First described in 1912, Bowen’s disease (BD) is a form of intraepidermal squamous cell carcinoma (in situ SCC) [10]. In two thirds of patients, a solitary, sharply demarcated erythematous and scaly or crusted plaque ranging in size from a few millimeters to several centimeters can be found, mostly located on the head, neck, hands, and lower leg [11–13]. Often the pilosebaceous apparatus is involved [14]. Less common sites or variants include pigmented BD, subungual/periungual, palmar, genital, perianal, and verrucous BD. Its mucosal variant is called erythroplasia of Queyrat. A minority (<5 %) become invasive although this figure may be higher (10 %) in genital lesions (erythroplasia of Queyrat) [15]. Various radiotherapy techniques (soft X-rays, orthovoltage, or electron therapy) and regimens have been used to treat BD, but there are no studies directly comparing other treatments with RT, and data are sparse regarding dosing and toxicity. RT is advantageous in patients who refuse surgery, for lesions in cosmetically sensitive areas, for large and multiple lesions (Fig. 8.2a, b), and for patients with keloid formation [13]. Several retrospective studies indicate local control rates from 89 to 100 % (Table 8.2) despite wide ranges in doses used. Local recurrences seem to be equally low in patients treated with high- and low-dose regimens. Patients with grade 4 toxicities according to Cox et al. [16] (necrosis of cartilage/bone damage and/or ulceration with an additional requirement for a duration of >3 months) more often had hypofractionated regimens (dose per fraction >4 Gy) in an extremity location. In the study of 59 lower extremity BD lesions by Cox and Dyson [17], one fifth also failed to heal after RT. Dupree et al. [12] reported nonhealing ulcers in 25 % of patients with BD after a median of 27.5 months following RT, all of them on the lower extremity. Most patients with this side effect were treated with orthovoltage X-rays. Recent review articles on managing patients with BD emphasize the multitude of treatments for these patients [15, 18]. Despite this, RT remains an excellent and well-tolerated therapeutic option in selected patients with BD (in particular on digital, penile, or perianal sites), but risk factors for poor healing on the lower leg, such as poor vascularity, size of the lesion (>4 cm), and large fraction size (>4 Gy), should be taken into account [12, 13, 15]. When other treatments have failed, RT can be effective [19].