PURPOSE: Compared to conventional linacs with rotating gantries, a fixed-beam
radiotherapy system could be smaller, more robust and more cost-effective. In
this work, we developed and commissioned a prototype x-ray radiotherapy system
utilizing a fixed vertical radiation beam and horizontal patient rotation.
METHODS: The prototype system consists of an Elekta Synergy linac with gantry
fixed at 0° and a custom-built patient rotation system (PRS). The PRS was
designed to immobilize patients and safely rotate them about the horizontal axis.
The interlocks and emergency stops of the linac and PRS were connected. Custom
software was developed to monitor the system status, control the motion of the
PRS and modify treatment plans for the fixed-beam configuration. Following
installation, the prototype system was commissioned for three-dimensional (3D)
conformal therapy based on guidelines specified in AAPM TG-45 and TG-142, with
modifications for the fixed-beam geometry made where necessary.
RESULTS: The system and control software was tested in a variety of machine
states and executed motion, stop and beam gating commands as expected. Interlocks
and emergency stops of the linac and PRS were found to correctly stop PRS motion
and both kV and MV radiation beams when triggered. For 3D conformal treatments,
the prototype system met all AAPM TG-45 and TG-142 specifications for geometric
and dosimetric accuracy. Motion of the PRS was within 0.6 ± 0.3 mm and
0.10° ± 0.07° of input values for translation and rotation respectively. The axis
of rotation of the PRS was coincident with the radiation beam axis to less than
1 mm. End-to-end treatment verification for 6 MV conformal treatments showed less
than 2% difference between planned and delivered dose for all fields.
CONCLUSION: In this work, we have developed and commissioned a radiotherapy
system that utilizes a fixed vertical radiation beam and horizontal patient
rotation. This system is a proof-of-concept prototype for a fixed-beam treatment
system without a rotating gantry. Fixed-beam systems that are smaller and more
cost-effective could help in improving global access to radiotherapy.