1. Error Estimation of Radiotherapy Patient Posture by using Three-Dimensional Motion Analysis
Yousif Mohamed Y. Abdallah1*,Khalid Eltom 1, Abdelazeem Khalifa2
1Radiotherapy and Nuclear Medicine Department, College of Medical Radiological Science, Sudan University of Science and Technology, Khartoum, Sudan
2Oncology Department, National Cancer Institute (NCI), University of Gazeria, Madani, Sudan
Tel: , , 52
Abstract
The aim of radiotherapy treatment is to deliver a homogenous dose of radiation to an accurately localized target volume in order to produce tumor control with minimal effect on surrounding normal tissue. This study describes the technology and methods involved in a system for automatically checking the position of patients at radiotherapy units. The patient Alignment and position monitoring is carried out by comparing the current laser positions of the markers with those of an initial reference position acquired during the simulation procedure and/or the first irradiation session. The study was performed to measure the accuracy of conventional laser centering techniques for patient repositioning. Inaccuracies due to breathing and random movements were also taken into account. Professional radiotherapy technicians were asked to reposition twenty patients carefully using traditional laser centering procedures. The results revealed significant repositioning errors even in highly controlled conditions, affecting particularly body areas relatively far from the skin reference points used for laser alignment. The outcome of the experimental application of it confirms its potential as a tool for patient repositioning and automatic detection of any errors caused by breasting or other unpredictable movements. The results allow the radiotherapy technicians to take suitable countermeasures in case of significant errors (Conventional Set-up is equally ( mm) for x-direction reading, mm (x-direction reading) and mm and Laser Reading is equal mm, mm, mm). In addition, the use of the laser beam for automatic position control is envisaged.
Figure 4. (a) Properly installed cross-projecting laser, with horizontal on the same level as isocenter of the treatment unit. (b) Improperly installed cross-projecting laser, with the hole for vertical line on the same level as the isocenter of treatment unit.
Results
This study describes the technology and methods involved in a system for automatically checking the position of patients at radiotherapy units. The patient Alignment and position monitoring is carried out by comparing the current laser positions of the markers with those of an initial reference position acquired during the simulation procedure and/or the first irradiation session. The following tables and graphs show summary of the results including displacement of conventional set-up (mm) and laser set-up (mm). The set-up procedure using conventional set-up shows that the largest uncertainties appear in the y-direction. This effect appears spite claims that the positioning procedure feels comfortable and appropriate by the patient. Laser positioning system results in an increased accuracy. The precision is also higher and this is especially evident in the y-direction (Table 1 & Figure 3).
Introduction
Reliability, Stability and outstanding line quality are the hallmarks of fixed laser. Fixed lasers width of less than 1 mm at isocenter and a line depth of field 1.5 m- 4m. This ensures radiotherapy technicians precisely mark patients for therapy and reproduce position throughout a treatment schedule. Figerstrip controls provide independent adjustments for the angle of rotation of cross-lines. All fixed lasers include a custom-designed mounting plate. In radiation therapy precision and speed are foremost requirements for high patient throughput. Accurate planning and careful positioning are the keys of all treatment procedures. The positioning lasers display very fine, long lines on the isocenter of the machines, so the patient can be quickly and accurately placed on the couch in a reproducible position. LAP lasers set the standards in line quality, stability, reliability and ease of use. The advanced adjustment system is lead screw driven and externally accessible, to make fine adjustments fast and simple. (Figure 1)
Radiation therapy is a local treatment that is designed to treat the defined tumor and spare the surrounding normal tissue from receiving doses above specified dose tolerances.(1) There are many factors that may contribute to differences between the planned dose distribution and the delivered dose distribution. One such factor is uncertainty in patient position on the treatment unit. Guiding the placement of the treatment field is not a new concept (3). Since the advent of fractionated radiation therapy for the treatment of disease, techniques have been employed to help ensure the accurate placement of a treatment field. In general, at the time of 'planning' (whether a clinical mark up or a full simulation) the intended area for treatment is outlined by the radiation oncologist. Once the area of treatment was determined, marks were placed on the skin.
Displacement
Conventional Set-up (mm)
(Mean+Stdev.)
Laser Set-up (mm)
x-direction
y-direction
z-direction
Conclusion
The outcome of the Laser positioning system confirms its potential as tool for patient repositioning and automatic or manual detection of errors caused by breathing or other unpredictable movements. The laser alignment system feedback on the patient's position given by the system provides operator with appropriate visual indices and allows them to take suitable countermeasures in case of significant failures. In addition, the use of system output may be used for automatic control is envisaged. The maintenance of technical condition related errors within known and acceptable limits must be ensured by regular applying of Quality Assurance (QA) procedures for all equipment involved in radiotherapy procedures chain. Total geometrical error is built up of many smaller errors., which are presented by systemic and the random deviations can be predicted and use for correction strategy. Systematic errors introduced by target volume delineation, organ motion, and set-up errors should be reduced by clear delineation protocols, multimodality imaging, correct CT scan procedures, and by the application of electronic portal imaging with decision rules (protocols).
Figure 1. Shows laser positioning
Materials and Methods
A patient positioning system has been constructed using laser positions of the markers which allow the smooth translations from standing position horizontal position by means of reclining a treatment table. A conventional different body immobilization device has been used as support for the patient in supine or prone position. The same immobilization devices were used for both traditional laser centering procedures and initial reference position acquired during the simulation procedure and/or the first irradiation session. The same patient was asked to perform the alignment procedure at five separate sessions during treatment course. The reclining as well as conventional set-up procedure was performed consecutively. These procedures were performed at 10 fractions during 10 days, thus corresponding to long term course radiotherapy. The immobilization devices were positioned on the indexed treatment table and the table was then titled for the reclining positioning technique. Using the reclining technique, the patient was asked to remain the same position. Professional radiotherapy technicians were asked to reposition twenty patients carefully using traditional laser centering procedures. For traditional set-up procedure, the same patient was asked to climb onto the couch with immobilization devices already place. After each of set-set procedures, the position is recorded using laser positioning system. The laser positioning system thereby generates a displacement vector in the x-, y- and z- direction. The comparison procedure is based on comparison towards a reference image and/or position in first treatment session. The regions of interest used include the surface from lower pelvis and up to the head. Figure 1. The data was analyzed by using statistical package, Statistical Package for Social Studies (SPSS) under windows.
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