The OSI system is capable of detecting 0.1 +/- 0.1 mm 1D spatial displacement of a phantom in near real time and useful in head-motion monitoring. This new frameless SRS procedure using the mask-less head-fixation system provides immobilization similar to that of conventional frame-based SRS. Head-motion monitoring using near-real-time surface imaging provides adequate accuracy and is necessary for frameless SRS in case of unexpected head motion that exceeds a set tolerance.

The purpose of this study was to quantify the variability of the breast surface position when aligning whole-breast patients to bony landmarks based on MV portal films or skin marks alone. Surface imaging was used to assess the breast surface position of 11 whole-breast radiotherapy patients, but was not used for patient positioning. On filmed fractions, AlignRT v5.0 was used to capture the patient's surface after initial positioning based on skin marks (28 “preshifts” surfaces), and after treatment couch shifts based on MV films (41 “postshifts” surfaces). Translations and rotations based on surface captures were recorded, as well as couch shifts based on MV films. For nonfilmed treatments, “daily” surface images were captured following positioning to skin marks alone. Group mean and systematic and random errors were calculated for all datasets. Pearson correlation coefficients, setup margins, and 95% limits of agreement (LOA) were calculated for preshifts translations and MV film shifts. LOA between postshifts surfaces and the filmed treatment positions were also computed. All the surface captures collected were retrospectively compared to both a DICOM reference surface created from the planning CT and to an AlignRT reference surface. All statistical analyses were performed using the DICOM reference surface dataset. AlignRT reference surface data was only used to calculate the LOA with the DICOM reference data. This helped assess any outcome differences between both reference surfaces. Setup margins for preshifts surfaces and MV films range between 8.3–12.0 mm and 5.4–13.4 mm, respectively. The largest margin is along the left–right (LR) direction for preshift surfaces, and along craniocaudal (CC) for films. LOA ranges between the preshifts surfaces and MV film shifts are large (12.6–21.9 mm); these decrease for postshifts surfaces (9.8–18.4 mm), but still show significant disagreements between the two modalities due to their focus on different anatomical landmarks (patient's topography versus bony anatomy). Pearson's correlation coefficients further support this by showing low to moderate correlations in the anterior–posterior (AP) and LR directions (0.47–0.69) and no correlation along CC (< 0.15). The use of an AlignRT reference surface compared to the DICOM reference surface does not significantly affect the LOA. Alignment of breast patients based solely on bony alignment may lead to interfractional inconsistencies in the breast surface position. The use of surface imaging tools highlights these discrepancies, and allows the radiation oncology team to better assess the possible effects on treatment quality.

PurposeWe calculated setup margins for whole breast radiotherapy during voluntary deep‐inspiration breath‐hold (vDIBH) using real‐time surface imaging (SI).Methods and MaterialsPatients (n = 58) with a 27‐to‐31 split between right‐ and left‐sided cancers were analyzed. Treatment beams were gated using AlignRT by registering the whole breast region‐of‐interest to the surface generated from the simulation CT scan. AlignRT recorded (three‐dimensional) 3D displacements and the beam‐on‐state every 0.3 s. Means and standard deviations of the displacements during vDIBH for each fraction were used to calculate setup margins. Intra‐DIBH stability and the intrafraction reproducibility were estimated from the medians of the 5th to 95th percentile range of the translations in each breath‐hold and fraction, respectively.ResultsA total of 7269 breath‐holds were detected over 1305 fractions in which a median dose of 200 cGy was delivered. Each fraction was monitored for 5.95 ± 2.44 min. Calculated setup margins were 4.8 mm (A/P), 4.9 mm (S/I), and 6.4 mm (L/R). The intra‐DIBH stability and the intrafraction reproducibility were ≤0.7 mm and ≤2.2 mm, respectively. The isotropic margin according to SI (9.2 mm) was comparable to other institutions’ calculations that relied on x‐ray imaging and/or spirometry for patients with left‐sided cancer (9.8–11.0 mm). Likewise, intra‐DIBH variability and intrafraction reproducibility of breast surface measured with SI agreed with spirometry‐based positioning to within 1.2 and 0.36 mm, respectively.ConclusionsWe demonstrated that intra‐DIBH variability, intrafraction reproducibility, and setup margins are similar to those reported by peer studies who utilized spirometry‐based positioning.

3D surface imaging has the potential to provide submillimeter level head motion tracking. This is provided that a highly accurate camera-to-LINAC frame of reference calibration can be performed and that the reference ROI is of sufficient size and contains suitable surface features for registration.

We present a measurement of the left-right cross-section asymmetry (A LR ) for Z boson production by e + e − collisions. The measurement includes the final data taken with the SLD detector at the SLAC Linear Collider (SLC) during the period 1996-1998. Using a sample of 383,487 Z decays collected during the 1996-1998 runs we measure the pole-value of the asymmetry, A 0 LR , to be 0.15056±0.00239 which is equivalent to an effective weak mixing angle of sin 2 θ eff W = 0.23107±0.00030. Our result for the complete 1992-1998 dataset comprising 537 thousand Z decays is sin 2 θ eff W = 0.23097 ± 0.00027. The SLD Collaboration has performed a series of increasingly precise measurements of the left-right cross-section asymmetry in the production of Z bosons by e + e − collisions [1][2][3]. Submitted to Physical Review LettersIn this letter, we present a measurement based upon data recorded during the 1996 and 1997-98 runs of the SLAC Linear Collider (SLC), which represents about three quarters of our total sample and leads to improved statistical precision and reduced systematic uncertainty.The overall average given at the end of this Letter is based upon all the data from the completed SLD experimental program [4].The left-right asymmetry is defined as, where σ L and σ R are the e + e − production cross sections for Z bosons at the Z-pole energy with left-handed and right-handed electrons, respectively. The Standard Model predicts that this quantity depends upon the effective vector (v e ) and axial-vector (a e ) couplings of the Z boson to the electron current,where the effective electroweak mixing parameter is defined [5] as sin 2 θ eff W ≡ (1 − v e /a e )/4. 3The quantity A 0 LR is a sensitive function of sin 2 θ eff W and depends upon virtual electroweak radiative corrections including those which involve the Higgs boson and those arising from new phenomena outside of the scope of the Standard Model (SM). Presently, the most stringent upper bounds on the SM Higgs mass are provided by measurements of sin 2 θ eff W . We measured the left-right asymmetry by counting hadronic and (with low efficiency) τ + τ − final states produced in e + e − collisions near the Z-pole energy for each of the two longitudinal polarization states of the electron beam. The asymmetry formed from these rates, A LR , was then corrected for residual effects arising from pure photon exchange and Z-photon interference to extract A 0 LR . The measurement required knowledge of the absolute beam polarization, but did not require knowledge of the absolute luminosity, detector acceptance, or efficiency [6].The operation of the SLC with a polarized electron beam has been described previously [7]. The maximum luminosity of the collider was approximately 3×10 30 cm −2 sec −1 , and the longitudinal electron polarization at the e + e − collision point was typically ∼75%. Beginning in 1996, two additional detectors were operated in order to assist in the calibration of the primary spectrometer-based polarimeter. Both devices detected Comptonscattere...