Patient-specific absorbed dose calculation for nuclear medicine therapy is a topic of increasing interest. 3D dosimetry at the voxel level is one of the major improvements for the development of more ...accurate calculation techniques, as compared to the standard dosimetry at the organ level. This study aims to use the FLUKA Monte Carlo code to perform patient-specific 3D dosimetry through direct Monte Carlo simulation on PET-CT and SPECT-CT images. To this aim, dedicated routines were developed in the FLUKA environment. Two sets of simulations were performed on model and phantom images. Firstly, the correct handling of PET and SPECT images was tested under the assumption of homogeneous water medium by comparing FLUKA results with those obtained with the voxel kernel convolution method and with other Monte Carlo-based tools developed to the same purpose (the EGS-based 3D-RD software and the MCNP5-based MCID). Afterwards, the correct integration of the PET/SPECT and CT information was tested, performing direct simulations on PET/CT images for both homogeneous (water) and non-homogeneous (water with air, lung and bone inserts) phantoms. Comparison was performed with the other Monte Carlo tools performing direct simulation as well. The absorbed dose maps were compared at the voxel level. In the case of homogeneous water, by simulating 10(8) primary particles a 2% average difference with respect to the kernel convolution method was achieved; such difference was lower than the statistical uncertainty affecting the FLUKA results. The agreement with the other tools was within 3–4%, partially ascribable to the differences among the simulation algorithms. Including the CT-based density map, the average difference was always within 4% irrespective of the medium (water, air, bone), except for a maximum 6% value when comparing FLUKA and 3D-RD in air. The results confirmed that the routines were properly developed, opening the way for the use of FLUKA for patient-specific, image-based dosimetry in nuclear medicine.
Purpose: The calculation of patient-specific dose distribution can be achieved by Monte Carlo simulations or by analytical methods. In this study, fluka Monte Carlo code has been considered for use ...in nuclear medicine dosimetry. Up to now, fluka has mainly been dedicated to other fields, namely high energy physics, radiation protection, and hadrontherapy. When first employing a Monte Carlo code for nuclear medicine dosimetry, its results concerning electron transport at energies typical of nuclear medicine applications need to be verified. This is commonly achieved by means of calculation of a representative parameter and comparison with reference data. Dose point kernel (DPK), quantifying the energy deposition all around a point isotropic source, is often the one.Methods:
fluka
DPKs have been calculated in both water and compact bone for monoenergetic electrons (10–3 MeV) and for beta emitting isotopes commonly used for therapy (89Sr, 90Y, 131I, 153Sm, 177Lu, 186Re, and 188Re). Point isotropic sources have been simulated at the center of a water (bone) sphere, and deposed energy has been tallied in concentric shells. fluka outcomes have been compared to penelope v.2008 results, calculated in this study as well. Moreover, in case of monoenergetic electrons in water, comparison with the data from the literature (etran, geant
4, mcnpx) has been done. Maximum percentage differences within 0.8·R
CSDA and 0.9·R
CSDA for monoenergetic electrons (R
CSDA being the continuous slowing down approximation range) and within 0.8·X90 and 0.9·X90 for isotopes (X90 being the radius of the sphere in which 90% of the emitted energy is absorbed) have been computed, together with the average percentage difference within 0.9·R
CSDA and 0.9·X90 for electrons and isotopes, respectively.Results: Concerning monoenergetic electrons, within 0.8·R
CSDA (where 90%–97% of the particle energy is deposed), fluka and penelope agree mostly within 7%, except for 10 and 20 keV electrons (12% in water, 8.3% in bone). The discrepancies between fluka and the other codes are of the same order of magnitude than those observed when comparing the other codes among them, which can be referred to the different simulation algorithms. When considering the beta spectra, discrepancies notably reduce: within 0.9·X90, fluka and penelope differ for less than 1% in water and less than 2% in bone with any of the isotopes here considered. Complete data of fluka
DPKs are given as Supplementary Material as a tool to perform dosimetry by analytical point kernel convolution.Conclusions:
fluka provides reliable results when transporting electrons in the low energy range, proving to be an adequate tool for nuclear medicine dosimetry.
Peptide Receptor Radionuclide Therapy (PRRT) has proven its efficacy in the treatment of neuroendocrine and other somatostatin receptor expressing tumours (SR-tumours). Several clinical trials have ...confirmed that adverse effects are represented by possible renal impairment, which is the major concern, and low but not absent hematological toxicity. High kidney irradiation is a constant, despite the sparing of dose obtained by renal protectors. Hematological toxicity, although low, needs to be monitored. The clinical and dosimetry results collected in more than a decade have recognized weak points to unravel, increased knowledge, offering new views. When planning therapy with radiopeptides, the large patients' variability as for biodistribution and tumour uptake must be taken into account in order to tailor the therapy, or at least to avoid foreseeable gross treatments. Reliable and personalized dosimetry is more and more requested. This paper reviews through the literature the methods to study the biokinetics, the dosimetry outcomes, some clue information and correlations obtained once applying the radiobiological models. Special focus is given on recent improvements and indications for critical organ protection that light up challenging perspectives for PRRT.
•Test on radiomarked ex-vivo meningioma specimens confirmed feasibility of β-RGS.•Personalized minimal activity to be injected can be evaluated from PET images.•Effective dose is at a level of ...whole-body PET/CT and personnel exposure negligible.
Radio-guided surgery with β- decays is a novel technique under investigation. One of the main advantages is its capability to detect small (⩽0.1 ml) samples after injecting the patient with low activity of radiopharmaceutical. This paper presents an experimental method to quantify this feature based on ex-vivo tests on specimens from meningioma patients.
Patients were enrolled on the basis of the standard uptake value (SUV) and the tumour-to-non-tumour activity ratio (TNR) resulted from 68Ga-DOTATOC PET exams. After injecting the patients with 93–167 MBq of 90Y-DOTATOC, 26 samples excised during surgery were analyzed with a β- probe. The radioactivity expected on the neoplastic specimens was estimated according to the SUV found in the PET scan and the correlation with the measured counts was studied. The doses to surgeon and medical personnel were also evaluated.
Even injecting as low as 1.4 MBq/kg of radiotracer, tumour residuals of 0.1 ml can be detected. A negligible dose to the medical personnel was confirmed.
Radio-guided surgery with β- decays is a feasible technique with a low radiation dose for both personnel and patient, in particular if the patient is injected with the minimum required activity. A correlation greater than 80% was observed between the measured counts and the expected activity for the lesion samples based on the individual SUV and the TNR. This makes identifiable the minimum injectable radiotracer activity for cases where 90Y is the utilized radionuclide.
Highlights • A novel radio-guided-surgery technique using beta- radiation is under development. • Simulations and lab tests demonstrated its potential compared to state-of-the-art. • A ...proof-of-principle test on patient confirmed tracer uptake and probe sensitivity. • It also confirmed that the dose delivered to the medical staff is negligible. • This is a proof-of-principle, not a case report, nor a clinical trial.
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