Author: Yijian Cao, Sean T Grace, Marissa Joyce Vaccarelli 👨🔬
Affiliation: Northwell 🌍
Purpose:
This study investigates the dosimetric efficacy of significantly limiting gantry angles in prostate radiation therapy to as a promising strategy to maintain plan quality while enhancing machine safety by reducing the risk of C-arm LINAC head damage and subsequent machine downtime from potential patient accidents with patients on the table with full bladder per institutional protocol.
Methods:
Eight VMAT prostate treatment plans of either SBRT (800cGyx5) and hypo-fractionation (250cGyx28) were retrospectively analyzed in Eclipse V 16.1. Treatment plans were designed with two fields of standard gantry design from 181° to 179° with standard collimator angles of 90° and 350°. In this work, two sets of significantly limited-angle plans were created: one with two fields and the other with three with limited gantry angles of 245° to 115°. All plans were subsequently re-optimized with the original optimization objectives, and dosimetric parameters were analyzed for OARs and PTV. Statistical evaluations of pertinent dosimetric criteria were performed using paired T-tests. Plan subtraction techniques were utilized to visualize dose distribution differences between the original and limited-angle plans.
Results:
Analysis of dose constraint metrics in the three-field plans for the bladder, rectum and PTV, respectively yielded high p-values, indicating a lack of statistically significant difference from the standard gantry plans. The two-field plans rendered statistical significance in SBRT cases for PTV D95% (p = .01) and rectum V2400 (p =.02). Visual inspection confirmed minimal isodose line variation, though a slight increase in anterior dose spill was observed in the limited-angle plans.
Conclusion:
Significantly limiting gantry angles utilizing a three-field technique can serve as a viable option for reducing the likelihood of LINAC head damage from patient accidents with preservation of dosimetric efficacy in prostate treatment plan quality. Refinement of optimization parameters can address minor anterior dose distribution changes for future clinical deployment.