Changes in Gross Tumor Volume and Organ Motion Analysis During Neoadjuvant Radiochemotherapy in Patients With Locally Advanced Pancreatic Cancer Using an In-House Analysis System.

Background And Purpose: During radiation treatment, movement of the target and organs at risks as well as tumor response can significantly influence dose distribution. This is highly relevant in patients with pancreatic cancer, where organs at risk lie in close proximity to the target.

Material And Methods: Data sets of 10 patients with locally advanced pancreatic cancer were evaluated. Gross tumor volume deformation was analyzed. Dose changes to organs at risk were determined with focus on kidneys both without adaptive radiotherapy compensation and with replanning based on weekly acquired computed tomography scans.

Results: During irradiation, gross tumor volume changes between 0% and 26% and moves within a radius of 5 to 16 mm. Required maximal dose to organs at risk for kidneys can be met with the current practice of matching computed tomography scans during treatment and adjusting patient position accordingly. Comparison of the mean doses and V15, V20 volumes demonstrated that weekly replanning could bring a significant dose sparing of the left kidney.

Conclusion: Manual matching with focus on bony structures can lead to overall acceptable positioning of patients during treatment. Thus, tolerance doses of organs at risk, such as the kidneys, can be met. With adequate margins, normal tissue constraints to organs at risk can be kept as well. Adaptive radiotherapy approaches (in this case with weekly rescanning) reduced dose to organs at risk, which may be especially important for hypofractionated approaches.