Intensity-Modulated Radiotherapy Plan Optimisation for Skull Base Lesions: Practical Class Solutions for Dose Escalation

Abstract

Aims To identify practical intensity-modulated radiotherapy planning solutions when attempting dose escalation in the skull base. Materials and methods Twenty cases of skull base meningioma were re-planned using a variation of beam number (three, five, seven and nine), beam arrangement (coplanar vs non-coplanar) and multileaf collimator (MLC) width (2.5 mm vs 10 mm) to 60 Gy/30 fractions. Plan quality and planning target volume coverage was assessed using planning target volume V 95%, equivalent uniform dose (EUD) and integral dose. Results Critical structures were maintained below clinical tolerance levels. The 2.5 mm MLC achieved an average improvement in V 95% by 22.8% ( P = 0.0003), EUD by 3.7 Gy ( P = 0.002) and reduced the integral dose by 13.4 Gy ( P = 0.0001). V 95% and the integral dose improved with five vs three beams and seven vs five beams, but did not change with nine vs seven beams. There was no effect of beam number on EUD. There was no difference in V 95% ( P = 0.54), integral dose ( P = 0.44) or EUD ( P = 0.47) for beam arrangement used. Segments per plan increased by a factor of 1.5 with each addition of two beams to a plan, and by a factor of 2.5 for 2.5 mm MLC plans vs 10 mm MLC plans. Conclusions We present evidence-based planning solutions for skull base intensity-modulated radiotherapy, and show that 2.5 mm MLC and five to seven beams can achieve safe dose escalation up to 60 Gy. This must be balanced with an increase in segmentation, which will increase treatment times.