Update of Comparison of Low-Dose and Standard-Dose Total Skin Electron Beam Therapy for Mycosis Fungoides

Abstract

Total skin electron beam therapy (TSEBT) is has been shown to be an effective treatment for mycosis fungoides (MF). Doses of 30-36 Gy have traditionally been used with high response rates, although treatment is associated with toxicity and most patients ultimately progress. Recent studies have proposed 12 Gy as an effective and tolerable dose, and our institution has been utilizing this regimen to treat MF patients since 2015. We compare our experiences using low-dose TSEBT and standard-dose TSEBT. Between 2010 and 2016, 26 patients with Stage IB – IVA MF were treated with TSEBT at our institution. Thirteen patients received a total of 16 courses of low-dose TSEBT to 12 Gy, with 3 of these patients received a repeat course of low-dose TSEBT during this time. As a comparison group, 13 patients received standard-dose TSEBT between 30-36 Gy, all from 2015 and prior. We compare response rates, time to progression and toxicity between these treatment groups. Median follow-up was 15.8 months. Patients who received low-dose TSEBT were more likely to have had prior local radiation treatment (50% versus 8%, p = 0.013). All patients experienced at least a partial response to treatment, with 31% of the low-dose TSEBT courses and 77% of the standard-dose TSEBT courses resulting in initial clinical complete response (p = 0.014). Patients who underwent a repeat course of low-dose TSEBT had a 67% complete response rate as compared to 13% with single course low-dose TSEBT and 77% with standard-dose TSEBT (p = 0.020). Fourteen of 16 courses of low-dose TSEBT and 12 of 13 courses of standard-dose TSEBT resulted in progression. The average time to progression for low-dose TSEBT was 3.2 months versus 8.2 months for standard-dose TSEBT (p = 0.030). Common toxicity to both treatment arms was pain and pruritus. Compared to low-dose TSEBT, standard-dose TSEBT trended toward increased toxicity with hyperpigmentation/erythema (23% versus 6%, p = 0.19) and dry desquamation (46% versus 19%, p = 0.11). Low-dose TSEBT trended towards higher rates of skin dryness compared to standard-dose TSEBT (56% versus 23%, p = 0.071). Rates of dry desquamation increased to 33% with repeat low-dose TSEBT compared to 15% with single course low-dose TSEBT and 46% with standard-dose TSEBT (p = 0.24). Low-dose TSEBT was associated with a significantly lower complete response rate and shorter time to progression compared to standard-dose TSEBT, although rates of complete response improved with a repeat course of low-dose TSEBT. In addition, low-dose TSEBT trended toward lower rates of toxicity compared to standard-dose TSEBT. Given the high rate of progression regardless of treatment regimen, the use of low-dose TSEBT should be considered for the treatment of MF as this approach allows for re-treatment with complete response rates rivaling that of standard-dose TSEBT with a better toxicity profile.