ABSTRACT
PURPOSE: To evaluate a formalism for transit dosimetry using a phantom study and prospectively evaluate the protocol on a patient population undergoing 3D conformal radiotherapy. METHODS: Amorphous silicon EPIDs were calibrated for dose and used to acquire images of delivered fields. The measured EPID dose map was back-projected using the planning CT images to calculate dose at pre-specified points within the patient using commercially available software, EPIgray (DOSIsoft, France). This software compared computed back-projected dose with treatment planning system dose. A series of tests were performed on solid water phantoms (linearity, field size effects, off-axis effects). 37 patients were enrolled in the prospective study. RESULTS: The EPID dose response was stable and linear with dose. For all tested field sizes the agreement was good between EPID-derived and treatment planning system dose in the central axis, with performance stability up to a measured depth of 18cm (agreement within -0.5% at 10cm depth on the central axis and within -1.4% at 2cm off-axis). 126 transit images were analysed of 37 3D-conformal patients. Patient results demonstrated the potential of EPIgray with 91% of all delivered fields achieved the initial set tolerance level of ΔD of 0±5-cGy or %ΔD of 0±5%. CONCLUSIONS: The in vivo dose verification method was simple to implement, with very few commissioning measurements needed. The system required no extra dose to the patient, and importantly was able to detect patient position errors that impacted on dose delivery in two of cases.
Subject(s)
Neoplasms/radiotherapy , Radiometry/methods , Radiotherapy Planning, Computer-Assisted/methods , Radiotherapy, Conformal/methods , Calibration , Cohort Studies , False Positive Reactions , Humans , Imaging, Three-Dimensional , Phantoms, Imaging , Prospective Studies , Radiation Dosage , Reproducibility of Results , Software , Tomography, X-Ray ComputedABSTRACT
Twenty patients treated by surgery for Perthes' disease were studied between 4 and 9 years postoperatively. In the clinical investigation eight patients complained of persistent stress-induced pain. In nine patients flexion, extension, ab- and adduction of the hip joint was limited. In the MRI-study of ten hip joints a reduction of fatty marrow was seen in the femoral head. In 11 hip joints of patients complaining of persistent pain, a deformation of the femoral head (n = 2), a dysplasia of the femoral metaphysis (n = 2), and diaphysis (n = 4) or both (n = 2) were seen. In another five patients an additional dysplasia of the acetabulum was visualized. All these findings were diagnosed by X-ray studies as well. However, only by MRI were the extents of the postoperative defects of femoral spongiosa diagnosed in fifteen hip joints.
