EPID based in vivo dosimetry system: clinical experience and results.
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ABSTRACT:
SUBMITTER: Celi S
PROVIDER: S-EPMC5690938 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:We proposed to perform a basic dosimetry commissioning on a new imager sys-tem, the Varian aS1200 electronic portal imaging device (EPID) and TrueBeam 2.0 linear accelerator for flattened (FF) and flattening filter-free (FFF) beams, then to develop an image-based quality assurance (QA) model for verification of the system delivery accuracy for intensity-modulated radiation therapy (IMRT) treat-ments. For dosimetry testing, linearity of dose response with MU, imager lag, and effectiveness of backscatter shielding were investigated. Then, an image-based model was developed to convert images to planar dose onto a virtual water phantom. The model parameters were identified using energy fluence of the Acuros treatment planning system (TPS) and, reference dose profiles and output factors measured at depths of 5, 10, 15, and 20 cm in water phantom for square fields. To validate the model, its calculated dose was compared to measured dose from MapCHECK 2 diode arrays for 36 IMRT fields at 10 cm depth delivered with 6X, 6XFFF, 10X, and 10XFFF energies. An in-house gamma function was used to compare planar doses pixel-by-pixel. Finally, the method was applied to the same IMRT fields to verify their pretreatment delivery dose compared with Eclipse TPS dose. For the EPID commissioning, dose linearity was within 0.4% above 5 MU and ~ 1% above 2 MU, measured lag was smaller than the previous EPIDs, and profile symmetry was improved. The model was validated with mean gamma pass rates (standard deviation) of 99.0% (0.4%), 99.5% (0.6%), 99.3% (0.4%), and 98.0% (0.8%) at 3%/3 mm for respectively 6X, 6XFFF, 10X, and 10XFFF beams. Using the same comparison criteria, the beam deliveries were verified with mean pass rates of 100% (0.0%), 99.6% (0.3%), 99.9% (0.1%), and 98.7% (1.4%). Improvements were observed in dosimetric response of the aS1200 imager compared to previous EPID models, and the model was successfully developed for the new system and delivery energies of 6 and 10 MV, FF, and FFF modes.
| S-EPMC5690494 | biostudies-literature
Project description:Normalize the response of electronic portal imaging device (EPID) is the first step toward an EPID-based standardization of Linear Accelerator (linac) dosimetry quality assurance. In this study, we described an approach to generate two-dimensional (2D) pixel sensitivity maps (PSM) for EPIDs response normalization utilizing an alternative beam and dark-field (ABDF) image acquisition technique and large overlapping field irradiations. The automated image acquisition was performed by XML-controlled machine operation and the PSM was generated based on a recursive calculation algorithm for Varian linacs equipped with aS1000 and aS1200 imager panels. Cross-comparisons of normalized beam profiles and 1.5%/1.5 mm 1D Gamma analysis was adopted to quantify the improvement of beam profile matching before and after PSM corrections. PSMs were derived for both photon (6, 10, 15 MV) and electron (6, 20 MeV) beams via proposed method. The PSM-corrected images reproduced a horn-shaped profile for photon beams and a relative uniform profiles for electrons. For dosimetrically matched linacs equipped with aS1000 panels, PSM-corrected images showed increased 1D-Gamma passing rates for all energies, with an average 10.5% improvement for crossline and 37% for inline beam profiles. Similar improvements in the phantom study were observed with a maximum improvement of 32% for 15 MV and 22% for 20 MeV. The PSM value showed no significant change for all energies over a 3-month period. In conclusion, the proposed approach correct EPID response for both aS1000 and aS1200 panels. This strategy enables the possibility to standardize linac dosimetry QA and to benchmark linac performance utilizing EPID as the common detector.
| S-EPMC5768011 | biostudies-literature
Project description:Osteosarcoma is the most frequent primary malignant bone tumour, and its incidence is higher in children and adolescents, for whom it represents more than 10% of solid cancers. Despite the introduction of adjuvant and neo-adjuvant chemotherapy that markedly increased the success rate in the treatment, aggressive surgery is still needed and a considerable percentage of patients do not survive due to recurrences or early metastases. Boron Neutron Capture Therapy (BNCT), an experimental radiotherapy, was investigated as a treatment that could allow a less aggressive surgery by killing infiltrated tumour cells in the surrounding healthy tissues. BNCT requires an intense neutron beam to ensure irradiation times of the order of 1 h. In Italy, a Radio Frequency Quadrupole (RFQ) proton accelerator has been designed and constructed for BNCT, and a suitable neutron spectrum was tailored by means of Monte Carlo calculations. This paper explores the feasibility of BNCT to treat osteosarcoma using this neutron source based on accelerator.The therapeutic efficacy of BNCT was analysed evaluating the dose distribution obtained in a clinical case of femur osteosarcoma. Mixed field dosimetry was assessed with two different formalisms whose parameters were specifically derived from radiobiological experiments involving in vitro UMR-106 osteosarcoma cell survival assays and boron concentration assessments in an animal model of osteosarcoma. A clinical case of skull osteosarcoma treated with BNCT in Japan was re-evaluated from the point of view of dose calculation and used as a reference for comparison.The results in the case of femur osteosarcoma show that the RFQ beam would ensure a suitable tumour dose painting in a total irradiation time of less than an hour. Comparing the dosimetry between the analysed case and the treated patient in Japan it turns out that doses obtained in the femur tumour are at least as good as the ones delivered in the skull osteosarcoma. The same is concluded when the comparison is carried out taking into account osteosarcoma irradiations with photon radiation therapy.The possibility to apply BNCT to osteosarcoma would allow a multimodal treatment consisting in neo-adjuvant chemotherapy, high-LET selective radiation treatment and a more conservative surgery.
| S-EPMC5557419 | biostudies-other
Project description:PurposeTo evaluate the errors caused by metal implants and metal artifacts in the two-dimensional entrance fluences reconstructed using the back-projection algorithm based on electronic portal imaging device (EPID) images.MethodsThe EPID in the Varian VitalBeam accelerator was used to acquire portal dose images (PDIs), and then commercial EPID dosimetry software was employed to reconstruct the two-dimensional entrance fluences based on computed tomography (CT) images of the head phantoms containing interchangeable metal-free/titanium/aluminum round bars. The metal-induced errors in the two-dimensional entrance fluences were evaluated by comparing the γ results and the pixel value errors in the metal-affected regions. We obtained metal-artifact-free CT images by replacing the voxel values of non-metal inserts with those of metal inserts in metal-free CT images to evaluate the metal-artifact-induced errors.ResultsThe γ passing rates (versus PDIs obtained without a phantom in the beam field (PDIair ), 2%/2 mm) for the back-projected two-dimensional entrance fluences of phantoms containing titanium or aluminum (BPTi /BPAl ) were reduced from 92.4% to 90.5% and 90.6%, respectively, relative to the metal-free phantom (BPmetal-free ). Titanium causes more severe metal artifacts in CT images than aluminum, and its removal resulted in a 0.0022 CU (median) reduction in the pixel value of BPTi artifact-free relative to BPTi in the metal-affected region. Moreover, the mean absolute error (MAE) and root mean square error (RMSE) decreased from 0.0050 CU and 0.0063 CU to 0.0034 CU and 0.0040 CU, respectively (vs. BPmetal-free ).ConclusionMetal implants increase the errors in back-projected two-dimensional entrance fluences, and metals with higher electron densities cause more errors. For high-electron-density metal implants that produce severe metal artifacts (e.g., titanium), removing metal artifacts from the CT images can improve the accuracy of the two-dimensional entrance fluences reconstructed by back-projection algorithms.
| S-EPMC10647983 | biostudies-literature
Project description:A 3D dosimetry system is described which consists of two parts: a radiochromic plastic dosimeter PRESAGE (which responds to absorbed dose with a linear change in optical-density) and the Duke large-field-of-view optical-CT scanner (DLOS). The DLOS/PRESAGE system has recently been commissioned and benchmarked for clinical use and, in particular, for verification and commissioning of complex radiation treatments.DLOS commissioning involved determining the dynamic range, spatial resolution, noise, temporal, and other characteristics of the light source and imaging components. Benchmarking tests were performed on the combined DLOS/PRESAGE system to establish baseline dosimetric performance. The tests consisted of delivering simple radiation treatments to PRESAGE dosimeters, and comparing the measured 3D relative dose distributions with the known gold standard. The gold standard distribution was obtained from machine beam-data or the treatment planning system (TPS). All studies used standardized procedures to ensure consistency.For commissioning, isotropic spatial resolution was submillimeter (MTF > 0.5 for frequencies of 1.5 lp/mm) and the dynamic range was -60 dB. Flood field uniformity was within 10% and stable after 45 min of warm-up. Stray-light is small, due to telecentricity, but even the residual can be removed through deconvolution by a point-spread-function. For benchmarking, the mean 3D passing NDD (normalized dose distribution) rate (3%, 3mm, 5% dose threshold) over the benchmark data sets was 97.3% +/- 0.6% (range 96%-98%), which is on par with other planar dosimeters used in external beam radiation therapy indicating excellent agreement. Noise was low at < 2% of maximum dose (4-12 Gy) for 2 mm reconstructions. The telecentric design was critical to enabling fast imaging with minimal stray-light artifacts.This work presents the first comprehensive benchmarking of a 3D dosimetry system for clinical use. The DLOS/PRESAGE benchmark tests show consistently good agreement to simple known distributions. The system produces accurate isotropic 2 mm dose data over clinical volumes (e.g., 16 cm diameter phantoms, 12 cm height), in under 15 min. It represents a uniquely useful and versatile new tool for commissioning and verification of complex therapy treatments.
| S-EPMC3165434 | biostudies-other
Project description:Purpose:To characterize the clinical utility of a new commercially available system for daily patient treatment quality assurance using electronic portal imaging detector (EPID) exit dose images. Methods and Materials:The PerFRACTION automated quality assurance system was used to acquire integrated EPID images for every field every day for 60 treatment courses for 57 patients. Four thousand seventy-nine field values from 855 fractions were analyzed. Gamma passing rates were computed by the system for each field daily. Passing rates and pass-fail status were recorded by treatment modality (intensity modulated radiation therapy or 3-dimensional conformal radiotherapy) and location. When failures occurred, an attempt was made to determine the reason. Results:Overall, 23% and 8% of fields failed at 2%/2 mm and 3%/3 mm, respectively. Forty-eight percent and 24% of fields failed at least once during the course of therapy for the 2 tolerance settings. Eighteen percent and 8% of all fractions failed and 60% and 28% of courses failed for the 2 tolerance settings, respectively. Eighteen percent of daily field passing rates were below 75% for 3%/3 mm tolerances. Intensity modulated radiation therapy had higher passing rates than 3-dimensional conformal radiation therapy. For 3%/3 mm tolerances, the fraction fail rate for the brain, extremity, and spine treatment sites failed the least, whereas the abdomen, chest, and head and neck failed more often. The most commonly identified reason for failure was body position change, but the reason for about half the daily field value failures could not be identified. Conclusions:This is the first report of the clinical utility of a commercial daily patient treatment quality assurance system using EPID exit images. Variations were found in a clinically relevant percentage of images, and these potentially indicate important treatment variations. Reasons for failures are not always discernable. The system was practical to use because of automation and continues to be used for monitoring of nearly every patient in every field every day.
| S-EPMC6817722 | biostudies-literature
Project description:With interest in the potential of optical fibres as the basis of next-generation thermoluminescence dosimeters (TLDs), the development of suitable forms of material and their fabrication has become a fast-growing endeavour. Present study focuses on three types of Ge-doped optical fibres with different structural arrangements and/or shapes, namely conventional cylindrical fibre, capillary fibre, and flat fibre, all fabricated using the same optical fibre preform. For doses from 0.5 to 8 Gy, obtained at electron and photon energies, standard thermoluminescence (TL) characteristics of the optical fibres have been the subject of detailed investigation. The results show that in collapsing the capillary fibre into a flat shape, the TL yield is increased by a factor of 5.5, the yield being also some 3.2 times greater than that of the conventional cylindrical fibre fabricated from the same perform. This suggests a means of production of suitably sensitive TLD for in-vivo dosimeter applications. Addressing the associated defects generating luminescence from each of the optical fibres, the study encompasses analysis of the TL glow curves, with computerized glow curve deconvolution (CGCD) and 2(nd) order kinetics.
| S-EPMC4551967 | biostudies-other
Project description:To establish a dose-response relationship between radiation-induced DNA damage and the corresponding absorbed doses in blood irradiated with radionuclides in solution under ex vivo conditions, the absorbed dose coefficient for 1 ml for 1 h internal ex vivo irradiation of peripheral blood (dBlood) must be determined. dBlood is specific for each radionuclide, and it depends on the irradiation geometry. Therefore, the aim of this study is to use the Monte Carlo radiation transport code GATE/Geant4 to calculate the mean absorbed dose rates for ex vivo irradiation of blood with several radionuclides used in Nuclear Medicine.MethodsThe Monte Carlo simulation reproduces the irradiation geometry of a blood sample of 7 ml mixed with 1 ml of a water equivalent radioactive solution in an 8 ml vial. The simulation was performed for ten different radionuclides: 18F, 68Ga, 90Y, 99mTc, 123I, 124I, 131I, 177Lu, 223Ra, and 225Ac. Two sets of simulations for each radionuclide were performed with 1x109 histories. The first set was simulated with a mass density of 1.0525 g/cm3 of the blood plus water mixture. The second set of simulations was performed with a mass density of 1 g/cm3 for comparison with previous studies.ResultsThe values of dBlood for ten radionuclides were calculated. The values range from 10.23 mGy∙ml∙MBq-1 for 99mTc to 15632.02 mGy∙ml∙MBq-1 for 225Ac. The maximum relative change compared to previous studies was 13.0% for 124I.ConclusionThis study provides a comprehensive set of absorbed dose coefficients for 1 ml for 1 h internal ex vivo irradiation of peripheral blood in a special vial geometry and radionuclides typically used in Nuclear Medicine. Furthermore, the method proposed by this work can be easily adapted to a variety of internal irradiation conditions and serve as a reference for future studies.
| S-EPMC10082371 | biostudies-literature
Project description:BackgroundA novel remote method for external dosimetric TPS-planned auditing of intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for clinical trials using electronic portal imaging device (EPID) has been developed. The audit has been applied to multiple centers across Australia and New Zealand. This work aims to assess the audit outcomes and explores the variables that contributed to the audit results.MethodsThirty audits were performed of 21 radiotherapy facilities, 17 facilities underwent IMRT audits and 13 underwent VMAT audits. The assessment was based on comparisons between the delivered doses derived from images acquired with EPIDs and planned doses from the local treatment planning systems (TPS). Gamma pass-rate (GPR) and gamma mean value (GMV) were calculated for each IMRT field and VMAT arc (total 268 comparisons). A multiple variable linear model was applied to the GMV results (3%/3 mm criteria) to assess the influence and significance of explanatory variables. The explanatory variables were Linac-TPS combination, TPS grid resolution, IMRT/VMAT delivery, age of EPID, treatment site, record and verification system (R&V) type and dose-rate. Finally, the audit results were compared with other recent audits by calculating the incidence ratio (IR) as a ratio of the observed mean/median GPRs for the remote audit to the other audits.ResultsThe average (± 1 SD) of the centers' GPRs were: 99.3?±?1.9%, 98.6?±?2.7% & 96.2?±?5.5% at 3%, 3 mm, 3%, 2 mm and 2%, 2 mm criteria respectively. The most determinative variables on the GMVs were Linac-TPS combination, TPS grid resolution and IMRT/VMAT delivery type. The IR values were 1 for seven comparisons, indicating similar GPRs of the remote audit with the reference audits and?>?1 for four comparisons, indicating higher GPRs of the remote audit than the reference audits.ConclusionThe remote dosimetry audit method for clinical trials demonstrated high GPRs and provided results comparable to established more resource-intensive audit methods. Several factors were found to influence the results including some effect of Linac-TPS combination.
| S-EPMC6142693 | biostudies-literature
Project description:PurposeA clinical-prototype, dedicated, cone-beam breast computed tomography (CBBCT) system with offset detector is undergoing clinical evaluation at our institution. This study is to estimate the normalized glandular dose coefficients ( DgNCT ) that provide air kerma-to-mean glandular dose conversion factors using Monte Carlo simulations.Materials and methodsThe clinical prototype CBBCT system uses 49 kV x-ray spectrum with 1.39 mm 1st half-value layer thickness. Monte Carlo simulations (GATE, version 8) were performed with semi-ellipsoidal, homogeneous breasts of various fibroglandular weight fractions ( fg=0.01,0.15,0.5,1) , chest wall diameters ( d=8,10,14,18,20 cm), and chest wall to nipple length ( l=0.75d ), aligned with the axis of rotation (AOR) located at 65 cm from the focal spot to determine the DgNCT . Three geometries were considered - 40×30 -cm detector with no offset that served as reference and corresponds to a clinical CBBCT system, 30×30 -cm detector with 5 cm offset, and a 30×30 -cm detector with 10 cm offset.ResultsFor 5 cm lateral offset, the DgNCT ranged 0.177-0.574 mGy/mGy and reduction in DgNCT with respect to reference geometry was observed only for 18 cm ( 6.4%±0.23% ) and 20 cm ( 9.6%±0.22% ) diameter breasts. For the 10 cm lateral offset, the DgNCT ranged 0.221-0.581 mGy/mGy and reduction in DgNCT was observed for all breast diameters. The reduction in DgNCT was 1.4%±0.48% , 7.1%±0.13% , 17.5%±0.19% , 25.1%±0.15% , and 27.7%±0.08% for 8, 10, 14, 18, and 20 cm diameter breasts, respectively. For a given breast diameter, the reduction in DgNCT with offset-detector geometries was not dependent on fg . Numerical fits of DgNCTd,l,fg were generated for each geometry.ConclusionThe DgNCT and the numerical fit, DgNCTd,l,fg would be of benefit for current CBBCT systems using the reference geometry and for future generations using offset-detector geometry. There exists a potential for radiation dose reduction with offset-detector geometry, provided the same technique factors as the reference geometry are used, and the image quality is clinically acceptable.
| S-EPMC9007273 | biostudies-literature