Particle Physics Probes Of Extra Spacetime Dimensions

The possibility that spacetime is extended beyond the familiar 3+1-dimensions has intrigued physicists for a century. Indeed, the consequences of a dimensionally richer spacetime would be profound. Recently, new theories with higher dimensional spacetimes have been developed to resolve the hierarchy problem in particle physics. These scenarios make distinct predictions which allow for experiment to probe the existence of extra dimensions in new ways. We review the conceptual framework of these scenarios, their implications in collider and short-range gravity experiments, their astrophysical and cosmological effects, as well as the constraints placed on these models from present data.Comment: Submitted to Annual Review of Nuclear and Particle Science, 29 page

Feasibility Study of Dual Energy Radiographic Imaging for Target Localization in Radiotherapy for Lung Tumors

Purpose Dual-energy (DE) radiographic imaging improves tissue discrimination by separating soft from hard tissues in the acquired images. This study was to establish a mathematic model of DE imaging based on intrinsic properties of tissues and quantitatively evaluate the feasibility of applying the DE imaging technique to tumor localization in radiotherapy. Methods We investigated the dependence of DE image quality on the radiological equivalent path length (EPL) of tissues with two phantoms using a stereoscopic x-ray imaging unit. 10 lung cancer patients who underwent radiotherapy each with gold markers implanted in the tumor were enrolled in the study approved by the hospital's Ethics Committee. The displacements of the centroids of the delineated gross tumor volumes (GTVs) in the digitally reconstructed radiograph (DRR) and in the bone-canceled DE image were compared with the averaged displacements of the centroids of gold markers to evaluate the feasibility of using DE imaging for tumor localization. Results The results of the phantom study indicated that the contrast-to-noise ratio (CNR) was linearly dependent on the difference of EPL and a mathematical model was established. The objects and backgrounds corresponding to ΔEPL less than 0.08 are visually indistinguishable in the bone-canceled DE image. The analysis of patient data showed that the tumor contrast in the bone-canceled images was improved significantly as compared with that in the original radiographic images and the accuracy of tumor localization using the DE imaging technique was comparable with that of using fiducial makers. Conclusion It is feasible to apply the technique for tumor localization in radiotherapy

Radioembolization with Y-90 resin microspheres of neuroendocrine liver metastases after initial peptide receptor radionuclide therapy

Purpose Peptide receptor radionuclide therapy (PRRT) and radioembolization are increasingly used in neuroendocrine neoplasms patients. However, concerns have been raised on cumulative hepatotoxicity. The aim of this sub-analysis was to investigate hepatotoxicity of yttrium-90 resin microspheres radioembolization in patients who were previously treated with PRRT. Methods Patients treated with radioembolization after systemic radionuclide treatment were retrospectively analysed. Imaging response according to response evaluation criteria in solid tumours (RECIST) v1.1 and clinical response after 3 months were collected. Clinical, biochemical and haematological toxicities according to common terminology criteria for adverse events (CTCAE) v4.03 were also collected. Specifics on prior PRRT, subsequent radioembolization treatments, treatments after radioembolization and overall survival (OS) were collected. Results Forty-four patients were included, who underwent a total of 58 radioembolization procedures, of which 55% whole liver treatments, at a median of 353 days after prior PRRT. According to RECIST 1.1, an objective response rate of 16% and disease control rate of 91% were found after 3 months. Clinical response was seen in 65% (15/23) of symptomatic patients after 3 months. Within 3 months, clinical toxicities occurred in 26%. Biochemical and haematological toxicities CTCAE grade 3–4 occurred in ≤ 10%, apart from lymphocytopenia (42%). Radioembolization-related complications occurred in 5% and fatal radioembolization-induced liver disease in 2% (one patient). A median OS of 3.5 years [95% confidence interval 1.8–5.1 years] after radioembolization for the entire study population was found. Conclusion Radioembolization after systemic radionuclide treatments is safe, and the occurrence of radioembolization-induced liver disease is rare