Respiratory motion management for radiotherapy of pancreatic cancer patients

Pancreatic cancer has one of the worst prognosis with an overall mean 5-year survival of 7%. The only curative treatment remains surgery, but this treatment is often hampered by a difficult anatomical tumor location. The addition of adjuvant (chemo)radiation treatment may be beneficial and may increase the chance on a complete surgical resection. A major geometric uncertainty during radiation delivery is the respiratory-induced motion. This intrafractional motion results in a blurring of the dose distribution with respect to the tumor and this needs to be accounted for.
The respiratory-induced tumor motion cannot be accurately predicted by a single pretreatment 4DCT and simply including the complete motion in the treatment volume is a conservative approach. The use of a mid-ventilation technique or probabilistic planning could reduce the target volume and thus the dose to surrounding healthy tissues. However, these techniques are still dependent on the pretreatment 4DCT.
Another option is to use breath-holding to eliminate the respiratory-induced motion. Surprisingly, the assumption that the tumor position is fixed during breath-holding is invalid since we found substantial tumor motion during inhalation breath-holding. Using exhalation breath-holding reduced the organ motion significantly, but may be more difficult to maintain for pancreatic cancer patients. Also, the position variation between consecutive breath-holds would have to be taken into account.
Since tumor motion cannot be accurately predicted, motion reduction would be the optimal solution. However, future research is needed in order to optimize the breath-holding procedures.