Robustness analysis of surface-guided DIBH left breast radiotherapy: personalized dosimetric effect of real intrafractional motion within the beam gating thresholds.

PURPOSE: The robustness of surface-guided (SG) deep-inspiration breath-hold (DIBH) radiotherapy (RT) for left breast cancer was evaluated by investigating any potential dosimetric effects due to the residual intrafractional motion allowed by the selected beam gating thresholds. The potential reduction of DIBH benefits in terms of organs at risk (OARs) sparing and target coverage was evaluated for conformational (3DCRT) and intensity-modulated radiation therapy (IMRT) techniques. METHODS: A total of 192 fractions of SGRT DIBH left breast 3DCRT treatment for 12 patients were analyzed. For each fraction, the average of the real-time displacement between the isocenter on the daily reference surface and on the live surface ("SGRT shift") during beam-on was evaluated and applied to the original plan isocenter. The dose distribution for the treatment beams with the new isocenter point was then calculated and the total plan dose distribution was obtained by summing the estimated perturbed dose for each fraction. Then, for each patient, the original plan and the perturbed one were compared by means of Wilcoxon test for target coverage and OAR dose-volume histogram (DVH) metrics. A global plan quality score was calculated to assess the overall plan robustness against intrafractional motion of both 3DCRT and IMRT techniques. RESULTS: Target coverage and OAR DVH metrics did not show significant variations between the original and the perturbed plan for the IMRT techniques. 3DCRT plans showed significant variations for the left descending coronary artery (LAD) and the humerus only. However, none of the dose metrics exceeded the mandatory dose constraints for any of the analyzed plans. The global plan quality analysis indicated that both 3DCRT and IMRT techniques were affected by the isocenter shifts in the same way and, generally, the residual isocenter shifts more likely tend to worsen the plan in all cases. CONCLUSION: The DIBH technique proved to be robust against residual intrafractional isocenter shifts allowed by the selected SGRT beam-hold thresholds. Small-volume OARs located near high dose gradients showed significant marginal deteriorations in the perturbed plans with the 3DCRT technique only. Global plan quality was mainly influenced by patient anatomy and treatment beam geometry rather than the technique adopted.

Surface-guided DIBH radiotherapy for left breast cancer: impact of different thresholds on intrafractional motion monitoring and DIBH stability.

PURPOSE: To compare two left breast cancer patient cohorts (tangential vs. locoregional deep-inspiration breath-hold - DIBH treatment) with different predefined beam gating thresholds and to evaluate their impact on motion management and DIBH stability. METHODS: An SGRT-based clinical workflow was adopted for the DIBH treatment. Intrafractional monitoring was performed by tracking both the respiratory signal and the real-time displacement between the isocenter on the daily reference surface and on the live surface ("SGRT shift"). Beam gating tolerances were 5 mm/4 mm for the SGRT shifts and 5 mm/3 mm for the gating window amplitude for breast tangential and breast + lymph nodes locoregional treatments, respectively. A total of 24 patients, 12 treated with a tangential technique and 12 with a locoregional technique, were evaluated for a total number of 684 fractions. Statistical distributions of SGRT shift and respiratory signal for each treatment fraction, for each patient treatment, and for the two population samples were generated. RESULTS: Lateral cumulative distributions of SGRT shifts for both locoregional and tangential samples were consistent with a null shift, whereas longitudinal and vertical ones were slightly negative (mean values < 1 mm). The distribution of the percentage of beam on time with SGRT shift > 3 mm, > 4 mm, or > 5 mm was extended toward higher values for the tangential sample than for the locoregional sample. The variability in the DIBH respiration signal was significantly greater for the tangential sample. CONCLUSION: Different beam gating thresholds for surface-guided DIBH treatment of left breast cancer can impact motion management and DIBH stability by reducing the frequency of the maximum SGRT shift and increasing respiration signal stability when tighter thresholds are adopted.

How the detector resolution affects the clinical significance of SBRT pre-treatment quality assurance results.

PURPOSE: Aim of this work was to study how the detector resolution can affect the clinical significance of SBRT pre-treatment volumetric modulated arc therapy (VMAT) verification results. METHODS: Three detectors (PTW OCTAVIUS 4D 729, 1500 and 100 SRS) used in five configurations with different resolution were compared: 729, 729 merged, 1500, 1500 merged and 1000 SRS. Absolute local gamma passing rates of 3D pre-treatment quality assurance (QA) were evaluated for 150 dose distributions in 30 plans. Five different kinds of error were introduced in order to establish the detection sensitivity of the three devices. Percentage dosimetric differences were evaluated between planned dosevolume histogram (DVH) and patients' predicted DVH calculated by PTW DVH 4D® software. RESULTS: The mean gamma passing rates and the standard deviations were 92.4% ±â€¯3.7%, 94.6% ±â€¯1.8%, 95.3% ±â€¯4.2%, 97.4% ±â€¯2.5% and 97.6% ±â€¯1.4 respectively for 729, 729 merged, 1500, 1500 merged and 1000 SRS with 2% local dose/2mm criterion. The same trend was found on the sensitivity analysis: using a tight gamma analysis criterion (2%L/1mm) only the 1000 SRS detected every kind of error, while 729 and 1500 merged detected three and four kinds of error respectively. Regarding dose metrics extracted from DVH curves, D50% was within the tolerance level in more than 90% of cases only for the 1000 SRS. CONCLUSIONS: The detector resolution can significantly affect the clinical significance of SBRT pre-treatment verification results. The choice of a detector with resolution suitable to the investigated field size is of main importance to avoid getting false positive.

Atomic force microscopy of histological sections using a chemical etching method.

Physiology and pathology have a big deal on tissue morphology, and the intrinsic spatial resolution of an atomic force microscope (AFM) is able to observe ultrastructural details. In order to investigate cellular and subcellular structures in histological sections with the AFM, we used a new simple method for sample preparation, i.e. chemical etching of semithin sections from epoxy resin-embedded specimens: such treatment appears to melt the upper layers of the embedding resin; thus, removing the superficial roughness caused by the edge of the microtome knife and bringing into high relief the biological structures hidden in the bulk. Consecutive ultrathin sections embedded in epoxy resin were observed with a transmission electron microscope (TEM) to compare the different imaging properties on the same specimen sample. In this paper we report, as an example, our AFM and TEM images of two different tissue specimens, rat pancreas and skeletal muscle fibres, showing that most of the inner details are visible with the AFM. These results suggest that chemical etching of histological sections may be a simple, fast and cost-effective method for AFM imaging with ultrastructural resolution.

Ultracompact autocorrelator for multiphoton microscopy.

Pulse temporal characterization is a fundamental task when operating a Ti:Sapphire ultrafast laser system for multiphoton microscopy applications. In the present report, an ultracompact autocorrelator setup and a simple procedure is reported to perform pulse width measurements at the focal plane of the microscope objective without the need of any further instrumentation, aside from a few optical elements, since the confocal microscope, detection, data acquisition, processing, and displaying capabilities are used.