RONC-11. EVALUATION OF DIFFERENT RADIOTHERAPY TECHNIQUES ON INCIDENTAL RADIATION DOSES TO THE WHOLE VENTRICULAR SYSTEM DURING FOCAL IRRADIATION FOR NON GERMINOMATOUS GERM CELL TUMOURS AFTER CHEMOTHERAPY

In Europe, patients with localized nongerminomatous germ cell tumours (NGGCT) are treated with focal radiotherapy. It is not sure whether this approach leads to excess periventricular recurrences in patients with a germinomatous component in the tumour. Data suggest that a dose of 20 Gy may be sufficient to control microscopic geminomatous disease. We evaluated the dose received to the whole ventricular system (WVS) using different techniques when delivering 54 Gy to the tumourbed. MATERIALS AND

The WVS was delineated on the treatment planning CT of five patients diagnosed with NGGCT (2 pineal, 2 suprasellar and one bifocal). All patients had received proton radiotherapy following chemotherapy. We generated five photon plans: two coplanar, one noncoplanar and one tomotherapy plan. For the purpose of comparison the original proton radiotherapy plans were slightly modified. Mean WVS dose and the WVS volume receiving 20 Gy (V₂₀) were analysed.

Mean WVS dose with photons was 37 Gy [range 27-47] (coplanar: 35 Gy [27-41], noncoplanar: 38 Gy [33-43], tomotherapy: 40 Gy [34-47]) and with protons 35 Gy [28-42]. The WVS V₂₀ was 78 % [range 58-90] with photons (coplanar: 73% [56-90], noncoplanar: 81% [73-90], tomotherapy: 88% [71-100]) and 68 % [55-80] with protons.

The unintentional WVS dose varies between the different treatment techniques. Careful pattern of failure studies correlated with radiation dosimetry and clinical-pathological features are needed to define the role of WVS irradiation in NGGCTS.