Dose-de-escalated focal radiotherapy for primary cutaneous T-cell lymphoma: a lesion-based retrospective cohort study.

BACKGROUND AND PURPOSE: Radiotherapy (RT) is effective for cutaneous T-cell lymphoma (CTCL), but the optimal focal dose remains debated. We evaluated lesion response, local control, toxicity and patient satisfaction after 2 × 4 Gy compared with higher-dose regimens. Patient/material and methods: This single-centre retrospective study included CTCL patients treated with RT between 1990 and 2019 at a German university hospital. Lesions receiving 2 × 4 Gy (low-dose) were compared with lesions treated with higher doses (median 34 Gy). Endpoints were complete response (CR), overall response (OR), 1- and 5-year local control rate (LCR; Kaplan-Meier/log-rank), in-field relapse and toxicity (common terminology criteria for adverse events/ Radiation Therapy Oncology Group (RTOG)-European Organisation for Research and Treatment of Cancer). Patient satisfaction Freiburg Index of Patient Satisfaction (FIPS) was assessed in a subsample.

RESULTS: Thirty-two patients with 227 lesions were analysed (195 low-dose; 32 higher-dose). CR was achieved in 88.2% vs 90.6% and OR in 94.4% vs 100%, respectively (low- vs higher-dose). LCR was inferior after low-dose RT, with 1- and 5-year LCR estimates of 82 and 67% versus 100 and 96% after higher-dose RT (log-rank p = 0.013). In-field relapse occurred in 20.1% (37/184) vs 3.6% (1/28) of lesions with follow-up (Fisher p = 0.034). No toxicity > grade 2 was observed, and did not differ between groups (p = 0.695 and p = 0.657). In 11 FIPS questionnaires, satisfaction was high (mean score 1.27; median 1).

INTERPRETATION: Low-dose 2 × 4 Gy yields excellent initial response with minimal toxicity, but inferior local control compared with higher-dose focal RT. Findings support intent-based dosing: 2 × 4 Gy for symptom-driven treatment with re-irradiation as a pragmatic option, and higher-dose RT when durable local control is the primary objective.