Validation of a pretreatment delivery quality assurance method for the CyberKnife Synchrony system.

PURPOSE: To evaluate the geometric and dosimetric accuracies of the CyberKnife Synchrony respiratory tracking system (RTS) and to validate a method for pretreatment patient-specific delivery quality assurance (DQA). METHODS: An EasyCube phantom was mounted on the ExacTrac gating phantom, which can move along the superior-inferior (SI) axis of a patient to simulate a moving target. The authors compared dynamic and static measurements. For each case, a Gafchromic EBT3 film was positioned between two slabs of the EasyCube, while a PinPoint ionization chamber was placed in the appropriate space. There were three steps to their evaluation: (1) the field size, the penumbra, and the symmetry of six secondary collimators were measured along the two main orthogonal axes. Dynamic measurements with deliberately simulated errors were also taken. (2) The delivered dose distributions (from step 1) were compared with the planned ones, using the gamma analysis method. The local gamma passing rates were evaluated using three acceptance criteria: 3% local dose difference (LDD)/3 mm, 2%LDD/2 mm, and 3%LDD/1 mm. (3) The DQA plans for six clinical patients were irradiated in different dynamic conditions, to give a total of 19 cases. The measured and planned dose distributions were evaluated with the same gamma-index criteria used in step 2 and the measured chamber doses were compared with the planned mean doses in the sensitive volume of the chamber. RESULTS: (1) A very slight enlargement of the field size and of the penumbra was observed in the SI direction (on average <1 mm), in line with the overall average CyberKnife system error for tracking treatments. (2) Comparison between the planned and the correctly delivered dose distributions confirmed the dosimetric accuracy of the RTS for simple plans. The multicriteria gamma analysis was able to detect the simulated errors, proving the robustness of their method of analysis. (3) All of the DQA clinical plans passed the tests, both in static and dynamic conditions. No statistically significant differences were found between static and dynamic cases, confirming the high degree of accuracy of the Synchrony RTS. CONCLUSIONS: The presented methods and measurements verified the mechanical and dosimetric accuracy of the Synchrony RTS. Their method confirms the fact that the RTS, if used properly, is able to treat a moving target with great precision. By combining PinPoint ion chamber, EBT3 films, and gamma evaluation of dose distributions, their DQA method robustly validated the effectiveness of CyberKnife and Synchrony system.

Effects of somatostatin analogues on acromegalic cardiomyopathy: results from a prospective study using cardiac magnetic resonance.

OBJECTIVE: Left ventricular (LV) hypertrophy is the main finding of patients with active acromegaly at cardiac magnetic resonance (CMR). The aim of the study was to evaluate heart changes in acromegalic patients treated with somatostatin analogues (SMSA) using CMR. DESIGN AND PATIENTS: This was a prospective study. Fourteen consecutive patients (8 women, mean age 46+/-10 yr) with untreated active acromegaly were submitted to CMR and 2D-color Doppler echocardiography before and after a 6-month SMSA course. MEASUREMENTS: LV volume, mass (LVM) and wall thickness. RESULTS: CMR: Mean LVM and LVM index (i) decreased from 151+/-17 g and 77+/-9 g/m2, to 144+/-24 g and 70+/-12 g/m2, respectively (p=0.047 and p<0.0001, respectively); LV hypertrophy reverted in 6 out of 10 patients (p=0.016). Systolic function, evaluated by measuring LV ejection fraction remained normal in all patients (67+/-11%). There was not a correlation between changes in LVMi and changes in serum IGF-I concentrations. However, patients with controlled disease had higher reduction of LVMi than those with uncontrolled acromegaly (DeltaLVMi, -8.2+/-4.2 vs 4.0+/-5.3 p<0.05). 2D-echo cardiography: Mean LVMi decreased from 110+/-24 g/m2 to 100+/-20 g/m2 (p=0.026); hypertrophy, revealed in 5 patients (36%) at baseline, reversed in 2 patients (p=0.500) after SMSA; abnormal diastolic function [evaluated by isovolumic relaxation time or early (E) to late of atrial (A) peak velocities ratio] found in 4 patients (29%) at the study entry, improved in a patient. Systolic function remained within the normal range in all patients during the study period. CONCLUSIONS: CMR detects changes in LVMi in most patients with acromegaly treated with SMSA, which are more evident if the disease is controlled.

Refractive astigmatism acts predominantly as a source of high spatial frequency image distortion: the associated lineal distortions can be overcome by using a low pass spatial filter!

PURPOSE: Surprisingly, an important characteristic of astigmatism has been overlooked by ophthalmic and clinical scientists. Apparently, refractive astigmatism is due largely to a form of high spatial frequency image distortion. METHODS: Characteristic astigmatic image distortion can be minimized or eliminated by using a low-pass spatial filter (here, a ground glass plate was employed for this purpose). The ground glass is placed a short distance in front of a visual acuity chart, or it may be used with other tests, such as vernier acuity. RESULTS: This test has been performed by us on large numbers of patients and test subjects. A clinician can try this test for himself/herself. Place a +2.00 D.C. (any axis) lens in front of the eye; the usual distortions will be observed. Locate the ground glass plate as described. The usual distortions associated with the conoid of Stürm will not be visible or will be virtually eliminated, although some image blur will remain. CONCLUSIONS: This technique has significance, e.g., in visual screening programs in developing nations, or in assessing patients with media disorders prior to ophthalmic surgery.