SU-E-T-417: A Method for Predicting and Correcting the Dosimetric Effect of a Radiotherapy Treatment Couch in Actual Treatment Position
Purpose: Although radiation attenuation by the treatment couch can be included in the calculation of radiotherapy dose, difference between planned and actual treatment couch positions can generate significant dose discrepancies. We propose a method to predict and correct the dosimetric effect of the couch in actual treatment position. Methods: The couch transmission factor, T, varies with beam angle, G, couch lateral position, x, and vertical position, y, i.e., T=T(x,y,G). If T(x,y,G) is known for a fixed couch vertical position y=h, the transmission of central-axis beam (CAX) T(x,y,G) can be obtained by T(x,y,G)=T(x{sup +},h,G), where x{sup +}=x-(y-h)tan(G) and G is the angle between the beam and the vertical axis. Similarly, the transmission of any off-CAX point can be obtained using a similar formula. We measured CAX couch transmission at a fixed couch vertical position over the couch lateral motion range for all gantry angles by continuously scanning rotating arc beams. A 2D couch transmission correction matrix can thus be generated from T(x,h,G) for each treatment field for the actual couch position. By applying the transmission correction matrix to the planned field dose, the couch effect can be predicted and corrected. To verify this method, we measured couch transmission T(x, y=10cm, G=225°)(225°=IECmore »
- Publication Date:
- OSTI Identifier:
- 22369569
- Resource Type:
- Journal Article
- Resource Relation:
- Journal Name: Medical Physics; Journal Volume: 41; Journal Issue: 6; Other Information: (c) 2014 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 60 APPLIED LIFE SCIENCES; ATTENUATION; BEAMS; COMPARATIVE EVALUATIONS; CORRECTIONS; DOSES; MATRICES; RADIOTHERAPY; TANTALUM NITRIDES; TRANSMISSION