Background Obesity results from an imbalance between energy intake and expenditure. In rodents and newborn humans, brown adipose tissue helps regulate energy expenditure by thermogenesis mediated by the expression of uncoupling protein 1 (UCP1), but brown adipose tissue has been considered to have no physiologic relevance in adult humans. Methods We analyzed 3640 consecutive 18F-fluorodeoxyglucose (18F-FDG) positron-emission tomographic and computed tomographic (PET–CT) scans performed for various diagnostic reasons in 1972 patients for the presence of substantial depots of putative brown adipose tissue. Such depots were defined as collections of tissue that were more than 4 mm in diameter, had the density of adipose tissue according to CT, and had maximal standardized uptake values of 18F-FDG of at least 2.0 g per milliliter, indicating high metabolic activity. Clinical indexes were recorded and compared with those of date-matched controls. Immunostaining for UCP1 was performed on biopsy specimens from t...

/pdf/identification-and-importance-of-brown-adipose-tissue-in-550n982569.pdf

Identification and Importance of Brown Adipose Tissue in Adult Humans

Geant4 is a software toolkit for the simulation of the passage of particles through matter. It is used by a large number of experiments and projects in a variety of application domains, including high energy physics, astrophysics and space science, medical physics and radiation protection. Over the past several years, major changes have been made to the toolkit in order to accommodate the needs of these user communities, and to efficiently exploit the growth of computing power made available by advances in technology. The adaptation of Geant4 to multithreading, advances in physics, detector modeling and visualization, extensions to the toolkit, including biasing and reverse Monte Carlo, and tools for physics and release validation are discussed here.

/pdf/recent-developments-in-geant4-3pgbpf1ko3.pdf

Recent developments in GEANT4

Background Radiomic features may quantify characteristics present in medical imaging. However, the lack of standardized definitions and validated reference values have hampered clinical use. Purpose To standardize a set of 174 radiomic features. Materials and Methods Radiomic features were assessed in three phases. In phase I, 487 features were derived from the basic set of 174 features. Twenty-five research teams with unique radiomics software implementations computed feature values directly from a digital phantom, without any additional image processing. In phase II, 15 teams computed values for 1347 derived features using a CT image of a patient with lung cancer and predefined image processing configurations. In both phases, consensus among the teams on the validity of tentative reference values was measured through the frequency of the modal value and classified as follows: less than three matches, weak; three to five matches, moderate; six to nine matches, strong; 10 or more matches, very strong. In the final phase (phase III), a public data set of multimodality images (CT, fluorine 18 fluorodeoxyglucose PET, and T1-weighted MRI) from 51 patients with soft-tissue sarcoma was used to prospectively assess reproducibility of standardized features. Results Consensus on reference values was initially weak for 232 of 302 features (76.8%) at phase I and 703 of 1075 features (65.4%) at phase II. At the final iteration, weak consensus remained for only two of 487 features (0.4%) at phase I and 19 of 1347 features (1.4%) at phase II. Strong or better consensus was achieved for 463 of 487 features (95.1%) at phase I and 1220 of 1347 features (90.6%) at phase II. Overall, 169 of 174 features were standardized in the first two phases. In the final validation phase (phase III), most of the 169 standardized features could be excellently reproduced (166 with CT; 164 with PET; and 164 with MRI). Conclusion A set of 169 radiomics features was standardized, which enabled verification and calibration of different radiomics software. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Kuhl and Truhn in this issue.

https://pubs.rsna.org/doi/pdf/10.1148/radiol.2020191145

The Image Biomarker Standardization Initiative: Standardized Quantitative Radiomics for High-Throughput Image-based Phenotyping

The text consists of two sections, one for those studying or practicing diagnostic radiology, nuclear medicine and radiation oncology; the other for those engaged in the study or clinical practice of radiation oncology--a new chapter, on radiologic terrorism, is specifically for those in the radiation sciences who would manage exposed individuals in the event of a terrorist event. The 17 chapters in Section I represent a general introduction to radiation biology and a complete, self-contained course especially for residents in diagnostic radiology and nuclear medicine that follows the Syllabus in Radiation Biology of the RSNA. The 11 chapters in Section II address more in-depth topics in radiation oncology, such as cancer biology, retreatment after radiotherapy, chemotherapeutic agents and hyperthermia.

Radiobiology for the Radiologist

The FLUKA Code: Developments and Challenges for High Energy and Medical Applications

Purpose: The IAEA TRS-398 code of practice details the reference conditions for reference dosimetry of proton beams using ionization chambers and the required beam quality correction factors (kQ). Pencil beam scanning (PBS) requires multiple spots to reproduce the reference conditions. The objective is to demonstrate, using Monte Carlo (MC) calculations, that kQ factors for broad beams can be used for scanned beams under the same reference conditions with no significant additional uncertainty. We consider hereafter the general Alfonso formalism (Alfonso et al, 2008) for non-standard beam. Methods: To approach the reference conditions and the associated dose distributions, PBS must combine many pencil beams with range modulation and shaping techniques different than those used in passive systems (broad beams). This might lead to a different energy spectrum at the measurement point. In order to evaluate the impact of these differences on kQ factors, ion chamber responses are computed with MC (Geant4 9.6) in a dedicated scanned pencil beam (Q_pcsr) producing a 10×10cm2 composite field with a flat dose distribution from 10 to 16 cm depth. Ion chamber responses are also computed by MC in a broad beam with quality Q_ds (double scattering). The dose distribution of Q _pcsr matches the dose distribution of Q_ds. k_(Q_pcsr,Q_ds) is computed for a 2×2×0.2cm3 idealized air cavity and a realistic plane-parallel ion chamber (IC). Results: Under reference conditions, quality correction factors for a scanned composite field versus a broad beam are the same for air cavity dose response, k_(Q_pcsr,Q_ds) =1.001±0.001 and for a Roos IC, k_(Q_pcsr,Q_ds) =0.999±0.005. Conclusion: Quality correction factors for ion chamber response in scanned and broad proton therapy beams are identical under reference conditions within the calculation uncertainties. The results indicate that quality correction factors published in IAEA TRS-398 can be used for scanned beams in the SOBP of a high-energy proton beam. Jefferson Sorriaux is financed by the Walloon Region under the convention 1217662. Jefferson Sorriaux is sponsored by a public-private partnership IBA - Walloon Region

SU-F-BRD-15: Quality Correction Factors in Scanned Or Broad Proton Therapy Beams Are Indistinguishable

Purpose: At present the most promising method for an in vivo and noninvasive monitoring of radiation treatments with protonbeams is positron emission tomography(PET). This study investigates the sensitivity and accuracy of the PET/CT treatment verification method in the presence of highly inhomogeneous tissue regions as well as in the presence of metallic implants. Method and Materials: A circular SOBP proton field has been delivered to a sophisticated in house designed phantom consisting of polymethyl methacrylate (PMMA), lung and bone equivalent slabs. The bone material contained authentic dental gold implants as well as tin lead alloy implants in different shapes. PET data were acquired in listmode starting within 15 min after irradiation at a commercial PET/CT scanner. The measured PET distributions were compared to full‐blown simulations of the PET signal based on Geant4 and FLUKA Monte Carlo(MC) codes. Results: Activation profiles were analyzed behind air‐lung, air‐bone and lung‐bone interfaces parallel to the beam as well as downstream interfaces angled at 6°. In general, a good agreement between measured and simulated PET distributions was found. Measured PET images reflected even small characteristic changes in the dose distribution. This showed the potential of PET/CT treatment verification in the presence of highly inhomogeneous tissue regions. CT artifacts due to metal implants can trick all dose calculation algorithms and lead to the prediction of a proton range overshoot behind metal implants, whereas in reality a range undershoot occurs. The PET/CT treatment verification method can detect such dose calculation errors. Conclusion: This preliminary study indicates the feasibility of PET/CT treatment verification to detect the full characteristic of the delivered dose distribution even in the presence of complex tissue inhomogeneities and metal implants.

Quantitative assessment of the accuracy of proton beam range verification with PET/CT

Ep-1587 cell survival responses to modulated proton beams delivered by passive scattering and pencil beam scanning

Purpose: Application of an image guided 4D Monte Carlo framework to the evaluation of intra/inter fraction motion effects between patient organ‐movement and dynamic delivery effects Materials & Methods: An IGMC toolkit that accounts for time‐dependent geometries of organ motion and dynamic delivery and provides accurate dosimetry was developed for lungcancer patients. Fluence calculation for VARIAN‐2100C/D photon accelerator is performed with EGSnrc and for patient dose calculation we use dose‐planning‐method. The time dependent beam delivery information is obtained from the treatment‐planning program in the form of MLC leaf‐sequencing files, while the organ motion pattern was obtained with the use of RPM signal and 4D‐CT. A voxel displacement map is used to quantify the motion of the organ in the voxelized geometry. The study was performed for lung patient for several breathing phases. The data analysis was performed with the freely available package VODCA. Results: Differences between the conventional CORVUS dose plan and the Monte Carlo dose results suggest that Monte Carlo dose calculation is vital for assessing effects in lungtissue. For the free breathing CT, CORVUS was under‐dosing the lung‐tumor by approximately 3Gy. When accounting for temporal effects, comparison between IGMC dose distributions for free breathing, inhale and exhale phases, show that dose coverage of the primary/secondary tumors was significant worse in the inhale phase relative to the exhale/free‐breathing phases. For inhale phase, 5–10% of the volume was receiving 10Gy less than in exhale or free‐breathing phases, leading to large cold spots inside the tumor. This is mainly due to the motion of the diaphragm, which subsequently moves the tumor in the superior‐inferior by more than 2 cm. Conclusions:Image guided 4DMC methods can significantly improve the planning of lungtumor treatments by accurately modeling the motion of the tumors and large heterogeneity in the tumor region. Supported NIH/NCI‐R01/CA111590.

TU-C-M100J-05: Image Guided 4D Monte Carlo Study of the Dosimetric Effects of Intra/inter Fraction Motion in Lung Tumors

A Geometric Knowledge-Based Model to Quickly Predict the Patient-Specific Benefits of Proton Therapy in Clival Chordoma Patients

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