IMRT

Precise dose computation DURING fluence profile optimization is immensely expensive!

• computation time issue • computer memory issue (10.000 beamlets can be ~Gigabyte memory)

This is why some planning system calculate simplified beamlet doses:  too steep and/or truncated penumbra, esp. in presence of inhomogenieties

 thus, OARs may wrongly appear sufficiently spared

 the final, more precise dose calculation reveals such initial simplifications! → plan degradation of segmented plan!

5 cm!

4 mm x 2 mm beamlet, 15 MV, 3D-PB

ESTRO IMRT course 2015 IMRT optimization: algorithms&cost functions Brussels October 5th, 2015

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