Spot Scanning Research Articles

Performance of a scintillation imaging system for relative dosimetry in pencil beam scanning proton therapy

The proton spot scanning system requires extensive periodic quality assurance procedures to guarantee the conformality of planned dose distribution to the tumor. Detectors with stable, accurate, and fast data acquisition properties make the quality assurance procedures more efficient. For this purpose, a camera-based scintillation imaging system has been developed. A high scintillation efficiency screen coupled with a high-performance camera improved the dose sensitivity and precision required for the measurements. The dose distribution within the scintillating screen can be analyzed from the captured light distribution image in a relatively straightforward way.In this study, we investigated the performance of a 2D detection system by using a scintillating screen (silver-activated zinc sulfide powder deposited on the surface of a plastic scintillator HND-S2) for dose distribution measurement. The characteristics of the system in terms of response reproducibility, linear dose–response, and beam spot size dependence on proton dose were assessed in a series of proton irradiations. To evaluate the accuracy of lateral dose profiles measured by the ZnS: Ag based scintillating screen, we compared the results with plastic scintillator BC-408 and some commercial quality control devices. Several measurements were conducted with proton energies ranging from 70–235 MeV. We found that the detector showed stable response reproducibility (better than 1.6%) and good dose–response linearity (R2¿0.999). The beam spot size was independent of proton dose when the response of the pixel value was between 10% and 90% of the maximum. The in-air spot size measured by the ZnS: Ag based scintillating screen was found to be slightly smaller than the Lynx detector while the BC-408 showed a slightly bigger spot size. The inter-comparison results for scanned fields showed good agreements. The observed differences in beam profile measurement between the inorganic and organic scintillating screens were mainly due to their optical properties and structures. The developed scintillation imaging system with an effective resolution of 0.12 mm proved to be a reliable device for efficiently performing the quality checks for two-dimensional proton dosimetry.

DR-only Carbon-ion radiotherapy treatment planning via deep learning

PurposeTo evaluate the feasibility of patient-specific digital radiography (DR)-only treatment planning for carbon ion radiotherapy in anthropomorphic thorax-and-abdomen phantom and head-and-neck patients. MethodsThe study was conducted on the anthropomorphic phantom and head-and-neck patients. We collected computed tomography (CT) and DR images of the phantom and cone beam CT (CBCT) and DR images of the patients, respectively. Two different deep neural networks were established to correlate the relationships between DR and digitally reconstructed radiograph (DRR) images, as well as DRR and CT images. The similarity between CT and predicted CT images was evaluated by computing the mean absolute error (MAE), root mean square error (RMSE), peak signal-to-noise ratio (PSNR) and structural similarity (SSIM), respectively. Dose calculations on the predicted CT images were compared against the true CT-based dose distributions for carbon-ion radiotherapy treatment planning with intensity-modulated pencil-beam spot scanning. Relative dose differences in the target volumes and organ-at-risks were computed and three-dimensional gamma analyses (3 mm, 3%) were performed. ResultsThe average MAE, RMSE, PSNR and SSIM of the framework were 0.007, 0.144, 37.496 and 0.973, respectively. The average relative dose differences between the predicted CT- and CT-based dose distributions at the same carbon-ion irradiation settings for the phantom and the patients were <2% and ≤4%, respectively. The average gamma pass-rates were >98% for the predicted CT-based versus CT-based carbon ion plans of the phantom and the patients. ConclusionWe have demonstrated the feasibility of a patient-specific DR-only treatment planning workflow for heavy ion radiotherapy by using deep learning approach.

Determination of Integral Depth Dose in Proton Pencil Beam Using Plane-parallel Ionization Chambers.

PurposeThis study aimed to determine the integral depth-dose curves and assess the geometric collection efficiency of different detector diameters in proton pencil beam scanning.Materials and MethodsThe Varian ProBeam Compact spot scanning system was used for this study. The integral depth-dose curves with a proton energy range of 130 to 220 MeV were acquired with 2 types of Bragg peak chambers: 34070 with 8-cm diameter and 34089 with 15-cm diameter (PTW), multi-layer ionization chamber with 12-cm diameter (Giraffe, IBA Dosimetry), and PeakFinder with 8-cm diameter (PTW). To assess geometric collection efficiency, the integral depth-dose curves of 8- and 12-cm chamber diameters were compared to a 15-cm chamber diameter as the largest detector.ResultsAt intermediate depths of 130, 150, 190, and 220 MeV, PTW Bragg peak chamber type 34089 provided the highest integral depth-dose curves followed by IBA Giraffe, PTW Bragg peak chamber type 34070, and PTW PeakFinder. Moreover, PTW Bragg peak chamber type 34089 had increased geometric collection efficiency up to 3.8%, 6.1%, and 3.1% when compared to PTW Bragg peak chamber type 34070, PTW PeakFinder, and IBA Giraffe, respectively.ConclusionA larger plane-parallel ionization chamber could increase the geometric collection efficiency of the detector, especially at intermediate depths and high-energy proton beams.

Shortening the delivery time of proton therapy by real-time compensation method with raster scanning

Among the various scanning techniques, spot and raster scanning are the most frequently adopted. Raster scanning turns off the beam only when each isoenergy slice irradiation is completed. This feature intrinsically solves the leakage dose and frequent beam-switching problems encountered during spot scanning. However, to shorten the delivery time of raster scanning, a sophisticated dose control strategy is required to guarantee dose distribution. In this study, a real-time compensation method with raster scanning for synchrotron systems was designed. It is characterized by a small spot-spacing planning strategy and real-time subtraction of the transient number of particles delivered between two planning-spot positions from the planned number of particles of the subsequent raster point. The efficacy of the compensation method was demonstrated by performing accurate raster scanning simulations with an in-house simulation code and accurate final dose evaluations with a commercial treatment planning system. Given the similar dose evaluation criteria under a practical high scanning speed, compared with the spot scanning method, the total delivery time of the compensated raster scanning method was significantly shortened by 53.3% in the case of irradiating a cubical target and by 28.8% in a pelvic case. Therefore, it can be concluded that real-time compensated raster scanning with a fast scanning configuration can significantly shorten the delivery time compared to that of spot scanning. It is important to reduce the pressure on patients caused by prolonged immobilization and to improve patient throughput capacity at particle therapy centers.

Nanosecond pulsed laser sintering of carbon nanotube – Silver nanocomposite thin films on a flexible substrate: In-situ temperature measurements and post-process characterizations

Cracks could be induced in metallic components of flexible electronics due to repeated large deformations during their service. This could affect their reliability and durability, which may be potentially enhanced by replacing the metal with a metal nanocomposite reinforced by carbon nanotubes (CNTs). Such nanocomposite thin films can be fabricated onto a flexible substrate via laser sintering of metallic nanoparticles (NPs) and CNTs, which is a fabrication method with several potential advantages. Despite previous studies by the authors on continuous-wave (CW) laser sintering, a systematic experimental study on the nanocomposite thin film fabrication by pulsed laser sintering has been seldomly reported in a paper to the best knowledge of the authors'. This current paper has reported experimental study on nanosecond (ns) laser pulse sintering of CNT-reinforced silver matrix nanocomposite thin-film lines on a substrate of polyimide. Both in-process time-resolved measurements of temperatures and post-process characterizations are performed. For the studied conditions, it has been discovered that with the same laser spot scanning speed and time-averaged power, 100 kHz laser pulses can produce much lower nanocomposite electrical resistivity than that by 25 kHz. The fundamental mechanism has been revealed through in-situ measurements of temperatures. It is expected to be related to the pulse-to-pulse heat accumulation effect generated by the laser pulses with the 100 kHz repetition rate, leading to a silver melt pool that is more continuous in time and has a longer lifetime. It has been found that with the same given average laser power, an optimum laser scanning speed exists, which leads to the minimum electrical resistivity of the sintered nanocomposite. At the corresponding optimum speeds and with the same average laser power, compared with the CW laser sintering, the ns laser pulse sintering can produce nanocomposite thin-film lines with similar (slightly smaller) electrical resistivity and much narrower widths at a much faster speed. An interesting “two-region” phenomenon has been discovered in the ns laser sintering. Its fundamental mechanism has been analyzed, which is expected to be related to surface vaporization-induced recoil pressure during laser sintering.

Monitoring pencil beam scanned proton radiotherapy using a large format CMOS detector

Pencil beam scanning is an effective form of proton radiotherapy for cancer treatment. Small beams of protons are magnetically deflected in order to conform to a tumour shape, and exploiting the Bragg peak in order to minimise dose deposited in healthy tissues. Compared to other therapy modalities, it presents many dosimetric challenges requiring new methods of quality-assurance to ensure the best patient outcome possible. Position Sensitive Detectors (PSD) made from Complementary Metal–Oxide–Semiconductor (CMOS) technology offer one such solution for in-situ and in-vivo dosimetry, with ongoing developments towards high resolution imaging panels that are tolerant to high levels of ionising radiation. After confirming the linearity of the detector using a pulsed laser system, the suitability of CMOS technology, the vM2428 detector, a large-format CMOS device with 50μm pixel pitch, was investigated at the University College Hospitals London NHS Foundation Trust (UCLH) proton beam centre using a 220 MeV proton beam at clinical beam currents. The shape of the proton beam was intentionally distorted, enabling the comparison of the vM2428 detector and EBT3 film spot shapes in a fault-finding scenario for QA purposes. For stationary beams, it was found that the vM2428 detector was capable of acquiring 1D and 2D beam profiles comparable to EBT3 film within a single frame (≈4 ms). The detector was then exposed to laterally displaced beams of the same spot size (”spot scanning”) that emulates a clinical beam delivery and was found able to record the beam displacement in real time. The spot-to-spot separation was measured to be 5.35 ± 0.03 mm, in agreement with the planned 5.356 mm. These results highlight the versatility and potential of large-format CMOS detectors to proton beam therapy.

DIR-based models to predict weekly anatomical changes in head and neck cancer proton therapy

Objective. We proposed two anatomical models for head and neck patients to predict anatomical changes during the course of radiotherapy. Approach. Deformable image registration was used to build two anatomical models: (1) the average model (AM) simulated systematic progressive changes across the patient cohort; (2) the refined individual model (RIM) used a patient’s CT images acquired during treatment to update the prediction for each individual patient. Planning CTs and weekly CTs were used from 20 nasopharynx patients. This dataset included 15 training patients and 5 test patients. For each test patient, a spot scanning proton plan was created. Models were evaluated using CT number differences, contours, proton spot location deviations and dose distributions. Main results. If no model was used, the CT number difference between the planning CT and the repeat CT at week 6 of treatment was on average 128.9 Hounsfield Units (HU) over the test population. This can be reduced to 115.5 HU using the AM, and to 110.5 HU using the RIM3 (RIM, updated at week (3). When the predicted contours from the models were used, the average mean surface distance of parotid glands can be reduced from 1.98 (no model) to 1.16 mm (AM) and 1.19 mm (RIM3) at week 6. Using the proton spot range, the average anatomical uncertainty over the test population reduced from 4.47 ± 1.23 (no model) to 2.41 ± 1.12 mm (AM), and 1.89 ± 0.96 mm (RIM3). Based on the gamma analysis, the average gamma index over the test patients was improved from 93.87 ± 2.48 % (no model) to 96.16 ± 1.84% (RIM3) at week 6. Significance. The AM and the RIM both demonstrated the ability to predict anatomical changes during the treatment. The RIM can gradually refine the prediction of anatomical changes based on the AM. The proton beam spots provided an accurate and effective way for uncertainty evaluation.

Effect of laser quenching process on surface hardness and wear performance of cylindrical slideway on the upper base of combined vibration separation equipment

Abstract Combined vibration equipment is widely used in the separation and classification of grain, mineral and other granular materials. The cylindrical slideway on the upper part of the base of the combined vibration equipment bears all the weight of the vibrating silo and the particulate matter in the vibrating silo during the vibration process, and supports the combined vibration of the vibrating silo and the particulate matter in the vibrating silo, the cylindrical slideway on the upper part of the base is seriously worn. The vibrating silo can only vibrate horizontally and linearly along the cylindrical slide on the upper part of the base and swing back and forth around the center of the bottom surface of the cylindrical slide on the upper part of the base. It is required that the cylindrical slide on the upper part of the base has good strength and toughness, and the contact surface has a hardness of more than 35HRC to ensure wear resistance. The effect of laser surface quenching process on the surface hardness of the upper cylindrical slide of the base is studied by using the method of three factors and four levels. The experimental results show that after laser surface quenching, the minimum surface hardness and the maximum surface hardness of the upper cylindrical slide of the base are 35.6HRC and 39.6HRC, which meet the hardness requirements of vibration equipment for the slide of the base. When 1450W laser quenching power, 500mm/min laser scanning speed and 2.25mm laser spot diameter are used, the maximum surface hardness will be 39.6HRC, which is about 38.6% higher than that of the pretreated sample. The maximum section hardness of test sample 14 after laser quenching reaches 388HV, which is about 1.25 times higher than that of the matrix in the quenching areas of samples 13, 15 and 16. It is close to the matrix hardness when it is 1.6mm away from the surface. The thickness of the surface hardened layer exceeds 0.6mm, indicating that the greater the laser power, the greater the thickness of the hardened layer. In the wear test, the minimum wear amount of sample 14 is 0.0331g, which is about 25.2% of the matrix wear amount of 0.1312g. The larger the laser power is, the smaller the scanning speed and spot diameter are, which plays a positive role in promoting the reduction of sample wear. We will use the laser surface quenching process parameters of sample 14: laser power 1450W, spot diameter 2.25mm and scanning speed 500mm/min to conduct laser quenching on the upper cylindrical slide surface of the base of the combined vibration equipment in order to obtain a thicker hardened layer and higher hardness, and greatly improve the service life, safety and stability of the combined vibration equipment.

Acquisition of High Spectral Resolution Diffuse Reflectance Image Cubes (350-2500 nm) from Archaeological Wall Paintings and Other Immovable Heritage Using a Field-Deployable Spatial Scanning Reflectance Spectrometry Hyperspectral System.

There is growing interest in bringing non-invasive laboratory-based analytical imaging tools to field sites to study wall paintings in order to collect molecular information on the macroscale. Analytical imaging tools, such as reflectance imaging spectrometry, have provided a wealth of information about artist materials and working methods, as well as painting conditions. Currently, scientific analyses of wall paintings have been limited to point-measurement techniques such as reflectance spectroscopy (near-ultraviolet, visible, near-infrared, and mid-infrared), X-ray fluorescence, and Raman spectroscopy. Macroscale data collection methods have been limited to multispectral imaging in reflectance and luminescence modes, which lacks sufficient spectral bands to allow for the mapping and identification of artist materials of interest. The development of laboratory-based reflectance and elemental imaging spectrometers and scanning systems has sparked interest in developing truly portable versions, which can be brought to field sites to study wall paintings where there is insufficient space or electrical power for laboratory instruments. This paper presents the design and testing of a simple hyperspectral system consisting of a 2D spatial spot scanning spectrometer, which provides high spectral resolution diffuse reflectance spectra from 350 to 2500 nm with high signal to noise and moderate spatial resolution (few mm). This spectral range at high spectral resolution was found to provide robust chemical specificity sufficient to identify and map many artists’ materials, as well as the byproducts of weathering and conservation coatings across the surface of ancient and Byzantine Cypriot wall paintings. Here, we present a detailed description of the hyperspectral system, its performance, and examples of its use to study wall paintings from Roman tombs in Cyprus. The spectral/spatial image processing workflow to make maps of pigments and constituent painting materials is also discussed. This type of configurable hyperspectral system and the imaging processing workflow offer a new tool for the field study of wall paintings and other immovable heritage.

Fixed Beamline Optimization for Intensity Modulated Carbon-Ion Therapy.

A major obstacle for the adoption of heavy ion therapy is the cost and technical difficulties to construct and maintain a rotational gantry. Many heavy ion treatment facilities instead choose to construct fixed beamlines as a compromise, which we propose to mitigate with optimized treatment couch angle. We formulate the integrated beam orientation and scanning spot optimization problem as a quadratic cost function with a group sparsity regularization term. The optimization problem is efficiently solved using fast iterative shrinkage-thresholding algorithm (FISTA). To test the method, we created the fixed beamline plans with couch rotation (FBCR) and without couch rotation (FB) for intensity modulated carbon-ion therapy (IMCT) and compared with the ideal scenario where both the couch and gantry have 360 degrees of freedom (GCR). FB, FBCR, and GCR IMCT plans were compared for ten pancreas cases. The FBCR plans show comparable PTV coverage and OAR doses for each pancreas case. In conclusion, the dosimetric limitation of fixed beams in heavy ion radiotherapy may be largely mitigated with integrated beam orientation optimization of the couch rotation.

Wavefront engineered light needle microscopy for axially resolved rapid volumetric imaging.

Increasing the acquisition speed of three-dimensional volumetric images is important-particularly in biological imaging-to unveil the structural dynamics and functionalities of specimens in detail. In conventional laser scanning fluorescence microscopy, volumetric images are constructed from optical sectioning images sequentially acquired by changing the observation plane, limiting the acquisition speed. Here, we present a novel method to realize volumetric imaging from two-dimensional raster scanning of a light needle spot without sectioning, even in the traditional framework of laser scanning microscopy. Information from multiple axial planes is simultaneously captured using wavefront engineering for fluorescence signals, allowing us to readily survey the entire depth range while maintaining spatial resolution. This technique is applied to real-time and video-rate three-dimensional tracking of micrometer-sized particles, as well as the prompt visualization of thick fixed biological specimens, offering substantially faster volumetric imaging.

Epithelial thickness mapping: mechanical photorefractive keratectomy versus transepithelial photorefractive keratectomy

Aim The aim of this study was to compare mechanical photorefractive keratectomy (PRK) to transepithelial photorefractive keratectomy (tPRK), used to correct mild and moderate myopia, with respect to the epithelial thickness mapping (ETM).Setting The study was carried out at Al-Mashreq Eye Center, Cairo, Egypt.Patients and methods This is a prospective comparative study that was carried out on 20 myopic patients (40 eyes), with spherical equivalent (SE) ranging from −1.0 to −5.0 D. The cases were divided into two groups: group A included the right eyes (OD) of all patients, and group B included the left eyes (OS). Group A underwent mechanical PRK using ‘hockey stick’ and excimer laser, using Mel-90 excimer laser with 250 Hz mode, and 0.7-mm spot scanning. Group B underwent tPRK using Mel-90 (8-mm lamellar ablation for 55 μm, 250 Hz). Uncorrected visual acuity (UCVA), manifest refraction, and ETM using AngioVue spectral domain optical coherence tomography systems were performed. The ETM was measured preoperatively and at 1 week, 1 month, and 3 months postoperatively. In addition, postoperative pain was assessed.Results The median preoperative UCVA was 0.3 (range, 0.2–0.4) in both eyes (OU), whereas the median preoperative best-corrected visual acuity was 1 (range, 0.8–1). There was a statistically significant increase in UCVA across the postoperative period in both groups (P<0.001). The median UCVA improved to 0.5 (OU) after 1 week, and to 0.9 (OD) and 1.0 (OS) after 1 month and remained almost the same at 3 months postoperatively. There was a statistically significant decrease in SE at all points of the follow-up period in both groups (P<0.001). A slight change in SE was observed between the first and third month postoperatively in both groups, which was statistically insignificant. Patients reported postoperative pain on the first postoperative day, which was more in the tPRK group. There was a statistically significant change in epithelial thickness across the study period in both groups (P<0.001). The ETM showed a faster epithelial regeneration in group B, which was statistically significant at 1 week postoperatively (P=0.004). The epithelial thickness continued to increase in both groups to reach almost the preoperative value at the third month postoperatively. All cases that showed postoperative haze were less than grade 1.0 (Hanna’s scale).Conclusion Mechanical PRK and tPRK provided very similar results 3 months postoperatively. Both procedures were predictable, effective, and safe. The patients reported postoperative pain on the first postoperative day that was more in the tPRK group. The tPRK group expressed a faster epithelial regeneration than the PRK group at 1 week postoperatively. However, at 3 months postoperatively, the corneal epithelium reached an almost normal thickness in both groups. Visual recovery was noted to be faster in the tPRK group.

Power supply for fast-scanning magnet in proton therapy: Design and test

Proton therapy is one of the most effective radiation methods to combat cancer and offers a substantial advantage over conventional photon therapy. Magnetic scanning systems consisting of a magnet and power supply form an integral part of proton therapy and allow the beam position (x, y) to be controlled during spot scanning. Ensuring that the dose is rapidly and precisely distributed within the contour of the tumor requires a high-precision, fast-ramp-speed, and high-stability power supply with accurate control. The present work uses a three-phase bridge rectifier and multiple series-parallel H-bridge converters to propose a prototype power supply for the scanning magnet of a magnetic scanning system. The power supply is controlled using a proportional integral controller using digital signal processing. A prototype of the scanning power supply is developed and tested, and the results demonstrate an output current of ±500A, a ramp speed of ±40 kA/s, and a short- and long-term stability of less than 20 ppm.

The Features of Stomach Vascularisation Pattern and Their Impact on Oesophageal Reconstruction with a Gastric Pull-up.

Regardless of the reconstruction surgery used, the fundamental concepts of visceral reconstruction are based on the vascular support needed for the substituting graft. The vascular factor is the main element of any reconstruction technique, as an underlying condition for the visceral material stretch and, along with other factor, for the suture safety. In the case of the stomach, a consistent vascular flow and the minimal vascular anatomy variations are the first theoretical argument. A second argument is based on the intraparietal vascular network features allowing for supplementing visceral perfusion as the blood flow is stopped in one or more pediculi. Graft hypoperfusion is, however, a potential cause of failure, and the most frequently invoked complication is, therefore, a high risk of anastomosis fistulae. A series of modern techniques - arteriography data for the pre-operative vascular reconstruction or Doppler laser fluorometry intraoperative assessments, graft oximetry, laser speckle (spot) scan or the use of indocyanine green staining (ICG) - represent methods of early determination of the gastric graft perfusion/microperfusion quality used in reducing such risks. The doubts regarding the gastric perfusion mandate the use of vascular augmentation techniques. If such techniques are not used, the final outcome is uncertain and difficult to correct.

Utilizing Pencil Beam Scan Dynamics and a Scintillation Screen to produce 3D Dose Distribution of Proton Beams

This study describes a method for producing volumetric dose profiles of proton beams from 2D slices of optical scintillation images. The method relies on a high frame rate camera acquisition (100 frames per second), the spot scanning capabilities of current proton pencil beam scanning systems, and a water equivalent scintillation screen. The acquired slices are corrected for optical blurring and ionization quenching and stacked to produce volumetric dose distribution. The volumetric optical dose profile had a pass rate of 98.3% for 2%/2mm local gamma analysis, suggesting the method can accurately measure dose profiles. The method can potentially image all clinical proton beams for pencil beam scanning systems and can extend to imaging patient plans, with further verification.

Genome scan spots common variant differences between autism and ADHD

Genome scan spots common variant differences between autism and ADHD

Performance prediction of gamma electron vertex imaging (GEVI) system for interfractional range shift detection in spot scanning proton therapy

The maximum dose delivery at the end of the beam range provides the main advantage of using proton therapy. The range of the proton beam, however, is subject to uncertainties, which limit the clinical benefits of proton therapy and, therefore, accurate in vivo verification of the beam range is desirable. For the beam range verification in spot scanning proton therapy, a prompt gamma detection system, called as gamma electron vertex imaging (GEVI) system, is under development and, in the present study, the performance of the GEVI system in spot scanning proton therapy was predicted with Geant4 Monte Carlo simulations in terms of shift detection sensitivity, accuracy and precision. The simulation results indicated that the GEVI system can detect the interfractional range shifts down to 1 mm shift for the cases considered in the present study. The results also showed that both the evaluated accuracy and precision were less than 1–2 mm, except for the scenarios where we consider all spots in the energy layer for a local shifting. It was very encouraging results that the accuracy and precision satisfied the smallest distal safety margin of the investigated beam energy (i.e., 4.88 mm for 134.9 MeV).

Improved Intra-Pixel Sensitivity Characterization Based on Diffusion and Coupling Model for Infrared Focal Plane Array Photodetector.

The high-precision characterization of the intra-pixel sensitivity (IPS) for infrared focal plane array (FPA) photodetector is of great significance to high-precision photometry and astrometry in astronomy, as well as target tracking in under-sampled remote sensing images. The discrete sub-pixel response (DSPR) model and fill factor model have been used for IPS characterization in some studies. However, these models are incomplete and lack the description of physical process of charge diffusion and capacitance coupling, leading to the inaccuracy of IPS characterization. In this paper, we propose an improved IPS characterization method based on the diffusion and coupling physical (DCP) model for infrared FPA photodetector, which considering the processes of generation and collection of the charge, can improve the accuracy of IPS characterization. The IPS model can be obtained by convolving the ideal rectangular response function with the charge diffusion function and the capacitive coupling function. Then, the IPS model is convolved with the beam spot profile to obtain the beam spot scanning response model. Finally, we calculate the parameters of IPS by fitting the beam spot scanning response map with the proposed DCP model based on the Trust-Region-Reflective algorithm. Simulated results show that when using a 3 μm beam spot to scan, the error of IPS characterization based on DCP model is 0.63%, which is better than that of DSPR model’s 3.70%. Experimental results show that the fitting error of the beam spot scan response model based on DCP model is 4.29%, which is better than that of DSPR model’s 8.31%.

Simulation study using the spots deletion technique in spot scanning proton beam therapy for prostate cancers.

The aim of the present study was to investigate the effects on the dose distribution and beam delivery time in spot scanning proton beam therapy (PBT) incorporating the spot deletion technique. A spot scanning plan was created for 30 patients with prostate cancer. The plan was then modified via two processes: Spots with lower weighting depositions were deleted (process A) and spots that were distant from the clinical target volume (CTV) were deleted (process B). The dose distribution to the organs at risk (OAR), the expanded CTV (exCTV), which was defined by a uniform expansion of the CTV by a radius of 5 mm, and the beam delivery time were compared among initial and modified plans. The V50 Gy [relative biological effectiveness (RBE)] to the rectum and bladder, and V60 Gy(RBE) to the urethral bulb, inhomogeneity index (INH) of the exCTV showed a difference (P=1.1x10-14, P=6.4x10-14, P=2.7x10-7, P=3.2x10-17), although only changes by process B were significant. Modified plan by process B showed the V50 Gy(RBE) to the rectum and bladder decreased by -2.4±1.6 and -2.3±1.4%, and the V60 Gy (RBE) to the urethral bulb decreased by -15.9±19.4%. The INH of the exCTV increased by 0.05±0.03%. On the other hand, modification of the initial plan by process A did not affect the dose of the OAR, exCTV or beam delivery time. In spot scanning PBT, modification of the initial radiotherapy plan by systemic deletion of spots distant from the CTV could result in a dose reduction to the OAR.

Photoluminescence studies of optical centers generated by the B ion irradiation in Ib diamond

The photoluminescence (PL) spectra were employed to study the optical centers generated by the B ion irradiation in Ib diamond. The luminescent spectra with zero phonon lines (ZPLs) centered at 573, 575.8, 637.9, 390.8 nm and the most of the vibronic bands in vicinity of the ZPLs were detected using 532 and 325 nm lasers. The function of spot scan, surface scan and depth scan of Renishaw micro-Raman spectrometers were performed to understand spatial distribution of the resulting high density optical centers at 80 K. Through the spatial distribution of 575.8 and 637.9 nm optical centers, it was found that it’s more advantageous to form 575.8 nm optical centers for high density nitrogen diamond irradiated by B ion and subsequent annealing. Based on the principle of electrical neutrality and the degree of lattice distortion, it was proposed that a possible defect evolution process of the B-related optical center.