Skull base meningioma - comparison of intensity-modulated radiotherapy planning techniques using the moduleaf micro-multileaf collimator and helical tomotherapy.

AIMS

Therapeutic radiotherapy to lesions of the skull base is limited by complex target shapes and their proximity to organs at risk. Intensity-modulated radiotherapy (IMRT) using helical tomotherapy may result in improved dose distributions and safer dose escalation. The aim of this study was to compare plan efficacy and efficiency using, linac-based micro-multileaf collimator (mMLC) IMRT and helical tomotherapy.

MATERIALS AND METHODS

Five cases of skull base meningioma, previously treated with three-dimensional conformal radiotherapy (50 Gy/30 fractions) were identified. They were re-planned to a dose of 60 Gy/30 fractions using IMRT with Moduleaf mMLC (2.5 mm) and helical tomotherapy. Plan efficacy was compared using measures of PTV(60) coverage (D(min), D(max), V(90%), V(95%) and V(100%)). Plan efficiency was assessed by comparing estimated beam-on times.

RESULTS

The critical structure dose was limited to below predetermined tolerance levels in all cases, with similar doses obtained between techniques. The average PTV(60)D(max), D(min), D(med), D(mean), V(90%), V(95%) and V(100%) across the five cases achieved were as follows: mMLC IMRT: 64.9 Gy, 40.1 Gy, 60 Gy, 59.6 Gy, 95.4%, 88.8% and 69.2%, respectively; helical tomotherapy: 67.2 Gy, 50.3 Gy, 60 Gy, 59.9 Gy, 95.8%, 83.5% and 51.9%, respectively. The average treatment time per fraction was 18.4 min for IMRT with mMLC and 6.7 min for helical tomotherapy.

DISCUSSION

This study shows that safe dose escalation to a dose of 60G y to skull base lesions can be achieved; using either mMLC- or helical tomotherapy-based IMRT. A plan comparison between the two solutions is difficult, but they seem to be similar in efficacy with any small differences being difficult to interpret and of questionable clinical significance. Helical tomotherapy has the advantage of a significantly decreased beam-on time.