Monte Carlo methods in nuclear medicine

Auditore, L.; Pistone, Daniele; Amato, Ernesto; Italiano, A.

doi:10.1016/b978-0-12-822960-6.00136-8

Cited by 4 publications

(2 citation statements)

References 192 publications

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“…The Monte Carlo (MC) estimation of DPKs [9][10][11][12][13] is accomplished by scoring the energy deposited in concentric spherical shells, made of water or soft tissue, and reporting this distribution as a function of the distance from the source. Although MC simulation have reached high levels of accuracy also in terms of the implemented physics, general purpose MC codes such as Geant4, MCNP and FLUKA do not include among their physics processes the Internal Bremsstrahlung (IB).…”

Section: Introductionmentioning

confidence: 99%

Technical note: The contribution of internal bremsstrahlung to the ⁹⁰Y dose point kernel

et al. 2023

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Background: Internal dosimetry has an increasing role in the planning and verification of nuclear medicine therapies with radiopharmaceuticals. Dose Point Kernels (DPKs), quantifying the energy deposition all around a point source, in a homogenous medium, are extensively used for 3D dosimetry and nowadays are mostly evaluated by Monte Carlo (MC) simulation. To our knowledge, DPK for beta emitters is estimated neglecting the continuous photon emission due to the Internal Bremsstrahlung (IB), whose contribution to the absorbed dose can be relevant beyond the maximum range of betas, as evidenced in recent works. Purpose: Aim of this study was to investigate and quantify, by means of MC simulations,the contribution of IB photons to DPK calculated for 90 Y and provide the updated 90 Y DPK. Methods: The overall radiation due to the decay of a 90 Y point source, placed at the centre of concentric water shells of increasing radii from 0.02 cm to 20 cm, was simulated with GAMOS, including the IB source term whose spectral distribution was described by an analytical model.Energy deposition was scored in the shells as a function of the distance from the source, R, and DPK was estimated in terms of the scaled absorbed dose fraction, F(R/X 90 ), where X 90 is the range within which the beta particles deposit 90% of their energy. Results: A comparison between the two simulated absorbed dose distributions, calculated with or without IB, clearly shows that the latter (incomplete) choice is consistent with the findings of other Authors and systematically underestimates the absorbed dose imparted to the tissue. 90 Y DPK values currently used are underestimated by 20%-34% for R>2X 90 . Conclusions:The revised values provided in this work suggest that the inclusion of IB emission in DPK evaluations is advisable for pure beta emitters.

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Section: Introductionmentioning

confidence: 99%

Technical note: The contribution of internal bremsstrahlung to the ⁹⁰Y dose point kernel

et al. 2023

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“…3 DVKs are generally calculated exploiting MC simulations. 4 However, different MC codes and different processes-for example, direct MC simulation, MC-based volume integration of a dose-point kernel (DPK), which is the radial distribution of the AD per decay event due to an isotropic point source located inside a virtually infinite and homogeneous absorbing medium, and MC-derived analytical methods-have been adopted by different authors to generate the actual DVKs from simulations. Even if some sets of DVKs have been compared to each other, 5 to our knowledge, no specific investigation of the impact of using different DVKs on the AD calculation has been carried out yet in a systematic manner.…”

Section: Introductionmentioning

confidence: 99%

Technical note: Impact of dose voxel kernel (DVK) values on dosimetry estimates in ¹⁷⁷Lu and ⁹⁰Y radiopharmaceutical therapy (RPT) applications

Danieli,

Pistone,

Tranel

et al. 2023

Medical Physics

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BackgroundRadiopharmaceutical therapy (RPT) is an increasingly adopted modality for treating cancer. There is evidence that the optimization of the treatment based on dosimetry can improve outcomes. However, standardization of the clinical dosimetry workflow still represents a major effort. Among the many sources of variability, the impact of using different Dose Voxel Kernels (DVKs) to generate absorbed dose (AD) maps by convolution with the time‐integrated activity (TIA) distribution has not been systematically investigated.PurposeThis study aims to compare DVKs and assess the differences in the ADs when convolving the same TIA map with different DVKs.MethodsDVKs of 3 × 3 × 3 mm3 sampling—nine for 177Lu, nine for 90Y—were selected from those most used in commercial/free software or presented in prior publications. For each voxel within a 11 × 11 × 11 matrix, the coefficient of variation (CoV) and the percentage difference between maximum and minimum values (% maximum difference) were calculated. The total absorbed dose per decay (SUM), calculated as the sum of all the voxel values in each kernel, was also compared. Publicly available quantitative SPECT images for two patients treated with 177Lu‐DOTATATE and PET images for two patients treated with 90Y‐microspheres were used, including organs at risk (177Lu: kidneys; 90Y: liver and healthy liver) and tumors’ segmentations. For each patient, the mean AD to the volumes of interest (VOIs) was calculated using the different DVKs, the same TIA map and the same software tool for dose convolution, thereby focusing on the DVK impact. For each VOI, the % maximum difference of the mean AD between maximum and minimum values was computed.ResultsThe CoV (% maximum difference) in voxels of normalized coordinates [0,0,0], [0,1,0], and [0,1,1] were 5%(21%), 9%(35%), and 10%(46%) for the 177Lu DVKs. For the case of 90Y, these values were 2%(9%), 4%(14%), and 4%(16%). The CoV (% maximum difference) for SUM was 9%(33%) for 177Lu, and 4%(15%) for 90Y. The variability of the mean tumor and organ AD was up to 19% and 15% in 177Lu‐DOTATATE and 90Y‐microspheres patients, respectively.ConclusionsThis study showed a considerable AD variability due exclusively to the use of different DVKs. A concerted effort by the scientific community would contribute to decrease these discrepancies, strengthening the consistency of AD calculation in RPT.

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An analytic model to calculate voxel s-values for ¹⁷⁷Lu

Pistone¹,

Auditore²,

Italiano³

et al. 2022

Biomed. Phys. Eng. Express

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Objective: 177Lu is one of the most employed isotopes in targeted radionuclide therapies and theranostics, and 3D internal dosimetry for such procedures has great importance. Voxel S-Values (VSVs) approach is widely used for this purpose, but VSVs are available for a limited number of voxel dimensions. The aim of this work is to develop an analytic model for the calculation of 177Lu-VSVs in any cubic voxelized geometry of practical interest. Approach: Monte Carlo (MC) simulations were implemented with the toolkit GAMOS to evaluate VSVs in voxelized geometries of soft tissue from a source of 177Lu homogeneously distributed in the central voxel. Nine geometric setups, containing 15×15×15 cubic voxels of sides l ranging from 2 mm to 6 mm, in steps of 0.5 mm, were considered. For each l, the VSVs computed as a function of the “normalized radius”, Rn = R/l (with R = distance from the center of the source voxel), were fitted with a parametric function. The dependencies of the parameters as a function of l were then fitted with appropriate functions, in order to implement the model for deducing 177Lu-VSVs for any l within the aforementioned range. Main results: The MC-derived VSVs were satisfactorily compared with literature data for validation, and the VSVs computed with the analytic model agree with the MC ones within 2% for Rn ≤ 2 and within 6% for Rn > 2. Significance: The proposed model enables the easy and fast calculation, with a simple spreadsheet, of 177Lu-VSVs in any cubic voxelized geometry of practical interest, avoiding the necessity of implementing ad-hoc MC simulations to estimate VSVs for specific voxel dimensions not available in literature data.

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Monte Carlo methods in nuclear medicine

Cited by 4 publications

References 192 publications

Technical note: The contribution of internal bremsstrahlung to the ⁹⁰Y dose point kernel

Technical note: The contribution of internal bremsstrahlung to the ⁹⁰Y dose point kernel

Technical note: Impact of dose voxel kernel (DVK) values on dosimetry estimates in ¹⁷⁷Lu and ⁹⁰Y radiopharmaceutical therapy (RPT) applications

An analytic model to calculate voxel s-values for ¹⁷⁷Lu

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Monte Carlo methods in nuclear medicine

Cited by 4 publications

References 192 publications

Technical note: The contribution of internal bremsstrahlung to the 90Y dose point kernel

Technical note: The contribution of internal bremsstrahlung to the 90Y dose point kernel

Technical note: Impact of dose voxel kernel (DVK) values on dosimetry estimates in 177Lu and 90Y radiopharmaceutical therapy (RPT) applications

An analytic model to calculate voxel s-values for 177Lu

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Technical note: The contribution of internal bremsstrahlung to the ⁹⁰Y dose point kernel

Technical note: The contribution of internal bremsstrahlung to the ⁹⁰Y dose point kernel

Technical note: Impact of dose voxel kernel (DVK) values on dosimetry estimates in ¹⁷⁷Lu and ⁹⁰Y radiopharmaceutical therapy (RPT) applications

An analytic model to calculate voxel s-values for ¹⁷⁷Lu