PMMA Phantom Research Articles

CT dosimetry at the Australian Synchrotron for 25-100 keV photons and 35-160 mm-diameter biological specimens.

The dose length product (DLP) method for medical computed tomography (CT) dosimetry is applied on the Australian Synchrotron Imaging and Medical Beamline (IMBL). Beam quality is assessed from copper transmission measurements using image receptors, finding near 100% (20 keV), 3.3% (25 keV) and 0.5% (30-40 keV) relative contributions from third-harmonic radiation. The flat-panel-array medical image receptor is found to have a non-linear dose response curve. The amount of radiation delivered during an axial CT scan is measured as the dose in air alone, and inside cylindrical PMMA phantoms with diameters 35-160 mm for mono-energetic radiation 25-100 keV. The radiation output rate for the IMBL is comparable with that used for medical CT. Results are presented as the ratios of CT dose indices (CTDI) inside phantoms to in air with no phantom. Ratios are compared for the IMBL against medical CT where bow-tie filters shape the beam profile to reduce the absorbed dose to surface organs. CTDI ratios scale measurements in air to estimate the volumetric CTDI representing the average dose per unit length, and the dose length product representing the absorbed dose to the scanned volume. Medical CT dose calculators use the DLP, beam quality, axial collimation and helical pitch to estimate organ doses and the effective dose. The effective dose per unit DLP for medical CT is presented as a function of body region, beam energy and sample sizes from neonate to adult.

Study for pediatric protocol optimization in chest CT scans

Radiological exams are increasingly used in clinic for diagnostic analysis of different types of pathologies. These tests are associated with a dose that is received by the patient. In addition, the risks in exposure to ionizing radiation are different according to the group which the individual belongs. According to age, the group of children is more radiosensitive than adults. In this work we have obtained values of the air-weighted kerma index for chest scans studies in a Genereal Electric Computed Tomography (CT) scanner model Discovery with 64-channels. Using an adult protocol, two scans have been performed, one using a cylinder standard PMMA phantom while the second one has used an oblong chest phantom designed for a two year old pediatric patient. Furthermore, other protocols have been selected by varying the X-ray tube current but maintaining the same voltage, in order to obtain a reduction in the dose received by the pediatric patient but maintaining the image quality. The use of the adult protocol in the child phantom has generated a value in the air-weighted kerma index 89.47% greater than that received using the adult phantom. As small patients receive higher doses, the use of specific protocols for children is important for the dose reduction in CT tests. Due to the different characteristics of CT scanners and in order to optimize these protocols with regard to dose and diagnostic image quality, there is a need to have pediatric phantoms in health centers

Particle beam microstructure reconstruction and coincidence discrimination in PET monitoring for hadron therapy

Positron emission tomography is one of the most mature techniques for monitoring the particles range in hadron therapy, aiming to reduce treatment uncertainties and therefore the extent of safety margins in the treatment plan.In-beam PET monitoring has been already performed using inter-spill and post-irradiation data, i.e. while the particle beam is off or paused. The full beam acquisition procedure is commonly discarded because the particle spills abruptly increase the random coincidence rates and therefore the image noise. This is because random coincidences cannot be separated by annihilation photons originating from radioactive decays and cannot be corrected with standard random coincidence techniques due to the time correlation of the beam-induced background with the ion beam microstructure.The aim of this paper is to provide a new method to recover in-spill data to improve the images obtained with full-beam PET acquisitions. This is done by estimating the temporal microstructure of the beam and thus selecting input PET events that are less likely to be random ones. The PET detector we used was the one developed within the INSIDE project and tested at the CNAO synchrotron-based facility. The data were taken on a PMMA phantom irradiated with 72 MeV proton pencil beams. The obtained results confirm the possibility of improving the acquired PET data without any external signal coming from the synchrotron or ad hoc detectors.

Comparison of Planer Dose Equilibrium and Computed Tomography Dose Index and Implications for Reported Patient Dose Information

Technical developments are ongoing in CT, and there has been a continually increasing trend in patient prescription, resulting in increased exposure. Currently, doses delivered during CT are generally evaluated using computed tomography dose index (CTDI), which is measured with a 10 cm pencil ionization chamber placed in a 14 cm PMMA phantom. However, shortfalls in CTDI have been identified by the American Association of Physicists in Medicine (AAPM) who have proposed a new method, dose equilibrium (DEq). In this paper, the dose equilibrium was used to estimate the dose in two protocols (thoracic and abdominopelvic) and compared to CTDI values. In addition, a retrospective correction was applied to 20 patient CTDI’s by characterizing the specific DEq profile of the system scans. The results indicated the dose equilibrium estimations of two protocols, thoracic and abdominopelvic, were 29% and 30% respectively, higher than those informed by the CT scanner. In addition, a retrospective dose correction estimation of a random sample of twenty patients demonstrated an annual underestimation in absorbed dose by between 26% and 28%. Continued use of the CTDI method in quality assurance of modern CT could result in greater patient risk. AAPM Task Group 111 presents a more accurate, safer method to estimate dose and its adoption is paramount.

Scattering Noise Model Enhanced EM-TV Algorithm for Benchtop X-ray Fluorescence Computed Tomography Image Reconstruction

Current benchtop x-ray fluorescence computed tomography (XFCT) devices, which use x-ray tubes to stimulate x-ray fluorescence (XRF) photons, suffer from the contamination of Compton scatter background produced by the polychromatic incident beam. The conventional maximum-likelihood expectation-maximization (ML-EM) algorithm only considers the noise model of the XRF signal, which results in high statistical noise in reconstructed images caused by scattered photons. In this study, we proposed a scattering noise model enhanced EM-TV algorithm for benchtop XFCT image reconstruction in order to reduce the noise of scatter background and improve the sensitivity of XFCT images. The statistical noise of scattered photons was considered in the likelihood function and the EM iteration step was modified correspondingly to suppress the statistical noise caused by Compton scattered photons. The robustness of the EM iteration was improved by applying the reweighted total variation (TV) norm as the penalty function. Numerical simulations and imaging experiments of a PMMA phantom consisting of gadolinium (Gd) solutions were performed to validate the proposed algorithm. The phantom was irradiated by a cone-beam polychromatic source and the projection was recorded by a linear-array photon counting detector. For comparison, the XFCT images of Gd were reconstructed using different algorithms. Results indicate that compared with the conventional ML-EM algorithm, the proposed algorithm can obtain XFCT images with lower background noise and higher contrast, which may further improve the sensitivity and image performance of current benchtop XFCT systems.

Dose Optimization in Computer Tomography Pediatric Cranial Scans

Background and Objective: Nowadays, Computer Tomography is one of the best radiological imaging technics which can give right diagnostic information, among the detection of multiphasic adenomas, the detection of cardiac, cerebral and vascular abnormalities. Although these good qualities, this technic is too radiant for the patient. In this paper, we based on the irradiation doses delivered from the current protocols to find a practical method of their optimization during the pediatric cranial scan. Materials and Methods: This work relies on a collection of data from patients in the hospitals, so that analyze them, give the conclusions and, propose an optimal practical method to decrease the irradiation doses. To collect data, we performed a prospective study of seventeen months (from December 2017 to May 2019) carried out simultaneously in three hospitals of the city: The Centre Medical la Cathedrale (H1), the Yaounde Central Hospital (H2) and the Yaounde Gyneaco-Obstetric and pediatric hospital (H3). This study included a total of 192 cases of cerebral trauma, of which 11 cases excluded for incomplete information. The dosimetry quality control (CTDIvol) using the PMMA phantoms of 16 cm and 32 cm fulfilled. The scanographic parameters of the patient acquisition protocol were recorded and analyzed. Some of those parameters were modified and entered the CT with the help of a biomedical engineer to reduce the delivered dose. The relationship between CTDIvol and kV is statistically significant (p < 0.05) to identify significant differences in obtained results before and after the optimization of protocols. Results: Among patients, 172 are boys, and the remaining 9 are girls all were in the 0 to 15 age group. CTDIvol values varied from 34.2 mGy to 107.8 mGy and PDLs from 107.8 mGy.cm to 2214.5 mGy.cm in H1. In H2, CTDIvol varied from 5.8 mGy to 44 mGy and PDLs from 91.4 mGy.cm to 665.5 mGy.cm. CTDIvol varied between 9.34 mGy to 92.81 mGy and PDLs from 162.38 mGy.cm to 2713.67 mGy.cm in H3. All values are taken at 75th percentile, with or without contrast injection. Conclusion: The implementation of the optimization of protocols requires the display of the CT parameters to use and to respect during the traumatic brain tests. With displaying and respecting protocol, the CTDIvol decreased by almost 50 per cent.

The comparison of size-specific dose estimate in CT examination based on head and body PMMA phantom

Nowadays, a dose estimate for individual patients undergoing CT examination is carried out using the metric of size-specific dose estimate (SSDE), which is calculated by multiplying a volume CT dose index (CTDIvol) and a correction factor that is a function of patient size. Two CTDIvol values are based on head and body PMMA phantoms. There are also two values of correction factors (k), both for head and body PMMA phantoms. The purpose of this study was to compare the SSDE values calculated using head and body PMMA phantoms with their corresponding correction factors (k). The CTDIvol values were derived from the ImPACT 1.04 software for 12 CT scanners: Sensation 4, Sensation 16, Sensation 64, Light Speed, Light Speed 16, Light Speed VCT, Secura, Brilliance 16, Brilliance 64, Asteion Dual, Aquilion 4, and Aquilion 16. The size of the patients who underwent CT examination was characterized by a water-equivalent diameter (Dw) from 10 cm to 45 cm. The results indicated that the differences in SSDE values based on head and body CTDIvol were within 20%. Thus, the SSDE value can be calculated using the head or body CTDIvol bases with corresponding k value.

284. Protocol of verification of dose indicators of radiological equipment for the correct archiving and recording of dosimetric data

Purpose Dose report in radiological examination will be an issue soon with the Euratom directive 2013/59 [ [1] European Commission. Councile Directive 2013/59Euratom. Google Scholar ]. Our purpose is to analyze our results on approximately 10 years of dose control activity in our Hospital as required by the current regulations D.Lvo 187/00. The aim of the work is to analyze the measurement methods implemented on the installed radiological equipment DAP, KAP, CTDI, ESD, and compare them with our reference measurement. Methods During the acceptance tests and the annual constancy tests of all radiological equipment installed since 2007, we have set up a verification protocol of dose indicator through direct measurements with calibrated instruments [ [2] CEI EN 60580 Dose area product meter; 2001. Google Scholar ]. For DAP/KAP direct digital X-ray equipment, angiography systems radiography e fluoroscopy systems our adopted protocol controls the following parameters: accuracy, reproducibility, dependence on the field, dependence on the quality of the beam with an external calibrated DAP meter: Dose guard 100 (RTI electron ics). For CTDI vol values provided from CT scanners: Pencil ionization camera (Victoreen Instruments) and PMMA phantoms. For mammography (ESD and AGD displayed dose): measurements with calibrated dosimeter and phantoms in mammography. Results Conclusions Calibrations were requested on dose display devices in direct digital equipment (DAP) in 4% of equipments with a discrepancy of more than 20%, [Fig. 1] due to the loss of calibration due to the drop in tube efficiency. For the remaining equipment the discrepancies detected are within the limits. The verification protocol is reliable and compliant with the guidelines, useful in the preliminary phase to the registration of the dosimetric data protocol [ [3] AIFM Report: Radiation dose index monitoring (RDIM); 2016. Google Scholar ]. Dose report in radiological examination will be an issue soon with the Euratom directive 2013/59 [ [1] European Commission. Councile Directive 2013/59Euratom. Google Scholar ]. Our purpose is to analyze our results on approximately 10 years of dose control activity in our Hospital as required by the current regulations D.Lvo 187/00. The aim of the work is to analyze the measurement methods implemented on the installed radiological equipment DAP, KAP, CTDI, ESD, and compare them with our reference measurement. During the acceptance tests and the annual constancy tests of all radiological equipment installed since 2007, we have set up a verification protocol of dose indicator through direct measurements with calibrated instruments [ [2] CEI EN 60580 Dose area product meter; 2001. Google Scholar ]. For DAP/KAP direct digital X-ray equipment, angiography systems radiography e fluoroscopy systems our adopted protocol controls the following parameters: accuracy, reproducibility, dependence on the field, dependence on the quality of the beam with an external calibrated DAP meter: Dose guard 100 (RTI electron ics). For CTDI vol values provided from CT scanners: Pencil ionization camera (Victoreen Instruments) and PMMA phantoms. For mammography (ESD and AGD displayed dose): measurements with calibrated dosimeter and phantoms in mammography. Calibrations were requested on dose display devices in direct digital equipment (DAP) in 4% of equipments with a discrepancy of more than 20%, [Fig. 1] due to the loss of calibration due to the drop in tube efficiency. For the remaining equipment the discrepancies detected are within the limits. The verification protocol is reliable and compliant with the guidelines, useful in the preliminary phase to the registration of the dosimetric data protocol [ [3] AIFM Report: Radiation dose index monitoring (RDIM); 2016. Google Scholar ].

37. Intercomparison in digital angiography: Low contrast detectability and air kerma data collection from digital radiology AIFM working group members

Purpose The aim of this study is to collect Statistical Low Contrast Detectability (LCD) [1] data from different angiography using the same phantom and the same software for the analysis. Data from this study will define the reference value and the tolerance for quality control tests. Methods A phantom consisting of a square aluminum target and a 5-step-wedge (0.25–1.25 mmAl) was built. A Matlab software automatically calculates LCD values in terms of Pixel Value (PV) and contrast threshold (Cth); it also converts PV in mmAl, providing the LCD (mmAl). Phantoms and software have been distributed to the members of AIFM digital radiology working group. A simple protocol has been followed by all the physicists. Two different set up for Low Contrast Detectability measurement have been defined using, at least, two different attenuation phantoms: 16 cm PMMA phantom and 1.5 mmCu filter. Different acquisition protocols were used and LCD phantom has been employed in different modalities such as fluoroscopy, fluorography and DSA. Dosimetric data has been also collected. Results This method is able to collect low contrast detectability information from different modalities, clinical protocols and equipment by different vendors. Preliminary results have been reported in Table 1 . Conclusions The LCD phantom and statistical method can be easily implemented in angiography. Data from this study can be used to define the reference value and the tolerance for low contrast threshold quality control in digital angiography with flat panel detector. The same method can also be applied in mammography, CR and DR radiography.

Assessment of secondary neutron dose due to dental restorations in head and neck radiation therapy

Introduction: One of scientific concern is increasing of unwanted neutron dose to the patient, in head and neck radiation therapy due to the presence of some isotopes in dental restorations and head of medical linac. The aim of this study is to measure the equivalent dose of thermal and fast neutron due to head of Siemens Primus Linac and a healthy tooth, Amalgam, Ni-Cr alloy and Ceramco irradiated by 15 MV photon beams. Materials and Methods: To evaluation of production of secondary neutrons due to the various dental restorations and head of medical linac in in 15 MV photon beam of Siemens Primus linac (Siemens AG, Erlangen, Germany), three commercial dental materials were used. This dental phantom configuration was consisted of combination of two healthy teeth, a tooth filled with Amalgam, a Ni-Cr alloy and Ceramco which they were collected randomly from dentistry clinics. The dental phantom was placed in depth of 1 cm in PMMA. In order to score of thermal and fast neutron equivalent doses, CR-39 detector was used. All the results of equivalent dose are considered to the delivery of 100 cGy dose at the maximum depth of 3.1 cm in the PMMA phantom with 15 MV photon beam and 10 × 10 cm2 field. Results: It is found out the maximum fast neutron dose was scored on the phantom surface which is related to head of Siemens primus linac. About the dental restorations, maximum fast neutron equivalent dose is related to amalgam, Ceramco and Ni-Cr alloy with amount of 0.19 mSv, 1.04 mSv, and 0.97 mSv at depth of 1.8 cm, respectively and then they decrease as the depth increases. The minimum amount of thermal neutron dose was measured on the surface of phantom. In case of denture samples, after dental phantom, the trend of the thermal neutron dose is reduced. The results indicated that maximum amount of thermal equivalent dose is related to Amalgam, Ceramco and Ni-Cr alloy and is equal to 1.45 mSv, 1.38 mSv, and 1.32 mSv, respectively. Conclusion: This study indicates an interpretation about photoneutron production in presence of the various dental restorations and head of Siemens primus medical linac. Presence of some elements in metallic dentures and head of medical linac, on the path of high photon beam can leads to the additional dose in the patient body. According to these results, thermal and fast neutron equivalent dose are started with an increase then they are reduced at depths after the dental restorations. Therefore, according to these results, it is recommended that some attempt should be carried out to make sure that the dental restorations are not in the path of primary photon beam with high energy.

Usefulness of nanoparticles to making shield and protection of sensitive organs in chest CT scan test

Introduction: Recently, the use of nanoparticles has increased for many purpose in medicine. One of these is using the nano particles in shields structure to protect sensitive organs such as breast which placed inside the field of chest CT scan and receives high dose. The aim of this study was the use of nano Bi2O3 to making shield for protection breast in chest CT examination and evaluating their image quality. Method and Materials: The nano Bi2O3 powder was used for create shield at 1mm thickness. The 6-slice CT scan system and PMMA phantom were used for dose measurement. Dose measured once in present of the shield and once in absent of the shield. Also the image quality was measured. Results: Reference average dose was 8.6 mGy in chest CT scan test which changed to 7.4 mGy when Bi2O3 shield was placed on the phantom. Also CT number and noise were raised from 121 HU and 24 to 126 HU and 28. Conclusion: On the base of results, the Bi2O3 nano particles have enough potential for radiation protection and using as a shield for reducing of breast dose in CT scans with acceptable image.

104. Use of a RDIM system to analyse and optimize an interventional radiology procedure

Purpose To use NEXO[DOSE], a Radiation Dose Index Monitoring system, to collect and analyse dosimetric data to drive the optimization of the interventional radiology procedure for prostatic artery embolization (PAE). Methods NEXO[DOSE] extracts geometric (primary and secondary angles, table height) and dosimetric (irradiation type, KAP, voltage, filter) parameters from the Radiation Dose Structured Report, and calculates a skin dose map. NEXO[DOSE] separately lists the dose contribution from the acquisition mode and the fluoroscopy. In our institution, the PAE interventional procedure involved high Kerma Area Product (KAP) compared to other angiographic protocols and was associated with high risk of skin lesions. A low dose protocol was introduced and phantom characterization, i.e. entrance dose and image quality (LCD), was assessed on 24 to 30 cm PMMA phantom to better represent the patient geometry, considering that the highest dose contributions came from events with oblique angles. After optimization, patient dose was monitored using KAP and peak skin dose. Results We retrospectively analysed the exposure values of 84 patients, using NEXO[DOSE]. The acquisition dose in PAE is 70% of the total procedure: the first step was the introduction of an acquisition protocol with low entrance detector dose. The frame rate was reduced from 3 to 2 fps, and additional X-ray filtration of 1 mmAl + 0.1 mmCu was added. The fluoroscopy frame rate was also reduced from 15 to 7.5 fps. Entrance dose at the phantom surface was reduced by 49%, while the LCD reduction was 30% for details dimensions from 0.5 to 6 mm. The physicians assessed the loss of image quality to be acceptable. After optimization PAE procedures showed a 60% KAP reduction and a 49% peak skin dose reduction. Conclusions A RDIM software is a useful tool to highlight high dose procedures and to understand what parameters to modify, after a multidisciplinary team discussion.

285. Dose indices in direct digital mammography: Evaluation on phantom and on a patient sample compared with the structured dose report values

Purpose In DR mammography, comparison of the Entrance Skin Dose (ESD) and the Average Glandular Dose (AGD) data provided by the structured dose report (SR) with the measures performed on phantom and on patient. Methods Two identical mammography systems, Amulet (Fujifilm), working in AEC with W/Rh spectrum and voltage range of 26–32 kV, were taken into account. For a PMMA phantom (18 × 24 cm2, thickness of 20–70 mm) and for a sample of 21 patients, both ESD and AGD were estimated. The X-ray output was measured, while Compressed Breast Thickness (CBT), age, tube loading and voltage were taken from the SR. The analysed images are 83, grouped by patient age and CBT. The backscatter factor for the ESD is 1.08. The AGD was estimated according to the “European guidelines for quality assurance in breast cancer screening and diagnosis” (2006 and updates) [1] . In the phantom case, the breast equivalent thickness was considered. In the patient case, the average output of the two systems was used. Results The table summarises estimated mean, SD and average percentage difference between SR and estimated values for ESD and AGD by patient age and CBT. In the graph, the percentage differences are reported as a function of CBT for both PMMA and patients. In the latter case, the data were separated by age range. Conclusions Both PMMA and patient ESD from the SR are an overestimation of the calculated value of at least 20% for all the CBT considered. Percentage differences of AGD are comprised within ±15% for CBT greater than 40 mm, while for smaller thicknesses an overestimation results in the range of 15%-25%. The split of the patient AGD curve may come from the mammography systems, which may not consider the patient age in the dose calculation (hypothesis to verify with the systems producer). Download : Download high-res image (161KB) Download : Download full-size image

256. Synthesized 2D image reconstruction from Digital Breast Tomosynthesis (DBT)

Purpose Although DBT provides 3D insight into the breast, the community agrees on the necessity of two-dimensional images to facilitate comparison with previous examinations and the evaluation of microcalcifications. For this reason, more projections (at zero degree) are acquired, to provide the radiologist a conventional two-dimensional digital mammographic (DM) image. This method is often called “combo-mode” acquisition and the additional projections lead to almost double the Mean Glandular Dose (MGD). The 3D tomographic reconstruction technology of the volume under examination is based on the acquisition of images at different angles, – in this case 13 projections are used between −20 and 20 degrees – with a short-time scan. In this reconstruction process, the images are affected by artefacts that may affect the lesion identification process. Tomosynthesis, therefore, is able to identify the position of a lesion but is disturbed by artifacts. The purpose of this work is to reconstruct the zero degree projection of DBT in order to obtain a synthesized two-dimensional image with an in-house software. Methods The raw image from the central projection is processed through a denoising software based on a pyramidal decomposition of the image, a filtering by thresholding, and subsequent reconstruction of the image itself. The optimization of reconstruction parameters has been tested on the acquisition of a 45 mm thick PMMA phantom which contains 0.1 mm sheet of aluminium 1 cm2. Results A threshold parameter was identified for the denoising process for the reconstruction of the phantom and applied to clinical images. A good depiction of the microcalcifications has been found. Conclusions The proposed method offers the possibility of processing the tomosynthesis projection images and get similar results compared to DM image, without further radiation dose to the patient. The processing is very fast and can be performed during the DBT reconstruction time.

105. Upgrading Philips Allura Xper FD20 angiography system to Allura Clarity: Analysis of dose reduction and image quality

Purpose Our Allura Xper FD20 system was installed in 2013 and mainly used for stroke treatment. To reduce the radiation dose delivered to patients though maintaining the required image quality, the system was recently upgraded to Allura Clarity. The core characteristics of Allura Clarity family are new real-time image processing algorithms to reduce image noise. The aim of this work is to show the advantages obtained in terms of dose reduction for cardiac, vascular and electrophysiological studies following such upgrade. Methods For both angiographic systems, the patient dose was assessed by means of K a,e (Entrance Air Kerma) measurements, using a PMMA phantom to simulate patient attenuation. The measurement set up was the referred method indicated in the RP162 report [1] and extensively described by Martin [2] . For each investigated procedure, the measurements were carried out for most selectable fields of view and different PMMA thicknesses. The image quality was evaluated using Leeds TOR 18FG and FluoroMesh phantom for low contrast resolution and spatial resolution respectively. Results Depending on the procedure, the dose reduction is meaningful and ranges from 20% up to a factor of around 4 for fluorographic acquisitions. All K a,e values measured on Allura Clarity system are compliant with the Suspension Levels set out in the RP162 report [1] also for digital fluorographic acquisition mode. The image quality obtained with Allura Clarity is equivalent to that of the previous system. Conclusions The Allura Clarity delivers much lower dose to the patient for all clinical applications while maintaining an equivalent image quality.

135 Patient specific QA system: Experimental stress analysis by introducing intentional errors

PurposeQA procedures and their results are strictly connected to the measuring system. The purpose of this study is to investigate the sensitivity of Delta4 Phantom+ (Scandidos, 2015), by introducing intentional errors in some reference plans. It would be possible to evaluate the Delta4 ability to find errors related to the radiotherapy treatment. MethodsDelta4 Phantom+ consists of two orthogonal detector arrays placed in a 3D cylindrical PMMA phantom. Three VMAT reference plans were created in treatment planning system (Monaco, Version 5.11) and measured with Delta4 Phantom+. Reference plans are characterized by a simple geometry and involve anatomic parts such as prostate, head and neck and brain (stereotactic). The same plans were measured introducing errors during delivery. Errors introduced are: Monitor Unit variation (3%), collimator rotation by 5° and 10°, gantry error angle of 2° and 4°. The measurements were analyzed using the inherent gamma passing rate %GP (or gamma failure rate) with 2% and 2 mm criteria and 3% and 3 mm criteria. ResultsThe results show that the sensitivity of the system depends on the characteristics of irradiated plans. In particular, the stereotaxic plan shows a weakness due to the PTV volume considered and the reduced number of diodes directly interacting whit primary beam. When using 2% and 2 mm criteria and 95% as a pass rate the system detected 11 of 14 errors, while using 3% and 3 mm criteria only 6 of 14 errors were detected (Table 1). ConclusionsDelta4 Phantom+ is an efficient system for QA verification of VMAT, it will be interesting to further analyze the stereotactic case to identify the most suitable procedure.▪

High-precision compton imaging of 4.4 MeV prompt gamma-ray toward an on-line monitor for proton therapy

Proton therapy is a widely used and effective treatment for cancer. A high-dose concentration of proton beam reduces damage to normal tissues. However, it also requires a high accuracy of irradiation. PET is generally used to verify the proton range after irradiation, but, the distributions of positrons and the energy deposited by protons are not similar to each other. Recently, prompt gamma-ray imaging has attracted attention as a new, online imaging technique. In particular, 4.4 MeV gamma rays emitted from 12C* is one of the best probes to monitor the proton dose, however imaging techniques are far from established. We have developed a novel, 3-D position sensitive Compton camera based on Ce:GAGG scintillators coupled with multi-pixel photon counter (MPPC) arrays, thus making it optimized for imaging in the 1–10 MeV range. The angular resolution is 5 degrees (FWHM) at 4.4 MeV. We have established various methods to discriminate multiple-Compton and escape events, both of which can be critical backgrounds for precise imaging of prompt gamma rays. By irradiating a 70 MeV proton beam on the PMMA phantom, we demonstrated that 4.4 MeV gamma ray image is sharply concentrated on the Bragg peak, as was expected from the PHITS simulation.

Double-Field Hadrontherapy Treatment Monitoring With the INSIDE In-Beam PET Scanner: Proof of Concept

Positron emission tomography (PET) is a well established imaging technique for range monitoring in hadrontherapy. Multiple fields are standard protocol in treatments, but because of washout and residual activity background from previous irradiation plans, to this date quantitative verification of the particle range for each beam field is still an open issue. In this paper, a new method for the evaluation with a PET detector of the activity range of the second field of a treatment is discussed. Two treatment plans with two parallel-opposed beam fields, one using protons and one using carbon ions, were delivered on PMMA phantoms. In both cases, the second beam field was extracted from the first irradiation residual activity and compared with a reference image, obtained from the experimental acquisition of the second field alone. Results demonstrate good agreement between the extracted second field and the reference image, with average difference in the activity range along the preferential direction of the beam less than 0.5 mm for protons, and 1.5 mm for carbon ions. Without taking into account any preferential direction, differences within 0.5 mm were found for both cases. The method will soon be tested with nonhomogeneous phantoms and, subsequently, with in-vivo clinical data.

Real-time wireless personal dosimeter for Interventional Radiology Procedures

Medical procedures where real-time X-ray imaging is needed have rapidly increased in number in the past decades. Consequently, the personnel dosimetry for medical staff has become more important, also in light of the revision of worker safety regulations. Detailed knowledge of the dose-rate is needed to reduce the total absorbed dose during a single procedure. Real-time monitoring through wearable active devices would greatly facilitate this task. In this work, we will present the characterization of the RAPID wireless device (based on CMOS imager as X-ray sensing detector) in clinical conditions, with PMMA phantoms. The prototype has shown the capability to measure dose-rates with a frequency in the range of few Hz, and an uncertainty smaller than 10%.

In-phantom neutron dose measurement using Gafchromic film dosimeter for QA of BNCT beams

In order to improve the quality assurance (QA) procedure for beams of boron neutron capture therapy (BNCT), this study introduced using the Gafchromic film dosimeter for neutron dose measurement of BNCT beams. The crucial part of this study was investigating an approach to employ the Gafchromic film dosimeter placed inside a PMMA phantom irradiated by a BNCT beam. The spatial distribution of neutron dose of the film was determined using measurements and Monte Carlo calculations. By employing the present approach, the two-dimensional distributions of the neutron dose component of the film at specific depths in the phantom were successfully obtained. The determined neutron dose profiles were in good agreement with the calculated ones. This study also confirmed the finding that the film dosimeter is sensitive to thermal neutrons by comparing the depth-capture-reaction-rate and depth-dose distributions. Results of this work not only proved the feasibility of using the proposed method for the QA measurement of beam delivery but also revealed the advantages of easy-handling and remarkable spatial resolution of the film dosimeter when applied to BNCT fields. The present work can help to verify the dose uniformity and output stability of BNCT beams prior to clinical irradiation.