Diffusion-weighted MRI in paediatric oncology: lymphoma and nephroblastoma

Abstract

The aim of this thesis was to assess the value of MRI including DWI in paediatric lymphoma and nephroblastoma. Part I - lymphoma The use of FDG-PET/CT in staging paediatric lymphoma is generally incorporated into current guidelines.However, the most important disadvantage of FDG-PET/CT is the use of ionizing radiation. Especially relevant in the young population, not only because children will have more remaining years of life in which a radiation-induced tumour can develop, but also because rapidly dividing cells are more sensitive to radiation-induced effects. Therefore, MRI could serve as an attractive radiation-free alternative. Whole-body MRI has become a clinical feasible imaging technique, even in children. Besides, the excellent soft tissue contrast, it is possible to acquire functional informations, e.g diffusion weighted imaging (DWI). The concept behind the use of DWI in oncology imaging is that most tumours show high-cellularity with consequently impeded diffusion that can be measured and quantified with DWI. Research described in this thesis showed a good agreement between whole-body MRI-DWI and the FDG-PET/CT-based reference standard for staging paediatric lymphoma. Therefore, MRI could serve as a good radiation-free alternative to CT and FDG-PET for staging paediatric lymphoma. Differentiation between persisting or recurrent tumour from posttherapeutic change is important to guide patient management. Whole-body MRI with DWI has shown a good sensitivity for detecting viable lesions after completion of therapy. ADC measurements could increase the specificity of whole-body MRI. Because of the good outcome in pediatric Hodgkin lymphoma, treatment decisions are increasingly based on minimizing side effects. One of these treatment-related adverse effects is osteonecrosis.Osteonecrosis is a well-recognized complication in patients treated with corticosteroids. In particular epiphyseal located osteonecrosis may be complicated by articular collapse. MRI is regarded as the most sensitive and specific method for detecting early osteonecrosis. Whole-body MRI demonstrates osteonecrosis to be a common finding during therapy response assessment of paediatric Hodgkin lymphoma. Part II - nephroblastoma Wilms tumour or nephroblastoma is the most common malignant renal tumour in children. Overall, the survival rate is relatively good and therefore, identifying low- or high-risk type nephroblastoma might be relevant for treatment planning. Along with diffuse anaplastic nephroblastoma, blastema in residual tumour after preoperative chemotherapy is thought to represent chemoresistant parts that, when extensive, may require more intensive treatment. Therefore, identification of blastemal predominant lesions at presentation would be of great value and may direct personalized treatment decisions in the future. This thesis describes a method of whole-tumour ADC measurements that excludes less or non-enhancing parts of lesions as these areas can skew the ADC values. The intra- and interobserver variablility of this method was proven to be sufficiently precise. Whole-tumour ADC measurements in nephroblastoma at presentation and after pre-operative treatment related to histopathology showed three components of treatment-related effects: change in size, necrosis and shift in ADC values. Furthermore, lesions with predominant stromal histopathology showed a significant, moderate linear relation with median ADC. Unfortunately, both epithelial and blastemal subtype histopathology showed relatively marked diffusion restriction.