Lung transplantation in mechanically ventilated (MV) patients has been associated with decreased post-transplant survival. Under the Lung Allocation Score (LAS) system, patients at greatest risk of death on the waiting list, particularly those requiring MV, are prioritized for lung allocation. We evaluated whether pre-transplant MV is associated with poorer post-transplant survival in the LAS era. Using a national registry, we analyzed all adults undergoing lung transplantation in the U.S. from 2005-2010. Propensity scoring identified non-ventilated matched referents for 419 subjects requiring MV at the time of transplantation. Survival was evaluated using Kaplan-Meier methods. Risk of death was estimated by hazard ratios employing time-dependent covariates. We found that pre-transplant MV was associated with decreased overall survival after lung transplantation. In the first six-months post-transplant, ventilated subjects had a two-fold higher risk of death compared to non-ventilated subjects. However, after six-months post-transplant, survival did not differ by MV status. We also found that pre-transplant MV was not associated with decreased survival in non-cystic fibrosis obstructive lung diseases. These results suggest that under the LAS, pre-transplant MV is associated with poorer short-term survival post-transplant. Notably, the increased risk of death appears to be strongest the early post-transplant period and limited to certain pre-transplant diagnoses.
Studies systematically comparing the performance of health-related quality-of-life (HRQL) instruments in pulmonary arterial hypertension (PAH) are lacking. We sought to address this gap by comparing cardiac and respiratory-specific measures of HRQL in PAH. We prospectively assessed HRQL in 128 patients with catheterization-confirmed PAH at baseline and at 6, 12, and 24+ months. Cardiac-specific HRQL was assessed using the Minnesota Living with Heart Failure Questionnaire (LHFQ); respiratory-specific HRQL using the Airways Questionnaire 20 (AQ20); and general health status using the 36-item Short Form physical component summary (SF-36 PCS). The LHFQ and AQ20 were highly intercorrelated. Both demonstrated strong internal consistency and converged with the SF-36 PCS. Both discriminated among patients based on World Health Organization functional class (FC), 6-minute walk distance (6MWD), and Borg Dyspnea Index (BDI), except for a potential floor effect associated with low 6MWD. The LHFQ was more responsive than the AQ20 to changes over time in FC, 6MWD, and BDI. In multivariate analyses, the LHFQ and AQ20 were each longitudinal predictors of general health status, independent of FC, 6MWD and BDI. In conclusion, both cardiac-specific and respiratory-specific measures appropriately assess HRQL in most patients with PAH. Overall, the LHFQ demonstrates stronger performance characteristics than the AQ20.
Purpose: Megavoltage Cone‐Beam CT (MVCBCT) has recently been introduced in the clinic to improve patient alignment prior to dose delivery. The objective of this research was to evaluate the dose delivered to patients for MVCBCT acquisition. We also studied the possibility of making simple plan modifications to compensate for the dose delivered by daily MVCBCT imaging. Method and Materials: Because MVCBCT uses the treatment beam, conventional CT scans (pelvis and head and neck patients) were imported in a treatment planning system (Phillips, Pinnacle) to simulate an MVCBCT acquisition. To validate the dose obtained from Pinnacle, a simple water‐equivalent cylindrical phantom with spaces for MOSFETs and an ion chamber was used to measure the actual dose delivered during MVCBCT. Results: The MVCBCT dose delivered to the phantom, calculated from Pinnacle, was within 3% to all the MOSFET measurement points. The difference between Pinnacle and the ion chamber was 0.2%. For a typical MVCBCT (arc: 270° to 110°) the delivered dose forms an anterior‐posterior gradient. Head and neck patients receive dose ranging from 0.7 to 1.2 cGy per MVCBCT monitor unit (MU). The range is 0.6 to 1.2 cGy per MVCBCT MU for pelvis patients. The total dose for daily positioning using MVCBCT can be reduced and made uniform by alternating between two opposed imaging arcs. Dose‐volume histograms of a compensated plan for a pelvis patient imaged with 10 MU MVCBCTs for 40 fractions show no additional dose to the target and small increases at low doses. Conclusion: Given that clinical MVCBCTs are currently performed at doses ranging from 2–15 MU, simple plan modifications, such as reducing the total number of MU, can be used to nearly eliminate the dose used for daily positioning. Results for other body sites will also be presented. Conflict of Interest: Research sponsored by Siemens OCS.
Purpose: MV cone‐beam (CB) CT imaging can be used to position the patient prior to external‐beam radiotherapy. If calibrated, these images may also be used in dose calculations, opening the possibility to reconstruct the delivered dose or re‐optimize the treatment plan before delivery. This study investigates the effect of imaging artifacts on dosimetric accuracy. Method and Materials: Two water cylinders of 13 cm and 22.5 cm diameters were imaged using A) a MV CBCT system integrated with a Siemens accelerator and B) a conventional kV CT imager. Cupping trends observed in the MV CBCT were imposed on the kV CT images to create artificial data with simulated artifacts. Using the Phillips Pinnacle planning system, a 6 MV 10 × 16 cm2 field was applied to 1) the original kV CT of the smaller cylinder and 2) the kV CT with simulated artifacts. Similarly, a 18 × 18 cm2 field was applied to the original and artificial kV CT of the larger cylinder. Results: For the smaller cylinder, the MV CBCT water signal relative to air at the cylinder center differs from the radial and axial extremities by approximately 14% and 17% respectively. For the larger cylinder, the differences are 38% and 20% in radial and axial directions. The dose distributions for the artificial images show a systematic deviation which increases with depth. In the high‐dose, low‐gradient regions, the largest deviation for the smaller cylinder is 1% of the maximum delivered dose. For the larger cylinder, the largest deviation is 4%. Conclusion: Cupping artifacts in water phantoms produce dosimetric errors much smaller in magnitude than the cupping trend itself but as large as 4% for large phantoms. These results suggest that rough correction of MV CBCT artifacts may be sufficient for dosimetric accuracy. Conflict of Interest: Research supported by Siemens OCS.
Purpose: The ability to reconstruct the delivered patient dose can help ensure that the integrated doses to important structures faithfully adhere to prescription. The objective of this work is to develop and test a 3D dose reconstruction procedure based on exit‐dose measurements at treatment time and MV cone‐beam CT. Methods and Materials: The proposed dose reconstruction method uses a Megavoltage cone‐beam computed tomography (MVCBCT) image acquired on the treatment table prior to treatment, 2D portal images taken with an amorphous‐silicon electronic portal imaging device (EPID) during treatment, and an independent validated dose calculation engine. The energy fluence obtained from the EPID is back‐projected through the 3D MVCBCT image. A dose calculation engine based on a collapsed‐cone convolution algorithm subsequently calculates the dose in each voxel. To test the model, a MVCBCT of a cylindrical solid‐water QA phantom was acquired and the MVCBCT numbers mapped to appropriate attenuation coefficients. The phantom was then treated with a 5cmx5cm beam and a portal image acquired. During the treatment, a CC13 ion chamber and MOSFET detectors were used to measure the dose at 21 points to compare with reconstructed dose. A Pinnacle dose calculation using a conventional CT was also performed for comparison. Results: The mean difference between reconstructed and measured doses was −0.2% (standard deviation = 2.8%). The reconstructed dose in the inner regions of the cylinder differed less than 2% from the measured, although discrepancies of about 10% occurred at one point in the buildup region and at two other peripheral points. In comparison, the mean difference between Pinnacle calculations and measurements was −2.9% (standard deviation =1.6%). Conclusion: Preliminary calculations of reconstructed dose demonstrated good agreement with experiments. Further refinement of the model and its application to clinical conditions are under investigation. Conflict of Interest: Research supported by Siemens.
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