Intensity modulated arc therapy technique using sliding window dynamic multileaf collimation

The goal of external beam radiotherapy is to deliver a homogeneous tumouricidal radiation dose to a planned target volume (PTV) while sparing surrounding healthy tissue and avoiding critical structures. The PTV should encompass the tumour as well as subclinical invasions, with margins to account for variations in patient set up and allowance for tumour movement.; Traditional radiation therapy planning techniques employ the application of a number of open rectangular fields to achieve this aim. These fields may be shaped with lead blocks or a multileaf collimator in order to conform better to the target outline. Further improvements in delivery can be realised by employing fields that have non-uniform intensity profiles in order to correct for tissue heterogeneities and surface irregularities, as well as to conform high dose regions as closely as possible to prescribed treatment volumes or conformally avoid critical structures. Using non-uniform intensity fields is known as intensity modulated radiation therapy (IMRT).; While non-uniform intensities have been traditionally realised with static physical attenuators, there is increasing use of dynamic multileaf collimation (DMLC). These can modulate either single incident fields (as in step and shoot or sliding window DMLC), or a series of contiguous transverse slices delivered by a rotating modulated slit beam. The latter technique, called tomotherapy, requires a dedicated unit or a linac fitted with a specialised modulator. Alternately, a highly conformal 3D-dose distribution can be achieved by using multiple concentric arcs with an aperture defined at all angles by a varying MLC shape. This has been referred to as intensity modulated arc therapy (IMAT). IMAT has been touted as an alternative to tomotherapy that requires no specialised equipment beyond what is often present.; A model is presented for an improved IMAT delivery scheme. This involves the determination of multileaf motions as a function of gantry angle, which will produce conformal dose distributions in a single arc. The aperture is delivered using a series of sliding window DMLC segments during gantry rotation. Dosimetric verification of fields delivered, as well as comparisons to other conformal techniques, is presented.