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Chordoma is an uncommon neoplasm of the bone arising from embryonic remnants of the notochord. The overall age-adjusted incidence is about 8 per 10 million, but this figure is dependent on age, sex, and race (Jemal et al., 2007). This tumor typically occurs in the axial skeleton mainly involving the sacrococcygeal region and the base of the skull (Mirra et al., 2002). The natural history of such malignancy is of a slow but progressive growth ultimately translating into a local aggressive behaviour. Overall, five-year survival rates are near 60% to 70%, although 10-year survival drops to 35% to 40% (Dorfman, 1998). The rate of distant metastases (to lung, bone, soft tissue, lymph nodes, liver, and skin) varies in a range between 0% and 40% (Chambers et al., 1979) even though usually late detected with most patients succumbing to their local disease. Based on these considerations the control of primary disease remains the major therapeutic challenge. Given the rarity of this tumor, data on efficacy and safety of the treatments are limited and mainly based on few, small sized, retrospective series. The standard of care is considered surgery, when feasible, with the aim of establishing a definitive diagnosis and obtaining the maximal debulking of the lesion. Surgical outcomes depend on tumor location and size at diagnosis. Considering the large size of most sacral lesions and the proximity to critical healthy structures of skull base and vertebral chordomas, maximal resection usually entails a relevant morbidity with poor functional outcome in a significant proportion of patients. Therefore, even if local control and survival rates strictly depend on the achievement of negative margins, radical surgery can be rarely obtained (Cotler et al., 1983). In such scenario recurrence rates can approach 70%. This situation clearly supports the interest for radiation therapy as an adjuvant modality after residual disease even though the irregular and infiltrative nature of this tumor makes it difficult to be targeted. The role of irradiation either as a postoperative treatment or as a curative measure in inoperable lesions is widely debated. Chordomas have been historically considered radio resistant tumors requiring high doses of radiation (> 60 Gy) to respond best. However, a dose–response relationship has not been clearly reported across all series (Tai et al., 1995) and the doses needed to control the tumor in general exceed the tolerance dose levels of nearby normal structures (Pai, 2001; Slater, 1988). Several irradiation modalities have been proposed (particle therapy, intensity-modulated radiation therapy, stereotactic irradiation) without a clearly established superiority of one

The Role of Irradiation in the Treatment of Chordoma of the Base of Skull and Spine