Implementation of pencil beam redefinition algorithm (PBRA) for intraoperative electron radiation therapy (IOERT) treatment planning.

PURPOSE: Similar to other radiation therapy techniques, intraoperative electron radiation therapy (IOERT) can benefit from an online treatment planning system (TPS). Among all the analytical electron dose calculation algorithms, pencil beam redefinition algorithm (PBRA) has shown an acceptable accuracy in inhomogeneities. The input dataset for PBRA includes electron planar fluence, mean direction and root mean square (RMS) spread about the mean direction which had been introduced based on the conventional linear accelerator geometry in former studies. Herein, three methods for implementing PBRA for IOERT system are presented. METHODS: The initialization parameters were identified using Monte Carlo (MC) simulation of a dedicated IOERT system equipped with a cylindrical 10 cm applicator, irradiating a water phantom. Phase space distribution of electrons was recorded on a plane below the applicator. The input dataset was extracted for 2 × 2 mm2 pixels and energy bin width of 1 MeV. RESULTS: PBRA was implemented with three initialization methods and compared to MC. The 3D gamma analysis of the algorithm with the Formula method, which was in best agreement with MC in a simple water phantom, showed passing rates of more than 99 % for all nominal energies and it was 97.1 % for 8 MeV in the presence of protecting disk and irregular surface. Implementing PBRA on CUDA C++ resulted in 5 s run time for 8 MeV nominal energy in a water phantom. CONCLUSIONS: The agreement between PBRA dose calculation and MC is promising for the development of an intraoperative TPS for IOERT.

Deep learning-based denoising of low-dose SPECT myocardial perfusion images: quantitative assessment and clinical performance.

PURPOSE: This work was set out to investigate the feasibility of dose reduction in SPECT myocardial perfusion imaging (MPI) without sacrificing diagnostic accuracy. A deep learning approach was proposed to synthesize full-dose images from the corresponding low-dose images at different dose reduction levels in the projection space. METHODS: Clinical SPECT-MPI images of 345 patients acquired on a dedicated cardiac SPECT camera in list-mode format were retrospectively employed to predict standard-dose from low-dose images at half-, quarter-, and one-eighth-dose levels. To simulate realistic low-dose projections, 50%, 25%, and 12.5% of the events were randomly selected from the list-mode data through applying binomial subsampling. A generative adversarial network was implemented to predict non-gated standard-dose SPECT images in the projection space at the different dose reduction levels. Well-established metrics, including peak signal-to-noise ratio (PSNR), root mean square error (RMSE), and structural similarity index metrics (SSIM) in addition to Pearson correlation coefficient analysis and clinical parameters derived from Cedars-Sinai software were used to quantitatively assess the predicted standard-dose images. For clinical evaluation, the quality of the predicted standard-dose images was evaluated by a nuclear medicine specialist using a seven-point (- 3 to + 3) grading scheme. RESULTS: The highest PSNR (42.49 ± 2.37) and SSIM (0.99 ± 0.01) and the lowest RMSE (1.99 ± 0.63) were achieved at a half-dose level. Pearson correlation coefficients were 0.997 ± 0.001, 0.994 ± 0.003, and 0.987 ± 0.004 for the predicted standard-dose images at half-, quarter-, and one-eighth-dose levels, respectively. Using the standard-dose images as reference, the Bland-Altman plots sketched for the Cedars-Sinai selected parameters exhibited remarkably less bias and variance in the predicted standard-dose images compared with the low-dose images at all reduced dose levels. Overall, considering the clinical assessment performed by a nuclear medicine specialist, 100%, 80%, and 11% of the predicted standard-dose images were clinically acceptable at half-, quarter-, and one-eighth-dose levels, respectively. CONCLUSION: The noise was effectively suppressed by the proposed network, and the predicted standard-dose images were comparable to reference standard-dose images at half- and quarter-dose levels. However, recovery of the underlying signals/information in low-dose images beyond a quarter of the standard dose would not be feasible (due to very poor signal-to-noise ratio) which will adversely affect the clinical interpretation of the resulting images.

Manufacturing and evaluation of a multi-purpose Iranian head and neck anthropomorphic phantom called MIHAN.

A new multi-purpose Iranian head and neck (MIHAN) anthropomorphic phantom was designed and manufactured to be used in diagnostic and therapeutic applications. Geometry of MIHAN phantom was determined based on the average dimensions acquired by CT scans of twenty patients without any medical problems in their head and neck site. Because the phantom was expected to be used with different modalities with a wide range of photon energies, attenuation coefficients of some selected materials were determined using Monte Carlo simulation. Based on analytical and simulation results, acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) were found suitable choices for soft and bony tissues, respectively. They were used in the 3D printer to build the phantom. The suitability of the materials was checked by CT number value comparison between the organs included in the phantom and the corresponding body tissues and also film dosimetry of a typical intensity-modulated radiation therapy (IMRT) plan.. Hounsfield Unit agreement and 95% ± 2% pass rate for the IMRT plan verification proved the suitability of material selection. Also, the film dosimetry showed feasibility of using MIHAN in radiotherapy plan verification workflow. In addition, PLA was introduced as a spongy bone tissue substitute for the first time.

A novel approach to classify urinary stones using dual-energy kidney, ureter and bladder (DEKUB) X-ray imaging.

OBJECTIVES: Detection of urinary stone composition before treatment can help in its management. The purpose of this work is to study the feasibility of classifying the kidney stone compositions in vivo by dual-energy kidney, ureter, and bladder (DEKUB) X-ray imaging. METHODS: Six urinary stone compositions with nine diameters were simulated in a water phantom, and two 70- and 120-kVp images were acquired by radiography tally of the Monte Carlo code. Six image features among 10 were selected for classification of the kidney stones. Four classification algorithms were applied to the dataset using MatLab software. Five-fold cross-validation was applied to the most accurate algorithm for 1000 times and the true and false detection rates were reported. RESULTS: The obtained accuracy of kidney stone classification was 96 ± 2% and this decreased with increasing noise level. The DEKUB was successful in distinguishing brushite, calcium oxalate monohydrate, cystine, and calcium phosphate stones from other types. CONCLUSIONS: Acceptable results achieved by the low-cost, low-dose DEKUB system in detection of kidney stone composition not only obviates a need for complicated imaging systems such as dual-energy computed tomography, but also provides an available and useful aid for physicians to choose between treatment approaches.

In vitro evaluation of an iodine radionuclide dosimeter (IRD) for continuous patient monitoring.

In vivo dosimetry of the patients treated by I-131 is important from patient dosimetry and radiation protection points of view. Knowledge of delivered dose to the target volume and adjacent normal tissues can improve the effectiveness of radioiodine treatment. Herein, design, fabrication, and assessment processes of an iodine radionuclide dosimeter (IRD) are explained. Two CsI(Tl) scintillator crystals coupled to photodiodes were used in IRD fabrication with specifications derived from Monte Carlo (MC) simulation. Linearity, sensitivity, and long-term performance of the system were tested. Delivered dose due to a known administered activity of I-131 was calculated by MC simulation which was validated based on the Medical Internal Radiation Dose (MIRD) Committee formalism, and the calibration factor was provided. Using the current mode signal acquisition method, the system showed a linear response up to 8.2 GBq radioiodine activity to prohibit the pile-up error without a need for correction factor. On the other hand, IRD was sensitive down to the rarely detectable activity of 7.4 MBq. A prototype version of the IRD system has been developed to guide the hospital staff for the safe release of iodine - administered patients and to provide an insight for physicians about the delivered dose to the thyroid and nearby organs. Graphical abstract IRD attached to MIHAN.

Proposition of a practical protocol for obtaining a valid radiology image using radiography tally of MCNPX Monte Carlo Code.

BACKGROUND AND OBJECTIVE: Over the past years, Monte Carlo codes have widespread use in the radiation research field. Radiography tally of MCNPX Monte Carlo code can be a popular and applicable tool for simulation of radiography images. However, validation is the most important prerequisite before using its results. METHODS: Herein, validation of MCNPX radiography tally with experimental results based on the output image parameters has been investigated. Three cubic phantoms with different thicknesses and aluminum, water, and acrylic inserts were studied. The effects of uniformity correction, the detector efficiency of X-ray in different energies, as well as noise caused by a high statistical error in the simulation were also evaluated. RESULTS: Based on the proposed protocol to correct the error and uniformity of simulated images versus experimental ones, the maximum difference of less than 5% was achieved. CONCLUSIONS: Consequently, using the presented method with fewer steps than previous similar works, the MCNPX radiography tally of Monte Carlo code is a useful and validated tool for medical investigation of radiology images.

Statistical analysis for obtaining optimum number of CT scanners in patient dose surveys for determining national diagnostic reference levels.

OBJECTIVES: To statistically determine an 'optimum number of CT scanners' for obtaining 'diagnostic reference levels' (DRLs) in CT examinations as close as possible to 'ideal DRLs' when all available CT scanners are considered. METHODS: First, six 'ideal DRLs' (CTDIVol and DLP) were determined for head, chest and abdomen/pelvis examinations by using patient-dose survey data of 100 CT scanners of different models in Tehran. Then, a 'random sampling method' was applied to different percent fractions of patient dose data of 100 CT scanners. The percent differences (PD) of the DRLs obtained from 'ideal DRLs' and their coefficients of variation (CVs) were calculated. The 'optimum number of CT scanners' determined met those of 'ideal DRL' criteria; i.e. precision (CV ≤ 10%) and accuracy (PD ≤ 10%). RESULTS: 'Optimum number of CT scanners' for determining DRLs as close as possible to 'ideal DRLs', fulfilling the stated criteria, is 43 instead of using 100. CONCLUSION: 'Optimum number of CT scanners' for obtaining DRLs as close as possible to 'ideal DRLs' was determined. This optimum number can be effectively applied in patient-dose survey situations with limited resources in a time- and cost-effective manner. KEY POINTS: • Ideal DRLs were determined by a CT patient-dose survey applied to available scanners. • 'Optimum number of CT scanners' statistically determined for DRLs is 43%. • Optimum number can be used for DRLs as if 'ideal DRLs' were determined by all scanners.

Comparison between performance of single-fiber reflectance spectroscopy (SFRS) system and colposcopy: a phase III trial.

Herein, the performance of single-fiber reflectance spectroscopy (SFRS) in detection of cervical pre-cancerous squamous intraepithelial lesions (SIL) was compared with colposcopy. Based on the previous results obtained from 167 samples and finding the contributing parameters in differentiating SILs from non-SILs, a user-friendly interface was developed to detect the SILs using SFRS system. Detection of SILs in 301 patients was performed by both SFRS system and routine colposcopy. In addition to physician-determined sites, four quarters of the cervix were measured by SFRS system and suspicious lesions detected by either method were biopsied. Histopathologic results of the biopsied species were compared to the physician judgments based on colposcopy and the results of SFRS system. SFRS could differentiate between SILs and non-SILs with mean sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 38.3, 60.9, 15.2, and 84.3%, respectively. These values were obtained as 88.3, 10.6, 15.4, and 83.1% for the colposcopy, respectively. Although sensitivity of SFRS in detection of SILs is about twofold less than the colposcopy, it can reduce the number of unnecessary biopsies by a factor of more than 5.5. Therefore, the aid of SFRS system to the physician can reduce the number of unnecessary biopsies. On the other hand, both colposcopy and SFRS methods equally suffer from low detection worth in terms of positive/negative predictive values. In conclusion, using the online, simple and non-invasive SFRS system to choose between several suspicious sites in a patient in the clinic may be recommended.

The Effect of Probe Pressure on In Vivo Single Fiber Reflectance Spectroscopy.

Introduction: Single fiber reflectance spectroscopy (SFRS) is a noninvasive procedure to quantitate tissue absorption and scattering properties. It can be used to diagnose different diseases such as malignancy and pre-cancerous conditions. The measurement is done with a fiber optic probe in contact with the tissue surface. Herein, the effect of probe pressure on the extracted parameters from human lip spectra was studied. Methods: Thirty-three normal subjects were examined with three exerted pressure levels on the right, middle and left parts of their lips. Results: The results showed variation of spectroscopic parameters with different pressure levels. However, the effect was seen between a very mild contact (pressure 1) and the other reasonably practical pressure levels normally used in the medical centers. Conclusion: SFRS can be used as a reliable diagnostic tool in clinics.

Applicability of optical reflectance spectroscopy for detection of precancerous lesions in uterine cervix in vivo.

BACKGROUND: We assessed the performance of single fiber reflectance spectroscopy (SFRS) in discriminating cervical squamous intraepithelial lesions (SIL) from non-SILs and the probable influence of environmental factors on its performance. METHODS: SFRS was used to measure the reflected light from cervical tissue of 157 patients undergoing standard colposcopy. Seven parameters extracted from the spectra in addition to two biographic parameters were used to compare the biopsy-confirmed SILs with non-SILs. The tissue classification capability was reported by receiver operating characteristic (ROC) curves. In addition, the effect of five interfering parameters, including the probe, clinician, hospital, menopausal status and age of the patient on spectroscopic parameters were investigated by the Kruskal-wallis test. RESULTS: The average vessel diameter and beta-carotene concentration were found to be the parameters contributing to tissue discrimination. SFRS could differentiate between SILs and non-SILs with sensitivity, specificity and area under the ROC curve of 63% ± 6%, 68% ± 6% and 0.69 ± 0.04, respectively. None of the five environmental parameters interfered with the discriminator spectroscopic parameters. CONCLUSIONS: SFRS was found as a noninvasive, fast, compact, cost-effective, independent, and acceptably accurate system to help the clinician to reduce the number of unnecessary biopsies during the colposcopy procedure.

The use of optical spectroscopy for in vivo detection of cervical pre-cancer.

In order to investigate the effectiveness of optical spectroscopy for in vivo diagnosis of cervical pre-cancerous conditions, a series of published studies are surveyed. The six optical technologies investigated include fluorescence spectroscopy, reflectance spectroscopy, and their combination using point probe or multispectral imaging approaches. Searching in the well-known databases, the most recent published works were sought out. Various aspects of the studies were evaluated including the details of the technology used, the pathologic threshold for tissue classification and the gold standard, the study population and prevalence of disease in this population, the method of measurement, the number of clinicians involved in the study, the classification and validation algorithms, and the performance in terms of sensitivity, specificity and, when available, the area under the receiver operating characteristic curve. Forty-four studies conducted from 1994 to 2012 were evaluated. The data are gathered in two comprehensive tables, and five illustrations are provided to simplify a comparison between studies from different points of view. There is a broad band of studies from small pilot studies through phase III clinical trials. Among the reviewed articles, only three factors were found to influence the performance of the optical spectroscopy studies. Multispectral approaches show higher specificity than the point probe approaches (p = 0.001). The use of acetic acid before measurement and prevalence of disease among the studied population, also, have an impact on the sensitivity and specificity of the studies (p < 0.05), respectively.

Single fiber reflectance spectroscopy on cervical premalignancies: the potential for reduction of the number of unnecessary biopsies.

We have assessed the value of single fiber reflectance (SFR) spectroscopy in prediction of cervical squamous intraepithelial lesions (SIL). SFR was used to measure reflected light from 32 patients undergoing standard colposcopy. Seven parameters extracted from the spectra in addition to two biographic parameters were compared in biopsy-confirmed SIL versus nonSIL. The significant parameters in the model were determined using stepwise logistic regression. The classification performance was evaluated by a leave-one-out cross-validation method and reported by receiver operating characteristic (ROC) curves. Light absorption properties and biographic characteristics of the patient contributed significantly to the accuracy of the model. Combining important parameters, the best retrospective sensitivity, specificity and area under the ROC curve for SIL sites versus nonSIL were 89%, 80% and 0.89%, respectively. SFR spectroscopy shows promise as a noninvasive, real-time method to guide the clinician in reducing the number of unnecessary biopsies. Discrimination of SIL from other abnormalities compares favorably with that obtained by fluorescence alone and by fluorescence combined with reflectance spectroscopy while the simplicity and low cost of the presented system are dominant.

Dosimetric evaluation of a novel high dose rate (HDR) intraluminal / interstitial brachytherapy applicator for gastrointestinal and bladder cancers.

High dose rate (HDR) brachytherapy is one of the accepted treatment modalities in gastro-intestinal tract and bladder carcinomas. Considering the shortcoming of contact brachytherapy routinely used in gastrointestinal tract in treatment of big tumors or invasive method of bladder treatment, an intraluminal applicator with the capability of insertion into the tumor depth seems to be useful. This study presents some dosimetric evaluations to introduce this applicator to the clinical use. The radiation attenuation characteristics of the applicator were evaluated by means of two dosimetric methods including well-type chamber and radiochromic film. The proposed 110 cm long applicator has a flexible structure made of stainless steel for easy passage through lumens and a needle tip to drill into big tumors. The 2mm diameter of the applicator is thick enough for source transition, while easy passage through any narrow lumen such as endoscope or cystoscope working channel is ensured. Well-chamber results showed an acceptably low attenuation of this steel springy applicator. Performing absolute dosimetry resulted in a correlation coefficient of R = 0.9916 (p-value ≈ 10-7) between standard interstitial applicator and the one proposed in this article. This study not only introduces a novel applicator with acceptable attenuation but also proves the response independency of the GAFCHROMIC EBT films to energy. By applying the dose response of the applicator in the treatment planning software, it can be used as a new intraluminal / interstitial applicator.