radiation exposure of people from public from patient after radiopharmaceutical therapy with 177Lu considering the radioactive biological waste containing 177Lu.

MATERIALS AND METHODS: The time of patient release from the hospital was determined upon reaching the previously proposed release criteria based on the patient dose rate. The ambient dose equivalent rate for the patient after therapy with 177Lu labeled radiopharmaceuticals were determined based on the experimental data available in the literature. Various scenarios of exposure of individuals in contact with the patient after release from the hospital were developed; effective doses after contact with the patient were estimated based on the developed scenarios. The activity of 177Lu generated in patient biological waste after therapy was determined as well. Based on the assessments, activity concentration of 177Lu was determined in wastewater of residential sewage systems and in transport during patient traveling to the place of residence. Using specialized MCNP software, the doses of public exposure in transport from 177Lu generated in wastewater in tanks of transport biotoilets were modeled and estimated.

RESULTS: Doses to some categories of people from the public after the contact with a patient released immediately after administration of a radiopharmaceutical with 177Lu may exceed the dose limit of 1 mSv, but release in 4–6 hours after therapy when the release criterion is reached, established in accordance with the approach of NRB-99/2009, will not lead to dose limit exceedance. The activity concentration of 177Lu, generated in transport biotoilet tanks after the patient with 177Lu travelling, exceeds the limit value for classifying liquid waste as radioactive (0.025 kBq/g). Doses to passengers and crew members may be higher than 100 μSv. Doses from a patient may be higher than 1 mSv after release of patient in 4–6 hours in the case of a long-distance travel (several days on a train).

DISCUSSION: Exceeding the dose limit to the public is unacceptable and therefore the patient cannot be released immediately after 177Lu administration. Due to the likelihood of exceeding passenger and crew dose limits in transport during long-distance travel of a patient with administered 177Lu, it is necessary to limit the travel of patients by long-distance trains.

CONCLUSION: To ensure radiation safety of the public, the optimal approach is the previously used approach when establishing release criteria in NRB-99/2009 for other radionuclides. According to this approach, the value of the release criterion for the dose rate at 1 meter from the patient after therapy with 177Lu is 29 μSv/h. The greatest questions in terms of radiation safety arise when releasing non-residence patients who will have to get to their place of residence in distant regions. Thus, it is reasonable to limit the patient traveling after radiopharmaceutical therapy with 177Lu using long-distance trains (instead of it is recommended to use air transport).