Dosimetric analysis of different whole brain radiotherapy treatment planning methods: three types of 3-dimensional versus hippocampal avoidant.

Abstract

Purpose: Our purpose was to compare four whole brain radiotherapy (WBRT) delivery types: opposed lateral (OL) 3-dimensional-conformal radiotherapy (3D-CRT), a novel opposed lateral sparing (OLS) 3D-CRT technique, 3D optimized dynamic conformal arcs (optDCA), and hippocampal-avoidant WBRT (HA-WBRT).

Materials and methods: Ten patients previously undergoing HA-WBRT were retrospectively planned using OL, OLS, and optDCA techniques. OLS technique involved multi-leaf collimator (MLC) modifications to protect the lacrimal and parotid glands. OptDCA was inverse-planned 3D-CRT with dynamic conformal arcs. A dosimetric, cost, and resource utilization comparison was performed.

Results: Planning target volume coverage to prescription dose between 3D planning techniques was not significantly different between OL and OLS techniques (96.8% vs. 96.6%, p = 0.855), or between OL, OLS, and optDCA (95.0%) techniques (p = 0.079). There was no difference in the heterogeneity index between 3D plans (p = 0.482); all were less heterogeneous than HA-WBRT (p < 0.001). OptDCA was more conformal than OL and OLS, and similar in conformity to HA-WBRT. OLS achieved significant sparing of lacrimal and parotid glands over OL. There were significant step-function reductions in organ at risk (OAR) dose when comparing OL to OLS to optDCA to HA-WBRT plans. HA-WBRT was 57% more expensive than OL and OLS technique. HA-WBRT took approximately six times longer to plan.

Conclusion: We showed adequate and equivalent target coverage using OL, OLS, and optDCA techniques. Lacrimal and parotid dosages can be greatly reduced with the implementation of minor MLC adjustments. OptDCA therapy represented further improvement of these modifications, and was comparable to HA-WBRT in terms of OAR dose, while being about two-thirds the cost and more efficient to plan.