Robustness Enhancement for VMAT-TBI Planning and Treatment Delivery for Patients Wider Than 48cm
Abstract
Purpose
To identify planning techniques that consistently result in robust VMAT-TBI plans for patients wider than 48cm that allow for patient setup uncertainty 5mm or more.
Methods
The Built-in auto-feathering function in Eclipse fails to produce good junction dose robustness when patients body width> 48cm. A shift of 1.6 mm or less can result in 10% dose change in the junction region. Various planning techniques were systematically explored to produce consistent and robust dose gradients in junction areas for extra wide patients.
Results
Successful strategies were identified as the combination of the following: A) Four half arc fields for each upper body plan are placed at off-axis isocenters so that arms outside field ≤4cm. B) Abdo plan iso at kidneys center, Thorax plan iso at lungs center. C) All fields are of 40cm wide in horizonal direction. D) The whole arm skin must be covered by at least one entrance field. E) a horizontal MLC field (20cm+1cm opening, collimator angle = 0o) covers head, and a vertical MLC field (1cm+14cm opening, collimator = 90o) covers neck. F) 90o collimator angle for all other fields, with MLC opening ≤14cm for fields covering lungs or kidneys OAR, and ≤20cm for the rest. G) fields between adjacent plans overlap at least 5cm. After these plan techniques were used, the junction dose maintains the robustness of 48cm, robustness in the junction dose can be achieved through the adoption of planning strategies.