Page 137 - Organ motion in children for high-precision radiotherapy - Sophie Huijskens

8.1 | Pediatric vs. adult radiotherapy
Treatment of pediatric cancer is a challenge for the multimodality treatment team due to the disease rarity, variety of subtypes, and complexity of treatment options that continuously undergo modifications and improvements. Moreover, radiotherapy techniques are evolving rapidly. Image- guided radiotherapy (IGRT), volumetric modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT), with either photons or protons, could lead to improved target conformality and reduce normal tissue dose. While these techniques could be potentially essential in children, research on implementation of these techniques is mainly focused on adult cancer types, and special emphasis on introducing these newer techniques in pediatric radiotherapy is limited. Therefore, achievements in adult radiotherapy are often pragmatically translated to a pediatric setting. An optimal treatment plan in radiotherapy aims to deliver a sufficiently high dose to kill the tumor while at the same time minimizing doses to surrounding healthy tissues, or organs at risk (OARs). The accuracy of the treatment plan and dose delivery is limited by geometrical uncertainties that need to be accounted for by safety margins. While these uncertainties are well studied in adults, pediatric data was lacking. In this thesis (chapter 2, 4, and 5), we have aimed to quantify these uncertainties and present a first estimation of more appropriate margin sizes in abdominal and thoracic areas in children. This thesis also shows that these uncertainties differ between children and adults (chapters 3 and 6), indicating that the size of the margins should potentially be different for children than for adults. This thesis underscored the need for child-specific treatment approaches, both for margin definitions in treatment planning, as well as child-specific imaging procedures and delivery techniques. In this last chapter, the results presented in this thesis are summarized and compared to findings from other pediatric studies. Furthermore, alternative options to account for organ motion are mentioned and future perspectives of pediatric radiotherapy will be discussed.
8.2 | Geometrical uncertainties and safety margins
Although research focusing on organ motion in children during radiotherapy is steadily growing, the use of relative small patient cohorts makes it difficult to derive population-based margins for children. For accurate margin definitions, an extensive understanding of all geometrical uncertainties is essential. The main sources of geometrical uncertainty are considered to be the patient set-up, interfractional position variation, intrafractional motion, and the delineation uncertainty.
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