Comparison between different Dosimetric Tools based on Intensity-modulated Radiotherapy (IMRT): A Phantom Study

This study examined the gamma passing rate (GPR) consistency during applying different kinds of gamma analyses and dosimeters to IMRT. Methods: Import treatment protocols for QA phantom irradiation have been recalculated. A gamma analysis was used for comparing the measured and calculated dose distribution of IMRT for different gamma criteria (2%/2mm, 3%/3mm, 4%/4mm, 3%/5mm, 3%/5mm). These criteria are evaluated when 5%, 10%, or 15% of the dose distribution is suppressed. Measured and calculated dose distribution was evaluated with gamma analysis to dose difference (DD) with DTA criteria (distance to agreement). IMRT QA plans to 25 patients from various sites were formed with the Varian Eclipse treatment planning system. Results: Results indicate different diverse hardware and software combinations show varied levels of agreement with expected analysis for the same pass-rate criterion. For a dosimetry audit of the IMRT technique, an EPID detector is superior to conventional methods comparable to Gafchromic EPT3 film and 2D array due to cost, time-consuming, and set up error to get result analysis. The gamma passing rate (GPR) average is increased by increasing the low-dose threshold for different dosimetric tools. For EPID, regardless of the gamma criterion employed, the %GP does not appear to be dependent on the low-dose threshold values (5%-15%) because it indicates that fulfilment the low-dose threshold to global normalization has little effect on patient-specific QA outcomes. Conclusions: It is concluded that GPRs differ depending on gamma, dosimetric tools, and the suppressing dose ratio. To get the best results of quality assurance, each institution should thus carefully develop its procedure for gamma analysis by defining the gamma index analysis and gamma criterion using its dosimetric tools.

Study the radioactive concentration for soil samples contaminated with depleted uranium in Al-Nahrawan site at Baghdad governorate using high purity germanium detector

This study is investigating the radioactivity in soil samples at the Al-Nahrawan site. The radiation survey appears there are 3000 square meters area are contaminated with DU in AL-Nahrawan site identified using Geiger–Müller (GM) for radiation survey and gamma spectrometry for 52 soil samples analysis taken from AL-Nahrawan site at different depths (0-70) cm and different locations. The results of gamma analysis using high-purity germanium show that the ratio between 235U/238U is less than 0.00720 (neutral ratio), and it has different values from 0.002-0.00588, and the average value of radioactive nuclides concentration for (238U, 235U and 40K) are (76019.61, 259.55 and 147.5) Bq/kg respectively, these values are higher than the (BG) radioactive concentration levels in Iraq for (238U and 235U) isotopes, and the analysis of 40K concentration appeared in the acceptable limits. The health effects of depleted uranium in the human body it is exposed to many health troubles through the entry of uranium oxide particles.

The Effect of Contrast Agents on Dose Calculations of Volumetric Modulated Arc Radiotherapy Plans for Critical Structures

Radiotherapy dose calculation requires accurate Computed Tomography (CT) imaging while tissue delineation may necessitate the use of contrast agents (CA). Acquiring these two sets is a common practice in radiotherapy. This study aims to evaluate the effect of CA on the dose calculations. Two hundred and twenty-six volumetric modulated arc therapy (VMAT) patients that had planning CT with contrast (CCT) and non-contrast CT (NCCT) of different cancer sites (e.g., brain, head, and neck (H&N), chest, abdomen, and pelvis) were evaluated. Treatment plans were recalculated using CCT, then compared to NCCT. The variation in Hounsfield units (HU) and dose distributions for critical structures and target volumes were analyzed using mean HU, mean and maximum relative dose values, D2%, D98%, and 3D gamma analysis. HU variations were statistically significant for most structures. However, this was not clinically significant as the difference in mean HU values was within 30 HU for soft tissue and 50 HU for lungs. Variation in target volumes’ D2% and D98% were insignificant for all sites except brain and nasopharynx. Dose maximum differences were within 2% for the majority of critical structures and target volumes. 3D gamma analysis results revealed that majority of plans satisfied the 2% and 2 mm criteria. CCT may be acquired for VMAT radiotherapy planning purposes instead of NCCT, since there is no clinically significant difference in dose calculations based on either image set.

Impact of Dose Algorithm and Calculation Angle Interval on in Vivo Dose Verification of Stereotactic Body Radiation Therapy: A Phantom Study

ObjectiveTo investigate the impact of different dose algorithms and calculation angle intervals (DCAI) on the in vivo dose (IVD) verification of small-field arc therapy in stereotactic body radiation therapy (SBRT).MethodsWe made an exit-dose-measuring and positioning device (EDPD) for the SRS MapCHECK (SMC) using polymethyl methacrylate (PMMA). Computed tomography data for the anthropomorphic head phantom, SMC, and EDPD combination were acquired with 1 mm slice thickness and spacing. SBRT partial arc plans were created using an SBRT cone, block, and a small square open field, with a gantry rotation angle of 60°. The dose distribution was calculated using three different dose algorithms [Pencil Beam (PB), CC Convolution (CCC), and Monte Carlo (MC)], with 1 mm isotropic resolution. We also used three different DCAIs (1°, 3°, 5°) with the PB and CCC algorithms to calculate the dose distribution of each plan three times. The uncertainty of each control point for the MC algorithm was set to 1%. The SMC was used to measure the exit dose outside the phantom for IVD verification, the detector plane was located 182.5 mm outside the scan center.ResultsWithin the phantom, the minimum passing rate of 3D gamma analysis (1%/1 mm) for the dose distributions calculated at different DCAIs was 99.1%, and the maximum relative deviation (RD) of the central point dose (CPD) was <0.2%. The average RD of the CPD for IVD verification was about 30% (range 16.71%–50.0%) for PB; -0.36% ± 1.82% (1° DCAI), -3.18% ± 7.83% (3° DCAI), and 3.69% ± 11.56% (1° DCAI) for CCC; and -0.38% ± 0.76 for the MC algorithm. The passing rates of 2D gamma analysis (3%/3 mm) between the predicted exit dose and the IVD were 100% for MC and >90% for the CCC algorithm at 1° DCAI.ConclusionThe DCAI for exit-dose calculations should be ≤1° using the CCC algorithm. Furthermore, among the three algorithms verified in the current study, the MC algorithm showed the highest accuracy, followed by CCC, with the PB algorithm having the worst performance. The PB algorithm is thus not suitable for exit-dose calculation or IVD verification of SBRT.

A Set Theory- And ROC-Based Patient-Specific QA Measure To Compare Planned And Delivered Isodose Distributions In Photon Radiotherapy

Background:The DVH-based and Gamma Index patient-specific QA measures commonly applied in radiotherapy planning are unable to simultaneously deliver detailed locations and magnitudes of discrepancy between isodoses of planned and delivered dose distributions. By exploiting the receiver operating characteristic (ROC) statistical classification tool, compliance between a planned and delivered isodose may be locally evaluated, both for OAR and PTV, at any given isodose level. Thus, a patient-specific QA tool may be developed to supplement those presently available in clinical radiotherapy.Materials and Methods:A method to locally establish and report dose delivery errors in 3-D isodoses of planned (reference) and delivered (evaluated) dose distributions as a function of both the dose level and spatial location was developed. At any given isodose level, the total volume of dose delivery containing the reference and the evaluated isodoses is locally decomposed into four subregions: true positive – subregions within both reference and evaluated isodoses, true negative – outside of both of these isodoses, false positive – inside the evaluated isodose occurs but not the reference one, and false negatives – inside the reference isodose but not the evaluated one, as established over the total volume of dose delivery. From this decomposition a confusion matrix is derived and various indices calculated to quantify the discrepancies between the given planned and delivered isodose distributions.Results:Examples of clinical photon radiotherapy plans underwent analysis using the method developed. At some isodose levels, at anatomically significant locations, dose delivery errors were found which would not be highlighted either by dose volume histogram (DVH)-based QA metrics or by gamma analysis.Conclusions:The proposed method which generalizes the DVH-based QA method approach and is able to spatially locate delivery errors at selected isodose levels may supplement the presently applied gamma analysis and DVH-based QA measures in patient-specific radiotherapy planning.

The dosimetric impact of deep learning-based auto-segmentation of organs at risk on nasopharyngeal and rectal cancer

Purpose To investigate the dosimetric impact of deep learning-based auto-segmentation of organs at risk (OARs) on nasopharyngeal and rectal cancer. Methods and materials Twenty patients, including ten nasopharyngeal carcinoma (NPC) patients and ten rectal cancer patients, who received radiotherapy in our department were enrolled in this study. Two deep learning-based auto-segmentation systems, including an in-house developed system (FD) and a commercial product (UIH), were used to generate two auto-segmented OARs sets (OAR_FD and OAR_UIH). Treatment plans based on auto-segmented OARs and following our clinical requirements were generated for each patient on each OARs sets (Plan_FD and Plan_UIH). Geometric metrics (Hausdorff distance (HD), mean distance to agreement (MDA), the Dice similarity coefficient (DICE) and the Jaccard index) were calculated for geometric evaluation. The dosimetric impact was evaluated by comparing Plan_FD and Plan_UIH to original clinically approved plans (Plan_Manual) with dose-volume metrics and 3D gamma analysis. Spearman’s correlation analysis was performed to investigate the correlation between dosimetric difference and geometric metrics. Results FD and UIH could provide similar geometric performance in parotids, temporal lobes, lens, and eyes (DICE, p > 0.05). OAR_FD had better geometric performance in the optic nerves, oral cavity, larynx, and femoral heads (DICE, p < 0.05). OAR_UIH had better geometric performance in the bladder (DICE, p < 0.05). In dosimetric analysis, both Plan_FD and Plan_UIH had nonsignificant dosimetric differences compared to Plan_Manual for most PTV and OARs dose-volume metrics. The only significant dosimetric difference was the max dose of the left temporal lobe for Plan_FD vs. Plan_Manual (p = 0.05). Only one significant correlation was found between the mean dose of the femoral head and its HD index (R = 0.4, p = 0.01), there is no OARs showed strong correlation between its dosimetric difference and all of four geometric metrics. Conclusions Deep learning-based OARs auto-segmentation for NPC and rectal cancer has a nonsignificant impact on most PTV and OARs dose-volume metrics. Correlations between the auto-segmentation geometric metric and dosimetric difference were not observed for most OARs.

Kilogram Sample Analysis by Nuclear Analytical Techniques: Complementary Opportunities for the Mineral and Geosciences

Sample-size reduction including homogenization is often required to obtain a test portion for element compositional analysis. Analyses of replicate test portions may provide insight into the sampling constant, and often much larger quantities are needed to limit the contribution of sampling error. In addition, it cannot be demonstrated that the finally obtained test portion is truly representative of the originally collected material. Nuclear analytical techniques such as neutron and photon activation analysis and (neutron-induced) prompt gamma activation analyses can now be used to study and overcome these analytical problems. These techniques are capable of obtaining multi-element measurements from irregularly shaped objects with masses ranging from multiple grams to multiple kilograms. Prompt gamma analysis can be combined with neutron tomography, resulting in position-sensitive information. The analysis of large samples provides unprecedented complementary opportunities for the mineral and geosciences. It enables the experimental assessment of the representativeness of test portions of the originally collected material, as well as the analysis of samples that are not allowed to be sub-sampled or dissolved, the analysis of materials that are difficult to be homogenized at large, and studies on the location of inhomogeneities. Examples of such applications of large-sample analyses are described herein.

A Beam Projection-Based Modified Gamma Analysis Scheme for Clinically Interpretable Pre-Treatment Dose Verification

Purpose: To investigate a novel gamma analysis system for dose verification results in terms of clinical significance. Methods and Materials: The modified scheme redefined the computational domain of the conventional gamma analysis with the projections of beams and the regions of interest (ROI). We retrospectively studied 6 patients with the conventional and the modified gamma analysis schemes while compared their performances. The cold spots ratio of the planning target volume (PTV) and the hot spots ratio of the organs at risk (OAR) were also computed by the modified scheme to assess the clinical significance. Results: The result of the gamma passing rate in the modified method was conformable to that in the conventional method with a cut-off threshold of 5%. The cold spots ratio of PTV and hot spots ratio of OAR were able to be evaluated by the modified scheme. For an introduced 7.1% dose error, the discrimination ratio in gamma passing rate of the conventional method was lower than 2%, while it was improved to 5% by the modified method. Conclusions: The modified gamma analysis scheme had a comparable quality as the conventional scheme in terms of dose inspection. Besides, it could improve the clinical significance of the QA result and provide the assessment for ROI-specific discrepancy. The modified scheme could also be conveniently integrated into the conventional dose verification process, benefiting the less developed regions where high-end 3D dose verification devices are not affordable.

Validation of Monaco Treatment Planning System for Intensity-Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT®) on ELEKTA Infinity™ Linear Accelerator

The objective of this study is to evaluate the dosimetric precision of the Monte Carlo (MC) algorithm to validate the Monaco® (Elekta) treatment planning system for the two radiotherapy techniques IMRT and VMAT® on the Infinity™ Elekta linear accelerator. Several irradiation plans were created on the Monaco® treatment planning system (TPS) and calculated by the integrated MC algorithm for its validation. The same plans were applied experimentally using the Matrixx Evolution 2D array with its appropriate phantom. All measurements were performed by superimposition with those calculated on the Infinity™ linear accelerator (ELEKTA). The calculated and measured dosimetric data were overlaid to make the comparison of what is realistic and what was simulated using the MyQA (IBA) software associated with the Matrixx. Good agreement was observed between calculated and measured data using 3%, 3mm distance to agreement (DTA) and low dose threshold 5% criteria. Global gamma analysis passing rates for all tests are greater than 95%. An agreement less than 2 mm is shown for open fields and homogenous dose test. However, there was increase in the agreement criteria above 3 mm for chair and pyramid test as a result of high gradient dose regions especially at the edge of target volumes. Results obtained from this study allowed, in one hand to confirm the accuracy of our MC model dose calculation with Monaco® TPS, and in the other hand, the use of the matrix detector as a standard tool for IMRT/VMAT® patient quality control.