[MEDRADSC 3S03] - Final Exam Guide - Everything you need to know! (62 pages long)

• School: McMaster University
• Department: Medical Radiation Sciences
• Course: MEDRADSC 3S03
• Professor: Dawn Danko

Document Summary

Region at the edge of the beam over which the dose rate changes rapidly as a function of distance from the central axis. Physical penumbra: the lateral distance between two specified isodose curves at a specified depth. Between the 90% and 20% curves (at depth of dmax-but can be any depth) 3 components to penumbra: geometric penumbra, function of the physical construction of the rx machine, depends on source size, distance from the source, source diaphragm distance, transmission penumbra, scatter penumbra. Drawn at equal increments of % depth dose, representing the variation in dose as a function of depth and transverse distance from the central axis. Sad: measured at the depth of isocentre. High dose or (cid:858)hor(cid:374)s(cid:859) (cid:374)ear the surface i(cid:374) the peripher(cid:455) of the field. Under-compensate near the surface in order to obtain flat isdose curves at greater depths (10 cm) Factors that affect the appearance of an isodose chart. Field size: ca depth dose larger for larger fs.