USE OF A MULTILEAF COLLIMATOR AS A DYNAMIC MISSING-TISSUE COMPENSATOR

A dynamic multileaf collimator (D-MLC) was used to investigate the fea sibility of producing missing-tissue compensators. The modulation of t he x-ray field in two dimensions produced by conventional physical com pensators was mimicked by delivering a sequence of D-MLC-shaped subfie lds. A method is introduced to calculate monitor units (MU) for dynami cally compensated fields that is analogous to and expands upon methods used for conventional compensating filter MU calculations. In this in vestigation, the tissue deficit at the surface of an anatomical phanto m was measured using a Moire camera. The tissue deficit data were used to generate a series of D-MLC subfields that, delivered in sequence, provided the compensated treatment. Film was used to integrate the dos e delivered to a specified depth of compensation. Isodose distribution s were measured for uncompensated fields, fields compensated with a co nventional lead or plastic filter, and fields compensated with the D-M LC. A comparison of the dose distributions shows the compensation achi eved with the dynamic compensating filter is comparable to that achiev ed using conventional physical compensating filters. (C) 1996 American Association of Physicists in Medicine.