Poster Presentation 35th Lorne Cancer Conference 2023

Fractionated radiotherapy is required to accurately mimic neurostructural late effects in preclinical models (#164)

Meegan Howlett 1 , Jacqueline Whitehouse 1 , Jessica Buck 1 , Kale Somers 2 , Jessica Lawler 1 2 , Hilary Hii 1 , Brooke Carline 1 , Mani Kuchibhotla 1 , Bhedita J Sewoo 3 4 , Tim Rosenow 3 , Kirk Feindel 3 , Martin A Ebert 3 5 , Andrew JH Mehnert 3 6 , Nicholas G Gottardo 1 7 , Raelene Endersby 1
  1. Brain Tumour team, Telethon Kids Cancer Centre, Telethon Kids Institute, and the University of Western Australia, Perth, WA, Australia
  2. School of Paediatrics, Child Health and Centre for Child Health Research, University of WA, Perth, WA, Aus
  3. University of Western Australia, Perth, WA, Australia
  4. Perron Institute for Neurological and Translational Sciences, Perth, WA, Australia
  5. Sir Charles Gairdner Hospital, Perth, WA, Australia
  6. Lions Eye Institute, Perth, WA, Australia
  7. Paediatric and adolescent oncology/ haematology, Perth Children's Hospital, Perth, WA, Australia

Pediatric brain cancer patients treated with fractionated radiotherapy commonly develop significant, detrimental long-term side effects, termed “late effects.” These include, but are not limited to hormonal deficiencies, growth defects and cognitive declines. Preclinical models of late effects have been developed that use a single, high dose of radiotherapy, which does not mimic the fractionated schedule children receive clinically. This study aimed to create a mouse model of late effects using clinically-relevant fractionated radiotherapy, and to measure the effects on the developing brain.

Juvenile mice were treated at postnatal day 16 with a single dose of 8Gy whole brain radiation, or a mathematically-equivalent fractionated dose of 18Gy (9 x 2Gy daily fractions). Sham control mice received a CT scan, or 9 x sham CT scans. Mice were allowed to grow to young adulthood (63 days). Ex vivo anatomical MRI scans were performed along with diffusion tensor imaging (DTI) and histology. Mice receiving a single 8Gy radiation dose exhibited significantly decreased volumes in areas including the olfactory bulbs (-19%), hippocampus (-7%), corpus callosum (-9%) and motor cortex (-9%). In contrast, mice receiving fractionated radiotherapy showed fewer significantly decreased regions, although olfactory bulbs were reduced (-12%). Furthermore, doublecortin-positive cells were significantly reduced in the dentate gyrus following both single and multi-fractionated doses, indicating profound effects of radiotherapy on murine neural stem cells. Few radiotherapy-induced differences were observed by DTI, and immunohistochemistry revealed no changes in myelin basic protein, suggesting that white matter is minimally altered in mice following radiotherapy.

Together, these results show that common experimental approaches of single dose radiotherapy induce more neurological changes than an equivalent fractionated dose, thus may over-estimate radiotherapy-induced late effects. We have developed a clinically-relevant, fractionated radiotherapy dosing protocol in mice which replicates late effects experienced by children. This model can be used to measure late effects of novel chemo/radiotherapy treatment combinations in future studies, ensuring children with brain cancer receive both effective and safe treatments, giving them the best chance to live longer and healthier lives.