Methods to optimize conformal dynamic arcs in radiation therapy treatment planning

Abstract

Conformal Dynamic Arcs (CDA) can provide a useful alternative in certain clinical situations which require a higher level of 3-dimensional (3D) conformation than shaped static fields but for which modulated fields (fixed or arc) are inappropriate. Due to lack of modulation, the quality of the dose distribution produced by a CDA is highly dependent on the specific patient geometry. The ideal geometry for a CDA, in terms of achievable conformation and uniformity, is a spherical target perfectly centered in a cylindrical medium or body and utilizing a full 360 degree of rotation. This manuscript will provide or review several methods a treatment planner may employ to improve dose distributions produced by CDA as the patient and/or target geometry or degrees of arc rotation vary from the ideal. These include: 1. Weighting arc segments to improve homogeneity. 2. Defining asymmetric margins for fitting leaves. 3. Hybrid static/CDA compensating for CDA with limited degrees of rotations. 4. Improving conformation in irregular target via use of pseudo-PTV. 5. Creating concave features via the use of avoidance structures. 6. Editing CDA multi-leaf collimator (MLC) to remove irregular hot spots.

Keywords: 3D treatment plan; Arc field; Avoidance structure; CDA; Concavity; Conformal dynamic arcs; Densities; Dose distribution; Dosimetry; Dynamic arc; Fit and shield; MLC; Multileaf collimators; Offset target; Treatment planning techniques; Wedge.