Advances in childhood cancer treatment have resulted in a growing population of long-term survivors. However, many survivors experience lifelong physical, cognitive, and psychosocial late effects related to their treatment, including radiotherapy. These complications are particularly important for children receiving treatment to the brain and head and neck, where radiation exposure to healthy tissues can contribute to neurocognitive impairment, endocrine dysfunction, and reduced quality of life. Although modern image-guided radiotherapy allows treatment to be delivered with greater precision than ever before, planning target volume (PTV) margins used in pediatric practice have changed little over time. As a result, opportunities may exist to safely reduce radiation exposure to healthy tissues while maintaining effective tumour treatment.

The purpose of this pilot study is to determine whether PTV margins can be safely reduced in selected pediatric patients without compromising tumour coverage and ultimately, control. Specifically, we aim to identify whether reduced PTV margins can safely be employed, quantify reductions in irradiated normal tissue, and generate feasibility data to support future practice changes in pediatric radiotherapy care.

This study uses retrospective radiotherapy planning and imaging data from a previously completed prospective cohort of pediatric patients treated without anesthesia. Pre-treatment planning CT and MRI scans, together with on-treatment cone beam CT (CBCT) images, are reviewed to evaluate patient positioning and target motion throughout treatment. Radiation therapists regenerate treatment plans using smaller PTV margins and assess whether target coverage can be safely maintained. Comparisons between the original and reduced-margin plans are then performed to evaluate changes in radiation dose to normal tissues, including critical structures associated with long-term neurocognitive and endocrine outcomes.

Preliminary analyses demonstrate that reduced PTV margins are feasible in carefully selected pediatric patients and can decrease radiation exposure to healthy brain and head-and-neck tissues without compromising target coverage. Statistical analyses are ongoing to quantify the magnitude of normal tissue sparing across treatment sites, model impact on long term outcomes, such as IQ, and establish feasibility for broader clinical implementation.

By improving the precision of pediatric radiotherapy, this work has the potential to reduce treatment-related toxicity while maintaining excellent cancer related outcomes. The findings will inform revised institutional radiotherapy planning guidelines and provide the foundation for a prospective clinical trial evaluating margin-reduced radiotherapy. Ultimately, this project seeks to improve the long-term quality of life of childhood cancer survivors.

For more information, please contact Renu Jeyapala.