ABSTRACT
Therapy ............................................................................................ 175 8.2.4 Radiotherapy Simulators, CT Scanners, and CT Simulators ... 176 8.2.5 Tomotherapy ................................................................................... 176 8.2.6 Proton Therapy ............................................................................... 177
8.3 Design of Treatment and Imaging Facilities .......................................... 177 8.3.1 Exposure Limits and Constraints, Legislative
Requirements.................................................................................. 177 8.3.2 Linear Accelerator Bunkers .......................................................... 178
8.3.2.1 Primary Barriers .............................................................. 180 8.3.2.2 Secondary Barriers, Mazes, and Bunker
Geometry .......................................................................... 182 8.3.2.3 Neutrons ........................................................................... 183 8.3.2.4 Other Considerations ..................................................... 184 8.3.2.5 Design Constraints: Calculating Barrier
Thicknesses ...................................................................... 185 8.3.3 Kilovoltage, CT Simulator, and CT Rooms................................. 191 8.3.4 Tomotherapy Bunkers ................................................................... 193
8.4 Radiation Surveys ...................................................................................... 193 8.5 Other Acceptance Tests Relating to Safety ............................................ 195
8.5.1 Head Leakage ................................................................................. 195 8.5.2 Treatment Accessories ................................................................... 196 8.5.3 Emergency Off Buttons ................................................................. 196
8.6 Patient Safety .............................................................................................. 196 8.6.1 Treatment Planning ....................................................................... 197 8.6.2 Equipment Design ......................................................................... 198
8.7 Miscellaneous Radiation Protection Issues ........................................... 198 8.7.1 A Cobalt Source Becomes Stuck in the “On” Position ............. 198 8.7.2 Activation of Materials Due to Neutrons from High-
Energy X-Ray Units ....................................................................... 199 8.7.3 Accidental Irradiation of Persons in a Bunker ..........................200 8.7.4 Shielding for Intensity-Modulated Radiotherapy (IMRT) .......200
8.8 Ongoing Quality Assurance ....................................................................200 8.8.1 Safety Checks .................................................................................200 8.8.2 Radiation Surveys .......................................................................... 201 8.8.3 Staff Monitoring ............................................................................. 201 8.8.4 Staff Education ............................................................................... 202 8.8.5 Radiation Incident Reporting ....................................................... 202
References ............................................................................................................ 202
External beam radiotherapy involves the delivery of high doses of radiation of up to about 80 Gy with the aim of curing a tumor by killing all the proliferating cells or of providing palliation by restricting the rate at which the tumor is spreading. To prevent adverse reactions from healthy tissue in the path of the radiation, radiotherapy is usually delivered with two or more beams each directed at the tumor from different angles, so that the total dose to the tumor is greater than that to any of the surrounding tissue. Also, tumor cells and normal tissue cells have a different capacity to recover from radiation damage. Radiation treatment aims to exploit this difference by delivering the radiation dose progressively over a period of up to 8 weeks, typically in 2 Gy fractions given five times per week.
