Biting the magic bullet: celebrating a decade of the EANM Dosimetry Committee

Abstract

In 1946 Seidlin et al. [1] treated metastatic thyroid cancer with a ‘cocktail’ of 3,774 MBq I and 759 MBq I in several fractions. Pretherapy tracer studies were performed to identify iodine-avid lesions, and the cumulative absorbed doses delivered to both the tumour and to the blood were determined from measurements with a Geiger counter and specific lesion mass estimates. Extensive scanning was performed with the aim that radioiodine therapy would continue for as long as there was visible uptake. Biomarkers of response were measured to establish that while the leucocyte count from administration from I was temporarily depressed, there was no significant effect from I. Autoradiography of a biopsy sample showed that the radioiodine localized in tumour cells. The patient was reported to have a good response. Radioiodine therapy has proven highly successful in the ablation of thyroid remnants. This has helped to perpetuate the illusion that a successful cancer treatment is simply a matter of identifying the ‘magic bullet’. Unfortunately this is not the case for other cancers and still remains untrue for high-risk thyroid cancer. The scientific method, as applied in that first study, subsequently became largely lost. Even by 1953 Rawson et al. [2] remarked that ‘Some of our earlier attempts to treat metastatic cancer of the thyroid with radioactive iodine were without therapeutic effect. This was true probably because we were satisfied with minimal, even poor, uptake of the isotope by the metastatic lesions’ and that ‘Unfortunately, ...patients have been treated empirically with frequent comparatively small doses of radioactive iodine by the calendar rather than by considerations of the capacity of such tumors to concentrate radioiodine or of the radiosensitivity of the tumors.’ An increasing number of therapeutic radiopharmaceuticals have been introduced to the clinic to treat a range of diseases, although little has changed in the half century since that publication with regard to the rationale underlying methods of administration. In particular, the single most important factor governing response to any form of radiotherapy—the absorbed doses delivered to tumours and to normal organs—is almost universally ignored. The Dosimetry Task Group, which subsequently became a committee of the EANM, was formed in 2001 at the behest of the former EANM president, Dr Wolfgang Becker. In the last decade much has been accomplished: