ESTRO 2022 - Abstract Book

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Abstract book

ESTRO 2022

We retrospectively analyzed 42 patients (pts) with MB treated at our Institute, from 1999 to 2019. All pts had a minimum follow up of 12 months and underwent craniospinal irradiation (CSI) followed by a boost to whole posterior cranial fossa (W-PCF) and/or to the primary tumour site. Alopecia was assessed according to CTCAE v5.0 scale. Before 2010 pts were treated with 3D CRT technique. Since 2010 IMRT has been used for the PCF boost planning and from 2015 volumetric technique by helical Tomotherapy has become the standard treatment. In a subgroup of pts (N=27) the dose to the skin using Eclipse software (Varian Inc) was accurately assessed by scalp contouring. In this subgroup the skin was fully contoured across the scalp and manually defined as the volume from the outer surface of the skin to a depth of 3 mm up to a maximum thickness of 5mm. Median dose (D), mean D, D98%, D2%, D50% and skin volume were estimated through DVH curves analysis of the whole skin and the W-PCF skin, in the CSI, boost area and sum plan. Any relationship between presence of alopecia (partial or complete) and other characteristics was investigated by an appropriate univariate and multivariate analysis. For each significant predictor variable, a receiver operating characteristic curve was drawn for calculating the Area Under the Curve and identifying the optimal discriminatory cut-off value for prediction of alopecia In this study we analyzed a cohort of MB survivors with a median follow up of 10 years. Whole brain CSI doses ranged from 23.4 to 39.0 Gy. All 42 pts were boosted with either the entire PCF or the involved field of the tumour bed, with a total dose ranging from 54.0 to 69.0 Gy. High-dose and conventional chemotherapy were not significantly correlated with occurrence of permanent hair loss. Table 1 shows characteristics of pts according to grade of toxicity (no hair loss vs partial/complete hair loss). The best predictor for the occurrence of alopecia was the dose of CSI (OR: 1.002; 95%CI: 1.001-1.003; p=0.003), with an optimal discriminatory cut-off value of 30.9 Gy (Fig.1). In Eclipse subgroup D2% and D50% were found to be significant only on univariate analysis. The best predictor was D median hair skin (OR: 1.216; 95%CI: 1.030-1.435; p=0.021), with an optimal discriminatory cut- off value of 28.7 Gy (Fig. 1) Results