ESTRO 2024 - Abstract Book

S1132

Clinical - Haematology

ESTRO 2024

large cells were present in more than 25% of tumour cell infiltrates or clusters of cells had a diameter more than four times that of normal lymphocytes. Patients were identified using electronic medical records; data of radiotherapy intent, dose, technique and outcomes were collected from patient charts, with follow-up close-out date of 15/06/22.

Results:

83 patients were eligible. Median follow up was 8 years (95% CI: 6, 11). Median age at diagnosis of LCTMF was 67 (range 37-87) years, with a slight preponderance for males (53, 64%). The extent of LCTMF involvement at the time of diagnosis was cutaneous-only in 63 (76%) patients (31 unilesional; 31 multifocal; 1 unknown), cutaneous plus extracutaneous in 14 (17%), and uncertain in 6 (7%). The most common first-line therapies were localised radiotherapy-alone in 40 (48%) patients, and multiagent chemotherapy-alone in 19 (23%). Subsequent lines of therapy were required for relapse/ progression in 68 (82%) patients. Considering all lines of therapy, most patients received multi-modality treatment, with 66 (80%) patients receiving systemic therapy and 60 (72%) receiving localised radiotherapy. Of these 60 patients who received localised radiotherapy during their treatment course, radiotherapy was delivered definitively in 40 patients and with palliative-intent in 20 patients. Radiotherapy details were available for 155 irradiated LCTMF lesions (from 49 patients). 88 lesions were treated definitively with median equivalent total dose in 2Gy per fraction (EQD2) of 36Gy (range, 17-46) with response assessment available in 85 lesions: overall response rate (defined as both complete response (CR) and partial response (PR)) was 100% (CR 95%, PR 5%). 67 lesions were treated with palliative radiotherapy, with median EQD2 of 20Gy (range, 5-36) and response assessment available in 61 lesions: of these, overall response rate was 87% (CR 13%, PR 74%). All LCTMF lesions responded (CR/PR) to EQD2 of ≥12Gy (assuming α/β of 10), correlating biologically effective dose (BED) was ≥14.4Gy. Of the 155 lesions irradiated, data on relapse patterns were known for 144 lesions. Of these 144 lesions, in-field progression/relapse occurred in 6 lesions: 4 skin lesions that were treated with definitive radiotherapy (median EQD2 30.6Gy, range 17-40) and 2 skin lesions treated with palliative radiotherapy (median EQD2 18Gy, range 12-23). In this cohort, 22 (27%) patients presented with unilesional cutaneous-only LCTMF and were treated definitively with local radiotherapy alone. At the time of diagnosis, 14 (64%) were tumours of LCTMF. The median dose and fractionation was 34Gy (range, 18-42) in 16 fractions (range, 10-20) with median EQD2 and BED of 35Gy and 42Gy respectively. Electron therapy was the most common RT technique, using 4-12MeV electrons with tissue equivalent bolus, and median field diameter of 6.5cm (range, 4.5-25cm). Response assessment was available in 21 of the 22 patients, with CR rate of 100%. At the close-out date, 9 (41%) remained relapse-free from LCT, 12 (55%) had out-of field relapse with LCT (10 cutaneous, 1 both cutaneous and extracutaneous, 1 extracutaneous only) and only 1 (5%) patient had both infield and out-of-field relapse with LCT. No patients relapsed solely in-field.

Conclusion:

To our knowledge, this is the largest series to describe radiotherapy doses and outcomes in patients with LCTMF. Radiotherapy achieved excellent responses, as demonstrated in both the definitive and palliative intent settings; overall response (CR/PR) was seen with doses EQD2 ≥12Gy (BED ≥14.4Gy). In the setting of early stage unilesional cutaneous LCTMF, definitive radiotherapy-alone may achieve durable infield disease control. Longer follow up is required to determine potential for “cure -from- LCT” in this subgroup of patients with unilesional LCTMF treated with definitive radiotherapy.