Optically guided intensity modulated radiotherapy

Background and Purpose: Previously, we reported on development of an optica lly guided system for 3D conformal intracranial radiotherapy using multiple noncoplanar fixed fields. In this paper we report on the extension of our system for stereotactic fractionated radiotherapy to include intensity modu lated static ports. Methods and Materials: A 3D treatment plan with maximum beam separation is developed in the stereotactic space established by an optically guided syst em, Gantry angles are chosen such that each beam has a unique entrance and exit pathway, avoids the critical structures, and has a minimal beam's eye view projection. Once, a satisfactory treatment plan is found using this ge ometric approach an inverse treatment plan is developed using the beam port als established previously. The purpose of adding inverse planing is two fo ld, on the one hand it allows further reduction of margins around the PTV, while on the other hand it affords the possibility of conformal avoidance o f critical structures that are close to or abut the PTV. Results: The use of the optically guided system in conjunction with intensi ty modulated noncoplanar radiotherapy treatment planning using fixed fields allows the generation of highly conformal treatment plans that exhibit sma ller 90, 70, and 50% of prescription dose isodose volumes, improved PITV ra tios, comparable or improved EUD, smaller NTDmean for the critical structur es, and an inhomogeneity index that is within generally accepted limits. Conclusion: Because optically guided technology improves the accuracy of pa tient localization relative to the linac isocenter and allows real-time mon itoring of patient position, the planning target volume needs to be correct ed only for the limitations of image resolution. Intensity modulated static beam radiotherapy planning then provides the user the ability to further r educe margins on the PTV and to conform very closely to this smaller target volume, and enhances the normal tissue sparing, and high degree of conform ality possible with 3D conformal radiotherapy. In addition, since optically guided technology affords improved patient localization and online monitor ing of patient position during treatment delivery it allows for safe and ef ficient delivery of intensity modulated radiotherapy.(C) 2001 Elsevier Scie nce Ireland Ltd. All rights reserved.