Real-time optical measurement of the dynamic body surface for use in guided radiotherapy.

Optical measurements are increasingly used in radiotherapy. In this paper we present, in detail, the design and implementation of a multi-channel optical system optimized for fast, high spatial resolution, dynamic body surface measurement in guided therapy. We include all algorithmic modifications and calibration procedures required to create a robust, practical system for clinical use. Comprehensive static and dynamic phantom validation measurements in the radiotherapy treatment room show: conformance with simultaneously measured cone beam CT data to within 1 mm over 62% ± 8% of the surface and 2 mm over 90% ± 3%; agreement with the measured radius of a precision geometrical phantom to within 1 mm; and true real-time performance with image capture through to surface display at 23 Hz. An example patient dataset is additionally included, indicating similar performance in the clinic.

An analysis of breast motion using high-frequency, dense surface points captured by an optical sensor during radiotherapy treatment delivery.

Patient motion is an important factor affecting the quality of external beam radiotherapy in breast patients. We analyse the motion of a dense set of surface points on breast patients throughout their treatment schedule to assess the magnitude and stability of motion, in particular, with respect to breast volume. We use an optical sensor to measure the surface motion of 13 breast cancer patients. Patients were divided into two cohorts dependent upon breast volume. Measurements were made during radiotherapy treatment beam delivery for an average of 12 fractions per patient (total 158 datasets). The motion of each surface point is parameterized in terms of its period, amplitude and relative phase. Inter-comparison of the motion parameters across treatment schedules and between patients is made through the creation of corresponding regions on the breast surfaces. The motion period is spatially uniform and is similar in both patient groups (mean 4 s), with the small volume cohort exhibiting greater inter-fraction period variability. The mean motion amplitude is also similar in both groups with a range between 2 mm and 4 mm and an inter-fraction variability generally less than 1 mm. There is a phase lag of up to 0.4 s across the breast, led by the sternum. Breast patient motion is reasonably stable between and during treatment fractions, with the large volume cohort exhibiting greater repeatability than the small volume one.

Animation and radiobiological analysis of 3D motion in conformal radiotherapy.

PURPOSE: To allow treatment plans to be evaluated against the range of expected organ motion and set up error anticipated during treatment. METHODS: Planning tools have been developed to allow concurrent animation and radiobiological analysis of three dimensional (3D) target and organ motion in conformal radiotherapy. Surfaces fitted to structures outlined on CT studies are projected onto pre-treatment images or onto megavoltage images collected during the patient treatment. Visual simulation of tumour and normal tissue movement is then performed by the application of three dimensional affine transformations, to the selected surface. Concurrent registration of the surface motion with the 3D dose distribution allows calculation of the change in dose to the volume. Realistic patterns of motion can be applied to the structure to simulate inter-fraction motion and set-up error. The biologically effective dose for the structure is calculated for each fraction as the surface moves over the course of the treatment and is used to calculate the normal tissue complication probability (NTCP) or tumour control probability (TCP) for the moving structure. The tool has been used to evaluate conformal therapy plans against set up measurements recorded during patient treatments. NTCP and TCP were calculated for a patient whose set up had been corrected after systematic deviations from plan geometry were measured during treatment, the effect of not making the correction were also assessed. RESULTS: TCP for the moving tumour was reduced if inadequate margins were set for the treatment. Modelling suggests that smaller margins could have been set for the set up corrected during the course of the treatment. The NTCP for the rectum was also higher for the uncorrected set up due to a more rectal tissue falling in the high dose region. CONCLUSION: This approach provides a simple way for clinical users to utilise information incrementally collected throughout the whole of a patient's treatment. In particular it is possible to test the robustness of a patient plan against a range of possible motion patterns. The methods described represent a move from the inspection of static pre-treatment plans to a review of the dynamic treatment.

High technology to simplify the planning and delivery of radiotherapy.

Two techniques for the automatic selection of individual leaf positions of a Philips multi-leaf collimator are described. Target volumes are identified either on simulator images or on cross-sectional images from CT or MR scanners. The setting of each leaf is computed to position the beam edge to cover the target with an appropriate, user defined, margin. An important consideration in the development of the system was its robustness and so the applications initially implemented have been relatively simple, comprising single field, parallel opposed fields and coplanar 4 field box techniques. Attention has been paid to the overall integrity of the planning and treatment delivery process. Before treatment commences, the beam shapes, which have been generated by the computer and transferred to the MLC control computer over a local area network, are checked against a printed template representing each beam. All data used for planning is archived and is accessible for review or, if necessary, for treatment modification.

Computer-assisted generation of multi-leaf collimator settings for conformation therapy.

Techniques for the automatic set up of the individual leaf positions of a Philips multi-leaf collimator system to cover a defined target volume are described. Tumour outline data for multi-field treatments may be obtained from one of two techniques, either from simulator images or from cross-sectional computed tomography (CT) slices. In the first technique, simulator images are digitized directly from image intensifier video signals or from conventional film radiographs using a CCD camera. Corrections for image distortion are carried out before reformatting the digitized images to a common data structure. Target outlines are subsequently traced interactively on the digital image to create an outline file. In the second technique, target volumes are defined on several individual CT slices and these are then used to obtain projected graphical views from any desired angle. In both techniques, a scaled graphical representation of leaf positions is then displayed and set relative to the outer edge of the target outline. Both techniques allow interactive repositioning of single leaves when required, or the operator can specify a margin around the projected target volume. Leaf prescription data files are created and are transferred via a Decnet-OSI-Opennet network link to an Intel microcomputer, which is used to drive the device itself. Examples of both techniques are given.