Proton Facility Economics: Single-Room Centers

ObjectiveWe have previously described the central nature of simple cases for financial feasibility of proton beam therapy centers—especially four- to five-room centers. In the 5 years since that publication, such construction has slowed drastically, and smaller, single-room projects are in vogue. We now seek to show under what circumstances a single-room system is optimally financially viable.Materials and MethodsA “standard” construction cost and debt for a single gantry system of $40 million was presumed, with 75% of the construction funded through standard 20-year financing. We then modeled a statistical analysis, deriving the optimal case mix required daily to cover construction and debt service costs.ResultsWe previously published that a single gantry treating only complex patients would need to apply 85% of its treatment slots simply to service debt, though it would cover its debt treating 4 hours of simple patients. As the business model has changed, debt maintenance, profit and operational costs have somewhat reduced the business case for adding a large number of simple patients. Debt maintenance is possible with as little as 13% of daily patients for a 40% Medicare case mix, but these numbers are critically sensitive to continued patient throughput.ConclusionsEven in a single-room system, reducing overall debt, using tax-exempt financing, and having a case load emphasizing simple, private payer patients is paramount to fiscal health of the facility. Unused capacity is a huge risk if insufficient patients are available.     

Varus malalignment of the lower limb increases the risk of femoral neck fracture: A biomechanical study using a finite element method

IntroductionThe understanding of the stresses and strains and their dependence on loading direction caused by an axial deformity is very important for understanding the mechanism of femural neck fractures. The hypothesis of this study is that lower limb malalignment is correlated with a substantial stress variation on the upper end of the femur. The purpose of this biomechanical trial using the finite element method is to determine the effect of the loading direction on the proximal femur regarding the malalignment of the lower limb, and also enlighten the relation between the lower limb alignment and the risk of a femoral neck fracture.MethodsTen segmentations of CT scans were considered. An axial compression load was applied to the femoral head to digitally simulate the physiological configuration in neutral position as well as in different axial positions in varus/valgus alignment.ResultsThe stress at the proximal femur changes as the varus _valgus angle does. It can be observed the smaller absolute stress at angle 10° (valgus) and the higher absolute stress at angle -10° (varus). The mean maximum von Mises stress value was 14.1 (SD=±3.48) MPa for 0°, while the mean maximum von Mises stress value was 17.96 MPa (SD=4.87) for -10° in varus. The fracture risk indicator of the proximal femoral epiphyses changes inversely with angle direction. The FRI was the highest at -10° and the lowest at 10°.ConclusionBased on the biomechanical findings and the fracture risk indicator determined in this preliminary study, varus malalignment increases the risk of femoral neck fracture. Consideration of other parameters such as bone mineral density and morphological parameters should also help to plan preventive medical strategy in the elderly.     

Do positional changes of the inferior alveolar canal after sagittal split mandibular osteotomy affect neurosensory recovery?

The purpose of this study was to assess the pre- and postoperative position and dimensions of the inferior alveolar canal (IAC) following sagittal split osteotomy (SSO) and identify any association with postoperative neurosensory deficit (NSD) at 1 year. This retrospective cohort study enrolled consecutive patients who had SSO performed to correct skeletal malocclusion. The pre- and postoperative cone beam computed tomography data were superimposed to visualize differences in IAC position and dimensions. Subjective and objective neurosensory tests were used to determine NSD in the inferior alveolar nerve distribution. A total of 20 subjects were included. The preoperative distance from the lateral cortex of the IAC to the inner aspect of the lateral cortex of the mandible was significantly greater in sides with NSD when compared to sides without NSD (P = 0.01). A significantly greater reduction in the postoperative distance measurement was seen in sides with NSD when compared to sides without NSD (P = 0.01). The magnitude of mandibular movement was significantly increased in sides with NSD (P = 0.02). The preoperative location of the IAC, as well as certain changes in the mediolateral and vertical positions as a result of SSO, are risk factors for postoperative NSD.     

Changes to foot pressure pattern in post-stroke individuals who have started to walk independently during the convalescent phase

BackgroundAbnormal foot contact patterns following stroke affect functional gait; however, objective analysis targeting independent walking is lacking.Research questionHow do walking abilities and foot pressure patterns differ between post-stroke individuals who achieved independent walking and healthy controls? Secondarily, how do the abilities and patterns in post-stroke individuals change before and after achieving independent walking? Can these changes become criteria for permitting independent walking?MethodsTwenty-eight individuals with hemiplegia and 32 controls were enrolled. Motor dysfunction score (MDScore), walking speed (WSpeed), and foot pressure patterns were measured when they were first able to walk without orthosis or physical assistance (1st assessment) and when they achieved independent walking around discharge (2nd assessment). Foot pressure patterns were measured using insole-type foot pressure-measuring system. Ratios of partial foot pressure to body weight (%PFP), ratios of anteroposterior length of center of pressure (COP; %Long), and backward moving distance of COP to the foot length (%Backward) were calculated. Parameters during the 2nd assessment were compared with those of controls and those during the 1st assessment. During the 2nd assessment, relationships among the parameters, MDScore, and WSpeed were analyzed.ResultsDuring the 2nd assessment, no difference was observed in both %Long and %Backward between the non-paretic limbs and the controls. While the %Backward was higher, the %PFP of toes and %Long were lower in the paretic limb than in the controls. Although the %Backward was lower, both %PFP of toes and %Long of the paretic limb were higher in the 2nd assessment than in the 1st assessment. During the 2nd assessment, both %Long and % Backward values of the paretic limb moderately correlated with MDScore and WSpeed.SignificanceAfter improvement of foot pressure in toes, both an increase in anteroposterior length and a decrease in backward moving of COP path were objective signs permitting independent walking.