New radiation techniques
The potential for RT to increase the late effects of treatment is particularly important in AYAs in whom ES is treated with curative intent. Modern RT techniques, image guided RT, intensity modulated photon radiotherapy (IMRT) and particle beam therapy such as proton beam therapy (PBT), deliver improved conformal RT to the target while reducing the volume of normal tissue that receive damaging doses of RT. As a result of the physical characteristics of PBT, significantly less whole-body dose is delivered compared to IMRT, reducing low as well as high doses outside the target (Fig. 2). This may reduce late effects of RT as well as the risk of radiation-induced malignancies and this dosimetric benefit has been sufficient to introduce PBT as the preferential radiation modality in the treatment of many pediatric and AYA cancers.112-115 Data on outcomes for these techniques in ES is limited but PBT was well tolerated by a small series of children with ES with a low incidence of significant toxicity.116
The risk of ovarian dysfunction from pelvic RT pelvis increases with radiation dose. 117-119 PBT avoids significant dose to at least one of the ovaries potentially reducing the risk of infertility and premature menopause.151 Surgical transposition or translocation may be used to move one or both ovaries away from the RT target if indicated.120
Modern RT techniques also facilitate dose escalation, both in ES at challenging sites (head and neck, pelvis and spine) and in the more radioresistant OS that require high RT doses.83,121PBT to treat OS, alone or in combination with photons to a mean dose of 68.4Gy, resulted in a 5 year LC rate of 72%.81Internal fixation with carbon fibre and PEEK, particularly along the spinal axis, is encouraged to improve the homogeneity and reliable delivery of RT at these sites.122