Variations in the practice of molecular radiotherapy and implementation of dosimetry: results from a European survey

Background Currently, the implementation of dosimetry in molecular radiotherapy (MRT) is not well investigated, and in view of the Council Directive (2013/59/Euratom), there is a need to understand the current availability of dosimetry-based MRT in clinical practice and research studies. The aim of this study was to assess the current practice of MRT and dosimetry across European countries. Methods An electronic questionnaire was distributed to European countries. This addressed 18 explicitly considered therapies, and for each therapy, a similar set of questions were included. Questions covered the number of patients and treatments during 2015, involvement of medical specialties and medical physicists, implementation of absorbed dose planning, post-therapy imaging and dosimetry, and the basis of therapy prescription. Results Responses were obtained from 26 countries and 208 hospitals, administering in total 42,853 treatments. The most common therapies were 131 I-NaI for benign thyroid diseases and thyroid ablation of adults. The involvement of a medical physicist (mean over all 18 therapies) was reported to be either minority or never by 32% of the responders. The percentage of responders that reported that dosimetry was included on an always/majority basis differed between the therapies and showed a median value of 36%. The highest percentages were obtained for 177 Lu-PSMA therapy (100%), 90 Y microspheres of glass (84%) and resin (82%), 131 I-mIBG for neuroblastoma (59%), and 131 I-NaI for benign thyroid diseases (54%). The majority of therapies were prescribed based on fixed-activity protocols. The highest number of absorbed-dose based prescriptions were reported for 90 Y microsphere treatments in the liver (64% and 96% of responses for resin and glass, respectively), 131 I-NaI treatment of benign thyroid diseases (38% of responses), and for 131 I-mIBG treatment of neuroblastoma (18% of responses). Conclusions There is a wide variation in MRT practice across Europe and for different therapies, including the extent of medical-physicist involvement and the implementation of dosimetry-guided treatments.