Purpose: Dynamic Conformal Arcs (DCA) are an efficient planning alternative to VMAT. Recent published techniques include variable dose rate or additional inverse planning. Pointed Flattening Filter Free (FFF) beams is more challenging. This algorithm presents a concise forward planning constant dose rate DCA procedure for rapid SBRT FFF planning.
Methods: Qualifying PTV contours are smooth concave shapes without close proximity or overlap with critical structures. Basically the technique is suitable if it is determined that a conformal dose distribution will meet all constraints.A partial arc with isocenter near the PTV center is first selected to conform to the target shape as much as possible. The dose is normalized to 100% at isocenter and the 95% isodose is converted into a structure S95. A Boost structure is then defined as Boost = PTV – S95.The “FIT and SHIELD” feature in ECLIPSE treatment planning system can automatically create additional arcs to simultaneously treat the Boost but avoid additional dose to S95. Often two arcs are sufficient. The relative weights of the initial arc conforming to the entire PTV and the Boost arcs are adjusted to provide the desired distribution. If necessary a new Boost structure is created and the process repeated. Note that normalization that may create a desired area of high dose in the PTV will also increase the 50% isodose volume and consequently the Gradient Index.
Results: The algorithm was successfully tested using phantom plans with various PTV configurations. Three peripheral lungs and two adrenal cases were planned which were comparable to acceptable protocol SBRT VMAT plans.
Conclusion: An algorithm for rapid forward SBRT DCA planning was developed and tested. Unlike previous techniques only DCA are used at constant dose rate. Applications include use for high throughput without IMRT patient specific QA and adaptive therapy with automated script planning.
Not Applicable / None Entered.