Towards MRI guided radiotherapy of renal cell carcinoma

Abstract

MRI-guided radiotherapy for RCC is a non-invasive state-of-the-art treatment option and will be available on the MRI-linac in the near future. The present thesis focuses on the preparation of MRI-guided radiotherapy of renal cell carcinoma (RCC). Surgery is the current standard treatment for RCC. Other alternative treatment modalities such as radiofrequency ablation (RFA), cryoablation (CA), microwave ablation (MWA) and stereotactic body radiotherapy (SBRT) are minimally/less invasive. Image guided SBRT can be further improved by the implementation of MRI-guided SBRT, leading to a fully non-invasive curative treatment option. Besides improvements in RCC treatment, SBRT of RCC bone metastases can be optimized by using MRI for contouring of the metastatic lesion. It seems MRI represents the extent of the gross tumor volume (GTV) in RCC bone metastases more accurately. Contouring of RCC bone metastases on MRI results in clinically relevant and statistically significant larger lesions compared to contouring the same lesions on CT. In RCC treatment, with the clinical introduction of MRI-guided radiotherapy, a guideline for MRI based delineation was developed based on T2 weighted MR imaging. The recommendations and guideline described in this thesis can be used for the introduction of MRI-guided radiotherapy for primary RCC in the clinic. One of the major challenges in SBRT of RCC is motion of the kidney during treatment, especially breathing motion, which is complex and changes over time at an individual level. To deliver MRI-guided radiotherapy for RCC it is necessary to simulate the motion and drift of the kidney over a time period as long as a treatment fraction takes. The present results show that with the motion management techniques used, drift compensation would be able to reduce the motion margin by up to 75%. In general, SBRT treatments benefit from accurate imaging for precise contouring, localization and image guidance of the tumors and organs at risk (OARs) before and during treatment. The combination of three different reconstructions (DCE, 4D-MRI and 5D MRI) described in this thesis are unique and valuable in the context of MR-guided radiotherapy, for tumor characterization, accurate delineation, and mid-position volume generation. Before we can safely treat patients with RCC on the MRI-linac, we first need to gain more experience in treating RCC with SBRT and prepare for the integration of MRI in the treatment workflow of RCC. In the ARREST-study protocol, a fiducial marker cone-beam CT based SBRT treatment is described for inoperable patients with RCC. The ARREST-study is a precursor study for the full MRI-based approach for SBRT of RCC, which will be introduced within the coming years on the MRI-linac. MRI-guided SBRT for RCC will be more widely available in the coming years, delivering higher radiation doses (in less fractions) to increase local control, diminishing toxicity and improving the QoL for patients. To successfully implement SBRT in primary RCC treatment, inevitably a multidisciplinary approach will be required. Physicians in the field of Urology, Radiotherapy and Radiology should collaborate with each other and with the patient to determine the best treatment option.