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Does psoriasis need more radiation dose to clear recalcitrant plaques? A case series of lesions from a single subject


International Journal of Radiology & Radiation Therapy
Gerald B. Fogarty,1 Zoe Moutrie,2 Mel Cusi,3 Rachel Gibbs,1 Alexandra Allende4

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Abstract

Psoriasis vulgaris is a chronic benign disease of the whole thickness of the epidermis with symptomatic plaque formation impacting quality of life. Relatively low doses of fractionated radiotherapy (RT) have been used in the past to a total dose of four to six Gray (Gy). We present the case of an older male with seven recalcitrant plaques each treated with the same prescribed dose of RT. Superficial radiotherapy (SXRT) with a 100kV beam from a Xstrahl 300 machine to a total dose of 20 Gy in 10 fractions (#s) at five #s per week was used for six areas - four on the scalp and one on each elbow. At six months post treatment, four scalp areas had a continuing complete response (CR) whilst the elbows had a continuing partial response (PR). A seventh area, measuring 21 x 16cm on the lower back, was treated with volumetric modulated arc therapy (VMAT) using six megavoltage photons (MV) at the same prescribed dose. At four weeks, an infield CR was observed, but at eight weeks there was some infield recurrence. Pre- and post-RT biopsies from this field were compared. In the VMAT area with clinical recurrence, RT caused a histological PR. In the VMAT area with clinical CR, there was no histological evidence of disease. These findings raise radiobiological questions. Was the difference in clearance due to lower disease burden, kilovoltage backscatter from bone giving a higher relative dose, a difference in oxygenation or chronic sun exposure of tissues, or a difference in the relative biological effectiveness (RBE) between SXRT (1.2) relative to MV photons (1.0)? We recommend that future studies of RT in psoriasis start with 20Gy in 10#s, preferably with a modality that can penetrate the whole plaque epidermis, which can be quite thickened in patients suffering from psoriasis.

Keywords

Radiotherapy, radiobiology, superficial radiotherapy, volumetric modulated arc therapy, psoriasis, psoriatic plaques, benign, case study, histopathology

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