Heterogeneity in cell populations poses a major obstacle to understanding complex biological processes. Here we present a microfluidic platform containing thousands of nanoliter-scale chambers suitable for live-cell imaging studies of clonal cultures of nonadherent cells with precise control of the conditions, capabilities for in situ immunostaining and recovery of viable cells. We show that this platform mimics conventional cultures in reproducing the responses of various types of primitive mouse hematopoietic cells with retention of their functional properties, as demonstrated by subsequent in vitro and in vivo (transplantation) assays of recovered cells. The automated medium exchange of this system made it possible to define when Steel factor stimulation is first required by adult hematopoietic stem cells in vitro as the point of exit from quiescence. This technology will offer many new avenues to interrogate otherwise inaccessible mechanisms governing mammalian cell growth and fate decisions.

The 10XFFF phase-space data offered by the Varian Monte Carlo research team have been validated for clinical use using measured, interinstitutional beam data in water and with film dosimetry in inhomogeneous media.

The purpose of this study was to investigate amplitude gating combined with a coached breathing strategy for 10 MV flattening filter‐free (FFF) volumetric‐modulated arc therapy (VMAT) on the Varian TrueBeam linac. Ten patient plans for VMAT SABR liver were created using the Eclipse treatment planning system (TPS). The verification plans were then transferred to a CT‐scanned Quasar phantom and delivered on a TrueBeam linac using a 10 MV FFF beam and Varian's real‐time position management (RPM) system for respiratory gating based on breathing amplitude. Breathing traces were acquired from ten patients using two kinds of breathing patterns: free breathing and an interrupted (~5 s pause) end of exhale coached breathing pattern. Ion chamber and Gafchromic film measurements were acquired for a gated delivery while the phantom moved under the described breathing patterns, as well as for a nongated stationary phantom delivery. The gate window was set to obtain a range of residual target motion from 2–5 mm. All gated deliveries on a moving phantom have been shown to be dosimetrically equivalent to the nongated deliveries on a static phantom, with differences in point dose measurements under 1% and average gamma 2%/2 mm agreement above 98.7%. Comparison with the treatment planning system also resulted in good agreement, with differences in point‐dose measurements under 2.5% and average gamma 3%/3 mm agreement of 97%. The use of a coached breathing pattern significantly increases the duty cycle, compared with free breathing, and allows for shorter treatment times. Patients' free‐breathing patterns contain considerable variability and, although dosimetric results for gated delivery may be acceptable, it is difficult to achieve efficient treatment delivery. A coached breathing pattern combined with a 5 mm amplitude gate, resulted in both high‐quality dose distributions and overall shortest gated beam delivery times.PACS number: 87.55.Qr

Purpose: To develop a QA procedure for gated VMAT SABR liver cancer treatments and investigate the gating parameters for acceptable plan delivery in terms of the dose to a moving volume and treatment delivery time. Methods: 10 patient plans for VMAT SABR liver were created using the Eclipse™ TPS. The verification plans were then transferred to a CT‐scanned Quasar™ phantom and delivered on a TrueBeam™ linac using a 10FFF beam and Varian's RPM system for respiratory gating. Two kinds of breathing patterns were used: free breathing (FB) and an interrupted (∼5s pause) end of exhale coached breathing (CB) pattern. Ion chamber and Gafchromic™ film measurements were acquired for a gated delivery while the phantom moved under the described breathing patterns and a non‐gated, stationary phantom delivery. The gate window was set to obtain a range of residual target motion from 2–10 mm. Results: Preliminary chamber measurements indicate that the dose to the center of the PTV can vary considerably under gated delivery compared to the static case. The effect can be significant for free breathing; ∼4–12% over the selected range of residual target motion. The agreement was more consistent with CB pattern at ∼1–4%. Gamma analysis (3%, 3mm) showed an agreement above 99.74% for all gated deliveries compared to the static delivery. The treatment time with a gate width of 2 mm was ∼265s for the CB pattern compared to ∼740s under a typical FB pattern. A non‐gated delivery of the same plan took ∼100s. Conclusion: Gated VMAT treatments have been delivered successfully to a motorized phantom. FB patterns contain considerable variability and it is difficult to achieve acceptable results even with very small gate windows. However, a CB pattern combined with a sufficiently small gate, resulted in acceptable dose distributions that can be delivered in a reasonable amount of time. Francis Viel received funding from the Natural Sciences and Engineering Research Council of Canada. This work has been supported by the Varian Research Collaborations Program.