SU-E-T-514: Implementation and Commissioning of a Micro Multileaf Collimator in Pinnacle Treatment Planning System

To model and validate, in a Pinnacle treatment planning system, a Brainlab micromultileaf collimator mounted on a Primus Siemens accelerator. The objective is to take advantage of the collapsed cone convolution algorithm and the ability of this system modelling rounded leaf- end MLC's.

The micro multileaf collimator was modelled using fixed accelerator jaws with a value of 9.2×9.2 cm² . Profiles and depth dose curves for a wide range of square fields at SSD of 100 cm and depths of 1.5,5,10 and 20 cm were measured using a Scanditronix stereotactic SFD diode. Output factors were measured using a stereotactic unshielded diode for field sizes from 0.6×0.6 cm² to 3×3 cm² . For wider fields a Scanditronix ic15 ionization chamber was used. EDR2 films were used to measure adjacent fields in the transverse and longitudinal direction. The film measurements were compared to Pinnacle calculations to model and validate the leaf tip radius, leaf offset calibration values and tongue and groove width.

Pinnacle calculations and measurements agree within 2% or 2mm except for the tails of largest fields where differences are <3.5%. Comparison of film measurements and Pinnacle calculations give the optimal value for leaf tip radius of 15 cm and for tongue and groove width of 0.04 cm.

Pinnacle models a Brainlab micromultileaf collimator mounted on a Siemens Primus accelerator with acceptable results for clinical treatments.