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.
Purpose
Pathological complete response (pCR) following neoadjuvant chemoradiotherapy or radiotherapy in locally advanced rectal cancer (LARC) is reached in approximately 15–30% of cases, therefore it ...would be useful to assess if pretreatment of
18
F-FDG PET/CT and/or MRI texture features can reliably predict response to neoadjuvant therapy in LARC.
Methods
Fifty-two patients were dichotomized as responder (pR+) or non-responder (pR-) according to their pathological tumor regression grade (TRG) as follows: 22 as pR+ (nine with TRG = 1, 13 with TRG = 2) and 30 as pR- (16 with TRG = 3, 13 with TRG = 4 and 1 with TRG = 5). First-order parameters and 21 second-order texture parameters derived from the Gray-Level Co-Occurrence matrix were extracted from semi-automatically segmented tumors on T2w MRI, ADC maps, and PET/CT acquisitions. The role of each texture feature in predicting pR+ was assessed with monoparametric and multiparametric models.
Results
In the mono-parametric approach, PET homogeneity reached the maximum AUC (0.77; sensitivity = 72.7% and specificity = 76.7%), while PET glycolytic volume and ADC dissimilarity reached the highest sensitivity (both 90.9%). In the multiparametric analysis, a logistic regression model containing six second-order texture features (five from PET and one from T2w MRI) yields the highest predictivity in distinguish between pR+ and pR- patients (AUC = 0.86; sensitivity = 86%, and specificity = 83% at the Youden index).
Conclusions
If preliminary results of this study are confirmed, pretreatment PET and MRI could be useful to personalize patient treatment, e.g., avoiding toxicity of neoadjuvant therapy in patients predicted pR-.
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.
Purpose and objective
To test the hypothesis that a rectal and bladder preparation protocol is associated with an increase in prostate cancer specific survival (PCSS), clinical disease free survival ...(CDFS) and biochemical disease free survival (BDFS).
Patients and methods
From 1999 to 2012, 1080 prostate cancer (PCa) patients were treated with three-dimensional conformal radiotherapy (3DCRT). Of these patients, 761 were treated with an empty rectum and comfortably full bladder (RBP) preparation protocol, while for 319 patients no rectal/bladder preparation (NRBP) protocol was adopted.
Results
Compared with NRBP patients, patients with RBP had significantly higher BDFS (64% vs 48% at 10 years, respectively), CDFS (81% vs 70.5% at 10 years, respectively) and PCSS (95% vs 88% at 10 years, respectively) (log-rank test
p
< 0.001). Multivariate analysis (MVA) indicated for all treated patients and intermediate high-risk patients that the Gleason score (GS) and the rectal and bladder preparation were the most important prognostic factors for PCSS, CDFS and BDFS. With regard to high- and very high-risk patients, GS, RBP, prostate cancer staging and RT dose were predictors of PCSS, CDFS and BDFS in univariate analysis (UVA).
Conclusion
We found strong evidence that rectal and bladder preparation significantly decreases biochemical and clinical failures and the probability of death from PCa in patients treated without daily image-guided prostate localization, presumably since patients with RBP are able to maintain a reproducibly empty rectum and comfortably full bladder across the whole treatment compared with NRPB patients.
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.
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