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We proposed a novel tool-a dose linear energy transfer (LET)-volume histogram (DLVH)-and performed an exploratory study to investigate rectal bleeding in prostate cancer treated with intensity modulated proton therapy.The DLVH was constructed with dose and LET as 2 axes, and the normalized volume of the structure was contoured in the dose-LET plane as isovolume lines. We defined the DLVH index, DLv%(d,l) (ie, v% of the structure) to have a dose of ≥d Gy and an LET of ≥l keV/μm, similar to the dose-volume histogram index Dv%. Nine patients with prostate cancer with rectal bleeding (Common Terminology Criteria for Adverse Events grade ≥2) were included as the adverse event group, and 48 patients with no complications were considered the control group. A P value map was constructed by comparison of the DLVH indices of all patients between the 2 groups using the Mann-Whitney U test. Dose-LET volume constraints (DLVCs) were derived based on the P value map with a manual selection procedure facilitated by Spearman's correlation tests. The obtained DLVCs were further cross-validated using a multivariate support vector machine (SVM)-based normal tissue complication probability (NTCP) model with an independent testing data set composed of 8 adverse event and 13 control patients.We extracted 2 DLVC constraints. One DLVC was obtained, Vdose/LETboundary:2.5keVμmat 75 Gy to 3.2keVμmat8.65Gy1.27% (DLVC1), revealing a high LET volume effect. The second DLVC, V(72.2Gy,0keVμm)2.23% (DVLC2), revealed a high dose volume effect. The SVM-based NTCP model with 2 DLVCs provided slightly superior performance than using dose only, with an area under the curve of 0.798 versus 0.779 for the testing data set.Our results demonstrated the importance of rectal "hot spots" in both high LET (DLVC1) and high dose (DLVC2) in inducing rectal bleeding. The SVM-based NTCP model confirmed the derived DLVCs as good predictors for rectal bleeding when intensity modulated proton therapy is used to treat prostate cancer.

Following coverage by The ASCO Post, Jennifer L. Glass, PA-C, MS, of the Mayo Clinic dives into the major findings in prostate cancer from the 2019 ASCO Annual Meeting in Chicago and their implications for advanced practitioners.

We present single-pair fluorescence resonance energy transfer (spFRET) observations of individual opening and closing events of surface-immobilized DNA hairpins. Two glass-surface immobilization strategies employing the biotin-streptavidin interaction and a third covalent immobilization strategy involving formation of a disulfide bond to a thiol-derivatized glass surface are described and evaluated. Results from image and time-trace data from surface-immobilized molecules are compared with those from freely diffusing molecules, which are unperturbed by surface interactions. Using a simple two-state model to analyze the open and closed time distributions for immobilized hairpins, we calculate the lifetimes of the two states. For hairpins with a loop size of 40 adenosines and a stem size of either seven or nine bases, the respective closed-state lifetimes are 45 +/- 2.4 and 103 +/- 6.0 ms, while the respective open-state lifetimes are 133 +/- 5.5 and 142 +/- 22 ms. These results show that the open state of the hairpin is favored over the closed state of the hairpin under these conditions, consistent with previous diffusion fluorescence correlation spectroscopy (FCS) experiments on poly(A)-loop hairpins. The measured open-state lifetime is about 30 times longer than the calculated 3 ms open-state lifetime for both hairpins based on a closing rate scaling factor derived from a previous FCS study for hairpins in diffusion with 12-30 thymidines in their loops. As predicted, the closed-state lifetime is dependent on the stem length and is independent of the loop characteristics. Our findings indicate that current models should consider sequence dependence in calculating ssDNA thermostability. The surface immobilization chemistries and other experimental techniques described here should prove useful for studies of single-molecule populations and dynamics.

The advances in room temperature single molecule detection (SMD) and single molecule spectroscopy (SMS) by laser induced fluorescence provide new tools for testing semi- classical and quantum mechanical theories of light-matter interaction and molecular interactions. They also provide the tools for the study of individual synthetic and biological macromolecules under physiological conditions. Two properties of a single fluorescent probe attached to a macromolecule can be exploited to provide local structural information. The first, its the very high sensitivity of the fluorophore to its immediate local environment, including the sensitivity to the presence of other fluorophores and quenchers near-by. The second is its unique absorption and emission transition dipoles, which can be interrogated by polarized light. Recently, we have developed 'molecular rulers' which use SMD/SMS to measure nanometer distances and distance changes of macromolecules. We also demonstrated the ability to measure orientations and orientation changes of macromolecules with very high accuracy. The spectroscopic signature of the fluorescent light coming from two different color labels which are attached to two sites on the macromolecule is a sensitive measure for dynamic conformations. Distance changes between two sites on the macromolecule are measured via single-pair fluorescence resonance energy transfer and orientation changes are measured by detecting changes in the dipole orientation of a rigidly attached probe or changes in the degree of rotational diffusion of a tethered probe via single molecule fluorescence polarization anisotropy.

Time resolved tunnel current was measured over 4 orders of magnitude in separation between tip and sample using an ultrafast scanning tunneling microscope (USTM). These measurements reveal two distinct regimes for tip height dependence of the signal. In addition, we report 900 femtosecond temporal resolution with a sensitivity of 20 mV/√Hz in USTM measurements of voltage pulses on a coplanar transmission line, and we show that the microscope operates as a high impedance probe.