Author: Ahmad Amoush, Adam C. Riegel 👨🔬
Affiliation: Columbia University Irving Medical Center 🌍
Purpose: To investigate the dosimetric differences between the reference CT plan, the scheduled plan, and the adaptive plan for a bladder cancer patient treated with Varian Ethos system.
Methods: A patient with bladder cancer treated with Ethos adaptive with a prescribed dose of 55 Gy in 20 fractions. This study analyzed 8 out of the 20 fractions to compare the adapted plan with both the scheduled plan and the reference plan. Treatment sessions were exported from the Ethos system to Velocity. The dose summation from each plan was transferred to the reference CT using deformable image registration (DIR) and then compared. Since only 8 fractions were analyzed, the dose percentages for the targets and normal structures were reported. The following structures were analyzed: PTVp_55Gy, PTVn_55Gy, Rectum, Bladder, and Bowel Bag.
Results: Minimum, mean, and maximum doses were reported for each structure. For PTVp_55Gy: reference plan - 89.5%, 102.5%, and 109.7%; adaptive plan - 55.7%, 97.2%, and 106.9%; scheduled plan - 72.5%, 101.0%, and 108.5%. For PTVn_55Gy: reference plan - 93.8%, 103.6%, and 111.9%; adaptive plan - 82.7%, 101.3%, and 106.8%; scheduled plan - 89.8%, 102.5%, and 110%. Bowel Bag: reference plan - 1%, 29.9%, and 105%; adaptive plan - 1.2%, 28.8%, and 102%; scheduled plan - 1.2%, 29.6%, and 105.2%. Bladder: reference plan - 69.7%, 97%, and 108.5%; adaptive plan - 66%, 96.1%, and 106.8%; scheduled plan - 67.6%, 95.4%, and 107%. Rectum: reference plan - 6%, 39.5%, 102.7%; adaptive plan - 5.1%, 32.5%, 84.5%; scheduled plan - 6%, 46.2%, and 103.2%.
Conclusion: The online adaptive system shows promise in improving dosimetry for patients with bladder cancer who are expected to experience significant interfraction motions due to changes in bladder filling.