Implementation of a Knowledge-Based Planning Model for Node-Positive Prostate SBRT with Empty Bladder
Abstract
Purpose
Prostate stereotactic body radiation therapy (SBRT) delivered with a full bladder protocol is commonly associated with challenges in maintaining consistent bladder filling between simulation and treatment. The bladder volume achieved during planning computed tomography (CT) often does not accurately reflect the bladder volume at the time of treatment delivery. This variability contributes to increased daily image-guided radiotherapy (IGRT) corrections in patients treated with a full bladder protocol. The aim of this study is to develop and validate a knowledge-based planning (KBP) model for node-positive prostate SBRT using an empty bladder protocol.
Methods
The KBP model was created by Varian Rapid PlanTM(V.16.1) using 36 clinical plans. A dose of 36.35 Gy in 5 fractions was prescribed at the prostate planning target volume (PTV 36.35), and a Dose of 25 Gy in 5 fractions was prescribed at the nodal region (PTV 25). Volumetric Modulated Arc therapy (VMAT) plans were generated with a 10MV flattening filter-free beam with full arcs. The model was validated on 13 patients with the plans generated manually. Paddick conformity index (CI), homogeneity index (HI), Conformation Number (CN) for targets and dose to Organs at Risks (OARs), viz bladder, rectum, bowel and femoral heads were compared between clinical and KBP plans for each 13 patients. Statistical analysis was done using a t-test or Wilcoxon signed-rank test.
Results
Target coverage for PTV 36.25 and PTV 25 for both the plans was not significantly different with CI of p=0.901 and 0.76, respectively. In addition, CN for PTV 36.25 and PTV 25 for both the plans were not significantly different, with p=0.814 and 0.928, respectively. However, HI for PTV 36.25 was significantly better in KBP plans compared to the manual plans with p=0.032.
Conclusion
The KBP model for the prostate node-positive SBRT with an empty bladder was created and validated.