Photons or protons for non-central nervous system solid malignancies in children: a historical perspective and important highlights

Over the years, major advances have occurred in radiotherapy techniques, delivery, and treatment planning. Although radiotherapy is an integral treatment component of pediatric solid tumors, it is associated with potential acute and long-term untoward effects and risk of secondary malignancy particularly in growing children. Two major advances in external beam radiotherapy are intensity-modulated radiotherapy (IMRT) and proton beam radiotherapy. Their use in the treatment of children with cancer has been steadily increasing. IMRT uses multiple modulated radiation fields that enhance the conformality of the dose distribution to the target volume and avoid high doses to normal tissues. However, IMRT may be associated with increased volume of normal tissue that receives low doses and potential risk of secondary malignancy. Contrary to IMRT, proton beam radiotherapy uses a few beams and a fast dose fall-off distal to the target volume. Although both modalities require substantial personnel time and effort, the very high cost and limited availability of proton radiotherapy have constrained its widespread use. It is anticipated that both modalities may markedly improve tumor control and quality of life for long-term cancer survivors. Clinical trials with long-term follow-up are needed to confirm the premise that proton beam therapy will decrease late effects and secondary malignancies without compromising local control in pediatric patients with cancer.