Characterization of a low-cost PIN photodiode for dosimetry in diagnostic radiology

A commercial silicon PIN-photodiode was tested and characterized as ionizing radiation detector for radiological applications. A current-to-voltage amplification stage was designed and realized in order to acquire the photodiode signal in current mode. The system was tested with clinical beams routinely used for radiography and mammography. A Monte Carlo simulation of the detector was performed with the MCNPX code in order to model and fully understand, in particular, the impact of the sensor casing on the low energy response of the device. A reproducible output linearity was found over the dose range 0.03-4.5 mGy of great clinical relevance. The system sensitivity was found to be stable at 0.2 V s Gy(-1) for effective X-ray energies between 17 and 40 keV. The batch-to-batch reproducibility of the diodes was also experimentally investigated for two different batches of 14 diodes each. An inter-comparison with dosimeters routinely used in medical physics (i.e. Barracuda MPD RTI) showed a linear correlation between PIN-photodiode readout and absorbed dose measured with Barracuda, in the range of doses received by mammography and radiology patients

A Voxel-Based Assessment of Noise Properties in Computed Tomography Imaging with the ASiR-V and ASiR Iterative Reconstruction Algorithms

Given the inherent characteristics of nonlinearity and nonstationarity of iterative reconstruction algorithms in computed tomography (CT) imaging, this study aimed to perform, for the first time, a voxel-based characterization of noise properties in CT imaging with the ASiR-V and ASiR algorithms as compared with conventional filtered back projection (FBP). Multiple repeated scans of the Catphan-504 phantom were carried out. CT images were reconstructed using FBP and ASiR/ASiR-V with different blending levels of reconstruction (20%, 40%, 60%, 80%, 100%). Noise maps and their nonuniformity index (NUI) were obtained according to the approach proposed by the report of AAPM TG-233. For the homogeneous CTP486 module, ASiR-V/ASiR allowed a noise reduction of up to 63.7%/52.9% relative to FBP. While the noise reduction values of ASiR-V-/ASiR-reconstructed images ranged up to 33.8%/39.9% and 31.2%/35.5% for air and Teflon contrast objects, respectively, these values were approximately 60%/50% for other contrast objects (PMP, LDPE, polystyrene, acrylic, Delrin). Moreover, for all contrast objects but air and Teflon, ASiR-V showed a greater noise reduction potential than ASiR when the blending level was ≥40%. While noise maps of the homogenous CTP486 module showed only a slight spatial variation of noise (NUI < 5.2%) for all reconstruction algorithms, the NUI values of iterative-reconstructed images of the nonhomogeneous CTP404 module increased nonlinearly with blending level and were 19%/15% and 6.7% for pure ASiR-V/ASiR and FBP, respectively. Overall, these results confirm the potential of ASiR-V and ASiR in reducing noise as compared with conventional FBP, suggesting, however, that the use of pure ASiR-V or ASiR might be suboptimal for specific clinical applications

Response Assessment by Volumetric Iodine Uptake Measurement: Preliminary Experience in Patients with Intermediate-Advanced Hepatocellular Carcinoma Treated with Yttrium-90 Radioembolization

Purpose: To retrospectively compare early response to yttrium-90 radioembolization (Y90) according to volumetric iodine uptake (VIU) changes, Response Evaluation Criteria In Solid Tumor 1.1 (RECIST 1.1) and modified RECIST (mRECIST) in patients with intermediate-advanced hepatocellular carcinoma (HCC) and to explore their association with survival. Materials and Methods: Twenty-four patients treated with Y90 and evaluated with dual-energy computed tomography before and 6 weeks after treatment were included. VIU was measured on late arterial phase spectral images; 6-week VIU response was defined as: complete response (CR, absence of enhancing tumor), partial response (PR, ≥ 15% VIU reduction), progressive disease (PD, ≥ 10% VIU increase) and stable disease (criteria of CR/PR/PD not met). RECIST 1.1 and mRECIST were evaluated at 6 weeks and 6 months. Responders included CR and PR. Overall survival (OS) was evaluated by Kaplan–Meier analysis and compared by Cox regression analysis. Results: High intraobserver and interobserver agreements were observed in VIU measurements (k > 0.98). VIU identified a higher number of responders (18 patients, 75%), compared to RECIST 1.1 (12.5% at 6 weeks and 23.8% at 6 months) and mRECIST (29.2% at 6 weeks and 61.9% at 6 months). There was no significant correlation between OS and RECIST 1.1 (P = 0.45 at 6 weeks; P = 0.21 at 6 months) or mRECIST (P = 0.38 at 6 weeks; P = 0.79 at 6 months); median OS was significantly higher in VIU responders (17.2 months) compared to non-responders (7.4 months) (P = 0.0022; HR 8.85; 95% CI 1.29–88.1). Conclusion: VIU is highly reproducible; as opposite to mRECIST and RECIST 1.1, early VIU response correlates with OS after Y90 in intermediate-advanced HCC patients

Collinearity and Dimensionality Reduction in Radiomics: Effect of Preprocessing Parameters in Hypertrophic Cardiomyopathy Magnetic Resonance T1 and T2 Mapping

Radiomics and artificial intelligence have the potential to become a valuable tool in clinical applications. Frequently, radiomic analyses through machine learning methods present issues caused by high dimensionality and multicollinearity, and redundant radiomic features are usually removed based on correlation analysis. We assessed the effect of preprocessing—in terms of voxel size resampling, discretization, and filtering—on correlation-based dimensionality reduction in radiomic features from cardiac T1 and T2 maps of patients with hypertrophic cardiomyopathy. For different combinations of preprocessing parameters, we performed a dimensionality reduction of radiomic features based on either Pearson’s or Spearman’s correlation coefficient, followed by the computation of the stability index. With varying resampling voxel size and discretization bin width, for both T1 and T2 maps, Pearson’s and Spearman’s dimensionality reduction produced a slightly different percentage of remaining radiomic features, with a relatively high stability index. For different filters, the remaining features’ stability was instead relatively low. Overall, the percentage of eliminated radiomic features through correlation-based dimensionality reduction was more dependent on resampling voxel size and discretization bin width for textural features than for shape or first-order features. Notably, correlation-based dimensionality reduction was less sensitive to preprocessing when considering radiomic features from T2 compared with T1 maps

Toward an effective use of laser-driven very high energy electrons for radiotherapy: Feasibility assessment of multi-field and intensity modulation irradiation schemes.

Radiotherapy with very high energy electrons has been investigated for a couple of decades as an effective approach to improve dose distribution compared to conventional photon-based radiotherapy, with the recent intriguing potential of high dose-rate irradiation. Its practical application to treatment has been hindered by the lack of hospital-scale accelerators. High-gradient laser-plasma accelerators (LPA) have been proposed as a possible platform, but no experiments so far have explored the feasibility of a clinical use of this concept. We show the results of an experimental study aimed at assessing dose deposition for deep seated tumours using advanced irradiation schemes with an existing LPA source. Measurements show control of localized dose deposition and modulation, suitable to target a volume at depths in the range from 5 to 10 cm with mm resolution. The dose delivered to the target was up to 1.6 Gy, delivered with few hundreds of shots, limited by secondary components of the LPA accelerator. Measurements suggest that therapeutic doses within localized volumes can already be obtained with existing LPA technology, calling for dedicated pre-clinical studies

Phantom ADC along each of the main orthogonal directions (ADC_i - <i>i</i> = 1, readout/left-right; <i>i</i> = 2, phase-encoding/anterior-posterior; <i>i</i> = 3, slice-selection/head-foot) for scanner-A, scanner-B and scanner-C.

<p>The bar charts depict the mean of the average value within ROI_ref ± standard deviation across five repetitions. The dashed line represents the known phantom diffusion coefficient (2.14±0.03×10⁻³ mm²/s) at the reference temperature value of 22°C.</p

Non-uniformity of maps of phantom ADC along each of the main orthogonal directions ( - <i>i</i> = 1, readout/left-right; <i>i</i> = 2, phase-encoding/anterior-posterior; <i>i</i> = 3, slice-selection/head-foot) for scanner-A, scanner-B and scanner-C.

<p>The bar charts depict the mean value ± standard deviation across five repetitions.</p

Coefficient of variation for repeated measurements of phantom ADC along each of the main orthogonal directions ( - <i>i</i> = 1, readout/left-right; <i>i</i> = 2, phase-encoding/anterior-posterior; <i>i</i> = 3, slice-selection/head-foot) for scanner-A, scanner-B and scanner-C.

<p>The bar charts depict the mean value ± standard deviation within ROI_ref.</p