Dosimetry in molecular radiotherapy: challenges and future directions

When?

Tuesday 20 November 2012, 14:00

Where?

30BB03 Physics Seminar Room

Open to:

Staff, Public

Speaker:

Ana Denis-Bacelar, The Institute of Cancer Research: Royal Cancer Hospital, London

The purpose of dosimetry calculations in molecular radiotherapy is to improve the probability of cure or palliation by maximising the radiation absorbed dose to the tumour while minimising the absorbed dose to normal healthy tissue and avoiding toxicity. To date, dosimetry is not used to guide therapy, as regulatory authorities believe there is little evidence of its predictive quality. Therefore most radionuclide administration methods are based upon empirical and clinical experience (prescribed activity adjusted by body weight or surface area). This has resulted in the majority of patient treatments being performed with neither prospective, nor retrospective dosimetry. The estimation of patient absorbed doses resulting from molecular radiotherapy is complex, as the internal irradiation depends on the specific biokinetics of the radiopharmaceutical within the patient and the radioisotope used during the procedure. The development of patient-specific dosimetry calculations, as are routinely employed in external beam radiotherapy, is therefore of increasing importance for personalised cancer treatment in nuclear medicine.

An introduction to some of the radionuclide therapies performed at the Royal Marsden Hospital and the MIRD (Medical Internal Radiation Dose) approach used in clinical dosimetry will be presented. A retrospective study on personalised dosimetry calculations for cystic brain tumours treated with intracavitary 32P chromic phosphate radiocolloid will be discussed in more detail. This study showed the necessity of incorporating patient-specific 3D voxel Monte Carlo dosimetry methods into clinical protocols, with the potential to benefit treatment planning and improve therapy outcome.