Online verification of breath-hold reproducibility using kV-triggered imaging for liver stereotactic body radiation therapy.

PURPOSE: To introduce a new technique for online breath-hold verification for liver stereotactic body radiation therapy (SBRT) based on kilovoltage-triggered imaging and liver dome positions. MATERIAL AND METHODS: Twenty-five liver SBRT patients treated with deep inspiration breath-hold were included in this IRB-approved study. To verify the breath-hold reproducibility during treatment, a KV-triggered image was acquired at the beginning of each breath-hold. The liver dome position was visually compared with the expected upper/lower liver boundaries created by expanding/contracting the liver contour 5 mm in the superior-inferior direction. If the liver dome was within the boundaries, delivery continued; otherwise, beam was held manually, and the patient was instructed to take another breath-hold until the liver dome fell within boundaries. The liver dome was delineated on each triggered image. The mean distance between the delineated liver dome to the projected planning liver contour was defined as liver dome position error edome . The mean and maximum edome of each patient were compared between no breath-hold verification (all triggered images) and with online breath-hold verification (triggered images without beam-hold). RESULTS: Seven hundred thirteen breath-hold triggered images from 92 fractions were analyzed. For each patient, an average of 1.5 breath-holds (range 0-7 for all patients) resulted in beam-hold, accounting for 5% (0-18%) of all breath-holds; online breath-hold verification reduced the mean edome from 3.1 mm (1.3-6.1 mm) to 2.7 mm (1.2-5.2 mm) and the maximum edome from 8.6 mm (3.0-18.0 mm) to 6.7 mm (3.0-9.0 mm). The percentage of breath-holds with edome >5 mm was reduced from 15% (0-42%) without breath-hold verification to 11% (0-35%) with online breath-hold verification. online breath-hold verification eliminated breath-holds with edome >10 mm, which happened in 3% (0-17%) of all breath-holds. CONCLUSION: It is clinically feasible to monitor the reproducibility of each breath-hold during liver SBRT treatment using triggered images and liver dome. Online breath-hold verification improves the treatment accuracy for liver SBRT.

Prospects for daily online adaptive radiotherapy via ethos for prostate cancer patients without nodal involvement using unedited CBCT auto-segmentation.

PURPOSE:  Implementing new online adaptive radiation therapy technologies is challenging because extra clinical resources are required particularly expert contour review. Here, we provide the first assessment of Varian's Ethos™ adaptive platform for prostate cancer using no manual edits after auto-segmentation to minimize this impact on clinical efficiency. METHODS: Twenty-five prostate patients previously treated at our clinic were re-planned using an Ethos™ emulator. Clinical target volumes (CTV) included intact prostate and proximal seminal vesicles. The following clinical margins were used: 3 mm posterior, 5 mm left/right/anterior, and 7 mm superior/inferior. Adapted plans were calculated for 10 fractions per patient using Ethos's auto-segmentation and auto-planning workflow without manual contouring edits. Doses and auto-segmented structures were exported to our clinical treatment planning system where contours were modified as needed for all 250 CTVs and organs-at-risk. Dose metrics from adapted plans were compared to unadapted plans to evaluate CTV and OAR dose changes. RESULTS: Overall 96% of fractions required auto-segmentation edits, although corrections were generally minor (<10% of the volume for 70% of CTVs, 88% of bladders, and 90% of rectums). However, for one patient the auto-segmented CTV failed to include the superior portion of prostate that extended into the bladder at all 10 fractions resulting in under-contouring of the CTV by 31.3% ± 6.7%. For the 24 patients with minor auto-segmentation corrections, adaptation improved CTV D98% by 2.9% ± 5.3%. For non-adapted fractions where bladder or rectum V90% exceeded clinical thresholds, adaptation reduced them by 13.1% ± 1.0% and 6.5% ± 7.3%, respectively. CONCLUSION:  For most patients, Ethos's online adaptive radiation therapy workflow improved CTV D98% and reduced normal tissue dose when structures would otherwise exceed clinical thresholds, even without time-consuming manual edits. However, for one in 25 patients, large contour edits were required and thus scrutiny of the daily auto-segmentation is necessary and not all patients will be good candidates for adaptation.

Cooperative bi-exponential decay of dye emission coupled via plasmons.

Bi-exponential decay of dye fluorescence near the surface of plasmonic metamaterials and core-shell nanoparticles is shown to be an intrinsic property of the coupled system. Indeed, the Dicke, cooperative states involve two groups of transitions: super-radiant, from the most excited to the ground states and sub-radiant, which cannot reach the ground state. The relaxation in the sub-radiant system occurs mainly due to the interaction with the plasmon modes. Our theory shows that the relaxation leads to the population of the sub-radiant states by dephasing the super-radiant Dicke states giving rise to the bi-exponential decay in agreement with the experiments. We use a set of metamaterial samples consisting of gratings of paired silver nanostrips coated with Rh800 dye molecules, having resonances in the same spectral range. The bi-exponential decay is demonstrated for Au\SiO2\ATTO655 core-shell nanoparticles as well, which persists even when averaging over a broad range of the coupling parameter.