The team used radiobiological models to calculate the absorbed radiation doses needed to eradicate all the bone lesions in patients with castration-resistant prostate cancer (CRPC). They put forward a new model to predict the decrease in tumour size in patients treated with molecular radiotherapy (see also Molecular radiotherapy: a personalized approach).

The study was a collaboration between The Institute of Cancer Research, The Royal Marsden Hospital NHS Foundation Trust, Brighton and Sussex University Hospitals NHS Trust and Queen's University Belfast (Phys. Med. Biol. 62 2859).

Head of Radioisotope Physics Glenn Flux said: "Prostate cancer is the second most common cause of cancer mortality in males, accounting for 307,000 deaths worldwide each year. The vast majority of patients suffer from bone metastases, which are often treated with radiopharmaceuticals. At the moment, these therapies are still commonly performed with fixed administered activities, sometimes modified by patient weight, and therefore there was a need for a more personalized approach."

The researchers applied standard radiobiological models for tumour control, to assess the patient-specific absorbed radiation doses required to cure all metastatic bone lesions in 22 patients with CRPC bone metastases.

They developed a control model, which could be used to identify patients who would benefit more from treatment. The method provides a simple tool, which could be used in routine clinical practice to show the level of radioactivity required to achieve a predicted absorbed radiation dose, and subsequent reduction in tumour size.

Lead author Ana Denis-Bacelar said: "Our study has shown that a large benefit in metastatic burden reduction could be obtained in most patients for a small increase in the radiation doses delivered. Our methodology has the potential to personalize treatment, and could be used as a patient selection tool by relating potential treatment benefit and toxicity.

"Ninety-one per cent of the patients in our study group saw a potential large benefit in terms of tumour size reduction, achieved by a small increase in the mean absorbed radiation dose. However, the method also shows where the gains are reduced. For example, one patient in our study would have required very high patient mean absorbed radiation doses to obtain any significant metastatic reduction, which would likely result in bone marrow suppression."

"This is a first step, but we are hopeful that future studies of the model will allow it to be refined and validated."

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