Condensed Low Dose Total Skin Electron Beam Therapy for Mycosis Fungoides: A Single Institution Experience

Abstract

To determine safety and efficacy of condensed low dose total skin electron beam therapy (TSEBT), 12 Gy over two weeks, for mycosis fungoides (MF). We conducted a retrospective review of patients treated with condensed low dose TSEBT for MF at our institution. Patients were treated with 6-field Stanford technique to a total dose of 12 Gy in 2 Gy fractions, every other day over 2 weeks. A total of 18 patients with minimum 6 months follow up were included. Treatment response rate was defined as complete response (CR), near CR (<5% body surface area [BSA]), and partial response (PR). Duration of response as measured from TSEBT start date to date of progression requiring systemic therapy or death. Pain, pruritus, Dermatology Life Quality Index (DLQI) score , DLQI effect, modified Severity Weighted Assessment Tool (mSWAT), BSA, and TSEBT-related toxicities were also evaluated. Statistical analysis was performed with R (version 3.4.3). Linear mixed models with random effect of patient was used for estimation of pre vs. post comparisons on efficacy endpoints. We evaluated with two-sample t-test, Fisher's exact test, as well as Cox proportional hazards model in addition to summary statistics of baseline characteristics. Of the 18 patients, 14 were male and 4 were female. Median follow-up of 63 weeks. Median age 69 yo (range 37-85). Majority were Stage IB (44%). Three patients had large cell transformation. Overall response rate was 100 percent. Complete response (CR) was seen in 3 patients (17%), and near CR in 7 patients (39%), and PR in 8 patients (44%). Median duration of response was 56 weeks, with seven patients (39%) having progression. Four patients died, of which one had large cell transformation. Treatment response metrics were all significantly reduced after TSEBT. Pruritus had a mean difference of 2.694 (95% CI 1.354, 4.035, p<0.001), pain of 2.694 (95% CI 1.021, 4.368, p=0.003), mSWAT of 57.53 (95% CI 32.08, 82.98, p<0.001), BSA of 32.88 (95% CI 18.86, 46.91, p<0.001), and DLQI of 6.56 (95% CI 3.55, 9.57, p<0.001). Treatment was well tolerated with no toxicity ≥ Grade 3. Most common toxicity was Grade 1 fatigue (33%) and Grade 1 alopecia (22%). Two patients experienced nail loss and three patients had Grade 2 radiation dermatitis that self-resolved. Condensed low dose TSEBT shows excellent initial response with favorable duration of response, and effective palliation of symptoms. Further exploration with a prospective trial is warranted.