Probabilistic interfractional motion carbon ion radiation therapy dose distribution for prostate cancer shows rectum sparing with moderate target coverage degradation

Purpose: This observational study investigates the influence of interfractional motion on clinical target volume (CTV) coverage, planning target volume (PTV) margins, and rectum tissue sparing in carbon ion radiation therapy (CIRT). It reports dose coverage to target structures and organs at risk in the presence of interfractional motion, investigates rectal tissue sparing, and provides recommendations for further lowering the rate of toxicity. We also propose probabilistic DVH for consideration in treatment planning to represent probable dose to the clinic’s patient population.

Methods: At Gunma University Hospital intensity-modulated x-ray therapy (IMXT, aka IMRT) prostate cancer patients are positioned on a table which is shifted twice based on cone-beam computed tomography (CBCT) to align bones and then align prostate tissue to isocenter. These shifts thereby contain interfractional motion. 1306 such tableshifts from 85 patients were collected. Normal probability distributions we...