Industrial and Applied Physics(DIAP)
Industrielle et appliquée(DPIA)

---

Jerry J. BATTISTA
London Regional Cancer Centre, University of Western Ontario

On-Line CT Imaging for Precision Radiotherapy*

---

Radiation oncology has steadily evolved over the last century. From its beginnings with kilovoltage x and γ-rays (1900’s) to megavoltage cobalt radiation (developed in Canada in the 1950’s), linear accelerators (1960’s) are now used routinely to produce higher energy beams of electrons or x‑rays. Further advances have stemmed from: (1) multi-modality 3D imaging, which includes CT, MRI, ultrasound, and PET for better delineation of the targeted disease, (2) automation of beam collimation (MLCs) with programmable field shaping and intensity modulation (IMRT), and (3) image-guidance to verify patient alignment prior to treatment delivery. Current developments are focusing towards providing on-line CT imaging devices mounted “onboard” the gantry of the radiation therapy machine. Two new approaches are being investigated in Ontario: (a) fan-beam CT using a ring gantry design for both imaging and treatment with megavoltage (3.5 MV and 6 MV) x-rays (TomoTherapy Inc.) and (b) cone-beam CT using a standard C-arm gantry (Elekta Synergy System) that rotates an auxiliary x-ray tube (120 kVp) and a flat-panel detector (e.g. Gd₂O₂S:Tb, amorphous silicon). In this presentation, the pros and cons of each approach will be reviewed, including the imaging physics at kV and MV energies, image quality parameters, imaging dose, imaging time, and process flow. In the near future, the measured treatment beam transmission fluence will be combined with CT data sets to reconstruct the actual dose distribution delivered to the patient in vivo. This exciting development will expand research into adaptive radiotherapy, to allow a treatment fraction to be modified in mid-course as needed. Human radiobiology, that correlates clinical outcomes (i.e. tumour response and treatment complications) with the true dose pattern in tumour and surrounding normal tissues, respectively, becomes possible for the first time.

*In collabaration with: T. Kron¹, G. Hajdok², I. Cunningham³, J. Van Dyk¹ and G. Bauman¹, ¹London Regional Cancer Centre, ²University of Western Ontario and ³Robarts Research Institute.