DOE OSTI2014
Most Medical Physicists working in radiotherapy departments see few pediatric patients. This is because, fortunately, children get cancer at a rate nearly 100 times lower than adults. Children have not smoked, abused alcohol, or been exposed to environmental carcinogens for decades, and of course, have not fallen victim to the aging process. Children get very different cancers than adults. Breast or prostate cancers, typical in adults, are rarely seen in children but instead a variety of tumors occur in children that are rarely seen in adults; examples are germinomas, ependymomas and primitive neuroectodermal tumors, which require treatment of the child's brain or neuroblastoma, requiring treatment in the abdomen. The treatment of children with cancer using radiation therapy is one of the most challenging planning and delivery problems facing the physicist. This is because bones, brain, breast tissue, and other organs are more sensitive to radiation in children than in adults. Because most therapy departments treat mostly adults, when the rare 8 year-old patient comes to the department for treatment, the physicist may not understand the clinical issues of his disease which drive the planning and delivery decisions. Additionally, children are more prone than adults to developing secondary cancers after radiation. This fact has important implications for the choice of delivery techniques, especially when considering IMRT. For bilateral retinoblastoma for example, an irradiated child has a 50% chance of developing a second cancer by age 50. In the first presentation, an overview of childhood cancers and their corresponding treatment techniques will be given. These can be some of the most complex treatments that are delivered in the radiation therapy department. These cancers include leukemia treated with total body irradiation, medulloblastoma, treated with craniospinal irradiation plus a conformal boost to the posterior fossa, neuroblastoma, requiring focal abdominal irradiation to avoid kidney, liver, and vertebral body damage, retinoblastoma, requiring treatment to an eye while minimizing dose to surrounding tissues, and a variety of other tumors which occur anywhere in the body. Case studies will be presented showing the treatment technique and resulting dosimetry, highlighting the objectives for tumor coverage and organ-at-risk sparing. Practical issues that have to be faced when treating children will also be discussed such as daily sedation and immobilization. In the second presentation, specific focus will be on radiation therapy simulation, treatment planning guidelines, image guidance for delivery, and proton therapy for children. We will discuss uniqueness of pediatric simulation with different imaging modalities (CT, MRI, and PET). Some related issues are sedation for younger patients, radiation exposure reduction for CT, distortion and artifacts on pediatric MRI, and measuring pediatric organ motion. We will discuss the tradeoff of tumor coverage and normal tissue sparing in treatment planning using example organ data. Image guidance approaches for pediatric radiation therapy and methods for dose reduction will be reviewed. Finally, we will describe technical advances and trends in proton therapy for children. Advantages, caveats, and opportunities will be presented. Learning Objectives: Improve understanding about childhood cancer and treatment with radiation Understand treatment planning and delivery issues specific to children Become aware of specific treatment methods for the most challenging pediatric cancers Know the current status of state-of-the-art treatment techniques for pediatric radiation therapy.
60 APPLIED LIFE SCIENCES↗