PMC9047540_01
CT imaging depicting clinical target volume (green) changes approximately 1 year prior to MR-Linac treatment (A), immediately prior to MR-Linac treatment (B), and 6 months post MR-Linac treatment (C).
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Additionally, there was a markedly enlarged pelvic mass centered on the prostate with gross extra-capsular extension and invasion into the posterior bladder wall ( Figure 1A ). The imaging revealed multiple lobulated masses arising from the prostate encroaching onto the rectum, and new intramuscular masses in the right iliopsoas and right obturator internus ( Figure 1B ). One month following radiation treatment, the patient's PSA reduced to 21 and there was evidence of partial radiological response within the prostate ( Figure 1C ).
MR images collected during beam delivery for each fraction on the MR-Linac during treatment. Displayed is the clinical target volume (green), rectum (brown), bladder (yellow), and large bowel (olive).
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Over the course of 6 fractions, the CTV decreased in volume from 453 to 233 cc (49%) ( Figure 2 ).
Accumulated dose for all fractions on the reference MR scan for the clinically delivered treatment plan (A), and simulated dose distribution without daily adaptation (B) along with the dose difference for the adapted plan minus non-adapted plan (C). The accumulated DVH curves for both the adapted (solid lines) and non-adapted (dotted lines) are also illustrated (D).
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Using dose accumulation, the demonstrated cumulative dose to OARs was reduced with the use of daily adaptation compared with the simulated single offline adaptation ( Figure 3 ).