DEVELOPMENT OF TOOLS AND METHODOLOGY FOR IMAGE GUIDED RADIOTHERAPY

Abstract

This research aimed i) to further develop and test a novel device and software for image guided radiotherapy (IGRT) and ii) to develop a phase I radiotherapy (RT) dose escalation trial, using IGRT methodology to boost the gross target volume (GTV) after conventional chemoradiotherapy for lower oesophageal and oesophagogastric junctional (OGJ) cancers, using patient and health professional questionnaires for detailed toxicity recording, and incorporating translational radiobiology aspects.The feasibility of using a novel optical body surface sensor (OSS) using Fourier profilometry for patient positioning (setup) error measurement in RT was investigated in a pilot study of 11 patients receiving RT for thoracic or upper abdominal cancers. OSS setup error measurement approached, but did not reach, a clinically useful accuracy, apparently mainly due to optical surface inaccuracy. Other issues include the choice of reference surface (e.g. end-exhale or mean, from 4D CT or prior optical recordings), whether body surface and bony anatomy position are sufficiently well correlated to use surface matching for setup, and whether accurate surface matching is achievable using only surface topology, or whether additional surface detail, collected by the OSS, is needed.A greyscaling algorithm developed to allow dose calculation from on-treatment cone beam CT (CBCT) was assessed using the RT planning CT (RTP) and first CBCT for 10 patients treated with 3D conformal RT for lower oesophageal or OGJ cancer. Since the anatomy on RTP and CBCT differs, indirect comparisons were made. Each scan was bulk-corrected by setting the density of the lungs to 0.3 and other tissues to 1.0. The differences in doses on greyscaled CBCT and bulk-corrected CBCT were compared with the differences on RTP and bulk-corrected RTP. Preliminary results suggest that the CBCT greyscaling algorithm is sufficiently accurate for assessment of isocentre dose, mean target volume doses, GTV minimum and planning target volume (PTV) maximum doses and heart and lung doses. Further work is needed to determine the reasons for larger apparent errors in PTV minimum doses and spinal cord maximum doses.A novel model-based tool, SCULPTER, and greyscale intensity based tools, GeoCut and GeoCut3D, for computer-assisted delineation of anatomical volumes were assessed for their potential for speeding delineation and reducing inter-observer variation. SCULPTER was primed with delineations of oesophageal and OGJ tumours on RTP and on three CBCTs by two observers for each of nine patients (72 delineations), and tested using RTPs and CBCTs of six others. GeoCut and GeoCut3D were tested using two CT scans. SCULPTER was unsuitable for delineating oesophageal and OGJ tumours, as the statistical shape modelling approach fails for partial organ delineation where the delineated part is inconstant. GeoCut and GeoCut3D proved unsuitable because of a lack of greyscale contrast between areas to be segmented. SCULPTER should be assessed further for delineation of various organs at risk and for delineation of tumour sites where the whole organ is treated. Any greyscale tool for automating delineation would probably need to incorporate some shape knowledge, since greyscale differences are often limited or absent.A draft protocol for the Phase I trial was developed at a Federation of European Cancer Societies workshop. Several pieces of preparatory work were undertaken for the trial. A literature review and analysis showed that RT planning margins used in standard treatments may be inadequate to ensure tumour coverage without on-treatment imaging to adapt the plan. Since the proposed trial will dose-escalate with tight margins, a simple adaptive IGRT strategy will be used in the boost phase. In a planning study of five representative tumours, ICRU 50 and 62 constraints for PTV dose homogeneity could not be met using 3D conformal RT with a realistic type b dose calculation algorithm, and isocentre dose was not

Date of Award	31 Dec 2011
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Patricia Price (Supervisor)