Cone Beam CT-Based Daily Adaptive Planning or Defined-Filling Protocol for Neoadjuvant Gastric Cancer Radiation Therapy: A Comparison

PURPOSE: This study aimed to investigate, in the setting of neoadjuvant gastric irradiation with integrated boost, whether cone beam computed tomography (CBCT)-based adaptive radiation therapy compared with a defined-filling protocol would be beneficial in terms of feasibility and achieving daily reproducible dose volume indexes of the planning target volume (PTV) and organs at risk (OARs) and workflow. METHODS AND MATERIALS: Planning computed tomography (PCT) and 25 CBCT scans of a previously treated patient were used, and neoadjuvant therapy of gastric carcinoma was simulated offline. PTVs and OARs were defined per the TOPGEAR protocol (PTV: 45 Gy/1.8 Gy), and an integrated boost (gross tumor volume [GTV]: 50.4 Gy/2.016 Gy) was added. The patient followed a filling regimen consisting of 12-hour fasting followed by 200 mL of water intake (2 glasses of water) immediately before irradiation. OARs and PTVs were newly contoured on each CBCT. Nonrigid registration of PCT and CBCT scans was performed. Nonadapted plans were recalculated on each CBCT (R-CBCT). Furthermore, an adapted plan was created for the new anatomy (A-CBCT). Dose parameters and comparison of R-CBCT and A-CBCT for the kidneys, liver, and heart were analyzed using a paired t test. RESULTS: A total of 200 plans for R-CBCT and A-CBCT were obtained. Mean gastric volumes were 277.32 cm(3) (±54.40 cm(3)) in CBCT scans and 519.2 cm(3) in PCT. Mean doses to the PTV did not differ meaningfully within the CBCT scans, with an average of 1.54%. The D(95) improved in GTV coverage by 5.26% compared with the R-CBCT plan. Mean heart, liver, and right kidney doses were reduced with the A-CBCT plan by 35.74%, 10.71% and 29.47%, respectively. The R- and A-CBCT comparison for GTV and OARs was significantly different in all cases (P < .0001). CONCLUSIONS: Adaptive radiation therapy through deformable registration represents an important tool in neoadjuvant gastric irradiation, encompassing daily variability and organ motion, compared with the defined-filling protocol while improving OAR sparing.