Introduction Osteoporosis is a disease of weak bone. Our goal was to determine the measurement reproducibility of magnetic resonance assessment of proximal femur strength. Methods This study had institutional review board approval, and written informed consent was obtained from all subjects. We obtained images of proximal femur microarchitecture by scanning 12 subjects three times within 1 week at 3T using a high-resolution 3-D FLASH sequence. We applied finite element analysis to compute proximal femur stiffness and femoral neck elastic modulus. Results Within-day and between-day root-mean-square coefficients of variation and intraclass correlation coefficients ranged from 3.5 to 6.6 % and 0.96 to 0.98, respectively. Conclusion The measurement reproducibility of magnetic resonance assessment of proximal femur strength is suitable for clinical studies of disease progression or treatment response related to osteoporosis bone-strengthening interventions.

The model was then validated with a set of fifteen cases, ranging from one target to ten targets, with size ranging from one to 15cc. OAR DVH's were compared between those predicted by DVH Estimation Model and those generate by HyperArc. Plan quality was compared between clinical plan and HyperArc validation plan. Metrics evaluated were conformity, mean brain dose, and moderate isodose volume (V12Gy). Results: A model using the one hundred selected plans was successfully constructed. DVH estimates were generated for each of fifteen validations plans. The DVH estimates were then used as objective criteria to successfully generate plans using the HyperArc automated SRS planning tool. DVH estimates were reasonably accurate for most plans, and facilitated generation of HyperArc plans clinically equivalent to the plans actually delivered. Plan conformity was not statistically different between the clinical versions and the HyperArc versions of the valiation plans (p Z 0.46). Mean brain dose was not statistically different between the plan versions (pZ0.65). V12Gy was statistically different the two plan versions (p Z 0.043) but the absolute V12 difference was less than 10% for each case, and was not deemed to be clinically different. Conclusion: A robust intracranial SRS knowledge based planning model was created that can successfully generate accurate DVH predictions which can be used objective criteria for HyperArc to generate high quality SRS plans for a large range intracranial SRS plans, including those with solitary and numerous, as well as small and large targets.

Purpose To evaluate the efficacy of using bronchoscopically implanted anchored electromagnetic transponders (EMTs) as surrogates for 1) tumor position and 2) repeatability of lung inflation during deep‐inspiration breath‐hold (DIBH) lung radiotherapy. Methods Forty‐one patients treated with either hypofractionated (HF) or conventional (CF) lung radiotherapy on an IRB‐approved prospective protocol using coached DIBH were evaluated for this study. Three anchored EMTs were bronchoscopically implanted into small airways near or within the tumor. DIBH treatment was gated by tracking the EMT positions. Breath‐hold cone‐beam‐CTs (CBCTs) were acquired prior to every HF treatment or weekly for CF patients. Retrospectively, rigid registrations between each CBCT and the breath‐hold planning CT were performed to match to 1) spine, 2) EMTs and 3) tumor. Absolute differences in registration between EMTs and spine were analyzed to determine surrogacy of EMTs for lung inflation. Differences in registration between EMTs and the tumor were analyzed to determine surrogacy of EMTs for tumor position. The stability of the EMTs was evaluated by analyzing the difference between inter‐EMT displacements recorded at treatment from that of the plan for the CF patients, as well as the geometric residual (GR) recorded at the time of treatment. Results A total of 219 CBCTs were analyzed. The average differences between EMT centroid and spine registration among all CBCTs were 0.45±0.42 cm, 0.29±0.28 cm, and 0.18±0.15 cm in superior‐inferior (SI), anterior‐posterior (AP) and lateral directions, respectively. Only 59% of CBCTs had differences in registration < 0.5 cm for EMT centroid compared to spine, indicating that lung inflation is not reproducible from simulation to treatment. The average differences between EMT centroid and tumor registration among all CBCTs were 0.13±0.13 cm, 0.14±0.13 cm and 0.12±0.12 cm in SI, AP and lateral directions, respectively. Ninety‐five percent of CBCTs resulted in a < 0.5 cm change between EMT centroid and tumor registration, indicating that EMT positions correspond well with tumor position during treatments. Six out of the seven recorded CF patients had average differences in inter‐EMT displacements ≤0.26 cm and average GR ≤0.22 cm, indicating that the EMTs are stable throughout treatment. Conclusions Bronchoscopically implanted anchored EMTs are good surrogates for tumor position and are reliable for maintaining tumor position when tracked during DIBH treatment, as long as the tumor size and shape are stable. Large differences in registration between EMTs and spine for many treatments suggest that lung inflation achieved at simulation is often not reproduced.

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