A new methodology for inter- and intrafraction plan adaptation for the MR-linac

Abstract

The new era of hybrid MRI and linear accelerator machines, including the MR-linac currently being installed in the University Medical Center Utrecht (Utrecht, The Netherlands), will be able to provide the actual anatomy and real-time anatomy changes of the patient's target(s) and organ(s) at risk (OARs) during radiation delivery. In order to be able to take advantage of this input, a new generation of treatment planning systems is needed, that will allow plan adaptation to the latest anatomy state in an online regime. In this paper, we present a treatment planning algorithm for intensity-modulated radiotherapy (IMRT), which is able to compensate for patient anatomy changes. The system consists of an iterative sequencing loop open to anatomy updates and an inter- and intrafraction adaptation scheme that enables convergence to the ideal dose distribution without the need of a final segment weight optimization (SWO). The ability of the system to take into account organ motion and adapt the plan to the latest anatomy state is illustrated using artificial baseline shifts created for three different kidney cases. Firstly, for two kidney cases of different target volumes, we show that the system can account for intrafraction motion, delivering the intended dose to the target with minimal dose deposition to the surroundings compared to conventional plans. Secondly, for a third kidney case we show that our algorithm combined with the interfraction scheme can be used to deliver the prescribed dose while adapting to the changing anatomy during multi-fraction treatments without performing a final SWO.

An MRI‐compatible patient rotation system — design, construction, and first organ deformation results

“…More advanced adaptive strategies could also be applied to compensate for the anatomic deformation, which could bring the geometric accuracy of the therapy to the levels seen after the nonrigid registration step. One interesting approach to adaptive radiotherapy was recently proposed in ref . In this work, the plan was adaptively updated in response to the real‐time position of the organs, while also taking into account the dose which has already been delivered.…”

Dosimetric advantages of a clinical daily adaptive plan selection strategy compared with a non-adaptive strategy in cervical cancer radiation therapy

“…Also, the use of online plan adaptations based on daily MRI will be implemented [25]. First of all, MRI guidance can be introduced to avoid plan selection difficulties due to limited CBCT image quality or to implement additional boost techniques based on tumor response.…”

“…First of all, MRI guidance can be introduced to avoid plan selection difficulties due to limited CBCT image quality or to implement additional boost techniques based on tumor response. Moreover, the clinical introduction of MRI-guided RT allows online plan adaptations and could be the next step in online ART in cervical cancer [25].…”

Properties of the anisotropy of dose contributions: A planning study on prostate cases

“…Thus, the previously considered ideas for ad hoc plan adaptation are particularly interesting for the next generation of linear accelerators, the MR‐linac. Various fluence‐based concepts for adaptive planning have been developed . On the other side, the current state of MR‐linac technology does not yet offer dynamic arcs and thus excludes VMAT.…”