ABSTRACT
When an electron beam is incident upon a stepped surface, such as that which exists when a slab of bolus is present with it's square edge within the portal, the dose distribution is strikingly perturbed. An easily demonstrable explanation is given which utilizes the customary, flat-incident surface electron beam dose distribution.
Subject(s)
Radiotherapy Dosage , Radiotherapy/methods , Electrons , Humans , Models, TheoreticalABSTRACT
Many radiotherapy linear accelerators use electron beam applicators which extended close to the patient's surface when treating at the regular distance. The relatively large size of these applicators often necessitates the use of a larger SSD than that designed by the manufacturer. In such cases, the addition of shielding blocks to the applicator can significantly alter the factors which should be used to calculate the dose rate at the new SSD as compared with the unshielded beam condition. In some typical clinical situations, errors of greater than 60% may result from failure to account for this perturbation. This paper presents the proper correction of the dose vs SSD function for the presence of such shielding blocks for the Clinac-18 linear accelerator.
Subject(s)
Electrons , Particle Accelerators , Radiotherapy, High-Energy/instrumentation , Humans , Radiation Protection , Radiometry , Radiotherapy DosageABSTRACT
Conventional port planning techniques for radiation therapy do not adequately determine the superior and inferior limits of prostatic tumor. A localization device has been devised which provides better boost volume localization. The accuracy of this device has been confirmed by computed axial tomography.
