Minicursos

Medicina Nuclear/Nuclear Medicine

Internal dosimetry with 177-Lu

 

Michael Ljungberg, PhD, professor
Department of Medical Radiation Physics, Clinical Sciences Lund, Lund University, Sweden

 

Peptide receptor radiotherapy (PRRT) using 177-Lu-DOTATATE is currently being given for treatment of neuroendocrine tumours. The most commonly applied protocol is four treatments separated by approximately 2-3 months. The dose limiting organs are the bone marrow and the kidneys. The bone marrow function is regularly monitored by clinical means. Kidneys are late responding and their reaction cannot be monitored close to therapy. Their tolerance in terms of absorbed dose or biologically effective dose (BED) have not yet been generally established but in Lund, our clinical protocol use BED limits of 27 Gy (Step 1) or 40 Gy (Step 2), depending on the presence of risk factors. Based on these limits the number of treatments is calculated for individual patient based on accurate dosimetry, with the hypothesis that this individualization will provide a better tumour response than fixed four treatments given to all patients.

 

These lectures will describe the methodology behind 177-Lu dosimetry and the headlines will be as follows.

 

  1. Overview of the general MIRD formalism for internal dosimetry and how this is applicable also for patient-specific 177-Lu dosimetry.
  2. Problem associated with obtaining quantitative 3D SPECT images of the 177-Lu activity distribution over the time-points.
  3. MIRD Pamphlet #23 and #26 guidelines for quantitative SPECT in general and for 177-Lu, respectively.
  4. Different types of dosimetry methods going from quantitative 3D SPECT images to image-based absorbed dose maps
  5. Clinical experiences of our ongoing 177-Lu-DOTATATE clinical trial at the Lund University Hospital.
  6. Monte Carlo simulations of medical imaging of 177-Lu. Part of these lectures will also focus on the Monte Carlo program SIMIND in general and how this program can be used to evaluate the dosimetry calculations based on SPECT and on planar imaging.