The effect of different adaptation strengths on image quality and radiation dose using Siemens Care Dose 4D

The purpose of this study was to evaluate the effect of different choices of adaptation strengths on image quality and radiation exposure to the patient with Siemens automatic exposure control system called CARE Dose 4D. An anthropomorphic chest phantom was used to simulate the patient and computed tomography scans were performed with a Siemens SOMATOM Sensation 16 and 64. Owing to adaptation strengths, a considerable reduction (26.6-51.5 % and 27.5-49.5 % for Sensation 16 and Sensation 64, respectively) in the radiation dose was found when compared with using a fixed tube current. There was a substantial difference in the image quality (image noise) between the adaptation strengths. Independent of selected adaptation strengths, the level of image noise throughout the chest phantom increased when CARE Dose 4D was used (p < 0.0001). We conclude that the adaptation strengths can be used to obtain user-specified modifications to image quality or radiation exposure to the patient.

Cu filtration for dose reduction in neonatal chest imaging

As neonatal chest images are frequently acquired to investigate the life-threatening lung diseases in prematurely born children, their optimisation in terms of X-ray exposure is required. The aim of this study was to investigate whether such dose-optimisation studies could be performed using a Monte Carlo computer model. More specifically, a Monte Carlo computer model was used to investigate the influence of Cu filtration on image quality and dose in neonatal chest imaging. Monte Carlo simulations were performed with the MCNPX code and used with voxel models representing prematurely born babies (590 and 1910 g). Physical image quality was derived from simulated images in terms of the signal difference-to-noise ratio and signal-to-noise ratio (SNR). To verify the simulation results, measurements were performed using the Gammex 610 Neonatal Chest Phantom, which represents a 1-2 kg neonate. A figure of merit was used to assist in evaluating the optimum balance between the image quality and the patient dose. The results show that the Monte Carlo computer model to investigate dose and image quality works well and can be used in dose-optimisation studies for real clinical practices. Furthermore, working at a specific constant incident air kerma (K(a,I)), additional filtration proved to increase SNR with 30 %, whereas working at a specific constant detector dose, extra Cu filtration reduces the lung dose with 25 %. Optimum balance between patient dose and image quality is found to be 60 kVp (using extra filtration).

Harmonisation of the appearance of digital radiographs from different vendors by means of common external image processing

The aim of the present study was to evaluate the use of common external image processing to compensate for differences in appearance between digital X-ray images from different vendors. Twenty posteroanterior chest radiographs were collected from each of three different modalities from different vendors (GE, Siemens and Canon) with vendor-specific image processing applied. The images were also extracted with neutral process parameters and processed with external image-processing software. Six experienced radiologists rated the quality and the similarity of the images with the original Siemens images. The externally processed GE images were rated of higher quality than the original GE images and more similar to the original Siemens images (p < 0.001). The opposite was obtained for the Canon images. The externally processed Siemens images were rated of similar quality as the original images. The present study indicates the possibility of using common external image processing to harmonise the appearance of images from different vendors, although the exposure parameters may need to be adjusted for individual vendors.

An airway phantom to standardize CT acquisition in multicenter clinical trials

RATIONALE AND OBJECTIVES

The purpose of this study was to demonstrate the use of a phantom to standardize low-dose chest computed tomographic (CT) protocols in children with cystic fibrosis.

MATERIALS AND METHODS

Spiral chest CT scans of a Plexiglas phantom simulating airway sizes (internal diameter, 1.1-16.4 mm; wall thickness, 0.4-4.6 mm) in children with cystic fibrosis were obtained using two multidetector CT (MDCT) scanners (GE VCT and Siemens Sensation 64). Quantitative airway measurements from both scanners were compared with micro-CT airway measurements over a range of doses (0.2-1.8 mSv) to evaluate bias and variance of measurements. The effective doses for CT protocols were estimated using the ImPACT CT Patient Dosimetry Calculator.

RESULTS

Both MDCT scanners were able to accurately measure airway sizes down to 3 mm internal diameter and 1.3 mm airway wall thickness, with errors of <3.5%. ImPACT estimates of effective dose were different for the MDCT scanners for a given peak tube voltage and product of tube current and exposure time. Accuracy and precision were not found to be associated with dose parameters for either machine. Bias in all measurements was strongly associated with airway diameter (P values < .00001), but the magnitude of bias was small (mean, 0.07 mm; maximum, 0.21 mm). Differences between machines in error components were on the order of a few micrometers.

CONCLUSIONS

The use of a standard airway phantom confirms that different MDCT scanners have similar results within dose ranges planned for potential future clinical trials. Standardized protocols can be developed that adjust for differences in radiation exposure for different MDCT scanners.

Volumetric measurement pulmonary ground-glass opacity nodules with multi-detector CT: effect of various tube current on measurement accuracy--a chest CT phantom study

RATIONALE AND OBJECTIVES

The purpose of this study was to evaluate the effect of various tube currents on the accuracy of volumetric measurements of ground-glass opacity (GGO) nodules using a chest phantom.

MATERIALS AND METHODS

A chest phantom containing 13 artificial GGO nodules with known volumes was scanned using a 64-slice computed tomographic scanner at different tube currents (30, 60, 90, 120, 150, 180, and 210 mA). Volumetric measurements were performed using software. The relative percentage error and the absolute percentage error between the volume measures on computed tomography and the reference-standard volumes were calculated. Correlations between the mean absolute percentage error and the mean attenuation of nodules and between the ratio of solid component and the mean attenuation of nodules were analyzed.

RESULTS

The relative percentage errors showed that there was substantial underestimation of nodule volumes at 30, 60, and 90 mA and substantial overestimation of volumes at 120, 150, 180, and 210 mA, but there was no statistically significant difference in absolute percentage errors (P = .876). Pearson's correlation coefficient of the mean absolute percentage errors of nodules on volumetric measurement versus the mean attenuation value of nodules showed a negative correlation, and the ratio of solid component to whole nodule versus the mean attenuation of nodules showed a positive correlation.

CONCLUSION

Volume measurement is a promising method for the quantification of GGO nodule volume. It is important to know that different tube currents can affect the accuracy of volumetric measurements.

[Optimization of histogram analysis for pediatric digital chest radiography using flat panel detector system]

Optical density of the lung area in pediatric digital chest radiography using an indirect flat panel detector (FPD) system were changed enormously by the influence of such factors as the size of lung area, gas of retroperitoneum, and so on. Our purpose in this study was to improve the stability of lung density on output images by means of optimizing histogram analysis. Chest images of a lung phantom were taken at various X-ray tube voltages and processed using a half-type region of interest (ROI) for the lung area. The shape of the histogram obtained by two different calculation methods including frequency distribution and cumulative relative frequency were compared, and digital chest images of 110 clinical cases in our hospital were classified into three age-groups (under 6 years old, over 6 years old and under 13 years old, and over 13 years old) and their histograms were analyzed. In conclusion, it was important that to analyze the histograms of age-groups, a cumulative relative frequency histogram should be used because the influence of X-ray tube voltage was lower than the frequency distribution histogram, and stabilized lung density under 6 years old could be obtained if the value of the imaging parameter for lung density from default was 90% to 85% or 80% because the distribution of lung area and its center value were significantly lower than in those over 13 years old.

Detectability of regional lung ventilation with flat-panel detector-based dynamic radiography

This study was performed to investigate the ability of breathing chest radiography using flat-panel detector (FPD) to quantify relative local ventilation. Dynamic chest radiographs during respiration were obtained using a modified FPD system. Imaging was performed in three different positions, ie, standing and right and left decubitus positions, to change the distribution of local ventilation. We measured the average pixel value in the local lung area. Subsequently, the interframe differences, as well as difference values between maximum inspiratory and expiratory phases, were calculated. The results were visualized as images in the form of a color display to show more or less x-ray translucency. Temporal changes and spatial distribution of the results were then compared to lung physiology. In the results, the average pixel value in each lung was associated with respiratory phase. In all positions, respiratory changes of pixel value in the lower area were greater than those in the upper area (P < 0.01), which was the same tendency as the regional differences in ventilation determined by respiratory physiology. In addition, in the decubitus position, it was observed that areas with large respiratory changes in pixel value moved up in the vertical direction during expiration, which was considered to be airway closure. In conclusion, breathing chest radiography using FPD was shown to be capable of quantifying relative ventilation in local lung area and detecting regional differences in ventilation and timing of airway closure. This method is expected to be useful as a new diagnostic imaging modality for evaluating relative local ventilation.

Is targeted reconstruction necessary for evaluating contrast-enhanced chest computed tomography using a liquid crystal display monitor?

PURPOSE

The aim of this study was to examine whether 20-cm field-of-view (FOV) targeted reconstruction (TR) on contrast-enhanced (CE) chest computed tomography (CT) might improve the diagnostic value compared with simple zooming (SZ) from whole-thorax FOV images using a 2 million (2M)-pixel liquid crystal display (LCD) monitor.

MATERIALS AND METHODS

We prospectively evaluated 44 patients. SZ images were magnified from a FOV of 26-34 cm (mean 29.7 cm). Parameters were 512 x 512 matrix and 3 mm thickness and interval. Images were reconstructed using a soft-tissue kernel. Three radiologists evaluated contour, spiculation, notch, pleural tag, invasion, and internal characteristics of the lesions using 5-scale scores. We also performed a phantom study to evaluate the spatial resolution of images.

RESULTS

The diagnostic value of the TR images was similar to that of the SZ images, with the findings identified in 88%-100% of the cases. Artifacts from high-density structures deteriorated the image quality in six (14%), and the SZ images were judged to be preferable in five of them. In the phantom study, there was little difference in spatial resolution between the two images.

CONCLUSION

The SZ images from whole-thorax FOV on CE chest CT were similar in quality to TR images using a 2M-pixel LCD monitor.

Patient doses and image quality in digital chest radiology

Chest X-ray examination is one of the most frequently required procedures used in clinical practice. For studying the image quality of different X-ray digital systems and for the control of patient doses during chest radiological examinations, the standard anthropomorphic lung/chest phantom RSD 330 has been used and exposed in different digital modalities available in Slovakia. To compare different techniques of chest examination, a special software has been developed that enables researchers to compare digital imaging and communications in medicine header images from different digital modalities, using a special viewer. In this paper, this special software has been used for an anonymous correspondent audit for testing image quality evaluation by comparing various parameters of chest imaging, evaluated by 84 Slovak radiologists. The results of the comparison have shown that the majority of the participating radiologists felt that the highest image quality is reached with a flat panel, assessed by the entrance surface dose value, which is approximately 75% lower than the diagnostic reference level of chest examination given in the Slovak legislation. Besides the results of the audit, the possibilities of using the software for optimisation, education and training of medical students, radiological assistants, physicists and radiologists in the field of digital radiology will be described.

Correlation of image quality with exposure index and processing protocol in a computed radiography system

The correlation of image quality with the exposure index (EI) and the processing protocol was investigated in a Kodak computed radiography (CR) system using clinical radiographs and a water phantom containing an aluminium and a copper step-wedge. The phantom was exposed to different dose levels and the acquired images were processed using four clinical protocols. The quality of these images was evaluated in terms of image brightness, contrast and noise. In clinical radiographs, there was no straightforward correlation of image quality with EI. In phantom images, higher EI values improved contrast and reduced noise but after a point this improvement does not justify the implied increase in patient dose. Image brightness, contrast and noise were also strongly dependent on the processing protocol. To obtain the images of satisfactory quality with the Kodak CR system, a dose slightly higher than those used in 400 relative speed screen-film systems and a processing protocol designated for the specific radiographic examination are required.

Thoracic imaging in the ICU

Imaging in the ICU plays a crucial role in patient care. The portable chest radiograph (CXR) is the most commonly requested radiographic examination, and, despite its limitations, it often reveals abnormalities that may not be detected clinically. Recent advances in CT technology have made it possible to obtain diagnostic-quality images even in the most dyspneic patient. This article reviews the significant contribution thoracic imaging makes in diagnosing and managing critically ill patients.

[Bedside chest radiography and optimization of radiographic conditions in the NICU with the Fuji Computed Radiography System]

We devised an application that uses the "Maximum value reading method (AutoIV)" for bedside chest radiography in a neonatal intensive care unit (NICU) that used the Fuji Computed Radiography (FCR) System. The application, named AutoIV-N, uses the relationship for density correction between radiographic conditions (mAs) and the Display Parameter (GS). GS=f (mAs) can be considered the relationship that connects FCR and the X-ray generator. When AutoIV-N is used, radiographic image contrast does not change. Further, radiographic image density fluctuation can be eliminated by random elements such as X-ray output fluctuation of the X-ray generator and the decline of photo-stimulated luminescence caused by fading of the imaging plate. Accordingly, image recording that is suitable for follow-up chest radiography is made possible. We choose nine patients and performed a comparison of radiographic density fluctuation in AutoIV-N and Fix. AutoIV-N was found to be more stable than Fix. It is possible to use the radiographic imaging condition that is optimized for all patients in the NICU by AutoIV-N. This facilitates radiation exposure optimization in medicine. (Article in Japanese).

Portable TL dosemeter--ESD phantom combination for chest and lumbar spine radiography

A thermoluminescence dosemeter (TLD)-entrance surface dose (ESD) phantom combination was calibrated in terms of air-kerma in IEC RQR X-ray radiation qualities between 50 and 150 kV. The ESD phantom was designed and constructed as a part of the work. With the combination, air-kermas were measured for four radiological examinations (two chest and two lumbar spine examinations in two hospitals), and converted to ESDa using Monte-Carlo calculated BSF data tabulated for different tube voltages, filtrations and beam diameters at 1 m distance. The results agreed with the ionisation-chamber measurements within the reported overall uncertainty of the TLD method. In the calibration, the ESD phantom can be replaced by the ISO water slab phantom unaffecting the reported overall uncertainty. Backscatter-related parameters for the ISO water slab phantom and the newly designed ESD phantom were determined for the IEC RQR qualities used in the secondary standard dosimetry laboratory of STUK at 1 m distance, including an approximate Hp(10)/Hp(0.07) ratio.

[Image quality of thickened slabs in multislice CT chest examinations: postprocessing vs. direct reconstruction]

PURPOSE

Postprocessing offers the possibility of real-time creation of thickened slabs from a set of thin slices. This allows the interactive change from thick to thin slices for better evaluation of unclear lesions. As a result the clinical workflow of MSCT evaluation can be improved. However, to be able to apply this postprocessing software in the clinical routine, degradations in the image quality (compared to standard original reconstructed images) have to be avoided. The purpose of this study was to compare the image quality of thickened slabs from MSCT chest examinations that have either been directly reconstructed from the raw data or have been retrospectively generated via postprocessing.

MATERIALS AND METHODS

Chest MSCT examinations of 20 patients (mean age: 56 years) were performed on a 16-slice MSCT scanner (Mx8000IDT16, Philips, Best, Netherlands) using the following scan parameters: 120 kV, 94 effective mAs, 16 x 1.5 mm collimation, 512 x 512 matrix, field of view 371 x 371 mm, CTDIvol = 6.3 mGy, DLP = 210 mGyxcm). Slices with a thickness of 3 and 5 mm were generated for each examination both directly from the raw data and via postprocessing. Corresponding images from postprocessing and direct reconstruction (lung/soft tissue window) were evaluated by two radiologists with respect to 5 criteria on the basis of a five-point scale: organ structure, contour of small objects, contrast, image noise and artifacts. Differences between both data sets regarding image quality were assessed for each of the 5 criteria using a Wilcoxon test with Bonferroni correction. In addition, image noise was analyzed quantitatively in a region of interest in the aorta.

RESULTS

For the lung and soft tissue window, both reviewers and all criteria, no differences in image quality were detected between the thickened slices obtained via direct reconstruction and the postprocessing method. In 96 % and 95 % of the cases images of the two reconstruction methods were graded identically for 3 mm and 5 mm slices. In the remaining 4 % and 5 %, the evaluations differed only by one point on the five-point scale. The median grade of the first reviewer was 1 and that of the second reviewer was 2. There were no differences in the quantitative analysis of image noise between both methods.

CONCLUSION

The interactive creation of thickened slices is an effective tool for the evaluation of MSCT examinations. For the defined scan parameters in this study there were no differences in image quality between postprocessing methods (e. g. slab viewer) and direct image reconstruction.

Detectability of lung nodules using flat panel detector with dual energy subtraction by two shot method: Evaluation by ROC method

The aim of this study was to evaluate the effectiveness of dual-exposure dual energy subtraction technique in flat-panel chest radiography for lung nodules detection. Chest radiographs were acquired in 100 patients (57 men and 43 women; mean age, 60.2 years; range, 18-89 years) using a flat-panel digital chest system. These images were evaluated by seven radiologists. A continuous rating scale of 0-100 was used to represent each observer's confidence level regarding the presence or absence of lung nodules. Observer performance for detection of lung nodules with subtraction images was tested by using receiver operating characteristic (ROC) analysis of individual and averaged reader data. The average area under the ROC curve (Az value) significantly increased with subtraction images (Az=0.79 in standard radiographs versus Az=0.84 with subtraction images, p<0.05). In conclusion, the two-exposure dual-energy subtraction chest radiography significantly would improve detection of lung nodules.

Influence of display quality on radiologists' performance in the detection of lung nodules on radiographs

The purpose of this study was to evaluate the influence of display quality on radiologists' performance in the detection of lung nodules. Display systems with various technical properties were considered based on their general availability in a radiology department. Their quality was assessed by physical tests. Multireader-multicase receiver operating characteristic (ROC) analysis was used to evaluate observer performance. The area under the curve (Az) was used as a metric for detectability of simulated lung nodules with diameters of 5 mm and 10 mm, and peak contrast values ranging from 0.1 (subtle) to 0.4 (evident) that were digitally superimposed on normal chest radiographs. Three experienced radiologists interpreted a batch of 60 radiographs on five different display systems; four monitors (two liquid crystal display (LCD) and two cathode ray tube (CRT) monitors) and one printed hardcopy. The physical tests showed superior performance of the two LCD monitors. ROC analysis resulted in the following Az scores: LCD-5MP Az = 0.78, hardcopy Az = 0.77, LCDc-2MP Az = 0.75, CRT-5MP Az = 0.72 and CRTc-1MP Az = 0.71. Difference in Az scores between the LCD-5MP monitor and both the CRT-5MP (p = 0.04) and CRTc-1MP (p = 0.01) monitors was significant. The primary class CRT-5MP monitor that showed reduced observer performance failed to comply with physical acceptance requirements. Luminance response was particularly observed to be insufficient. The results indicate that a quality assurance program has the potential to detect non-optimised display systems that could otherwise result in reduced observer performance.

A method to optimize the processing algorithm of a computed radiography system for chest radiography

A test methodology using an anthropomorphic-equivalent chest phantom is described for the optimization of the Agfa computed radiography "MUSICA" processing algorithm for chest radiography. The contrast-to-noise ratio (CNR) in the lung, heart and diaphragm regions of the phantom, and the "system modulation transfer function" (sMTF) in the lung region, were measured using test tools embedded in the phantom. Using these parameters the MUSICA processing algorithm was optimized with respect to low-contrast detectability and spatial resolution. Two optimum "MUSICA parameter sets" were derived respectively for maximizing the CNR and sMTF in each region of the phantom. Further work is required to find the relative importance of low-contrast detectability and spatial resolution in chest images, from which the definitive optimum MUSICA parameter set can then be derived. Prior to this further work, a compromised optimum MUSICA parameter set was applied to a range of clinical images. A group of experienced image evaluators scored these images alongside images produced from the same radiographs using the MUSICA parameter set in clinical use at the time. The compromised optimum MUSICA parameter set was shown to produce measurably better images.

[Relationship of the specifications and informative value of digital X-ray study in pulmonary tuberculosis]

Digital fluorographs used during mass chest screenings have different specifications that affect the diagnostic value of an obtained image. Visualization using on various apparatuses was compared in the context of early detection of tuberculosis of the most important skialogic signs of tuberculosis. The findings make it possible to substantively appraise the capacities of digital X-ray systems in detecting the early signs of tuberculosis and monitoring its process over time.

Revisit image control for pediatric chest radiography

PURPOSE

The aim of this study was to analyze the fraction defectiveness and efficacy of the patient immobilization device (PID) for pediatric chest radiography.

MATERIALS AND METHODS

We examined 840 plain chest radiographs in six hospitals, including four children's hospitals and two general hospitals. The mean age of the patients was 1.9 years (range 0-5 years). Two board-qualified pediatric radiologists rated (into three grades, by consensus) the degree of inspiration, rotation, lordosis, scoliosis, and cutoff or coning as well as the quality of the chest radiographs.

RESULTS

The incidence of "poor" and "very poor" quality examinations was 2/140 and 3/140 in each of two children's hospitals using PID. The corresponding figures were 9/139 and 17/140 in the two children's hospitals that did not use PID. The general hospital using PID had 14/140 "poor" and "very poor" examinations. The general hospital that did not use PID had 28/140 "poor" and "very poor" examinations. Thus, statistically better quality chest radiography was obtained with the use of PID (P < 0.001). Likewise, rotation, lordosis, and scoliosis were less frequently diagnosed as present when PID was used (P < 0.001, 0.001, 0.05). Cutoff or coning had no relation to the use of PID (P = 0.13). No significant difference was found between the degree of inspiration and the use of PID (P = 0.56).

CONCLUSION

Fraction defectiveness in the general hospital that did not use PID was as much as 14 times higher than that of the children's hospitals that used PID. The patient immobilization device is recommended for hospitals with technologists not specifically trained for pediatric examination.

Evaluation of pulmonary function using breathing chest radiography with a dynamic flat panel detector: primary results in pulmonary diseases

OBJECTIVES

Dynamic flat panel detectors (FPD) permit acquisition of distortion-free radiographs with a large field of view and high image quality. The present study was performed to evaluate pulmonary function using breathing chest radiography with a dynamic FPD. We report primary results of a clinical study and computer algorithm for quantifying and visualizing relative local pulmonary airflow.

MATERIALS AND METHODS

Dynamic chest radiographs of 18 subjects (1 emphysema, 2 asthma, 4 interstitial pneumonia, 1 pulmonary nodule, and 10 normal controls) were obtained during respiration using an FPD system. We measured respiratory changes in distance from the lung apex to the diaphragm (DLD) and pixel values in each lung area. Subsequently, the interframe differences (D-frame) and difference values between maximum inspiratory and expiratory phases (D-max) were calculated. D-max in each lung represents relative vital capacity (VC) and regional D-frames represent pulmonary airflow in each local area. D-frames were superimposed on dynamic chest radiographs in the form of color display (fusion images). The results obtained using our methods were compared with findings on computed tomography (CT) images and pulmonary functional test (PFT), which were examined before inclusion in the study.

RESULTS

In normal subjects, the D-frames were distributed symmetrically in both lungs throughout all respiratory phases. However, subjects with pulmonary diseases showed D-frame distribution patterns that differed from the normal pattern. In subjects with air trapping, there were some areas with D-frames near zero indicated as colorless areas on fusion images. These areas also corresponded to the areas showing air trapping on computed tomography images. In asthma, obstructive abnormality was indicated by areas continuously showing D-frame near zero in the upper lung. Patients with interstitial pneumonia commonly showed fusion images with an uneven color distribution accompanied by increased D-frames in the area identified as normal on computed tomography images. Furthermore, measurement of DLD was very effective for evaluating diaphragmatic kinetics.

CONCLUSIONS

This is a rapid and simple method for evaluation of respiratory kinetics for pulmonary diseases, which can reveal abnormalities in diaphragmatic kinetics and regional lung ventilation. Furthermore, quantification and visualization of respiratory kinetics is useful as an aid in interpreting dynamic chest radiographs.

Comparison between a built-in “dual side” chest imaging device and a standard “single side” CR

An integrated readout computed radiography system (Fuji XU-D1) incorporating dual-side imaging plates (ST-55BD) was analyzed in terms of modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) for standard beam qualities RQA 9 and RQA 5. NPS and DQE were assessed using a detector entrance air kerma consistent with clinical practice for chest radiography. Similar investigation was performed on a standard reader (Fuji FCR 5000) using single-side imaging plates (ST-VI). Negligible differences were found between the MTFs of the two imaging systems for RQA 9, whereas for RQA 5 the single-side system exhibited slightly superior MTF. Regarding noise response, the dual-side system turned out to be better performing for both beam qualities over a wide range of frequencies. For RQA 9, at 8 microGy, the DQE of the dual-side system was moderately higher over the whole frequency range, whereas for RQA 5, at 10 microGy, significant improvement was found at low- and midrange frequencies. As an example, at 1 cycle/mm, the following improvements in the DQE of the dual-side system were observed: +22% (RQA 9, at 8 microGy), +50% (RQA 9, at 30 microGy), and +45% (RQA 5, at 10 microGy).

Investigations of different kilovoltage x-ray energy for three-dimensional converging stereotactic radiotherapy system: Monte Carlo simulations with CT data

We are investigating three-dimensional converging stereotactic radiotherapy (3DCSRT) with suitable medium-energy x rays as treatment for small lung tumors with better dose homogeneity at the target. A computed tomography (CT) system dedicated for non-coplanar converging radiotherapy was simulated with BEAMnrc (EGS4) Monte-Carlo code for x-ray energy of 147.5, 200, 300, and 500 kilovoltage (kVp). The system was validated by comparing calculated and measured percentage of depth dose in a water phantom for the energy of 120 and 147.5 kVp. A thorax phantom and CT data from lung tumors (<20 cm3) were used to compare dose homogeneities of kVp energies with MV energies of 4, 6, and 10 MV. Three non-coplanar arcs (0 degrees and +/-25 degrees ) around the center of the target were employed. The Monte Carlo dose data format was converted to the XiO RTP format to compare dose homogeneity, differential, and integral dose volume histograms of kVp and MV energies. In terms of dose homogeneity and DVHs, dose distributions at the target of all kVp energies with the thorax phantom were better than MV energies, with mean dose absorption at the ribs (human data) of 100%, 85%, 50%, 30% for 147.5, 200, 300, and 500 kVp, respectively. Considering dose distributions and reduction of the enhanced dose absorption at the ribs, a minimum of 500 kVp is suitable for the lung kVp 3DCSRT system.