DPK AND EDK THEORY AND APPLICATIONS ON NUCLEAR MEDICINE DOSIMETRY

P. PEREZ; M. VALENTE; F. MALANO

Carlos Paz

Congreso; 7mo Congreso ALFIM & 13avo Congreso SAFIM; 2016

ALFIM & SAFIM

p { margin-bottom: 0.1in; direction: ltr; line-height: 120%; text-align: left; widows: 2; orphans: 2; }a:link { color: rgb(0, 0, 255); }Medicalpractices using radiopharmaceuticals based on alpha-, beta- andgamma-emitters radionuclides are commonly used in clinics withdifferent purposes, like neoplasic disease diagnose and treatment.The main reason of its use in nuclear medicine procedures becomesfrom their capability of localizing specific receptors like organs orcell groups, and from their ionizing radiation physicscharacteristics when interacting with human tissues. Energiesinvolved in radiopharmaceuticals irradiated spectra usually utilizedfor treatment purposes result in the need of analyzing radionuclidesperformance aiming at minimizing their potential damage or sideeffects to nearby tissues.Internaldosimetry framework attempts to calculate the corresponding radiationdose and the radiobiological quantities needed for estimating thepotential risks and the therapy effectiveness. Direct invivoabsorbed dose measurements might be the best option, but it resultsdifficult to implement in daily clinical practices. Then, thedelivered dose distribution within the patient needs to be inferredfollowing an internal dosimetry schema provided with biokineticmodels. For indirect dose assessment there are at least threeacceptable and widespread methods: the dosimetric schema based on theuse of S values, the dose distribution calculated from theconvolution of dose kernels and the delivered energy estimation bymeans of Monte Carlo radiation transport simulations.It is wellknown that the Monte Carlo technique constitutes the more accuratelycompute of absorbed dose in non homogeneous media accounting fordifferent tissues, but its elevated computational costs and timeconsuming in each simulation for a reliable dose assessment make thisoption not suitable for daily clinical use up today.The aim ofthis work is to provide a general overview of the basic physics forinternal dosimetry as well as to implement some methodologies thatmight be useful for nuclear medicine practices. The lack ofintegrated frameworks for computing dose distribution by differentapproaches analytical, deterministic and/or stochastic, organ and/orvoxel level, accounting or not for biokinetic, consideringsimultaneously alpha, beta and gamma emitters and including or nottissue inhomogeneities, highlights the relevance and potentialbenefits of the present work.In order toprovide a simplified calculation tool, all proposed models wereimplemented and integrated in dedicated software named DOSIS. Itincludes a user-friendly interface devoted to get the desireddosimetric approach guiding the user through the differentimplemented modalities. Planar dosimetry is performed usingscintillographic images and accounting for corresponding biokineticmodels. Patient SPECT-CT or PET-CT images are used for organ leveldosimetry as well as 3D voxel level methods by kernel convolution orfull stochastic calculations. This paper shows advances in thedevelopment of a novel calculation system aiming at integrating thedifferent steps involved in an internal dosimetry assessmentconsidering different calculation methods.