Hi. My Father Has An Anaplastic Astrocytoma In His Brain

Hi. My father has an anaplastic Astrocytoma in his brain and finished his first round of chemo (pills) and radiation on February 10th. He has his follow up mri next Friday. He has no energy or appetite, so I got him some marijuana. Is there any reason that he should not use it before his mri? Could it skew the results? Thank you!