Relative Electron Density Research Articles

Assessment of Dose Accuracy for MR-Guided Online Adaptive Radiotherapy for Nasopharyngeal Carcinoma

MR-guided radiotherapy relies on the daily assignment of a relative electron density (rED) map to acquire the fraction specific dose calculation. The approach to acquire the rED map is used bulk rED assignment based on the rED values of the delineated region of interests (ROIs) to generate a synthetic CT (sCT). This study aims to evaluate the dose accuracy of this approach for application in 1.5 T MR-Linac, to assess the reliability of this approach in the case of online adaptive MR-guided radiotherapy for Nasopharyngeal Carcinoma (NPC) patients.The original CT and MRI T2 were acquired for 10 NPC patients and targets, organs at risk (OARs), bone and air regions were delineated on original CT in a treatment planning software. Each patient's MRI/CT image pair was aligned using a rigid registration algorithm, and the contours were copied to MRI from original CT. The sCT was then generated in MRI using bulk rED assignment approach, based on the rED values of the delineated region of interests (ROIs). Three different types of sCT images were generated: The sCTICRU uses the rED values recommended by ICRU46, the sCTtailor uses the patient-specific mean rED values, and the sCTHomogeneity was created using water equivalent value of 1 g/cm3 for entire patient data set. The same treatment plan was calculated on three sCTs and original CT. The dose calculation accuracy was investigated in terms of gamma analysis, point dose comparison and dose volume histogram (DVH) parameters.For both criteria, 1%/1mm and 2%/2mm gamma passing rate results of plans on sCTtailor were always higher than plans on sCTICRU and sCTHomogeneity when compared with original CT based plans (P = 0.005). The difference on point dose in high dose planning target volume for each case calculated on sCTtailor (-0.14% ± 1.44%) was smaller if compared to those calculated on sCTICRU (-8.77% ± 2.33%) and sCTHomogeneity (1.65% ± 2.57%). The DVH differences for plan based on sCTtailor were much smaller than sCTICRU and sCTHomogeneity.The sCT generated with bulk rED assignment approach guarantees an acceptable level of dose accuracy for NPC patients with 1.5 T MR-Linac, making this approach suitable to online adaptive MR-guided radiotherapy. The accuracy can be improved by using patient-specific rED values.

Optimisation and validation of an integrated magnetic resonance imaging-only radiotherapy planning solution.

Background and purposeMagnetic resonance imaging (MRI)-only treatment planning is gaining in popularity in radiation oncology, with various methods available to generate a synthetic computed tomography (sCT) for this purpose. The aim of this study was to validate a sCT generation software for MRI-only radiotherapy planning of male and female pelvic cancers. The secondary aim of this study was to improve dose agreement by applying a derived relative electron and mass density (RED) curve to the sCT.Method and materialsComputed tomography (CT) and MRI scans of forty patients with pelvic neoplasms were used in the study. Treatment plans were copied from the CT scan to the sCT scan for dose comparison. Dose difference at reference point, 3D gamma comparison and dose volume histogram analysis was used to validate the dose impact of the sCT. The RED values were optimised to improve dose agreement by using a linear plot.ResultsThe average percentage dose difference at isocentre was 1.2% and the mean 3D gamma comparison with a criteria of 1%/1 mm was 84.0% ± 9.7%. The results indicate an inherent systematic difference in the dosimetry of the sCT plans, deriving from the tissue densities. With the adapted REDmod table, the average percentage dose difference was reduced to −0.1% and the mean 3D gamma analysis improved to 92.9% ± 5.7% at 1%/1 mm.ConclusionsCT generation software is a viable solution for MRI-only radiotherapy planning. The option makes it relatively easy for departments to implement a MRI-only planning workflow for cancers of male and female pelvic anatomy.

Determining tolerance levels for quality assurance of 3D printed bolus for modulated arc radiotherapy of the nose.

Given the existing literature on the subject, there is obviously a need for specific advice on quality assurance (QA) tolerances for departments using or implementing 3D printed bolus for radiotherapy treatments. With a view to providing initial suggested QA tolerances for 3D printed bolus, this study evaluated the dosimetric effects of changes in bolus geometry and density, for a particularly common and challenging clinical situation: specifically, volumetric modulated arc therapy (VMAT) treatment of the nose. Film-based dose verification measurements demonstrated that both the AAA and the AXB algorithms used by the Varian Eclipse treatment planning system (Varian Medical Systems, Palo Alto, USA) were capable of providing sufficiently accurate dose calculations to allow this planning system to be used to evaluate the effects of bolus errors on dose distributions from VMAT treatments of the nose. Thereafter, the AAA and AXB algorithms were used to calculate the dosimetric effects of applying a range of simulated errors to the design of a virtual bolus, to identify QA tolerances that could be used to avoid clinically significant effects from common printing errors. Results were generally consistent, whether the treatment target was superficial and treated with counter-rotating coplanar arcs or more-penetrating and treated with noncoplanar arcs, and whether the dose was calculated using the AAA algorithm or the AXB algorithm. The results of this study suggest the following QA tolerances are advisable, when 3D printed bolus is fabricated for use in photon VMAT treatments of the nose: bolus relative electron density variation within [Formula: see text] (although an action level at [Formula: see text] may be permissible); bolus thickness variation within [Formula: see text] mm (or 0.5 mm variation on opposite sides); and air gap between bolus and skin [Formula: see text] mm. These tolerances should be investigated for validity with respect to other treatment modalities and anatomical sites. This study provides a set of baselines for future comparisons and a useful method for identifying additional or alternative 3D printed bolus QA tolerances.

Evaluating the Effect of the Silicone Prosthesis on the Photon Dose Distribution in Radiation Therapy of Breast Cancer

Purpose: Breast cancer is the most common malignancy among women which in some cases is followed by breast reconstructions. The objective of the experimental study is to investigate the effect of the silicone prosthesis implementation on the dose distribution of radiotherapy. Materials and Methods: Initially CT images of 7 mastectomy breast patients with silicone prosthesis were imported to the Monaco treatment planning system. A treatment plan consisting of two tangential photon fields with a prescription dose of 50Gy was arranged. To study the effect and water equivalency of silicone prosthesis, dose distribution of treatment plan was acquired in two conditions: 1) considering the real electron density of silicone prosthesis; 2) modifying (Relative electron density) RED of silicone prosthesis to 1 to virtually assume it as soft tissue (water). The results were then compared by VeriSoft software to evaluate the gamma index. Results: The obtained results indicated that the RED for the silicon prosthesis varies between 0.7 and 1.14 while the RED for soft tissue is approximately 1. Also, the Dose-volume histogram curves for both conditions indicated that the minimum and maximum differences ranged from 1% to 4%. The significant differences might be due to the presence of the air cavity or bubbles in the silicone prosthesis implementation or air voxels between prostheses and soft tissue. Conclusion: The obtained results showed that if there is no air cavity in silicone prosthesis and the surgery is performed in a way that no volume of air is left between the prosthesis and breast tissue, the effect and presence of silicone prosthesis will be similar to soft tissue (water).

Implementation and experimental evaluation of Mega-voltage fan-beam CT using a linear accelerator

BackgroundMega-voltage fan-beam Computed Tomography (MV-FBCT) holds potential in accurate determination of relative electron density (RED) and proton stopping power ratio (SPR) but is not widely available.ObjectiveTo demonstrate the feasibility of MV-FBCT using a medical linear accelerator (LINAC) with a 2.5 MV imaging beam, an electronic portal imaging device (EPID) and multileaf collimators (MLCs).MethodsMLCs were used to collimate MV beam along z direction to enable a 1 cm width fan-beam. Projection data were acquired within one gantry rotation and preprocessed with in-house developed artifact correction algorithms before the reconstruction. MV-FBCT data were acquired at two dose levels: 30 and 60 monitor units (MUs). A Catphan 604 phantom was used to evaluate basic image quality. A head-sized CIRS phantom with three configurations of tissue-mimicking inserts was scanned and MV-FBCT Hounsfield unit (HU) to RED calibration was established for each insert configuration using linear regression. The determination coefficient ({R}^{2}) was used to gauge the accuracy of HU-RED calibration. Results were compared with baseline single-energy kilo-voltage treatment planning CT (TP-CT) HU-RED calibration which represented the current standard clinical practice.ResultsThe in-house artifact correction algorithms effectively suppressed ring artifact, cupping artifact, and CT number bias in MV-FBCT. Compared to TP-CT, MV-FBCT was able to improve the prediction accuracy of the HU-RED calibration curve for all three configurations of insert materials, with {R}^{2} > 0.9994 and {R}^{2} < 0.9990 for MV-FBCT and TP-CT HU-RED calibration curves of soft-tissue inserts, respectively. The measured mean CT numbers of blood-iodine mixture inserts in TP-CT drastically deviated from the fitted values but not in MV-FBCT. Reducing the radiation level from 60 to 30 MU did not decrease the prediction accuracy of the MV-FBCT HU-RED calibration curve.ConclusionWe demonstrated the feasibility of MV-FBCT and its potential in providing more accurate RED estimation.

Investigation of the effects of spinal surgical implants on radiotherapy dosimetry: A study of 3D printed phantoms.

The use of three-dimensional (3D) printing to develop custom phantoms for dosimetric studies in radiotherapy is increasing. The process allows production of phantoms designed to evaluated specific geometries, patients, or patient groups with a defining feature. The ability to print bone-equivalent phantoms has, however, proved challenging. The purpose of this work was to 3D print a series of three similar spine phantoms containing no surgical implants, implants made of titanium, and implants made of carbon fiber, for future dosimetric and imaging studies. Phantoms were evaluated for (a) tissue and bone equivalence, (b) geometric accuracy compared to design, and (c) similarity to one another. Sample blocks of PLA, HIPS, and StoneFil PLA-concrete with different infill densities were printed to evaluate tissue and bone equivalence. The samples were used to develop CT to physical (PD) and effective relative electron density (REDeff ) conversion curves and define the settings for printing the phantoms. CT scans of the printed phantoms were obtained to assess the geometry and densities achieved. Mean distance to agreement (MDA) and DICE coefficient (DSC) values were calculated between contours defining the different materials, obtained from design and like phantom modules. HU values were used to determine PD and REDeff and subsequently evaluate tissue and bone equivalence. Sample objects showed linear relationships between HU and both PD and REDeff for both PLA and StoneFil. The PD and REDeff of the objects calculated using clinical CT conversion curves were not accurate and custom conversion curves were required. PLA printed with 90% infill density was found to have a PD of 1.11±0.03g.cm-3 and REDeff of 1.04±0.02 and selected for tissue- equivalent phantom elements. StoneFil printed with 100% infill density showed a PD of 1.35±0.03g.cm-3 and REDeff of 1.24±0.04 and was selected for bone-equivalent elements. Upon evaluation of the final phantoms, the PLA elements displayed PD in the range of 1.10±0.03g.cm-3 -1.13±0.03g.cm-3 and REDeff in the range of 1.02±0.03-1.06±0.03. The StoneFil elements showed PD in the range of 1.43±0.04g.cm-3 -1.46±0.04g.cm-3 and REDeff in the range of 1.31±0.04-1.33±0.04. The PLA phantom elements were shown to have MDA of ≤1.00mm and DSC of ≥0.95 compared to design, and ≤0.48mm and ≥0.91 compared like modules. The StoneFil elements displayed MDA values of ≤0.44mm and DSC of ≥0.98 compared to design and ≤0.43mm and ≥0.92 compared like modules. Phantoms which were radiologically equivalent to tissue and bone were produced with a high level of similarity to design and even higher level of similarity of one another. When used in conjunction with the derived CT to PD or REDeff conversion curves they are suitable for evaluating the effects of spinal surgical implants of varying material of construction.

Technical Note: Volumetric computed tomography for radiotherapy simulation and treatment planning.

PurposeFor lung and liver tumors requiring radiotherapy, motion artifacts are common in 4D‐CT images due to the small axial field‐of‐view (aFOV) of conventional CT scanners. This may negatively impact contouring and dose calculation accuracy and could lead to a geographic miss during treatment. Recent advancements in volumetric CT (vCT) enable an aFOV up to 160 mm in a single rotation, which may reduce motion artifacts. However, the impact of large aFOV on CT number required for dose calculation needs to be evaluated before clinical implementation. The objective of this study was to determine the utility of a 256‐slice vCT scanner for 4D‐CT simulation by evaluating image quality and generating relative electron density (RED) curves.MethodsImages were acquired on a 256‐slice GE Revolution CT scanner with 40 mm, 80 mm, 120 mm, 140 mm, and 160 mm aFOV. Image quality was assessed by evaluating CT number linearity, uniformity, noise, and low‐contrast resolution. The relationship between each quality metric and aFOV was assessed.ResultsCT number linearity, uniformity, noise, and low‐contrast resolution were within the expected range for each image set, except CT number in Teflon and Delrin, which were underestimated. Spearman correlation coefficient (ρ) showed that the CT number for Teflon (ρ = 1.0, p = 0.02), Delrin (ρ = 1.0, p = 0.02), and air (ρ = 1.0, p = 0.02) was significantly related to aFOV, while all other measurements were not. The measured deviations from expected values were not clinically significant.ConclusionThese results suggest that vCT can be used for CT simulation for radiation treatment planning.

Radiation dosimetry effect evaluation of a carbon fiber couch on novel uRT-linac 506c accelerator

Recently, a diagnostic helical CT is integrated into a linear accelerator, called uRT-linac 506c, whose CT scanning dataset can be directly used to do simulation. This novel structure provides a possibility for online adaptive radiotherapy. For adaptive radiotherapy, the carbon fiber couch is an essential external device for supporting and positioning patients. And the effect on dose attenuation and distribution caused by a couch is inevitable and vital for precise treatment. In this research, the couch equipped with uRT-linac 506c was evaluated on the radiation dosimetry effect. The treatment couch equipped on the uRT-linac 506c accelerator was evaluated, and its effect on the attenuation, surface dose and dose buildup were measured for different phantom positions (offset = 0 cm, offset = + 10 cm and offset = − 10 cm, respectively) and different gantry angles. Since uRT-linac 506c is exclusively capable to provide diagnostic CT scanning data with real relative electron density (RED), this CT scanning data of the couch can be used directly in uRT-TPS to design plans. This scanned couch dataset was designated as the model A. The model B was a dummy structure of a treatment couch inserted with artificially preset RED. The dose calculation accuracy of these two models was compared using PB, CC, and MC on uRT-TPS. With the effect of carbon fiber couch, the surface dose was increased at least 97.94% for 25 × 25 cm2 field and 188.83% for 10 × 10 cm2 field, compared with those without. At different phantom positions (offset = 0, + 10, − 10 cm), the attenuation for 6 MV photon beam at gantry angle 180° were 4.4%, 4.4%, and 4.3%, respectively, and varied with changes of gantry angle. There do exists dose deviation between measurement and TPS calculation with the involvement of treatment couch, among the three algorithms, MC presented the least deviation, and the model A made less and steadier deviation than the model B, showing promising superiority. The attenuation, surface dose, and buildup effects of the carbon fiber couch in this study were measured similarly to most counterparts. The dose deviation calculated based on the couch dataset scanned by the diagnostic helical CT was smaller than those based on a dummy couch. This result suggests that an accelerator equipped with a diagnostic CT, which can help reduce the dose deviation of the carbon fiber couch, is a promising platform for online adaptive radiotherapy.

Radiological effects of varying the infill percentage and extrusion factor of 3D printed materials

The aim of this study was to investigate the radiological properties in the kilovoltage and megavoltage energy ranges of 3D printed materials which are currently used to create modern radiotherapy phantoms. In particular, the effect of printing parameters such as the percentage infill and extrusion factor were investigated. The 3D printed materials studied were Stonefil, PLA, GMASS, ABS and mABS, with dimensions 5x5x5cm3 and a range of different infill percentages and extrusion factors. Each material was characterised in terms of its relative electron density (RED) using a 6MV treatment beam of a linear accelerator and also using 120kV CT images of the materials.

Cone beam computed tomography based image guidance and quality assessment of prostate cancer for magnetic resonance imaging-only radiotherapy in the pelvis.

Radiotherapy (RT) based on magentic resonance imaging (MRI) only is currently used clinically in the pelvis. A synthetic computed tomography (sCT) is needed for dose planning. Here, we investigate the accuracy of cone beam CT (CBCT) based MRI-only image guided RT (IGRT) and sCT image quality. CT, MRI and CBCT scans of ten prostate cancer patients were included. The MRI was converted to a sCT using a multi-atlas approach. The sCT, CT and MR images were auto-matched with the CBCT on the bony anatomy. Paired sCT-CT and sCT-CBCT data were created. CT numbers were converted to relative electron (RED) and mass densities (DES) using a standard calibration curve for the CT and sCT. For the CBCT RED/DES conversion, a phantom and paired CT-CBCT population based calibration curve was used. For the latter, the CBCT numbers were averaged in 100 HU bins and the known RED/DES of the CT were assigned. The paired sCT-CT and sCT-CBCT data were averaged in bins of 10 HU or 0.01 RED/DES. The median absolute error (MeAE) between the sCT-CT and sCT-CBCT bins was calculated. Wilcoxon rank-sum tests were carried out for the IGRT and MeAE study. The mean sCT or MR IGRT difference from CT was≤2mm but significant differences were observed. A CBCT HU or phantom-based RED/DES MeAE did not estimate the sCT quality similar to a CT based MeAE but the CBCT population-based RED/DES MeAE did. MRI-only CBCT-based IGRT seems feasible but caution is advised. A MeAE around 0.1 DES could call for sCT quality inspection.

Determination of the test-samples electron density via dual energy computer tomography

In this work we determines electron density using data obtained via CT scanner with one radiation source operating in two modes: with 80 kV and 120 kV voltage. We perform tomography study of calibration phantom with predetermined electron densities. Single linear relationship between energy-subtracted Hounsfield unit and relative electron density is determined. Using determined relationship the relative electron densities of phantom calibration samples is calculated. The comparison of calculated and nominal values proves the possibility of the samples relative electron density determination using energy-subtracted Hounsfield unit with error less than 2%.

Feasibility of using megavoltage computed tomography to reduce proton range uncertainty: A simulation study.

PurposeTo demonstrate that variation in chemical composition has a negligible effect on the mapping curve from relative electron density (RED) to proton stopping power ratio (SPR), and to establish the theoretical framework of using Megavoltage (MV) computed tomography (CT), instead of kilovoltage (kV) dual energy CT, to accurately estimate proton SPR.MethodsA simulation study was performed to evaluate the effect of chemical composition variation on kVCT number and proton SPR. The simulation study involved both reference and simulated human tissues. The reference human tissues, together with their physical densities and chemical compositions, came from the ICRP publication 23. The simulated human tissues were created from the reference human tissues assuming that elemental percentage weight followed a Gaussian distribution. For all tissues, kVCT number and proton SPR were obtained through (a) theoretical calculation from tissue’s physical density and chemical composition which served as the ground truth, and (b) estimation from RED using the calibration curves established from the stoichiometric method. Deviations of the estimated values from the calculated values were quantified as errors in using RED to estimate kVCT number and proton SPR.ResultsGiven a chemical composition variation of 5% (1σ) of the nominal percentage weights, the total estimation error of using RED to estimate kVCT number was 0.34%, 0.62%, and 0.77% and the total estimation error of using RED to estimate proton SPR was 0.30%, 0.22%, and 0.16% for fat tissues, non‐fat soft tissues and bone tissues, respectively.ConclusionChemical composition had a negligible effect on the method of using RED to determine proton SPR. RED itself is sufficient to accurately determine proton SPR. MVCT number maintains a superb linear relationship with RED because it is highly dominated by Compton scattering. Therefore, MVCT has great potential in reducing the proton range uncertainty.

Analysis of target doses on various tissues in treatment of lung cancer: a simulation study

The success indicator of radiotherapy planning is that it can deliver a precise and maximum dose to the tumor, and at the same time, health tissues receive a minimum dose. The success can be achieved by understanding the density of the organs that go into the treatment beams because the dose distribution was directly affected by tissue inhomogeneity. Therefore, the study aimed to evaluate the tissue density of DICOM images and the homogeneity of the distribution of dose from treatment planning in lung cancer using 3D Slicer-SlicerRT. The method used in the study was used 3 data of CT and RT – Structures data from The Cancer Imaging Archive (TCIA), NSCLC-Radiomics with a diagnosis of stage IIIB squamous cell carcinoma, the location of right cancer, and only one nodule. The calculation of tissue density values using segment statistics in 3D Slicer was based on CT-DICOM information. While the treatment planning was built using 3D Slicer-SlicerRT with a prescription of 60 Gy/30 fractions. Treatment design used six fields, and optimization was done by combining a gantry angle and beam weight. The results represented that the calculation of tissue density was following the reference standard and relative electron density for each organ. Besides, the study had successfully designed a treatment planning system using 3D Slicer-SlicerRT that fulfilled the total dose standard, was excellent for OAR sparing, and had a homogeneity index for patient data ID 1 until 4 with values of 0.252, 0.009, 0.007, and 0.007, respectively.

Spectrophotometric and computational investigations of charge transfer complexes of chloranilic acid with tyrosine kinase inhibitors and application to development of novel universal 96-microwell assay for their determination in pharmaceutical formulations

The tyrosine kinase inhibitors (TKIs) are chemotherapeutic drugs used for targeted therapy of various types of cancer. In literature, there is no existing universal chromogenic reagent used for development of spectrophotometric assay for all TKIs regardless the diversity of their chemical structures. This work discusses, for the first time, the experimental and computational evaluation of chloranilic acid (CLA) as a universal chromogenic reagent for developing a novel 96-microwell spectrophotometric assay (MW-SPA) for TKIs. The reaction of CLA with seven TKIs was examined in different organic solvents of various dielectric constants and polarity indexes. The reaction resulted in an instantaneous formation of intensely purple coloured products with all the investigated TKIs. Spectrophotometric investigations confirmed that the reactions proceeded via the formation of charge-transfer complexes (CTC). The physical parameters (molar absorptivity, molar ratio, association constant and standard free energy) were determined for the CTC of all TKIs. Computational calculations for the relative electron densities on each atom of the TKI molecule and molecular modelling for the CTC were conducted, and the site(s) of interaction on each TKI molecule were determined. Under the optimized conditions, Beer’s law correlating the absorbances of the CTC with the concentrations of TKIs were obeyed in the range of 5–500 µg/well with good correlation coefficients (0.9991–0.9998). The limits of detection and quantitation were in the ranges of 1.89–5.09 and 5.74–15.42 µg/well, respectively. The proposed MW-SPA showed high precisions as the values of the relative standard deviations did not exceed 2.01 and 2.45% for the intra- and inter-assay precision, respectively. The accuracy of MW-SPA was proved by recovery studies as the recovery values were in the range of 98.8–103.7%. The proposed MW-SPA was successfully applied for the determination of all TKIs in their bulk forms and pharmaceutical formulations (tablets) with good accuracy and precisions. The proposed MW-SPA is the first assay that can analyse all the TKIs on a single assay system without modifications in the detection wavelength. Additional advantages of the proposed MW-SPA are simple, economic, and more importantly have high throughput. Therefore, the assay can be helpful and beneficial for routine analysis of TKIs in their pharmaceutical formulations in quality control laboratories.

Actual delivered dose calculation on intra-irradiation cone-beam computed tomography images: a phantom study

Cone-beam computed tomography (CBCT) images acquired during volumetric modulated arc therapy (VMAT; ii-CBCT) can be used to calculate actual delivered doses (ADDs). However, such ii-CBCT images are degraded by scattered megavoltage x-rays (MV-scatters). We aimed to evaluate the dose calculation accuracy of the MV-scatter uncorrected or corrected ii-CBCT images acquired during VMAT deliveries. For MV-scatter correction on concurrent kilovoltage projections (P MVkV), projections consisting only of MV-scatters (P MVS) were acquired under the same MV beam parameters and gantry angles and subtracted from P MVkV (P MVScorr). In addition, the projections by kilovoltage beams were acquired for reference (P kV). The corresponding CBCT images were reconstructed using the Feldkamp–Davis–Kress algorithm (CBCTMVkV, CBCTMVScorr, and CBCTkV as reference). A multi-energy phantom with rods of various relative electron densities (REDs) was used to generate a CBCT-number-to-RED conversion table. First, CBCTkV was reconstructed. Then, the mean CBCT-numbers within each rod were extracted, and a reference table was generated. Concurrent kilovoltage imaging with various field sizes was also demonstrated, and CBCTMVkV and CBCTMVScorr were reconstructed. The extracted CBCT-numbers of each ii-CBCT image were converted into REDs using the reference table. Next, the absolute differences of RED between the ii-CBCT image and CBCTkV were calculated. Ten VMAT plans using a 10 MV flattening-filter-free beam were used for concurrent imaging of an anthropomorphic torso phantom. Moreover, an iterative reconstruction algorithm (IRA) was used for CBCTMVScorr. The plans were recalculated for the corresponding CBCTMVkV, CBCTMVScorr, CBCTMVScorr+IRA, and CBCTkV with the reference table. Finally, the doses were evaluated using 3D gamma analysis (1%/1 mm). The median difference ranges between CBCTMVkV/CBCTMVScorr and the reference values were −0.58 to −0.10/−0.03 to 0.00. The median gamma pass rates of the doses on CBCTMVkV, CBCTMVScorr, and CBCTMVScorr+IRA to the rate on CBCTkV were 70.4, 99.5, and 98.2%, respectively. CBCTMVScorr were comparable with CBCTkV for calculating the ADD from VMAT.

The possibility of developing customized 3D-printed silicone hydrogel bolus for post-mastectomy radiotherapy

ABSTRACT 3D printing technology is widely used for fabricating bolus in post-mastectomy radiotherapy. 3D printed boluses are usually made from hard materials like Polylactic Acid, which can’t adhere to patients’ skin perfectly in clinical practice because of the patients’ uneven surfaces of chest walls and large radiotherapy area. In this work, the feasibility of 3D printing soft self-adhesion boluses using water tissue equivalent silicone hydrogel material in post-mastectomy radiotherapy was studied, and intensity modulated radiotherapy plans were designed to study the performance of the water tissue equivalent silicone hydrogel bolus by comparing to the results of using virtual boluses with the relative electron density of 1.09 in radiotherapy. The comparison demonstrated that water tissue equivalent silicone hydrogel boluses have better adhesive property than boluses made from hard materials. The average air gap volume between the water tissue equivalent silicone hydrogel bolus and patients’ skin is 9.5 cc. The average degree of adhesion and average maximuum air cavity dimension are 3.7% and 4.3 mm, respectively. The dose distribution of the virtual bolus and the water tissue equivalent silicone hydrogel bolus are roughly the same in Dose Volume Histogram.

Assessment of dose accuracy for online MR-guided radiotherapy for cervical carcinoma

ABSTRACT This study aims to evaluate the dose accuracy of synthetic CT based bulk relative electron density (rED) assignment for application in 1.5 T MR-Linac for cervical carcinoma patients. Five cervix patients previously treated on 1.5 T MR-Linac were retrospectively investigated. Two sCTs were generated assigning bulk values to the different bone regions: the sCTFH was generated with delineation of femoral head, and the sCTAB was generated with the delineation of all the bone regions. The rest tissue of the patient data was set to mean rED values of the region of interests in CT. The same treatment plan based on original CT was recalculated or reoptimized on the sCTFH and sCTAB. The result of gamma analysis showed that gamma passing rate of treatment plans based on sCTAB was higher than plans based on sCTFH. And the differences of dose volume parameters between plans on sCTs and original CT showed that the differences for plan based on sCTAB were much smaller than sCTFH. The sCT generated with bulk rED assignment approach guarantees an acceptable level of dose accuracy for cervix carcinoma patients with 1.5 T MR-Linac. The accuracy can be improved by using complete delineation of the pelvic bone regions.

Design and fabrication of a thoracic phantom for radiation dose verification in mega-voltage X-ray beam

To assess the radiological properties of racemosa wooden dust (RWD) and Poly (methyl methacrylate) (PMMA) for design and fabrication of a thoracic phantom for radiation dose verification in mega-voltage X-ray beam. The computed tomography images of RWD and PMMA were used to determine the radiological properties viz., Hounsfield units (HUs), relative electron density (RED) and mass density (MD). The estimated HUs, RED and MD were −828.2 ± 11.9, 0.172 ± 0.012, 0.150 ± 0.012 g/cc and 108.5 ± 7.3, 1.104 ± 0.004, 1.088 ± 0.005 g/cc for RWD and PMMA, respectively. The radiological properties of RWD and PMMA were in congruence with the value detailed in literature for lung tissue and muscle tissue of human body. Therefore, a phantom was design and fabricated using the combination of RWD and PMMA for radiation dose verification prior to radiation delivery to the cancer patients. The average deviation between dose computation engine and Ion-chamber estimations were within the stipulated tolerance (±3%). Thus, it was culminated that RWD and PMMA can be utilized for design and fabrication of phantom, which vindicates precise information about the quality assurance program for thoracic cancer patient treated using mega-voltage X-ray beam.

Computed tomography simulator conversion curve dependence on scan parameters and phantom dimension

Introduction: Using computed tomography (CT) and treatment planning systems (TPS) in radiotherapy, due to the difference in photon beam energy on CT and linear accelerator, it is necessary to convert Hounsfield units (HU) to relative electron density (RED) values. The aim of this dosimetric study was to determine whether there is a significant effect of potential in the CT tube, field of view size (FOV), and phantom dimensions on the CT conversion curve CT-RED. The second aim is whether there are significant differences between the CT-RED obtained by the Computerized Imaging Reference Systems (CIRS) Thorax 002LFC phantom and the “reference” curve in the TPS, obtained by the CIRS 062M pelvis phantom, at the same CT conditions.Methods: Heterogeneous CIRS 062M and CIRS Thorax 002LFC phantoms were used, which anatomically and dimensionally represent the human pelvis, head, and thorax, with a set of known RED inserts. They were scanned on a CT LightSpeed GE simulator and obtained CT-RED.Results: The high voltage in the CT tube had a significant effect on the HU (t = 10.72, p &lt; 0.001) for RED values &gt;1.1, while FOV as a parameter did not show statistical significance for the 062M pelvis phantom. Comparing the slopes (062M pelvis and head) of the CT-RED for RED ≥ 1.1, the obtained value is t = 1.404 (p = 0.163). In the case of a 062M pelvis and a 002LFC phantom, we have seen a difference in RED values (for the same HU value) of 5 % in the RED region ≥ 1.1 (bone).Conclusion: Patients should be imaged on a CT simulator only at the potential of the CT tube on which the conversion curve was recorded. The influence of the FOV and scanned phantom dimensions is not statistically significant on the appearance of the calibration curve (RED ≥ 1.1).

Technical Note: A methodology for improved accuracy in stopping power estimation using MRI and CT.

Proton therapy is becoming an increasingly popular cancer treatment modality due to the proton's physical advantage in that it deposits the majority of its energy at the distal end of its track where the tumor is located. The proton range in a material is determined from the stopping power ratio (SPR) of the material. However, SPR is typically estimated based on a computed tomography (CT) scan which can lead to range estimation errors due to the difference in x-ray and proton interactions in matter, which can preclude the ability to utilize protons to their full potential. Applications of magnetic resonance imaging (MRI) in radiotherapy have increased over the past decade and using MRI to calculate SPR directly could provide numerous advantages. The purpose of this study was to develop a practical implementation of a novel multimodal imaging method for estimating SPR and compare the results of this method to physical measurements in which values were computed directly using tissue substitute materials fabricated to mimic skin, muscle, adipose, and spongiosa bone. For both the multimodal imaging method and physical measurements, SPR was calculated using the Bethe-Bloch equation from values of relative electron density and mean ionization potential determined for each tissue. Parameters used to estimate SPR using the multimodal imaging method were extracted from Dixon water-only and (1 H) proton density-weighted zero echo time MRI sequences and CT, with both kVCT and MVCT used separately to evaluate the performance of each. For comparison, SPR was also computed from kVCT using the stoichiometric method, the current clinical standard. Results showed that our multimodal imaging approach using MRI with either kVCT or MVCT was in close agreement to SPR calculated from physical measurements for the four tissue substitutes evaluated. Using MRI and MVCT, SPR values estimated using our method were within 1% of physical measurements and were more accurate than the stoichiometric method for the tissue types studied. We have demonstrated the methodology for improved estimation of SPR using the proposed multimodal imaging framework.