Orateur
Description
In recent years, Targeted Radionuclide Therapy (TRT) is showing exponential increase of applications due to the availability of new receptor directed ligands, metabolic precursors, monoclonal antibodies, and innovative devices - such as microspheres embedded with radionuclides. A variety of radionuclides, emitting nuclear particles with a range of path lengths from nanometres to millimetres, and clinical strategies are currently used, for which various normal tissues become organs at risk.
The use of dosimetry to support TRT has gained considerably importance. An increased number of papers address dosimetry and some remarkable dese-effect relationships, and suggest that dosimetry-based treatments would improve outcomes, increase survival, and open the way toward personalised therapies.
Available evidence covers nearly all TRTs, including the treatment of thyroid cancer, benign thyroid disease, neuroblastomas, neuroendocrine tumours, bone pain palliation, radioembolization of primary and secondary liver cancer, and castration-resistant prostate cancer. The correlation findings between absorbed doses and response, toxicity, and survival have stimulated the study of radiobiology in this field.
To date, most radiobiological models of TRT start from the extrapolation from External Beam Radiation Therapy experience, the Linear Quadratic Model and the Biologically Effective Dose (BED) concept. The limits of a simple mathematic extrapolation concern the evident differences in the uniformity and dose rate of in radiation delivery (*), which in TRT are further dependent on specific radiopharmaceuticals, disease and individual metabolism. In any case, such basic models, considered as first attempt, have advanced the understanding, provided useful indications to guide treatments, and suggested modified protocols that have shown improvements in outcomes and safety.
This presentation overviews the most relevant studies of radiobiology/dose-response of tumour and/or normal tissues after a variety of TRT, showing results by means of normal tissue complication probability (NTCP) and tumour control probability (TCP), as well as hints and issues to be deepened.
(*) EBRT: uniform, acute or fractionated doses, constant dose rate, e.g. 1–5 Gy/min; brachytherapy: continuously slowing down dose rate by physical decay, e.g. 1–5 Gy/h; TRT: non-uniform, continuously slowing down dose rate depending to tissue uptake and effective half-life - e.g. of 2–8 Gy/day, overall absorbed dose up to 50 Gy over a period of days).
