title: Differences in 3D dose distributions due to calculation method of voxel S-values and the influence of image blurring in SPECT.
abstract: This study compares 3D dose distributions obtained with voxel S values (VSVs) for soft tissue, calculated by several methods at their current state-of-the-art, varying the degree of image blurring. The methods were: 1) convolution of Dose Point Kernel (DPK) for water, using a scaling factor method; 2) an analytical model (AM), fitting the deposited energy as a function of the source-target distance; 3) a rescaling method (RSM) based on a set of high-resolution VSVs for each isotope; 4) local energy deposition (LED). VSVs calculated by direct Monte Carlo simulations were assumed as reference. Dose distributions were calculated considering spheroidal clusters with various sizes (251, 1237 and 4139 voxels of 3 mm size), uniformly filled with (131)I, (177)Lu, (188)Re or (90)Y. The activity distributions were blurred with Gaussian filters of various widths (6, 8 and 12 mm). Moreover, 3D-dosimetry was performed for 10 treatments with (90)Y derivatives. Cumulative Dose Volume Histograms (cDVHs) were compared, studying the differences in D95%, D50% or Dmax (ΔD95%, ΔD50% and ΔDmax) and dose profiles.For unblurred spheroidal clusters, ΔD95%, ΔD50% and ΔDmax were mostly within some percents, slightly higher for (177)Lu with DPK (8%) and RSM (12%) and considerably higher for LED (ΔD95% up to 59%). Increasing the blurring, differences decreased and also LED yielded very similar results, but D95% and D50% underestimations between 30-60% and 15-50%, respectively (with respect to 3D-dosimetry with unblurred distributions), were evidenced. Also for clinical images (affected by blurring as well), cDVHs differences for most methods were within few percents, except for slightly higher differences with LED, and almost systematic for dose profiles with DPK (-1.2%), AM (-3.0%) and RSM (4.5%), whereas showed an oscillating trend with LED.The major concern for 3D-dosimetry on clinical SPECT images is more strongly represented by image blurring than by differences among the VSVs calculation methods. For volume sizes about 2-fold the spatial resolution, D95% and D50% underestimations up to about 60 and 50% could result, so the usefulness of 3D-dosimetry is highly questionable for small tumors, unless adequate corrections for partial volume effects are adopted.
authors: Department of Medical Physics, Azienda Ospedaliera San Camillo Forlanini, Rome, Italy.
authors: Massimiliano
authors: M
authors: Pacilio
authors: Ernesto
authors: E
authors: Amato
authors: Nico
authors: N
authors: Lanconelli
authors: Chiara
authors: C
authors: Basile
authors: Leonel Alberto
authors: LA
authors: Torres
authors: Francesca
authors: F
authors: Botta
authors: Mahila
authors: M
authors: Ferrari
authors: Nestor Cornejo
authors: NC
authors: Diaz
authors: Marco Coca
authors: MC
authors: Perez
authors: María
authors: M
authors: Fernández
authors: Michael
authors: M
authors: Lassmann
authors: Alex Vergara
authors: AV
authors: Gil
authors: Marta
authors: M
authors: Cremonesi
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008099:Liver / Q000000981:diagnostic imaging*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D012984:Software; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*; D015021:Yttrium Radioisotopes / Q000493:pharmacokinetics*
chemical_list: D019275:Radiopharmaceuticals; D015021:Yttrium Radioisotopes