Dose Course 2018_Flipping book

Dose per MU formalisms: factor-based dose calculations

Modulation with non-physical wedges

Non-physical wedges are delivered with one of the Y-jaws moving in or out during beam at variable dose rate and at variable speed. Wedge factors:

• do not depend on depth (no beam hardening) • vary with beam energy and off axis position

Varian EDW • Y-jaw motion into field (0.5 . cm from opposing) jaw; in variable speed and dose rate • Jaw positions per MU: stored lookup (GSTT) tables ; one per beam energy • 7 wedge angles in total (as combination of 60 ° wedged and open fields) • WF depends on energy, wedge angle, field size and off-axis position (along Y direction; asymmetric fields) • WF  0.4 - 1

Siemens VW • Y-jaw motion out of field, starting from 1 . cm of opposing jaw • Jaw positions per MU: calculated using a mathematical algorithm with energy dependent parameters. • Multiple wedge angles between 10 ° and 60 ° • WF depends on energy, wedge angle, field size and off-axis position (along Y direction; asymmetric fields) • WF  1 from calculation points on CAX

In MU formalisms WF for non-physical wedges are either derived from measurements or are calculated (from GSTT data)