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Purpose: To assess the accuracy of volumetric modulated arc therapy (VMAT) stereotactic body radiation therapy (SBRT) when treating moving targets (such as lung or liver lesions), focusing on the impact of the interplay effect in the event of complex breathing motion and when a gating window is used. Methods: A dedicated programmable motion platform was implemented. This platform can carry large quality assurance (QA) phantoms and achieve complex three‐dimensional (3D) motion. Volumetric modulated arc therapy SBRT plans were delivered with TrueBeam linac to this moving setup and the measured dose was compared to the computed one. Several parameters were assessed such as breathing period, dose rate, dose prescription, shape of the breathing pattern, the use of a planning target volume (PTV) margin, and the use of a gating window. Results: Loss of dose coverage (D95%) was acceptable in most situations. The doses received by 95% of the CTV, D95% (CTVm) ranged from 94 to 101% (mean 98%) and the doses received by 2% of the CTV D2% (CTVm) ranged from 94% to 110% of the prescribed dose. A visible interplay effect was observed when no margin was used or when the number of breathing cycles during the treatment delivery was lower than 20. Conclusions: In our clinical context, treating lung and liver lesions using VMAT SBRT is reasonable. The interplay effect was moderated and acceptable in all simulated situations. [ABSTRACT FROM AUTHOR]

A wide range of medical imaging applications benefits from the availability of realistic ground truth data. In the case of positron emission tomography (PET), ground truth data is crucial to validate processing algorithms and assessing their performances. The design of such ground truth data often relies on Monte-Carlo simulation techniques. Since the creation of a large dataset is not trivial both in terms of computing time and realism, we propose the OSSI-PET database containing 350 simulated [^11C]Raclopride dynamic scans for rats, created specifically for the Inveon pre-clinical PET scanner. The originality of this database lies on the availability of several groups of scans with controlled biological variations in the striata. Besides, each group consists of a large number of realizations (i.e., noise replicates). We present the construction methodology of this database using rat pharmacokinetic and anatomical models. A first application using the OSSI-PET database is presented. Several commonly used reconstruction techniques were compared in terms of image quality, accuracy and variability of the activity estimates and of the computed kinetic parameters. The results showed that OP-OSEM3D iterative reconstruction method outperformed the other tested methods. Analytical methods such as FBP2D and 3DRP also produced satisfactory results. However, FORE followed by OSEM2D reconstructions should be avoided. Beyond the illustration of the potential of the database, this application will help scientists to understand the different sources of noise and bias that can occur at the different steps in the processing and will be very useful for choosing appropriate reconstruction methods and parameters. [ABSTRACT FROM AUTHOR]

Purpose Holmium 166 ( 166 Ho) is a potential candidate for internal radiotherapy due to high-energy beta radiation (1.77 and 1.85 MeV) and gamma ray (80.6 keV) adapted to SPECT imaging albeit with poor spatial resolution (cm). The spatial resolution at which activity distribution is determined impacts the absorbed dose calculation algorithm that needs to be implemented: For example, SPECT spatial resolution will often lead to the Local Energy Deposition (LED) approximation. In this study, we investigated the potential of CT for holmium quantification, and compared various absorbed dose calculation algorithms in a context of micro-brachytherapy. Methods For CT calibration, acquisitions were performed on a General Electric BrightSpeed 16 using a CIRS 62 phantom with known holmium concentration in order to get a calibration curve. We then assessed holmium concentration in brain tumours implanted in Yucatan minipigs treated by 166 Ho microbrachytherapy. Acquisition parameters were as follows: voltage = 140 kV; reconstruction filter B31s, matrix size: 512 × 512; pixel size: 0.488 × 0.488 mm 2 ; slice thickness = 0.625 mm. Holmium segmentation was based-on pre and post injection CT image subtraction. From the CT calibration curve, and with a prior knowledge of 166 Ho specific activity, it was possible to get a 3D activity distribution. Different absorbed dose computation approaches were implemented: Local Energy Deposition (LED), superposition/convolution of dose-point kernels assuming homogenous or heterogeneous media, and Monte Carlo modelling (GATE) taken as the reference. Gamma-index criteria (0.1%, 0.5 mm) were used to compare approaches. Results The LED approach was clearly not appropriated due to 166 Ho range vs. CT resolution (0.15% passing rate according to the gamma-index criteria). Homogenous and heterogeneous convolution/superposition approaches provided 78% passing rate in a situation of homogenous soft tissues, compared to GATE. Discrepancies were mainly visible in a situation of heterogeneous densities. Conclusions CT-based holmium quantification can provide relevant density information with good spatial resolution (as compared to SPECT imaging), broadening the possibilities for absorbed dose calculation algorithms. This work was partially sponsored by BPI-France under the scope of the Industrial Strategic Innovation project (projet d’Innovation Stratégique Industrielle) “TheraneaM. [ABSTRACT FROM AUTHOR]

In radiotherapy, some limits of clinical algorithms have been reported in low-density media. When patients are treated during Deep Inspiration Breath-Hold (DIBH), lung density can fall to 0.12 g cm-3. Dose calculation with this density must be validated, in particular for Stereotactic (SBRT) treatment. We propose to evaluate the performance of Eclipse AAA algorithm (Varian) for SBRT lung treatment (including DIBH) with a Monte-Carlo model based on Geant4 (GATE). GATE, AAA, and measurements are compared for several phantoms including lung heterogeneity. A model of the Varian TrueBeam head was modelled using GATE. Validation was achieved by comparison with measurements in a homogeneous water tank for several static fields (3 × 3 to 20 × 20 cm2) and four beam modes. Subsequently, two phantoms containing layers of water-equivalent material and cork, corresponding to lung during DIBH and free-breathing (0.12 and 0.24 g cm-3) were implemented. Percentage depth dose (PDD) measured by Gafchromic films were compared to AAA and GATE. GATE model showed a good agreement with experimental results in homogeneous and heterogeneous phantoms. In lung heterogeneity, differences were observed between AAA and measurements. These differences are higher for small fields and lower densities. As an example, for 3 × 3 field size inside a 0.12 g cm-3 heterogeneity, relative dose was 56,6%, 56,2%, and 67,5% for measurement, GATE, and AAA respectively. In very low densities, AAA quickly showed its limits while GATE was validated. This will allow us to perform calculations for non measurable cases, for example patients treated by SBRT during DIBH. [ABSTRACT FROM AUTHOR]

Purpose The aim of EFOMP’s document is to clarify the position on article 60.3 (c–f) of the EU BSS Directive regarding optimization processes. Results The equipment used for interventional radiology and computed tomography and any new equipment used for planning, guiding and verification purposes, shall be able to inform the practitioner (radiologist, oncologist, technologist etc.) about the relevant parameters for assessing the quantity of radiation produced (angles, distances, exposure parameters, etc.). Furthermore, article 60.3(e) states that equipment used for interventional radiology and computed tomography must have the capacity to transfer this information to the record of the examination. The most common parameters used to quantify the radiation output will be discussed taking into account their impact on patient dosimetry. The Medical Physics Expert (MPE) role will be presented and discussed in: 1) Measuring the output of the radiological modality, estimating the related uncertainty, periodically verifying the calibration 2) Planning optimization strategies, dosimetric evaluations and quality controls 3) Comparing different modalities/equipment/protocols/exams with the purpose of optimizing the procedures. In this case, it might be necessary to translate the output metrics to effective dose and/or organ doses in order to compare doses between different modalities for optimization purposes. It is very important that the MPE defines the correct information to be captured that is related to the patient radiation dose. Some radiological metrics are not simple to understand (CTDI, SSDE for examples) and the MPE has to guide the medical community in their use. Conclusions EFOMP also recommends that all medical equipment should document the maximum uncertainty of the dosimetric index displayed. The uncertainties depend on the acquisition parameters. It is important that the manufacturers specify the maximum uncertainty of the dosimetric index. [ABSTRACT FROM AUTHOR]

Purpose EFOMP-IAEA collaboration in the field of Nuclear Medicine dosimetry is very active. Amongst other activities, the collaboration to disseminate knowledge can be seen in the IAEA support of ESMPE lectures in Prague, and EFOMP participation to ICTP-IAEA courses. In addition, EFOMP supports the IAEA project of a book focused on Molecular Radiotherapy dosimetry. The IAEA recently launched a Coordinated Research Project (CRP E2.30.05) on “Dosimetry in Radiopharmaceutical Therapy for personalized patient treatment” to support the standardization and dissemination of dosimetric methods in nuclear medicine therapy. The CRP will assist Member States in testing and adopting harmonized dosimetric protocols and to assess the typical accuracy with which dosimetry can be reached in nuclear medicine practice. Methods Within the CRP, Common activities will aim at: 1. Identify software and analysis methods appropriate for dosimetry of RPT. 2. Perform all the tasks needed to estimate tumour and normal organ absorbed doses on clinical and simulated data sets 3. Provide a written report, identifying the most challenging steps, or those that are subject to the greatest uncertainty. 4. Select one or more patient cases for whom dosimetry has been calculated at all the participating sites and assess the variability in absorbed dose determination. 5. Help disseminate each site’s experience, producing teaching material and tutorial documents on dosimetry for molecular radiotherapy based on the experience gained during the CRP. Conclusions The Call for Proposals, which included tentative research topics and the scoring methodology, was extensively advertised for CRP participants. Among the 33 research projects proposals received, 10 participating institutions have been selected from Colombia, Croatia, Cuba, France, India, Indonesia, South Africa and USA. The project has a 4 years duration, and the first Research Coordination Meeting took place in November 2017. All participants are currently working to derive the dosimetry of a set of clinical images. Discussions between participants are ongoing to define the prerequisite for the generation of simulated datasets. [ABSTRACT FROM AUTHOR]

The study of cell survival following exposure to nonuniform radiation fields is taking on particular interest because of the increasing evidence of a nonlinear relationship at low doses. We conducted in vitro experiments using the MCF7 breast cancer cell line. A 2.4 x 2.4 cm² square area of a T25 flask was irradiated by a Varian Novalis accelerator delivering 6 MV photons. Cell survival inside the irradiation field, in the dose gradient zone and in the peripheral zone, was determined using a clonogenic assay for different radiation doses at the isocenter. Increased cell survival was observed inside the irradiation area for doses of 2, 10, and 20 Gy when nonirradiated cells were present at the periphery, while the cells at the periphery showed decreased survival compared to controls. Increased survival was also observed at the edge of the dose gradient zone for cells receiving 0.02 to 0.01 Gy when compared with cells at the periphery of the same flask, whatever the isocenter dose. These data are the first to report cell survival in the dose gradient zone. Radiotherapists must be aware of this nonlinearity in dose response. [ABSTRACT FROM AUTHOR]

Lutetium-177 ( 177 Lu)-based post-therapeutic imaging allows visualization of treated lesions andabsorbed dose measurement. There is an increasing number of cadmium-zinc-telluride (CZT) gamma-cameras in nuclear medicine departments but until now these devices were not adapted to the medium-energy emission of 177 Lu photons. We present here in the first reported images acquired with a new collimator designed for CZT gamma-camera compared to a conventional sodium iodide (NaI) (Tl) gamma-camera. Post-therapeutic 177 Lu-DOTATATE imaging on a CZT device with a medium energy high resolution (MEHRS)-collimator are promising and support the widespread of both 177 Lu-based peptide-receptor radionuclide therapy (PRRT) and CZT gamma-cameras.

A wide range of medical imaging applications benefits from the availability of realistic ground truth data. In the case of positron emission tomography (PET), ground truth data is crucial to validate processing algorithms and assessing their performances. The design of such ground truth data often relies on Monte-Carlo simulation techniques. Since the creation of a large dataset is not trivial both in terms of computing time and realism, we propose the OSSI-PET database containing 350 simulated [(11)C]Raclopride dynamic scans for rats, created specifically for the Inveon pre-clinical PET scanner. The originality of this database lies on the availability of several groups of scans with controlled biological variations in the striata. Besides, each group consists of a large number of realizations (i.e., noise replicates). We present the construction methodology of this database using rat pharmacokinetic and anatomical models. A first application using the OSSI-PET database is presented. Several commonly used reconstruction techniques were compared in terms of image quality, accuracy and variability of the activity estimates and of the computed kinetic parameters. The results showed that OP-OSEM3D iterative reconstruction method outperformed the other tested methods. Analytical methods such as FBP2D and 3DRP also produced satisfactory results. However, FORE followed by OSEM2D reconstructions should be avoided. Beyond the illustration of the potential of the database, this application will help scientists to understand the different sources of noise and bias that can occur at the different steps in the processing and will be very useful for choosing appropriate reconstruction methods and parameters.

Intensity-modulated radiation therapy (IMRT) for total body irradiation (TBI) is practiced in several centers using the TomoTherapy System. In this context the planning target volume (PTV) is the entire body including the skin. A safety margin in the air surrounding the body should be added to take into account setup errors. But using inverse planning, over-fluence peak could be generated in the skin region to insure dose homogeneity. This work proposes to study the performance of the use of a virtual bolus (VB). A VB is a material placed on the skin surface during planning, but absent for the real treatment. The optimal VB that compensates large setup errors without introducing a high-dose increase or hot spots for small setup errors was determined. For two cylindrical phantoms, 20VBs with different densities, thicknesses or designs were tested. Dose coverage of the PTV (V95%) in the presence of simulated setup errors was computed to assess the VB performance. A measure of the dose increase in the phantom center due to the absence of the VB during treatment was also achieved. Finally, the fluence peak at the phantom edge was measured in complete buildup conditions using a large phantom and a detector matrix. Using these VBs, simulated setup errors were compensated to a minimum value of 2.6 and 2.1 cm for small and large phantom, respectively (and only 1.2 and 1.7 cm with no VB). An optimal double-layer VB was found with a density of 0.4 kg.m(-3) and a total thickness of 8mm; an inner layer of 5 mm was declared as the target for the treatment planning system and an additional layer of 3 mm was added to avoid the over-fluence peak. Using this VB, setup errors were compensated up to 2.9 cm. The dose increase was measured to be only +1.5% at the phantom center and over-fluence peak was strongly decreased.

With the increasing availability of alpha emitters, targeted α-particle therapy has emerged as a solution of choice to treat haematological cancers and micrometastatic and minimal residual diseases. Alpha-particles are highly cytotoxic because of their high linear energy transfer (LET) and have a short range of a few cell diameters in tissue, assuring good treatment specificity. These radiologic features make conventional dosimetry less relevant for that context. Stochastic variations in the energy deposited in cell nuclei are important because of the microscopic target size, low number of α- particle traversals, and variation in LET along the α-particle track. Microdosimetry provides a conceptual framework that aims at a systematic analysis of the stochastic distribution of energy deposits in irradiated matter. The different quantities of microdosimetry and the different methods of microdosimetric calculations were described in the early eighties. Since then, numerous models have been published through the years and applied to analyse experimental data or to model realistic therapeutic situations. Major results have been an accurate description of the high toxicity of α-particles, and the description of the predominant effect of activity distribution at the cellular scale on toxicity or efficacy of potential targeted α-particle therapies. This last factor represents a major limitation to the use of microdosimetry in vivo because determination of the source - target distribution is complicated. The future contributions of microdosimetry in targeted α-particle therapy research will certainly depend on the ability to develop high-resolution detectors and on the implementation of pharmaco-kinetic models at the tumour microenvironment scale.