Dynamic arc radiosurgery and radiotherapy: commissioning and verification of dose distributions.

Abstract

Conformal stereotactic radiosurgery and radiotherapy using a linear accelerator and a micromultileaf collimator (mMLC) offer the possibility of irradiating irregularly shaped target volumes. Dynamic arc radiosurgery and radiotherapy, i.e., stereotactic radiation therapy combining a moving gantry with a dynamic mMLC, enable the radiation even of lesions with concave structures. The dynamic arc method requires additional tools for quality assurance (QA) and three-dimensional verification at a high spatial resolution. A QA program was developed. Dose distributions of planning target volumes with concavities were investigated in polymer gel phantoms. The radiation-induced change of the relaxation rate R(2) was measured by magnetic resonance imaging. The distributions were compared with image processing tools. Using the therapy-planning software BrainSCAN 4.0 (and 4.1 beta) in combination with the mMLC m3, deviations between the planned and measured 90% isodoses of about 2 mm were registered in the isocenter plane. Three-dimensional verification was feasible in the range of accuracy achieved in planning and dose measurement. Dynamic arc radiosurgery and radiotherapy offer excellent conformation even for complicated planning target volumes with concavities. The dose distribution calculated with the treatment-planning software used can be accomplished with the available equipment. Patients can be treated by dynamic arc radiosurgery and radiotherapy.