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El uso de sistemas de imagen portal de MV puede simplificar el control de calidad de los equipos, y permite realizar nuevas pruebas sin aumentar el tiempo de medida. Por otra parte, no son los instrumentos de medida de dosis recomendados en los documentos de consenso, por lo que es preciso realizar un estricto proceso de validación específico para utilizarlo con dicho fin. En este trabajo se exponen un conjunto de pruebas de validación de las medidas y una serie de controles de calidad que se han implementado.

Introduction: The limit of the method of calculating organ doses using voxelised phantoms with a Monte Carlo simulation code is that dose calculation errors in the boundaries of the organs are especially relevant for thin, small or complex geometries. In this report, we describe a tool that helps overcome this problem, accurately calculating organ doses by applying the “parallel geometry” utility feature of Geant4 through the GAMOS framework. Methods and methods: We have tried to simplify the use of this tool by automatically processing the different DICOM image modalities (CT, PT, ST, NM), and by including the automatic conversion of the structures found in a DICOM RTSTRUCT file into Geant4 volumes that build the parallel geometry. For Nuclear Medicine applications, the DICOM PT, ST or NM images are converted into probabilities of generation of primary particles in each voxel, and the DICOM CT images into materials and material densities. For radiotherapy treatments, the DICOM RTPlan or RTIonPlan may also be used, hence the user only needs to describe the accelerator geometry. We also provide a Graphical User Interface for ease of use by for inexperienced users in Monte Carlo. Results: We have tested the functionality of the tool with an I-131 thyroid cancer treatment, and obtained the expected energy deposition and dose differences, given that the particle source, geometry and structures are defined. Conclusions: In summary, we provide an easy-to-use tool to calculate, with high accuracy, organ doses, taking into account their exact geometry as painted by the medical personnel on a voxelised phantom.

Purpose To investigate ion recombination correction and polarity effects in four ion chamber models in flattening-filter-free (FFF) beams to (1) evaluate their suitability for reference dosimetry; (2) assess the accuracy of the two-voltage technique (TVA) against the Bruggmoser formalism; and (3) examine the influence of the accelerator type on the recombination correction. Methods Jaffe plots were created for a variety of microchambers, small-volume and Farmer-type chambers to obtain kS, the recombination correction factor, using two different types of accelerators. These values were plotted against dose-per-pulse and Jaffe plots for opposite polarities were created to determine which chambers meet the AAPM TG-51 addendum recombination and polarity specifications. Results Nearly all small-volume chambers exhibited reference-class behavior with respect to ion recombination and polarity effects. The microchambers exhibited anomalous recombination and polarity effects, precluding their use for reference dosimetry in FFF beams. For the reference-class chambers, agreement between TVA-determined kS values and Jaffe and Bruggmoser formalisms-determined kS values was within 0.1%. No significant differences were found between the kS values obtained with the two different accelerators used in this work. Conclusions This study stresses the need to characterize ion recombination correction and polarity effects for small-volume chambers and microchambers on an individual chamber basis and with the more rigorous criteria of the AAPM TG-51 addendum. Furthermore, the study demonstrated the suitability of the TVA method for chambers that exhibit reference-class behavior in FFF beams. Finally, this work has shown that the recombination correction does not depend on the type of accelerator but on its dose-per-pulse.

In this study, we present a new procedure for the comparison of two dose matrices by means of a statistical test. A statistical distance is proposed to decide whether the difference between the two matrices is statistically significant. This statistical test is based on the square difference between the experimental and expected gamma matrix results. The expected gamma matrix is calculated by simulating the measurement process. For comparison purposes, the significance level of the test was chosen to give the same statistical significance as 90% of gamma-pass rate. The performance of the statistical distance is checked against 53 VMAT. The power of the presented test was compared using simulations with the 90% gamma-pass rate criteria for two cases in which intentional errors are introduced. In both cases, the test is uniformly more powerful. According to the test, two of the measured plans have a significant difference with calculated matrices, although the gamma pass rate measured was always greater than 90%.

We have studied each of the physics options that Geant4 offers to simulate an X-ray radiotherapy treatment with the aim of obtaining those that provide the best possible match to the experimental data of dose profiles and at the same time reduce the CPU time. The procedure has been repeated for two linac setups: an ELEKTA Versa HD with an Agility Multileaf Collimator using two nominal energies, 6 MV and 10 MV, both without flattening filter. After combining the results with those of a previous similar study of a 6 MV VARIAN Clinac 2100 C/D linac with flattening filter, we can propose a set of optimized Geant4 physics options of general use for radiotherapy simulation. Together with this, we have optimized the CPU time using several of the optimization techniques that GAMOS offers, reaching a reduction of several hundred times for each setup.

Purpose To evaluate the safety of peptide receptors radionuclide therapy (PRRT) of neuroendocrine tumors after 7.4 GBq 177Lu-DOTA-TATE by measurement of the radiation exposure rates. Methods For each patient the radiation levels (H∗(10)) were measured at 1 meter distance from the patient abdomen. Measurements were performed with a survey meter at different time points, over 4 days from the treatment administration of a prescribed activity of 7.4 GBq of 177Lu-DOTA-TATE. The first measure was accomplished at the end of the 177Lu-octreotate infusion and before voiding of bladder, while the others were done after emptied the bladder. Results 13 patients (36 cycles) were treated with a mean (standard deviation) activity of 6834 (688) MBq per cycle. Mean (maximum) dose rates measured at 1, 8, 24, 48 and 97 h (mean time) after treatment initiation were 32 (42), 15 (27), 9 (19) 7 (18) and 5 (11) μ Sv/h, respectively. At 8, 24, 48 and 97 h, 90% of the patients radiation levels were below 20, 16, 12 and 8.4 μ Sv/h, respectively. In relation to the first measurement, the mean uptakes were 47, 31, 24 and 16%. Considering the physical decay of the isotope, the dose limits for individual members of the public and an 8 h a day permanence at 1 m of the patient, the maximum dose rate allowed for patient release would be 13 μ Sv/h. Conclusions Taking into account the dose rates at 1 meter and the analysis of the specific conditions of the family and social environment of each patient, after 24 h of the treatment administration the patient can be released in 75% of cases.