Abstract #4256

Diffusion changes in prostate cancer patients undergoing radiation treatment on an MR-Linac system: Preliminary findings

Colleen Bailey^1,2, Rachel W Chan¹, Jay Detsky^3,4, Danny Vesprini^3,4, and Angus Z Lau^1,2

¹Odette Cancer Centre, Sunnybrook Research Institute, Toronto, ON, Canada, ²Medical Biophysics, University of Toronto, Toronto, ON, Canada, ³Department of Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, ⁴Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada

Eight prostate cancer patients undergoing radiation treatment were scanned on an MR-Linac with conventional ADC and high-b diffusion protocols at each of five treatment fractions. With the system’s weaker gradients and longer echo times, 6/8 patients had visible lesions at the maximum b-value of 2000 s/mm². Fits to the VERDICT model demonstrated higher intracellular fraction in the lesion, inversely correlated with ADC. In three patients, ADC increased starting at the third treatment time point; a fourth patient exhibited a transient ADC increase. Future work will correlate these changes with biochemical recurrence to test their relevance as a biomarker.

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