Accurate Dose Delivery Research Articles

Gel dosimetry for three dimensional proton range measurements in anthropomorphic geometries

Proton beams used for radiotherapy have potential for superior sparing of normal tissue, although range uncertainties are among the main limiting factors in the accuracy of dose delivery. The aim of this study was to benchmark an N-vinylpyrrolidone based polymer gel to perform three-dimensional measurement of geometric proton beam characteristics and especially to test its suitability as a range probe in combination with an anthropomorphic phantom.For single proton pencil beams as well as for 3×3cm2 mono-energy layers depth dose profiles, lateral dose distribution at different depths and proton range were evaluated in simple cubic gel phantoms at different energies from 75 to 115MeV and different dose levels. In addition, a 90MeV mono-energetic beam was delivered to an anthropomorphic 3D printed head phantom, which was filled with gel. Subsequently, all phantoms underwent magnetic resonance imaging using an axial pixel size of 0.68–0.98mm and with slice thicknesses of 2 or 3mm to derive a 3-dimensional distribution of the T2 relaxation time, which correlates with radiation dose. Indices describing lateral dose distribution and proton range were compared against predictions from a treatment planning system (TPS, for cubic and head phantoms) and Monte Carlo simulations (MC, for the head phantom) after manual rigid co-registration with the T2 relaxation time datasets.For all pencil beams, the FWHM agreement with TPS was better than 1mm or 7%. For the mono-energetic layer, the agreement with TPS in this respect was even better than 0.3mm in each case. With respect to range, results from gel measurements differed no more than 0.9mm (1.6%) from values predicted by TPS. In case of the anthropomorphic phantom, deviations with respect to a nominal range of about 61mm as well as in FWHM were slightly higher, namely within 1.0mm and 1.1mm respectively. Average deviations between gel and TPS/MC were similar (−0.3mm±0.4mm/−0.2±0.5mm).In conclusion, polymer gel dosimetry was found to be a valuable tool to determine geometric proton beam properties three-dimensionally and with high spatial resolution in simple cubic as well as in a more complex anthropomorphic phantom. Post registration range errors of the order of 1mm could be achieved. The additional registration uncertainty (95%) was 1mm.

Monte Carlo dosimetry modeling of focused kV x-ray radiotherapy of eye diseases with potential nanoparticle dose enhancement.

Eye plaque brachytherapy is the most common approach for intraocular cancer treatment. It is, however, invasive and subject to large setup uncertainty due to the surgical operation. We propose a novel-focused kV x-ray technique with potential nanoparticle (NP) enhancement and evaluate its application in treating choroidal melanoma and iris melanoma by Monte Carlo (MC) dosimetry modeling. A polycapillary x-ray lens was used to focus 45 kVp x rays to achieve pinpoint accuracy of dose delivery to small tumors near critical structures. In addition to allowing for beam focusing, the use of kV x rays takes advantage of the strong photoelectric absorption of metallic NPs in that energy regime and hence strong radiosensitization. We constructed an MC simulation program that takes into account the x-ray optic modeling and used GEANT4 for dosimetric calculation. Extensive phantom measurements using a prototype-focused x-ray system were carried out. The MC simulation of simple geometry phantom irradiation was first compared to measurements to verify the x-ray optic lens modeling in conjunction with the Geant4 dosimetric calculation. To simulate tumor treatment, a geometric eye model and two tumor models were constructed. Dose distributions of the simulated treatments were then calculated. NP radiosensitization was also simulated for two concentrations of 2 nm gold NP (AuNP) uniformly distributed in the tumor. The MC-simulated full width at half maximum (FWHM) and central-axis depth dose of the focused kV x-ray beam match those measured on EBT3 films within ~10% around the depth of focus of the beam. Dose distributions of the simulated ocular tumor treatments show that focused x-ray beams can concentrate the high-dose region in or close to the tumor plus margin. For the simulated posterior choroidal tumor treatment, with sufficient tumor coverage, the doses to the optic disc and fovea are substantially reduced with focused x-ray therapy compared to eye plaque treatment (3.8 vs 39.8 Gy and 11.1 vs 53.8 Gy, respectively). The eye plaque treatment was calculated using an Eye Physics plaque with I-125 seeds under TG43 assumption. For the energy spectrum used in this study, the average simulated dose enhancement ratios (DERs) are roughly 2.1 and 1.1 for 1.0% and 0.1% AuNP mass concentration in the tumor, respectively. Compared to eye plaque brachytherapy, the proposed focused kV x-ray technique is noninvasive and shows great advantage in sparing healthy critical organs without sacrificing the tumor control. The NP radiation dose enhancement is considerable at our proposed kV range even with a low NP concentration in the tumor, providing better critical structure protection and more flexibility for treatment planning.

A key-point based real-time tracking of lung tumor in x-ray image sequence by using difference of Gaussians filtering and optical flow

In radiation therapy, for accurate radiation dose delivery to a target tumor and reduction of the extra exposure of normal tissues, real-time tumor tracking is typically an important technique in lung cancer treatment since lung tumors move with patients’ respiration. To observe a tumor motion in real time, x-ray fluoroscopic devices can be employed, and various tracking techniques have been proposed to track tumors. However, development of a fast and accurate tracking method for clinical use is still a challenging task since the obscured image of the tumor can cause decreased tracking accuracy and can result in additional processing time for remedying the accuracy. In this study, a new key-point-based tumor tracking method, which is sufficiently fast and accurate, is presented. Given an x-ray image sequence, the proposed method employs a difference-of-Gaussians filtering technique to detect key points in the tumor region of the first frame which are robust against noise and outliers in the subsequent frames. In the subsequent frames, these key points are tracked using a fast optical flow technique, and tumor motion is estimated via their movement. To evaluate the performance, the proposed method has been tested on several clinical kV and MV x-ray image sequences. The experimental results showed that the average of the root mean square errors of tracking were and for kV and MV x-ray image sequences, respectively. This tracking performance was more accurate than previous tracking methods. In addition, the average processing times for each frame were and for kV and MV image sequences, respectively, and the proposed method was faster than previous methods as well as shorter than frame acquisition interval. Therefore, the proposed method has the potential for both highly accurate and fast tumor tracking in clinical applications.

A deep learning-based prediction model for gamma evaluation in patient-specific quality assurance.

Patient-specific quality assurance (QA) measurement is conducted to confirm the accuracy of dose delivery. However, measurement is time-consuming and places a heavy workload on the medical physicists and radiological technologists. In this study, we proposed a prediction model for gamma evaluation, based on deep learning. We applied the model to a QA measurement dataset of prostate cancer cases to evaluate its practicality. Sixty pretreatment verification plans from prostate cancer patients treated using intensity modulated radiation therapy were collected. Fifteen-layer convolutional neural networks (CNN) were developed to learn the sagittal planar dose distributions from a RT-3000 QA phantom (R-TECH.INC., Tokyo, Japan). The percentage gamma passing rate (GPR) was measured using GAFCHROMIC EBT3 film (Ashland Specialty Ingredients, Covington, USA). The input training data also included the volume of the PTV (planning target volume), rectum, and overlapping region, measured in cm3 , and the monitor unit values for each field. The network produced predicted GPR values at four criteria: 2%(global)/2mm, 3%(global)/2mm, 2%(global)/3mm, and 3%(global)/3mm. Adam, an algorithm for first-order gradient-based optimization of stochastic objective functions, was used for learning and for optimizing the CNN-based model. Fivefold cross-validation was applied to validate the performance of the proposed method. Forty cases were used for training and validation set in fivefold cross-validation, and the remaining 20 cases were used for the test set. The predicted and measured GPR values were compared. A linear relationship was found between the measured and predicted values, for each of the four criteria. Spearman rank correlation coefficients in validation set between measured and predicted GPR values at four criteria were 0.73 at 2%/2mm, 0.72 at 3%/2mm, 0.74 at 2%/3mm, and 0.65 at 3%/3mm, respectively (P<0.01). The Spearman rank correlation coefficients in the test set were 0.62 (P<0.01) at 2%/2mm, 0.56 (P<0.01) at 3%/2mm, 0.51 (P=0.02) at 2%/3mm, and 0.32 (P=0.16) at 3%/3mm. These results demonstrated a strong or moderate correlation between the predicted and measured values. We developed a CNN-based prediction model for patient-specific QA of dose distribution in prostate treatment. Our results suggest that deep learning may provide a useful prediction model for gamma evaluation of patient-specific QA in prostate treatment planning.

OA054] Short-lived positron emitters for in-beam positron emission tomography (PET) verification of helium therapy

Purpose Radiotherapy with helium ions is receiving considerable interest because helium ions combine advantages of both protons and carbon ions. Like other ions, range uncertainties limit the accuracy of dose delivery, thus demanding in vivo verification techniques. Previous studies [1] , [2] show the feasibility of in-beam PET monitoring of proton therapy using very short-lived positron emitters such as 12N ( T 1 / 2 = 11 ms). The extension of this approach to helium ions requires information on the production yield of these positron emitters. Given the absence of such information, we investigated the production of positron emitters for monitoring of helium therapy. Methods The cyclotron at KVI-CART was used to bombard water, graphite and calcium phosphate targets with 3He and 4He beams having a range in water of 22 mm (E = 59 and 50 MeV/u respectively). Nuclide production was assessed via the detection of the 511 keV annihilation gammas using a sodium iodide detector (NaI). The beam was delivered in beam-on/beam-off pulses to identify the PET nuclides via half-life analysis. Results The production of short-lived PET nuclides was observed in all irradiated targets. The irradiation of water and graphite targets shows a decay with a half-life of about 10 ms, indicating the production of 12N and/or 13O. The production of this short-lived component is 8.3 × 10 - 4 per 4He and 1.2 × 10 - 3 per 3He. On the water target also 18Ne ( T 1 / 2 = 1.67 s) and 19Ne ( T 1 / 2 = 17.2 s) were observed with 4He beam, whereas only 18Ne is seen with 3He. With the 4He beam on calcium phosphate target, a half-life contribution of 0.898 ± 0.039 s was observed. Since several short-lived nuclides, including 43Ti, 42Sc and 18Ne are expected, the contribution may result from one or more of these nuclides. Conclusions More detailed quantification of the production per helium ion will be given during the presentation. The large production of a 10 ms component, about 50% higher than for protons1; is promising for real-time verification of helium therapy.

Accuracy of TomoEDGE dynamic jaw field widths.

Dynamic jaw delivery on the TomoTherapy H‐series platform, entitled TomoEDGE™, is an effective tool to decrease the patient dose along the superior and inferior edges of the treatment target. The aperture of the TomoTherapy jaws, that is, field width (FW), defines the longitudinal dose profile. A consistent FW dose profile is an important quantity for accurate and reproducible dose delivery in TomoTherapy. To date, no evaluation has been made of the accuracy and precision of the dose profiles produced by dynamic jaws. This study aims to provide a long‐term evaluation of the dynamic jaw FW dose profiles obtained on TomoTherapy utilizing the TomoTherapy Quality Assurance procedure (TQA). A total of 840 dose profiles were measured during 84 TQA procedures, performed over a 2‐yr period. The full width at half maximum (FWHM) and constancy of the FW dose profile measurements were analyzed and compared with the tolerances proposed by AAPM Task Group 148 (TG‐148) and those used by the manufacturer. The FWHM evaluation showed that the FWs > 2.0 cm respect the TG‐148 tolerance of 1%, while the asymmetric FWs ≤ 2.0 cm were outside the limit in 17.3% of measurements. Constancy results evaluated along the full profiles showed that 95.2% of measurements were within 3% of the baseline for symmetric FWs and 94.8% of measurements were within 4% of the baseline for asymmetric FWs. In conclusion, the analysis confirms the accuracy and precision of TomoEDGE™ technology in jaw positioning. This study has identified the potential to establish an appropriate QA tolerance for the asymmetric FWs used in dynamic jaw movement. Finally, the clinical significance of the observed discrepancies should be studied further to understand the dosimetric effect on patient treatments.

Bladder Runner: Visual Analytics for the Exploration of RT‐Induced Bladder Toxicity in a Cohort Study

AbstractWe present the Bladder Runner, a novel tool to enable detailed visual exploration and analysis of the impact of bladder shape variation on the accuracy of dose delivery, during the course of prostate cancer radiotherapy (RT). Our tool enables the investigation of individual patients and cohorts through the entire treatment process, and it can give indications of RT‐induced complications for the patient. In prostate cancer RT treatment, despite the design of an initial plan prior to dose administration, bladder toxicity remains very common. The main reason is that the dose is delivered in multiple fractions over a period of weeks, during which, the anatomical variation of the bladder – due to differences in urinary filling – causes deviations between planned and delivered doses. Clinical researchers want to correlate bladder shape variations to dose deviations and toxicity risk through cohort studies, to understand which specific bladder shape characteristics are more prone to side effects. This is currently done with Dose‐Volume Histograms (DVHs), which provide limited, qualitative insight. The effect of bladder variation on dose delivery and the resulting toxicity cannot be currently examined with the DVHs. To address this need, we designed and implemented the Bladder Runner, which incorporates visualization strategies in a highly interactive environment with multiple linked views. Individual patients can be explored and analyzed through the entire treatment period, while inter‐patient and temporal exploration, analysis and comparison are also supported. We demonstrate the applicability of our presented tool with a usage scenario, employing a dataset of 29 patients followed through the course of the treatment, across 13 time points. We conducted an evaluation with three clinical researchers working on the investigation of RT‐induced bladder toxicity. All participants agreed that Bladder Runner provides better understanding and new opportunities for the exploration and analysis of the involved cohort data.

Applicability of Glass Dosimeters for In-vivo Dosimetry in Brachytherapy

During brachytherapy, confirming the dose delivered is very important in order to prevent radiation-associated side effects. Therefore, we aimed to confirm the accuracy of dose delivery near the source by inserting glass dosimeters within the applicator. We created an alternative pelvic phantom with the same shape and internal structures as the usual patient. In addition, we created a tandem for insertion of the glass dosimeters and measured the dose near the source by inserting the glass dosimeters into the tandem and evaluating the accuracy of the dwell position and time through the dose near the source. Errors between the values obtained from the five glass dosimeters and the values from the treatment planning system were −6.27, −2.1, −4.18, 6.31, and −0.39%, respectively. The mean error was 3.85%. This value was acceptable considering that the error of the glass dosimeter itself is approximately 3%. Even though a complement of the applicator and the error calibration is required in order to apply this technique clinically, we believe that radiation accidents and overdoses can be prevented through in-vivo dosimetry using a glass dosimeter for brachytherapy.

Estimation of extremely small field radiation dose for brain stereotactic radiotherapy using the Vero4DRT system

The purpose of this study was a dosimetric validation of the Vero4DRT for brain stereotactic radiotherapy (SRT) with extremely small fields calculated by the treatment planning system (TPS) iPlan (Ver.4.5.1; algorithm XVMC). Measured and calculated data (e.g. percentage depth dose [PDD], dose profile, and point dose) were compared for small square fields of 30 × 30, 20 × 20, 10 × 10 and 5 × 5 mm2 using ionization chambers of 0.01 or 0.04 cm3 and a diamond detector. Dose verifications were performed using an ionization chamber and radiochromic film (EBT3; the equivalent field sizes used were 8.2, 8.7, 8.9, 9.5, and 12.9 mm2) for five brain SRT cases irradiated with dynamic conformal arcs.The PDDs and dose profiles for the measured and calculated data were in good agreement for fields larger than or equal to 10 × 10 mm2 when an appropriate detector was chosen. The dose differences for point doses in fields of 30 × 30, 20 × 20, 10 × 10 and 5 × 5 mm2 were +0.48%, +0.56%, −0.52%, and +11.2% respectively. In the dose verifications for the brain SRT plans, the mean dose difference between the calculated and measured doses were −0.35% (range, −0.94% to +0.47%), with the average pass rates for the gamma index under the 3%/2 mm criterion being 96.71%, 93.37%, and 97.58% for coronal, sagittal, and axial planes respectively.The Vero4DRT system provides accurate delivery of radiation dose for small fields larger than or equal to 10 × 10 mm2.

Model-Based Sparse-to-Dense Image Registration for Realtime Respiratory Motion Estimation in Image-Guided Interventions.

Intra-interventional respiratory motion estimation is becoming a vital component in modern radiation therapy delivery or high intensity focused ultrasound systems. The treatment quality could tremendously benefit from more accurate dose delivery using real-time motion tracking based on magnetic-resonance (MR) or ultrasound (US) imaging techniques. However, current practice often relies on indirect measurements of external breathing indicators, which has an inherently limited accuracy. In this work, we present a new approach that is applicable to challenging real-time capable imaging modalities like MR-Linac scanners and 3D-US by employing contrast-invariant feature descriptors. We combine GPU-accelerated image-based realtime tracking of sparsely distributed feature points and a dense patient-specific motion-model for regularisation and sparse-to-dense interpolation within a unified optimization framework. We achieve highly accurate motion predictions with landmark errors of ≈ 1 mm for MRI (and ≈ 2 mm for US) and substantial improvements over classical template tracking strategies. Our technique can model physiological respiratory motion more realistically and deals particularly well with the sliding of lungs against the rib cage. Our model-based sparse-to-dense image registration approach allows for accurate and realtime respiratory motion tracking in image-guided interventions.

Tailored on demand anti-coagulant dosing: An in vitro and in vivo evaluation of 3D printed purpose-designed oral dosage forms

Coumarin therapy has been associated with high levels of inter- and intra-individual variation in the required dose to reach a therapeutic anticoagulation outcome. Therefore, a dynamic system that is able to achieve accurate delivery of a warfarin dose is of significant importance. Here we assess the ability of 3D printing to fabricate and deliver tailored individualised precision dosing using in-vitro and in-vivo models. Sodium warfarin loaded filaments were compounded using hot melt extrusion (HME) and further fabricated via fused deposition modelling (FDM) 3D printing to produce capsular-ovoid-shaped dosage forms loaded at 200 or 400 µg dose. The solid dosage forms and comparator warfarin aqueous solutions were administered by oral gavage to Sprague–Dawley rats. A novel UV imaging approach indicated that the erosion of the methacrylate matrix was at a rate of 16.4 and 15.2 µm/min for horizontal and vertical planes respectively. In vivo, 3D printed forms were as proportionately effective as their comparative solution form in doubling plasma exposure following a doubling of warfarin dose (184% versus 192% respectively). The 3D printed ovoids showed a lower Cmax of warfarin (1.51 and 3.33 mg/mL versus 2.5 and 6.44 mg/mL) and a longer Tmax (6 and 3.7 versus 4 and 1.5 h) in comparison to liquid formulation. This work demonstrates for the first time in vivo, the potential of FDM 3D printing to produce a tailored specific dosage form and to accurately titrate coumarin dose response to an individual patient.

Evaluation of dose profiles using Gafchromic EBT3 films in Leksell Gamma Knife 4C around inhomogeneities in the treatment of pituitary adenoma in anthropomorphic heterogeneous head phantom

PurposeThe Leksell Gamma Knife is a complete system for radiosurgery. Treatment dose planning of Gamma Knife assumes the human head as a homogenous media; thus received dose by target tissue and organs at risk may be lower or higher than predicted dose. Our main interest is to compare measured dose profiles in an anthropomorphic heterogeneous head phantom by EBT3 films with calculated dose by Leksell Gamma Plan. MethodsAn adult head phantom with size, shape and inhomogeneity the same as an adult human head was constructed. Then dose profiles across from isocenter and organs at risk were measured by EBT3 films and compared with those predicted by Leksell Gamma Plan. ResultsOur findings indicate that when isocenter placed at the target tissue near the frontal sinus cavity, overestimation and underestimation of the dose value affect the dose profiles. In some points of organs at risk, measured dose is more than calculated dose. Comparison of isodose curves near air-tissue interface shows that in higher isodose levels, dose perturbation is more seen. Distance to Agreement parameter for some isodose lines exceeds the total positioning error for Gamma Knife (± 2 mm). Also dose differences are more than numerical accuracy in dose delivery for stereotactic radiosurgery (± 5%). ConclusionsInhomogeneities in head impress dose distributions. Ignorance of inhomogeneities can cause the parts of target tissue receive under dosage and also in some points, organs at risk receive more dose. Results of this study are closer to reality because of anthropomorphic heterogeneous head phantom.

PV-0144: Are gantry angular speed variations relevant to dose delivery accuracy?

PV-0144: Are gantry angular speed variations relevant to dose delivery accuracy?

Variation in patient dose due to differences in calibration and dosimetry protocols

For precise and accurate patient dose delivery, the dosimetry system must be calibrated properly according to the recommendations of standard dosimetry protocols such as TG-51 and TRS-398. However, the dosimetry protocol followed by a calibration laboratory is usually different from the protocols that are followed by different clinics, which may result in variations in the patient dose. Our prime objective in this study was to investigate the effect of the two protocols on dosimetry measurements. Dose measurements were performed for a Co-60 teletherapy unit and a high-energy Varian linear accelerator with 6 and 15 MV photon and 6, 9, 12, and 15 MeV electron beams, following the recommendations and procedures of the AAPM TG-51 and IAEA TRS-398 dosimetry protocols. The dosimetry systems used for this study were calibrated in a Co-60 radiation beam at the Secondary Standard Dosimetry Laboratory (SSDL) PINSTECH, Pakistan, following the IAEA TRS-398 protocol. The ratio of the measured absorbed doses to water in clinical setting, Dw (TG-51/TRS-398), was 0.999 and 0.997 for 6 and 15 MV photon beams, whereas these ratios were 1.013, 1.009, 1.003, and 1.000 for 6, 9, 12, and 15 MeV electron beams, respectively. This difference in the absorbed doses-to-water Dw ratio may be attributed mainly due to beam quality (KQ) and ion recombination correction factor.

High-resolution CT Image Retrieval Using Sparse Convolutional Neural Network.

We propose a high-resolution CT image retrieval method based on sparse convolutional neural network. The proposed framework is used to train the end-to-end mapping from low-resolution to high-resolution images. The patch-wise feature of low-resolution CT is extracted and sparsely represented by a convolutional layer and a learned iterative shrinkage threshold framework, respectively. Restricted linear unit is utilized to non-linearly map the low-resolution sparse coefficients to the high-resolution ones. An adaptive high-resolution dictionary is applied to construct the informative signature which is highly connected to a high-resolution patch. Finally, we feed the signature to a convolutional layer to reconstruct the predicted high-resolution patches and average these overlapping patches to generate high-resolution CT. The loss function between reconstructed images and the corresponding ground truth high-resolution images is applied to optimize the parameters of end-to-end neural network. The well-trained map is used to generate the high-resolution CT from a new low-resolution input. This technique was tested with brain and lung CT images and the image quality was assessed using the corresponding CT images. Peak signal-to-noise ratio (PSNR), structural similarity index (SSIM) and mean absolute error (MAE) indexes were used to quantify the differences between the generated high-resolution and corresponding ground truth CT images. The experimental results showed the proposed method could enhance images resolution from low-resolution images. The proposed method has great potential in improving radiation dose calculation and delivery accuracy and decreasing CT radiation exposure of patients.

Secondary radiation measurements for particle therapy applications: charged particles produced by 4He and 12C ion beams in a PMMA target at large angle

Proton and carbon ion beams are used in the clinical practice for external radiotherapy treatments achieving, for selected indications, promising and superior clinical results with respect to x-ray based radiotherapy. Other ions, like have recently been considered as projectiles in particle therapy centres and might represent a good compromise between the linear energy transfer and the radiobiological effectiveness of ion and proton beams, allowing improved tumour control probability and minimising normal tissue complication probability. All the currently used p, and ion beams allow achieving sharp dose gradients on the boundary of the target volume, however the accurate dose delivery is sensitive to the patient positioning and to anatomical variations with respect to photon therapy. This requires beam range and/or dose release measurement during patient irradiation and therefore the development of dedicated monitoring techniques. All the proposed methods make use of the secondary radiation created by the beam interaction with the patient and, in particular, in the case of ion beams are also able to exploit the significant charged radiation component.Measurements performed to characterise the charged secondary radiation created by and particle therapy beams are reported. Charged secondary yields, energy spectra and emission profiles produced in a poly-methyl methacrylate (PMMA) target by and beams of different therapeutic energies were measured at 60° and 90° with respect to the primary beam direction. The secondary yield of protons produced along the primary beam path in a PMMA target was obtained. The energy spectra of charged secondaries were obtained from time-of-flight information, whereas the emission profiles were reconstructed exploiting tracking detector information. The obtained measurements are in agreement with results reported in the literature and suggests the feasibility of range monitoring based on charged secondary particle detection: the implications for particle therapy monitoring applications are also discussed.

Prototype volumetric ultrasound tomography image guidance system for prone stereotactic partial breast irradiation: proof-of-concept

Accurate dose delivery in stereotactic partial breast irradiation (S-PBI) is challenging because of the target position uncertainty caused by breast deformation, the target volume changes caused by lumpectomy cavity shrinkage, and the target delineation uncertainty on simulation computed tomography (CT) images caused by poor soft tissue contrast. We have developed a volumetric ultrasound tomography (UST) image guidance system for prone position S-PBI. The system is composed of a novel 3D printed rotation water tank, a patient-specific resin breast immobilization cup, and a 1D array ultrasound transducer. Coronal 2D US images were acquired in 5° increments over a 360° range, and planes were acquired every 2 mm in elevation. A super-compounding technique was used to reconstruct the image volume. The image quality of UST was evaluated with a BB-1 breast phantom and BioZorb surgical marker, and the results revealed that UST offered better soft tissue contrast than CT and similar image quality to MR. In the evaluated plane, the size and location of five embedded objects were measured and compared to MR, which is considered as the ground truth. Objects’ diameters and the distances between objects in UST differ by approximately 1 to 2 mm from those in MR, which showed that UST offers the image quality required for S-PBI. In future work we will develop a robotic system that will be ultimately implemented in the clinic.

4:21 PM Abstract No. 130 An automatic nonrigid co-registration algorithm for fusion of cone-beam computed tomography and magnetic resonance imaging: feasibility in Y90 radioembolization for hepatocellular carcinoma

Cone-beam CT (CBCT) during Y90 radioembolization (RE) of HCC allows precise selection of tumor-feeding arteries and improves accuracy of dose delivery. Co-registration with prior MRI provides additional guidance, particularly in poorly enhancing lesions. Clinically available rigid co-registration algorithms cannot account for anatomy deformations from respiratory motion and require manual interaction. Acceptable co-registration quality is unpredictable and user-dependent, limiting adoption of CBCT-MRI fusion into clinical practice. An automatic, non-rigid co-registration algorithm using the open source software packages ANTs, SLICER and Python was developed for fusion of preprocedural T1 late arterial phase MRI and CBCT acquired during the mapping phase of RE. Co-registration was performed in seven treatment-naive patients with ≤2 lesions measuring 2-10 cm. Clinically meaningful tumor and total liver volume overlays were assessed by two IR attending physicians on a nominal scale (0-5) and analyzed by the Wilcoxon test. Quantitative assessment of liver volume overlay by the non-rigid approach was performed using the dice similarity measure. Average scores for clinically meaningful overlay of target tumor(s) (4.3 vs. 4.3, p>0.99) and liver volumes (4.5 vs. 4.5, p>0.99) were identical for rigid and non-rigid algorithms. Dice similarity measure of liver volumes following non-rigid CBCT-MRI fusion was 0.88 ± 0.04. This is comparable to the best-reported measures in the literature for multi-modal, non-rigid liver co-registration. Clinically relevant CBCT-MRI fusion in HCC using an automatic, non-rigid co-registration algorithm from open source software is feasible. With further development, adoption of this approach may improve reliability and accuracy of image guidance for RE.

Determination of dose delivery accuracy and image quality in full - Field digital mammography

Accuracy of dose delivered, image quality and some technical parameters of the Fujifilm – Amuletf full field digital mammography X-ray equipment has been undertaken. The study was conducted to review the overall condition of the first full – field digital mammography equipment in Ghana with the aim of optimizing mammography practice. Quality control assessment and Mean glandular dose estimation was performed using the International Atomic Energy Agency Human Health Series 2 and 17 protocol and the European guidelines for quality assurance in breast cancer screening and diagnosis. Quantitative image analysis was performed with ImageJ software using the “Rose Model”. The results from the quality control test performed indicates that the system is functioning well. Signal-to-noise and contrast-to-noise values determined from images shows that the images are of standard quality. With the exception of 9.00 mm breast thickness which recorded a displayed Mean Glandular Dose (MGD) of 7.17 mGy, all other MGD calculated or displayed were well within the acceptable level. The percentage difference between the calculated and console displayed MGD was within the acceptable difference level of 50%. The phantom dose values obtained can be used as baseline data for future studies which can assist in setting optimization activities. The mammography X-ray equipment at the Korle-Bu teaching Hospital, Accra – Ghana is functioning under optimized conditions. It is therefore recommended for further usage.

Patient dose in image guided radiotherapy: Monte Carlo study of the CBCT dose contribution

Image Guided RadioTherapy (IGRT) is a technique whose diffusion is growing thanks to the well-recognized gain in accuracy of dose delivery. However, multiple Cone Beam Computed Tomography (CBCT) scans add dose to patients, and its contribution has to be assessed and minimized. Aim of our work was to evaluate, through Monte Carlo simulations, organ doses in IGRT due to CBCT and therapeutic MV irradiation in head-neck, thorax and pelvis districts. We developed a Monte Carlo simulation in GAMOS (Geant4-based Architecture for Medicine-Oriented Simulations), reproducing an Elekta Synergy medical linac operating at 6 and 10 MV photon energy, and we set up a scalable anthropomorphic model. After a validation by comparison with the experimental quality indexes, we evaluated the average doses to all organs and tissues belonging to the model for the three cases of irradiated district. Scattered radiation in therapy is larger than that diffused by CBCT by one to two orders of magnitude.