IMRT

Question 1

AAPM report for IMRT

Answer 1

TG120 dosimetry tools and techniques for IMRT

Question 2

differences between 3DCRT and IMRT dosimetry- challenges for IMRT

Answer 2

IMRT has to focus on cumulated dose not on QA of a single segment

• IMRT: fluence is varied during treatment so requires integrative dosimetric techniques
• IMRT- sometimes independent dose calculation methods are used as QA
• have to consider oblique-incidence response of clyndrical ion chambers for non-coplanar beams
• Volume averaging is an issue for detectors in small fields- dose will be underestimated due to averaging over the entire size of the detector
• if measuring profiles of dose distributions with rapidly spatially varying doses, the shape of the dose distribution will be blurred by volume averaging – use higher spatial resolution detector if accurate measurement of profile shape is needed
• small ion chamber is more sensitive to position errors