Assessment of improved organ at risk sparing for meningioma: Light ion beam therapy as boost versus sole treatment option

Purpose

To compare photons, protons and carbon ions and their combinations for treatment of atypical and anaplastical skull base meningioma.

Material and methods

Two planning target volumes (PTV_initial/PTV_boost) were delineated for 10 patients (prescribed doses 50 Gy(RBE) and 10 Gy(RBE)). Plans for intensity modulated photon (IMXT), proton (IMPT) and carbon ion therapy (¹²C) were generated assuming a non-gantry scenario for particles. The following combinations were compared: IMXT + IMXT/IMPT/¹²C; IMPT + IMPT/¹²C; and ¹²C + ¹²C. Plan quality was evaluated by target conformity and homogeneity (CI, HI), V_95%, D_2% and D_50% and dose-volume-histogram (DVH) parameters for organs-at-risk (OAR). If dose escalation was possible, it was performed until OAR tolerance levels were reached.

Results

CI was worst for IMXT. HI < 0.05 ± 0.01 for ¹²C was significantly better than for IMXT. For all treatment options dose escalation above 60 Gy(RBE) was possible for four patients, but impossible for six patients. Compared to IMXT + IMXT, ion beam therapy showed an improved sparing for most OARs, e.g. using protons and carbon ions D_50% was reduced by more than 50% for the ipsilateral eye and the brainstem.

Conclusion

Highly conformal IMPT and ¹²C plans could be generated with a non-gantry scenario. Improved OAR sparing favors both sole ¹²C and/or IMPT plans.