Abstract
This document is the report of a task group of the AAPM and has been prepared primarily to advise medical physicists involved in the external-beam radiation therapy of patients with thoracic, abdominal, and pelvic tumors affected by respiratory motion. This report describes the magnitude of respiratory motion, discusses radiotherapy specific problems caused by respiratory motion, explains techniques that explicitly manage respiratory motion during radiotherapy and gives recommendations in the application of these techniques for patient care, including quality assurance (QA) guidelines for these devices and their use with conformal and intensity modulated radiotherapy. The technologies covered by this report are motion-encompassing methods, respiratory gated techniques, breath-hold techniques, forced shallow-breathing methods, and respiration-synchronized techniques. The main outcome of this report is a clinical process guide for managing respiratory motion. Included in this guide is the recommendation that tumor motion should be measured (when possible) for each patient for whom respiratory motion is a concern. If target motion is greater than 5 mm, a method of respiratory motion management is available, and if the patient can tolerate the procedure, respiratory motion management technology is appropriate. Respiratory motion management is also appropriate when the procedure will increase normal tissue sparing. Respiratory motion management involves further resources, education and the development of and adherence to QA procedures.
Highlights
This section discusses imaging and treatment-planning guidelines for tumor sites affected by respiratory motion
Methods to reduce the impact of respiratory motion in radiotherapy can be broadly separated into five major categories: Motion-encompassing methods, respiratory gating techniques, breath-hold techniques, forced shallow-breathing techniques, and respiration-synchronized techniques
For internal and external tracking systems, a possible source of error is that the surrogate for tumor motione.g., tracking blocks, strain gauges, etc.͒ tracked by the gating system does not accurately correspond with the timedependent target positionFig. 4͒
Summary
This section will contain abbreviations of commonly used terms from the report as well as suggested terminology for instances when multiple words or phrases are used to describe the same object or function, such as: 4D. A device thatfor this applicationrestricts image acquisition or treatment delivery to a particular part of the GTV Hysteresis respiratory cycle Gross tumor volume The lagging of an effecte.g., tumor motionbehind its causee.g., muscular contractionsresulting in the tumor taking a different path during inhalation. For CT-planned lung cancer treatments, the gross tumor volumeGTV41,42 is outlined, and a margin is added to include the suspected microscopic spread48 ͓which when added to the GTV creates the clinical target volumeCTV͒. Using ICRU 6242 nomenclature, to obtain the planning target volumePTVfrom the CTV involves margins to account for intrafraction motion, interfraction motion, and setup error. Accounting for respiratory motion by adding treatment margins to cover the limits of motion of the tumor is suboptimal, because this increases the radiation field size and the volume of healthy tissues exposed to high doses. Because of the artifacts observed in CT images in which respiratory motion has not been accounted for, the magnitude of margin to allow for respiratory motion is difficult to quantify, for individual patients in whom a wide range of tumor motion is observed.
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