Advanced TP

MLC geometry: Varian (millenium MLC)

 120 MLC  max field size : 40 x 40 cm

- 20 cm : leaf width = 5mm, outside, 1 cm

20cm

10cm

 maximum overtravel in (IMRT) fields is 14.3 cm: - so, if an IMRT field width ≥ 14.3 cm splitting beam - field width ≈ 28 cm splitting again (‘ carriage positions ’)

 inter-digitating MLC’s  closing opposing leaf-pairs