Simplified bite-block immobilization of the head.
ABSTRACT The use of bite blocks to immobilize a patient's head for therapeutic radiology usually involves the mechanical positioning of a rod protruding from the block. This position must be recorded at simulation time and preset for each treatment session. The authors describe a device which simply requires the vertical positioning of an auxiliary bar which, in turn, is attached vertically to the primary rod at simulation time.
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ABSTRACT: Westmead Radiation Oncology Department like many radiation therapy department's has high demands on staffing and equip-ment resources within the mould room, while continuing to combat a dramatically increasing waiting list. The radiation oncolo-gist at Westmead specialising in cranial irradiation instigated the formation of a research group to explore the most resource effec-tive and accurate way of stabilising cranial patients and to confirm whether the cranial immobilisation protocols already in prac-tice within the department are suitable. Westmead Radiation Oncology employs four methods of cranial immobilisation; fixed and removable head frames that are used for stereotactic radiosurgery (SRS) and rigid plastic (uvex) and thermoplastic (orfit) casts. The latter two are used for brain lesions and head and neck treatments. With the advent of Intensity Modulated Radiation Therapy – IMRT, and modern day treat-ment, the field parameters employed are becoming smaller and the shielding more complex as the avoidance of critical organs which may be in the beams pathways is crucial. The necessity for rigid immobilisation and reproducibility on a daily basis is apparent. INTRODUCTION Westmead Radiation Oncology Department, like many other radiotherapy departments have excessive high demands on staffing and equipment resources both within the Mould Room and treatment areas whilst combating an escalating waiting list. The radiation oncologist specialising in cranial irradiation at Westmead instigated the formation of a research group to explore the most resourceful, effective and accurate way of stabilising cranial patients and to confirm whether the cranial immobilisa-tion protocols utilised at the present time within the department are effective. A glance backward to the middle of the last century, immo-bilisation techniques employed the use of rice bags and the time honoured sticky tape to support the head. Other aids employed, were tattooing the baseline once it was in a vertical position, for total cranial irradiation, and marking the field parameters with gentian violet. Smaller field parameters were again outlined with gentian, the field centre being tattooed. For those of you new to the profession, gentian violet is indelible and spillage caused no end of problems, especially to the hapless student who invariably was given the job of touching up the marks. Today we have personal masks slotted into custom made castboards for individual couch tops. See figure 1. Modern day radiotherapy utilises small field parameters with complex shielding to avoid critical organs which may be in the pathway of the beams. The necessity for rigid immobilisation and reproducibility on a daily basis is apparent. Westmead Immobilisation Methods Westmead employs four methods of Cranial Immobilisation: 1) Fixed and Relocatable head frames for Stereotactic Radiosurgery (SRS), 2) Rigid plastic and 3) Thermoplastic casts, complete the methods employed to render the cranium in a fixed position reproducible on a daily basis, so that radiation can be delivered in a safe and effective manner to the part of the brain the tumour may be situated. The importance of radiotherapy is to deliver dose to the tar-get volume while minimising risk to surrounding structures. Many cranial immobilisation systems have been developed over the years. The function is to maintain the patient's body in the same reproducible position while restricting mobility during treatment. The immobilisation device must be comfortable, yet simple to implement. In addition, it must not interfere with the treatment delivery. The system should not cause artifacts with the beam for planning purposes and have no beam attenuation for treatment purposes.05/2004; 51(51):29-33.
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ABSTRACT: Rigid immobilization of patients and accurate positioning of their targets have long been recognized as critically important aspects of quality radiotherapy. Radiobiological studies have indicated that the slope of the dose-response curve for many tumors is sufficiently large that a dose reduction of 3% to 5% to a portion of the tumor could significantly reduce the probability of local control. On the other hand, accurate positioning combined with rigid immobilization might permit reduced margins around the target, resulting in a decrease in dose to normal tissue and a potential increase in dose to the rarget. The increasing use of computed tomography-based three-dimensional treatment planning programs has made highly conformal dose distributions possible, thus further emphasizing the need for accurate positioning. The development of new immobilization materials and methods has made it possible to immobilize almost any area of the body of a cooperative patient to 3 mm, allowing the use of margins of no more than 5 mm except when target motion within the immobilized patient is an issue. Special techniques for intracrania targets or for targets in the head and neck can yield positioning accuracies of 1 to 2 mm, or even less for invasive immobilization. Through the use of electronic portal imagers, stereo video cameras, or stereo radiography, anatomical reference points can be followed during treatment and the target position varied as needed. Quantitative positioning studies are required for each disease site and immobilization method so that the target position uncertainty, which is the basis for the choice of treatment-planning margins, can be minimized and evaluated, leading to an increased level of uncomplicated local tumor control.Seminars in radiation oncology 05/1995; · 4.32 Impact Factor