The technical design and concept of a PET/CT linac for biology-guided radiotherapy

Abstract

This is a summary of the design and concept of the RefleXion X1, a system for biology-guided radiotherapy (BgRT). This system is a multi-modal tomography (PET, fan-beam kVCT, and MVD) treatment machine that utilizes imaging and therapy planes for optimized beam delivery of IMRT, SBRT, SRS, and BgRT radiotherapy regimens. For BgRT delivery specifically, annihilation photons emanating outward from a PET-avid tumor are used to guide the delivery of beamlets of radiation to the tumor at sub-second latency. With the integration of PET detectors, rapid beam-station delivery, real-time tracking, and high-frequency multi-leaf collimation, the BgRT system has the potential to deliver a highly conformal treatment to malignant lesions while minimizing dose to surrounding healthy tissues. Furthermore, the potential use of a single radiotracer injection to guide radiotherapy to multiple targets opens avenues for debulking in advanced and metastatic disease states.

Keywords: BgRT; Biological signature; Positron emission tomography; Real-time tracking; Sub-second latency.

Fig. 1

An overview of the BgRT system showing some of the major subcomponents.

Fig. 2

The linac produces high energy photons over a concise 5-μs time interval.

Fig. 3

Depiction of the couch movement during delivery.

Fig. 4

System latency in the BgRT radiotherapy system.

Fig. 5

Comparison of volumes used for ITV-based RT, such as SBRT (left) and BgRT (right). IM-internal margin, SM – setup margin, GTV – gross tumor volume, CTV – clinical target volume, ITV – internal target volume, PTV – planning target volume, BgM – biology – guidance margin, and BTZ-biology tracking zone.

Fig. 6

BgRT plan optimization (A) overview of BgRT TPS input and output. D = Dose Distribution, C = Cost function, A = Dose calculation matrix, P = Firing Matrix, the matrix-vector product P·X is assumed to be evaluated with 3D volume X linearized into a vector.

Fig. 7

Proposed clinical workflow of BgRT system.