Improving radiotherapy techniques for head and neck cancer

In head-and-neck cancer (HNC), radiotherapy (RT) is an important part of the treatment possibilities. It can be recommended as definitive treatment with or without chemotherapy, adjuvantly after surgery, or in the treatment of local failure after surgery. RT allows organ preservation and improved function preservation compared to surgery and can therefore be an elegant solution. However, radiation of HNC is often complex due to large planning tumour volumes (PTV), multiple target volumes and proximity to organs at risk (OAR). Furthermore, doses up to 60 Gy or 66 Gy post-operatively and 72 Gy in definitive RT may be prescribed. Irradiation of critical normal tissue can cause severe discomfort with increased acute and late morbidity. In the past, radiation oncologists have focussed on reducing dose to the parotid glands, oral cavity and swallowing apparatus to minimize xerostomia, mucositis and dysphagia respectively, as this has an important effect on quality of life (QoL), even years after RT. Newer techniques have been developed in RT over the past 20 years to improve delivery of RT, thereby protecting critical normal tissue while still giving a high enough dose to the tumour volume so that control rates are not compromised. In the early 1990's intensity modulated radiotherapy (IMRT) was mentioned for the first time. Closer shaping to the tumour contour was made possible by aiming multiple photon beams from different directions and with adjusted intensities. This allowed better sparing of the organs at risk resulting in less acute and late toxicity. In this PhD we want to examine where we can improve current radiotherapy methods and how we can prepare for newer and more conformal techniques. We realise that before more precise techniques can be applied, shortcomings of current techniques have to be identified and solutions need to be found and implemented. Critical surrounding tissue limits a radiation oncologist in the dose given to the tumour but conformal radiation techniques could increase the therapeutic index by causing less toxicity, yet ensuring good oncological outcomes. Tumour shrinkage and anatomic changes during RT are important factors to consider as these changes have not been taken into account in the initial planning stage. This can cause dosimetric variations, possibly leading to under dosage of tumour volume and a higher dose in OAR, which could lead to recurrences and increased toxicity respectively. Adaptive radiotherapy (ART) offers a possible solution by modifying RT plans to fit the new tumour volume/anatomy. However, such an adaptive approach is a strain on both time and human resources and would only benefit a small percentage of all HNC patients. There is currently no way to identify which patients might benefit from such an approach at an early time point during treatment. The objective is to make selection criteria available to select patients who may benefit from adaptive radiotherapy, which is an important technique in even more conformal radiotherapy options such as proton therapy. Proton therapy (PT) is a technique which is finding its way to radiotherapy departments all over the world, including University Hospitals Leuven. The theory behind the benefits of PT is that protons have a relatively large mass compared to photons and therefore scatter less easily and stay more focused around the target volume. According to the energy given to the protons, they will travel a certain distance into the irradiated tissue, but not further. An additional benefit is that most of the energy is transmitted in the last millimetres, called the Bragg peak. In summary, this results in less normal tissue being irradiated on the distal side of the tumour as well as the proximal side. The aim of this PhD is to find out where recurrences occur and how we can improve outcome after radiotherapy by revising delineation guidelines, correlating imaging with pathological specimens to further improve delineation and looking at benefits of modern techniques such as ART and PT.

Publication year:2020

Accessibility:Closed