TEDDI is a non-randomised phase II trial in Scandinavia. All pediatric patients, referred for radiotherapy in the thorax or abdomen and irrespective of diagnosis, are eligible. Deep inspiration breath-hold (DIBH) is a simple radiotherapy technique, which could have a dramatic impact on the risk of late effects in children. In DIBH, the radiotherapy is delivered while the patient holds his/her breath (4-6 sequential breath-holds). The anatomy is changed and imaging artifacts from respiratory movement are diminished. DIBH is widely used in adult patients with breast cancer and mediastinal lymphoma to minimize the risk of radiation-induced late effects due to a reduced dose to the healthy organs. Also, the technique is simple and cost-efficient. For pediatric patients, the investigators aim to: * Estimate the dosimetric benefit of radiotherapy using DIBH compared to free-breathing * Establish the compliance of DIBH * Determine if DIBH is an accurate and reproducible strategy * Optimize treatment planning considering the risk from loss of tumour control as well as the risk of late effects.