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ABSTRACT
Background
Volumetric Modulated Arc Therapy (VMAT) is a sophisticated radiotherapy technique that enables precise dose delivery while minimizing exposure to normal tissues. It integrates a dynamic multileaf collimator (MLC), variable dose rates, and adjustable gantry speeds to optimize treatment delivery. This study aimed to investigate the influence of selected planning parameters—specifically control points, arc number, and collimator angles—on plan quality and efficiency for localized prostate cancer using the Monaco Treatment Planning System (TPS).
Method
Standard VMAT prostate treatment plans were systematically modified to assess the dosimetric effects of varying control point density, number of arcs, and collimator angles. The evaluation metrics included dose-volume histograms, dose homogeneity index (DHI), conformity index (CI), and organ-at-risk (OAR) dose exposure. Plan efficiency was assessed by examining monitor unit (MU) usage relative to dosimetric benefit.
Result
Increased control points and additional arcs improved planning target volume (PTV) coverage up to a threshold, beyond which benefits plateaued and MU usage increased. A two-arc configuration achieved the best balance between target coverage and MU efficiency. Collimator angles between 40° and 60° offered optimal PTV coverage. For OAR sparing, collimator angles of 60°–80° reduced bladder dose, 70°–90° minimized rectal exposure, and 0°–30° reduced femur dose. However, larger angles (>70°) increased modulation complexity and reduced overall treatment efficiency without significant dosimetric gain.
Conclusion
Optimized VMAT planning for localized prostate cancer involves balancing PTV coverage, OAR sparing, and MU efficiency. A two-arc configuration with 100–150 control points offers optimal dosimetric outcomes without excessive MU use. Collimator angles of 60°–80° are generally optimal, though angle selection may be adjusted based on patient-specific anatomical considerations. Plans incorporating more than two arcs or excessively large collimator angles should be used cautiously, as they offer minimal benefit and may compromise treatment efficiency or target coverage.