A free database of radionuclide voxel S values for the dosimetry of nonuniform activity distributions

Abstract

The increasing availability of SPECT/CT devices with advanced technology offers the opportunity for the accurate assessment of the radiation dose to the biological target volume during radionuclide therapy. Voxel dosimetry can be performed employing direct Monte Carlo radiation transport simulations, based on both morphological and functional images of the patient. On the other hand, for voxel dosimetry calculations the voxel S value method can be considered an easier approach than patient-specific Monte Carlo simulations, ensuring a good dosimetric accuracy at least for anatomic regions which are characterized by uniform density tissue. However, this approach has been limited because of the lack of tabulated S values for different voxel dimensions and radionuclides. The aim of this work is to provide a free dataset of values which can be used for voxel dosimetry in targeted radionuclide studies. Seven different radionuclides (89Sr, 90Y, 131I, 153Sm, 177Lu, 186Re, 188Re), and 13 different voxel sizes (2.21, 2.33, 2.4, 3, 3.59, 3.9, 4, 4.42, 4.8, 5, 6, 6.8 and 9.28 mm) are considered. Voxel S values are calculated performing simulations of monochromatic photon and electron sources in two different homogeneous tissues (soft tissue and bone) with DOSXYZnrc code, and weighting the contributions on the basis of the radionuclide emission spectra. The outcomes are validated by comparison with Monte Carlo simulations obtained with other codes (PENELOPE and MCNP4c) performing direct simulation of the radionuclide emission spectra. The differences among the different Monte Carlo codes are of the order of a few per cent when considering the source voxel and the bremsstrahlung tail, whereas the highest differences are observed at a distance close to the maximum continuous slowing down approximation range of electrons. These discrepancies would negligibly affect dosimetric assessments. The dataset of voxel S values can be freely downloaded from the website www.medphys.it.

Impact of SPECT corrections on 3D‐dosimetry for liver transarterial radioembolization using the patient relative calibration methodology

“…16 An optimal treatment planning should include 3D voxelbased dosimetry, accounting for nonuniform absorbed dose distributions when studying dose-effect correlations. 9,[17][18][19][20][21][22][23] Image-based 3D dosimetry can be performed in several ways: direct Monte Carlo (MC) simulation, which is considered the gold standard; 9,[24][25][26][27][28][29][30] convolution calculations by voxel S-values, reliable in nearly uniform density tissue; 19,[31][32][33][34][35][36] local energy deposition method. 18,20,[36][37][38][39] Activity distribution quantification by SPECT is the major concern, due to physical and clinical degrading factors of the images.…”

Comparison of Macrodosimetric Efficacy of Transarterial Radioembolization (TARE) by Using 90Y Microspheres of Different Density of Activity

“…The mass of the target was 100 g, its density was 1.04 g/cm 3 , that is the density of the soft tissues [9]. The activity needed for an average target absorbed dose of 100 Gy was calculated by using the MIRD formalism:…”

“…The Si←h values for the voxel size of 2.21 mm were taken [9] Note that Ah is the activity in each h voxel, calculated by multiplying the number of microspheres randomly placed in that voxel by the density of activity δ a .…”

A review of 3D image-based dosimetry, technical considerations and emerging perspectives in 90Y microsphere therapy

“…MIRD pamphlet 17 originally produced VSVs for 3 voxel sizes and 5 isotopes although more recent work expanded these tables using simulations within the EGSnrc toolkit (and validated with PENELOPE and MCNP4c codes) with more isotopes and a larger range of voxel sizes more suited to modern scanners [94]. These VSV matrices are freely available 3 .…”

“…RE typically employs 90-yttrium microspheres ( 90 Y-MS -β-emitter, t ½ =64.2 hours, E β(av) =0. 94 MeV, average tissue penetration = 2.5 mm max. range = 1.1 cm) of which there are currently two types commercially available; a glass microsphere (TheraSphere, BTG Inc./MDS Nordion Inc., Ottawa, Canada) and a resin microsphere (SIRTeX Medical Ltd, Sydney, Australia) hereon denoted GMS and RMS respectively.…”