A feasibility study of "plan transformation": A novel workaround enabling patient transfer between different Varian machines

Abstract

Purpose: The objective of this work is to explore a methodology to enable plan transfers from Standard MLC (STD) to High Definition MLC (HD) Varian units without replanning. Using "Plan Transformation", we aim to utilize full departmental capacity to disperse patients from STD Varian units to HD units, when the former goes down for repair.

Methods: Our centre is equipped with four STD and two HD MLC Varian Truebeam units. Plan transformation is used to transfer patients from STD to HD units when needed. Static or manually segmented fields with Y jaws ≤ 21.6 cm are eligible for plan transformation. The MLC pattern for each field is exported out of Eclipse. An in-house program based on C# is used to convert those patterns from STD to HD. STD and HD MLCs are different in design but dosimetrically comparable for these type of plans. Still to avoid extra uncertainty, transformed plans are recalculated in Eclipse to enable the user to assess the quality of the process.

Results: On a given day, more than 25% of appointments on STD units were eligible for transformation. The majority of eligible plans were breast tangent and boost. The delivery and safety of plan transformation was examined directly on a Varian Truebeam linac. A gamma analysis comparison between measured and calculated transformed plans yields a pass-rate of 100% for 3%/3mm, identical to non-transformed plans.

Conclusion: Plan transformation is feasible and saves time for planners as it takes less than a quarter the time required for a replan.