Brain-sparing holo-cranial radiotherapy: a unique application of helical tomotherapy

Diffuse and extensive involvement of the scalp/skull by malignancy mandates holo-cranial radiotherapy with the aim to deliver homogeneous doses to the planning target volume (PTV) while minimising the dose to surrounding organs at risk (OARs). Previously described techniques result in significant heterogeneity, suboptimal coverage or poor conformity and need complicated beam matching. Here we report our preliminary experience of planning and delivery of brain-sparing holo-cranial radiotherapy with helical tomotherapy.

Three patients with extensive involvement of the scalp/skull by malignancy were planned and treated with image-guided intensity-modulated radiation therapy on helical tomotherapy. The plan evaluation was carried out using standardised dose metrics.

Helical tomotherapy achieved highly conformal and homogeneous dose distributions with substantial OAR sparing in all three patients. The volume of PTV receiving ≥95% of prescribed dose (V(95%)) was ≥98% in all three patients. The mean (standard deviation) homogeneity index and conformity index was 0.046 (0.006) and 0.783 (0.035), respectively. The mean dose to the brain parenchyma outside the PTV was 17.32 Gy (74%), 28.76 Gy (63.9%) and 26.7 Gy (59.3%) for the three patients. The mean (standard deviation) monitor units and beam-on time was 6939 (985) and 8.10 (1.137) min, respectively. Overall the treatment was very well tolerated with no significant acute toxicity. Early follow-up evaluation revealed a good clinicoradiological response and the absence of local disease progression with no significant sequelae, implying successful application of the treatment paradigm.

Helical tomotherapy is ideally suited for brain-sparing holo-cranial radiotherapy with its exceptional ability of tangential beam delivery resulting in highly conformal and homogenous dose distribution across large, complex target volumes with substantial OAR sparing.