ABSTRACT
To assist the radiation therapist/technologist with setting up patients for radiation therapy treatments, a set of accessories has been developed for placing a transparent template of the treatment-field border in the light-field of a radiation teletherapy unit. These accessories permit the efficient, accurate, and reproducible manual placement of independent lead-shielding blocks. Software has been developed to print templates on standard transparency sheets using a laser printer. A transparent template holder slides into the wedge slot of the teletherapy unit. The template holder features 2 alignment pegs to assure rapid, accurate, and reproducible placement of the template. A specially-developed hole-punch is used to cut, in the template, alignment holes that fit snugly over the pegs of the template holder. This system currently supports Siemens MX and KD units and the Theratronics Theratron 780C Co unit, as well as the Helax TMS block file format.
Subject(s)
Radiation Protection/instrumentation , Radiotherapy Planning, Computer-Assisted/methods , Equipment Design , Humans , LeadABSTRACT
The simulation of breast fields using an isocentric set-up technique can be a lengthy process involving the placement of the isocentre, the determination of the gantry angles, and the selection of the lung shields, which in our center is one of six standard blocks. We show that with a body contour taken through central axis, five measurements and a calculator program, it is possible to significantly decrease the amount of time required to simulate a breast patient. We have developed a program for an HP48GX handheld calculator to determine the gantry angles, the isocentre, the field width, the standard angled block, and the couch and collimator rotation. The calculations are based on measurements of the field length, the horizontal distance between midline and mid axillary line, and the vertical distances from the mid axillary line to the inferior and superior beam border and central axis at midline. We use spherical geometry to perform the calculations to reflect the true environment and do not make any assumptions about the average patient's shape. For the simulation process a jig was developed that is inserted into the tray holder of the simulator to show the optical and radiological shadow of the calculated shielding along the patient's midline for clinical assessment during simulation and on the simulation film. The jig also has a holder for an aluminum wedge to improve the image quality of the simulation film. We admit that the lung shield increases the dose to the contralateral breast because of increased scatter and transmission through the shield; however, the block decreases the volume of irradiated lung while keeping the beam edge along the midline of the patient. The technique has been in use for two years and has resulted in time savings of up to 30% per patient. It has proven to be an easy and accurate way of setting up isocentric treatments to the breast.
Subject(s)
Breast/radiation effects , Computers , Radiotherapy Planning, Computer-Assisted , Software , Female , HumansABSTRACT
On a radiotherapy accelerator, the dose monitoring system is the last level of protection between the patient and the extremely high dose rate which all accelerators are capable of producing. The risk of losing this level of protection is substantially reduced if two or more dose monitoring systems are used which are mechanically and electrically independent in design. This paper describes the installation of an independent radiation monitor in a dual-mode, computer-controlled accelerator with a moveable monitor chamber. The added device is fixed in the beam path, is capable of monitoring each beam pulse, and is capable of terminating irradiation within the pulse repetition period if any measured pulse is unacceptably high.
