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• We measured the absorbed dose to water, Dw, using. • LiF:Mg,Cu,P chips inside a liquid solution containing 90YCl 3. • We assessed the uncertainty budget related to Dw measurement. • We compared Dw measurements with Monte Carlo calculations. • Dw measurements from 90Y radionuclide solution using LiF:Mg,Cu,P TLDs turned out to be a viable technique. • Using this method, a relative combined standard uncertainty in the range 3.1–3.7% was obtained on each Dw measurement. In the last few years there has been an increasing interest in the measurement of the absorbed dose from radionuclides, with special attention devoted to molecular radiotherapy treatments. In particular, the determination of the absorbed dose from beta emitting radionuclides in liquid solution poses a number of issues when dose measurements are performed using thermoluminescent dosimeters (TLD). Finite volume effect, i.e. the exclusion of radioactivity from the volume occupied by the TLD is one of these. Furthermore, TLDs need to be encapsulated into some kind of waterproof envelope that unavoidably contributes to beta particle attenuation during the measurement. The purpose of this study is twofold: I) to measure the absorbed dose to water, D w , using LiF:Mg,Cu,P chips inside a PMMA cylindrical phantom filled with a homogenous 90YCl 3 aqueous solution II) to assess the uncertainty budget related to D w measurements. To this purpose, six cylindrical PMMA phantoms were manufactured at ENEA. Each phantom can host a waterproof PMMA stick containing 3 TLD chips encapsulated by a polystyrene envelope. The cylindrical phantoms were manufactured so that the radioactive liquid environment surrounds the whole stick. Finally, D w measurements were compared with Monte Carlo (MC) calculations. The measurement of absorbed dose to water from 90YCl 3 radionuclide solution using LiF:Mg,Cu,P TLDs turned out to be a viable technique, provided that all necessary correction factors are applied. Using this method, a relative combined standard uncertainty in the range 3.1–3.7% was obtained on each D w measurement. The major source of uncertainty was shown to be TLDs calibration, with associated uncertainties in the range 0.7–2.2%. Comparison of measured and MC-calculated absorbed dose per emitted beta particle provided good results, with the two quantities being in the ratio 1.08. [ABSTRACT FROM AUTHOR]

Purpose Radioembolization (RE) with 90 Y-microspheres is a well-established treatment modality for treating liver malignancies. At a time of increasing evidence for dose–effect relationships in RE with 90 Y microspheres [1,2] , the general consensus is that there is an urgent need for accurate dosimetry in patients undergoing RE treatment. This work aimed at estimating absorbed doses to lesions and normal liver in a novel anthropomorphic set-up. Methods AbdoMan is a 3D-printed phantom provided with a fillable liver section and multiple inserts for lesion representation. A SPECT/CT Symbia Intevo provided with the proprietary xSPECT quantitative software was used to image the phantom according to the acquisition protocol currently used for RE patients. Specific regions of interest (ROIs) were drawn on MIM 6.1.7 system. A homemade tool was developed in MATLAB for image analysis and dose calculation based on two methods: I) convolution kernel and II) local deposition method. The accuracy of the two different dosimetric methods was evaluated by comparing dose-rate volume histograms (DrVHs). Moreover, γ -index was used to compare the dose distributions obtained by the two activity-to-dose methods. Results Differences calculated by the 3D γ -index are within 2%-2 mm for all AbdoMan inserts. The dose-kernel results in a γ  < 1. The deposition method provided a poorest γ as well as several image artefacts. In particular, an apparent over-dosage (about 25%) was observed in inserts with larger diameter, most likely due to spill-in and spill-out phenomena. The DrVHs for considered ROIs are within 2%-2 mm for both methods. Conclusions In RE treatment planning the dose-kernel method proved to be more accurate with respect to deposition method based on full 3D dose distributions. [ABSTRACT FROM AUTHOR]

Purpose The high dose per pulse of electron beams produced by some mobile accelerators for intraoperative radiotherapy can affect output factor (OF) measurements, since the dose rate increases by a factor larger than two from the reference to the smallest radiation field. Aim of this work was to assess the capability of different types of detectors to measure OFs at high dose per pulse by comparison with alanine dosimeters, which are independent of dose rate. Methods Measurements were made in 9 and 7 MeV electron beams produced by a Novac 7 accelerator. PMMA cylindrical applicators with diameter of 100 mm (reference field), 70 mm, 60 mm, 50 mm and 40 mm were used. The dose per pulse varied from about 30 mGy, for the 100 mm applicator, to about 70 mGy, for the 40 mm applicator. OFs were determined using four types of plane-parallel ionization chambers (PTW Advanced Markus and Roos, IBA PPC40 and PPC05), two types of silicon diodes (PTW 60017 and IBA 3FG-3D), a PTW microDiamond and alanine dosimeters. Ionization chamber signals were corrected for ion recombination effects using a modified two-voltage-analysis method that includes the free-electron component. Results A fairly good agreement was found between OFs measured by the three types of solid-state detectors and those measured by alanine. Differences were generally below 1% and maximum discrepancies around 2%. For the Advanced Markus and the PPC05 chambers differences from alanine results were below 1.7%. For the Roos and the PPC40 chambers agreement with alanine was within 2.3% down to the 50 mm applicator, while differences of several percent were found for the smallest applicator, most likely due to volume averaging effect. The variation of ion recombination correction factor with field size was below 1% for the Advanced Markus and the PPC05 chambers and up to about 10% for the Roos and the PPC40 chambers. Conclusions Comparison with alanine measurements demonstrated that all the detectors considered in this work can be used to measure OFs in high-dose-per-pulse electron beams with an accuracy of 2%, provided that appropriate corrections for ion recombination effects are applied when using ionization chambers. [ABSTRACT FROM AUTHOR]

Purpose Radioembolization (RE) with 90 Y-microspheres has gained widespread acceptance as a safe and effective technique for treating liver malignancies. Accurate quantification in RE is a key step in treatment planning optimization and it is becoming a pressing issue in the light of the Directive 2013/59/EURATOM, stating that individual dose planning must be enforced in legislation by EU member states by February 2018. The aim of this study was to develop a SPECT/CT imaging protocol for quantitative imaging optimization in RE based on a novel anthropomorphic 3D-printed phantom. Methods and materials A SPECT/CT system provided with a novel software for imaging quantification was used to assess the quantitative accuracy of 99m Tc-MAA SPECT imaging for treatment planning in RE. Gamma camera calibration factors and recovery coefficients were determined performing preliminary SPECT/CT acquisitions of a homogeneous and a NEMA/IEC phantom, respectively. The quantification procedure was then validated using a 3D-printed anthropomorphic phantom provided with a fillable liver section and multiple inserts. Raw data reconstruction was performed using two independent software: i) the built-in xSPECT package, using both the Ordered Subset Expectation–Maximization (OSEM) and the Ordered Subset Conjugated Gradient (OSCG) algorithm; ii) the commercially available QSPECT software based on OSEM method. All reconstructed images were manually fused and appropriate regions of interest (ROIs) were drawn on the MIM 6.1.7 system. Results The measured activity concentration is consistent within 3% with the expected activity concentration values. This is in keeping with the overall accuracy ( < 10%) stated by the manufacturer. No substantial differences were reported between xSPECT with OSCG or OSEM in terms of relative activity. However, a 20% difference was found between ROIs extracted from images reconstructed with xSPECT and QSPECT using OSEM. Several artifacts were visible in the QSPECT reconstruction, likely due to the limited area used for attenuation and scatter corrections within the software. Conclusions The investigated protocol based on the innovative xSPECT tool allows an accurate absolute quantification within 3%. QSPECT software provides the poorest results with several artifacts as well as intrinsic dishomogeneities. [ABSTRACT FROM AUTHOR]