Four-dimensional imaging for radiotherapy planning in children and teenagers

Abstract

Respiratory-related organ motion (RROM) is a potential source of geometric uncertainty in RT planning and delivery. Approaches to mitigate its effects are well described in adults. For example, four-dimensional computed tomography (4DCT) mitigates the effects of RROM on image quality and motion-encompassing approaches to target volume delineation can incorporate individualised motion information from 4DCT into RT planning. This thesis explores the feasibility of adopting 4D imaging in children and teenagers for individualised motion assessment for radiotherapy planning. The feasibility of using 4DCT for upper abdominal motion assessment in children is assessed. Kidney motion is determined by extracting deformation vector field and centre of mass displacements from 4DCT datasets in 25 children. The effect of general anaesthetic on organ motion is examines as are potential associations between motion and patient related variables; age, height, weight and body surface area. Consideration of additional ionising radiation dose in children is important as children are inherently more sensitive to the deleterious effects of radiation exposure, in particular second malignancy induction. The feasibility of using 4DMR and ultrasound as alternative non-ionising imaging modalities for individualised motion assessment in children is explored. Feasibility and respiratory related organ displacements are presented per imaging modality and compared to 4DCT; the current gold standard for adult RT planning in tumour sites susceptible to RROM. The application of a respiratory motion encompassing RT planning technique is applied to upper abdominal neuroblastoma RT planning in children. The potential dosimetric benefits of using an internal target volume approach is described and compared to a conventional approach to RT planning. The introduction of advanced radiotherapy techniques in children often lags behind their adult counterparts. This thesis describes the feasibility of adopting individualised motion assessment in children and contributes to the understanding of RROM in children.