Relevance of Monte Carlo modelling in quantitative imaging and dosimetry in targeted therapy

 

PD Habib ZAIDI, Ph.D

 

Geneva University Hospital, Division of Nuclear Medicine, CH-1211 Geneva, Switzerland

Email: habib.zaidi@hcuge.ch

Web: http:dmnu-pet5.hcuge.ch/

 

Abstract. There is no doubt that the area where early Monte Carlo calculations in the field of medical physics have been performed is internal dosimetry computations and modelling of nuclear medicine instrumentation. The approach adopted by the Medical Internal Radiation Dose (MIRD) committee for a so-called macrodose calculation make extensive use of Monte Carlo calculations to derive specific absorbed fractions for electron and photon sources uniformly distributed in organs of mathematical phantoms. Nowadays, the applications of the Monte Carlo method in nuclear medicine cover almost all topics including detector modelling and imaging systems design, the assessment of image quality and the quantitative accuracy of radionuclide imaging including development and assessment of image correction and reconstruction techniques, pharmacokinetic modelling, with an increasing enthusiastic interest in exotic and exciting new applications such as on-line PET monitoring of radiation therapy beams. This trend has continued during the last decade and it is expected that Monte Carlo simulation techniques will find an increasingly important role in the future of applications of quantitative imaging and radiation dosimetry in targeted radiotherapy.

This lecture begins with an introduction to fundamental concepts in image reconstruction and quantification. Impact of physical degrading factors in radionuclides imaging including attenuation of photons and contribution from photons scattered in the patient and partial volume effect on diagnostic quality and quantitative accuracy of reconstructed images will be discussed. The specific role of Monte Carlo simulations for the development and assessment of quantitative imaging methodologies and patient-specific 3D dosimetry computations for treatment planning in targeted therapy will be highlighted and illustrated with examples from research carried out at the PET Instrumentation and Neuroimaging Laboratory of Geneva University Hospital and other research labs active in this field.

The combination of accurate models of the imaging process allows the simulation of nuclear medicine data that are ever closer to actual patient data. Monte Carlo simulation techniques will find an increasingly important role in the future of nuclear medicine in light of the further development of realistic computer phantoms, the accurate modelling of projection data and computer hardware. However, caution must be taken to avoid errors in the simulation process, and verification via comparison with experimental and patient data is essential.