Tumour control probability derived from dose distribution in homogeneous and heterogeneous models: assuming similar pharmacokinetics, ¹²⁵Sn–¹⁷⁷Lu is superior to ⁹⁰Y–¹⁷⁷Lu in peptide receptor radiotherapy

Association of a short beta range radionuclide (RN) with a long beta range RN appears well adapted to simultaneously treat small homogeneous and large heterogeneous tumours. Recent clinical trials on ¹⁷⁷Lu-⁹⁰Y therapy used empirical activity ratios and RN with larger beta maximal range could still favourably replace ⁹⁰Y. Tumour control probabilities (TCP) of several RN in combination with ¹⁷⁷Lu were computed for various homogeneous and heterogeneous tumour models. Using ¹⁷⁷Lu–⁹⁰Y with 75–25% activity proportions provided the best TCP. However, ¹⁷⁷Lu–¹²⁵Sn with 80–20% activity proportions achieved significantly better TCP. In addition,¹²⁵Sn production and its coupling to somatostatin analogue appear feasible. Clinical trials using RN combinations should use RN proportions tuned to the patient dosimetry. ¹²⁵Sn is potentially the best RN for combination with ¹⁷⁷Lu in peptide receptor radiotherapy justifying pharmacokinetics studies in rodents of ¹²⁵Sn labelled somatostatin analogues.

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