Recently,deep learning (DL)‐based methods for the generation of synthetic computed tomography (sCT) have received significant research attention as an alternative to classical ones. We present here a systematic review of these methods by grouping them into three categories, according to their clinical applications: (i) to replace computed tomography in magnetic resonance (MR) based treatment planning, (ii) facilitate cone‐beam computed tomography based image‐guided adaptive radiotherapy, and (iii) derive attenuation maps for the correction of positron emission tomography. Appropriate database searching was performed on journal articles published between January 2014 and December 2020. The DL methods' key characteristics were extracted from each eligible study, and a comprehensive comparison among network architectures and metrics was reported. A detailed review of each category was given, highlighting essential contributions, identifying specific challenges, and summarizing the achievements. Lastly, the statistics of all the cited works from various aspects were analyzed, revealing the popularity and future trends and the potential of DL‐based sCT generation. The current status of DL‐based sCT generation was evaluated, assessing the clinical readiness of the presented methods.

We present an experimental study of a novel method to verify the range of proton therapy beams. Differential cross sections were measured for 15 prompt gamma-ray lines from proton-nuclear interactions with (12)C and (16)O at proton energies up to 150 MeV. These cross sections were used to model discrete prompt gamma-ray emissions along proton pencil-beams. By fitting detected prompt gamma-ray counts to these models, we simultaneously determined the beam range and the oxygen and carbon concentration of the irradiated matter. The performance of the method was assessed in two phantoms with different elemental concentrations, using a small scale prototype detector. Based on five pencil-beams with different ranges delivering 5 × 10(8) protons and without prior knowledge of the elemental composition at the measurement point, the absolute range was determined with a standard deviation of 1.0-1.4 mm. Relative range shifts at the same dose level were detected with a standard deviation of 0.3-0.5 mm. The determined oxygen and carbon concentrations also agreed well with the actual values. These results show that quantitative prompt gamma-ray measurements enable knowledge of nuclear reaction cross sections to be used for precise proton range verification in the presence of tissue with an unknown composition.

For decades, lipid droplets have been considered as the main cellular organelles involved in the fat storage, because of their lipid composition. However, in recent years, some new and totally unexpected roles have been discovered for them: (i) they are active sites for synthesis and storage of inflammatory mediators, and (ii) they are key players in cancer cells and tissues, especially in cancer stem cells. In this review, we summarize the main concepts related to the lipid droplet structure and function and their involvement in inflammatory and cancer processes.

The enormous advances in the understanding of human anatomy, physiology and pathology in recent decades have led to ever-improving methods of disease prevention, diagnosis and treatment. Many of these achievements have been enabled, at least in part, by advances in ionizing radiation detectors. Radiology has been transformed by the implementation of multi-slice CT and digital x-ray imaging systems, with silver halide films now largely obsolete for many applications. Nuclear medicine has benefited from more sensitive, faster and higher-resolution detectors delivering ever-higher SPECT and PET image quality. PET/MR systems have been enabled by the development of gamma ray detectors that can operate in high magnetic fields. These huge advances in imaging have enabled equally impressive steps forward in radiotherapy delivery accuracy, with 4DCT, PET and MRI routinely used in treatment planning and online image guidance provided by cone-beam CT. The challenge of ensuring safe, accurate and precise delivery of highly complex radiation fields has also both driven and benefited from advances in radiation detectors. Detector systems have been developed for the measurement of electron, intensity-modulated and modulated arc x-ray, proton and ion beams, and around brachytherapy sources based on a very wide range of technologies. The types of measurement performed are equally wide, encompassing commissioning and quality assurance, reference dosimetry, in vivo dosimetry and personal and environmental monitoring. In this article, we briefly introduce the general physical characteristics and properties that are commonly used to describe the behaviour and performance of both discrete and imaging detectors. The physical principles of operation of calorimeters; ionization and charge detectors; semiconductor, luminescent, scintillating and chemical detectors; and radiochromic and radiographic films are then reviewed and their principle applications discussed. Finally, a general discussion of the application of detectors for x-ray nuclear medicine and ion beam imaging and dosimetry is presented.

Treatment delivery with active beam scanning in proton radiation therapy introduces the problem of interplay effects when pencil beam motion occurs on a similar time scale as intra-fractional tumor motion. In situations where fractionation may not provide enough repetition to blur the effects of interplay, repeated delivery or 'repainting' of each field several times within a fraction has been suggested. The purpose of this work was to investigate the effectiveness of different repainting strategies in proton beam scanning. To assess the dosimetric impact of interplay effects, we performed a series of simulations considering the following parameters: tumor motion amplitude, breathing period, asymmetry in the motion trajectory for the target and time required to change the beam energy for the delivery system. Several repainting strategies were compared in terms of potential vulnerability to a dose delivery error. Breathing motion perpendicular to the beam direction (representing superior-inferior type tumor motion in patients) was considered and modeled as an asymmetric sine function with a peak-to-peak amplitude of between 10 and 30 mm. The results show that motion effects cause a narrowing of the high-dose profile and widening of the penumbra. The 90% isodose area was reduced significantly when considering a large motion amplitude of 3 cm. The broadening of the penumbra appears to depend only on the amplitude of tumor motion (assuming harmonic motion). The delivered dose exhibits a shift of 10-15% of the tumor amplitude (or 1-5 mm) in the caudal direction due to breathing asymmetry observed for both sin(4)(x) and sin(6)(x) motion. Of the five repainting techniques studied, so-called 'breath sampling' turned out to be most effective in reducing dose errors with a minimal increase in treatment time. In this method, each energy level is repainted at several evenly spaced times within one breathing period. To keep dose delivery errors below 5% while minimizing treatment time, it is recommended that breath sampling repainting be employed using 5-10 paintings per field for an assumed tumor volume of 8.5 x 8.5 x 10 cm(3). For smaller tumor volumes more repaintings will be required, while for larger volumes five repaintings should be sufficient to achieve the required dose accuracy.

We present and validate a computed tomography (CT) metal artifact reduction method that is effective for a wide spectrum of clinical implant materials. Projections through low-Z implants such as titanium were corrected using a novel physics correction algorithm that reduces beam hardening errors. In the case of high-Z implants (dental fillings, gold, platinum), projections through the implant were considered missing and regularized iterative reconstruction was performed. Both algorithms were combined if multiple implant materials were present. For comparison, a conventional projection interpolation method was implemented. In a blinded and randomized evaluation, ten radiation oncologists ranked the quality of patient scans on which the different methods were applied. For scans that included low-Z implants, the proposed method was ranked as the best method in 90% of the reviews. It was ranked superior to the original reconstruction (p = 0.0008), conventional projection interpolation (p < 0.0001) and regularized limited data reconstruction (p = 0.0002). All reviewers ranked the method first for scans with high-Z implants, and better as compared to the original reconstruction (p < 0.0001) and projection interpolation (p = 0.004). We conclude that effective reduction of CT metal artifacts can be achieved by combining algorithms tailored to specific types of implant materials.