Efficiency of respiratory-gated delivery of synchrotron-based pulsed proton irradiation

Significant differences exist in respiratory-gated proton beam delivery with a synchrotron-based accelerator system when compared to photon therapy with a conventional linear accelerator. Delivery of protons with a synchrotron accelerator is governed by a magnet excitation cycle pattern. Optimal synchronization of the magnet excitation cycle pattern with the respiratory motion pattern is critical to the efficiency of respiratory-gated proton delivery. There has been little systematic analysis to optimize the accelerator's operational parameters to improve gated treatment efficiency. The goal of this study was to estimate the overall efficiency of respiratory-gated synchrotron-based proton irradiation through realistic simulation. Using 62 respiratory motion traces from 38 patients, we simulated respiratory gating for duty cycles of 30%, 20% and 10% around peak exhalation for various fixed and variable magnet excitation patterns. In each case, the time required to deliver 100 monitor units in both non-gated and gated irradiation scenarios was determined. Based on results from this study, the minimum time required to deliver 100 MU was 1.1 min for non-gated irradiation. For respiratory-gated delivery at a 30% duty cycle around peak exhalation, corresponding average delivery times were typically three times longer with a fixed magnet excitation cycle pattern. However, when a variable excitation cycle was allowed in synchrony with the patient's respiratory cycle, the treatment time only doubled. Thus, respiratory-gated delivery of synchrotron-based pulsed proton irradiation is feasible and more efficient when a variable magnet excitation cycle pattern is used.     

Causes of hypercapnic respiratory failure and associated in-hospital mortality

Background and Objective

Hypercapnic respiratory failure (HRF) can occur due to severe respiratory disease but also because of multiple coexistent causes. There are few data on the prevalence of antecedent causes for HRF and the effect of these causes on prognosis, especially where study inclusion has not been biased with respect to primary diagnosis, interventions received or clinical outcome. We sought to determine the prevalence of pre-specified conditions among patients with HRF and to determine the effect of these causes on in-hospital mortality.

Methods

Cross-sectional study of patients with HRF from 2013 to 2017. Inclusion criteria were PaCO₂ >45 mm Hg and pH ≤7.45. Causes of interest were identified using diagnosis codes from hospital records. We used directed acyclic graphs to inform logistic regression models for the outcome of in-hospital death.

Results

We identified 873 persons with HRF in the study period. Mean (SD) age was 69 years and 50.4% were males. Acidosis (pH <7.35) was present in 488 (55%) cases. Most (83%) had one or more of the following: obstructive lung disease, lower respiratory tract infection, congestive cardiac failure, sleep disordered breathing, neuromuscular disease, opioid or benzodiazepine use. In-hospital mortality was 12.8%. Obstructive lung disease and cardiac failure were associated with a lower risk of death, whereas respiratory tract infection and neuromuscular disease were associated with increased risk of death.

Conclusion

HRF is associated with a range of potentially causative conditions, which significantly impact hospital survival. Systematic evaluation of patients with HRF may increase detection of treatable comorbidities.