ESTRO 2023 - Abstract Book

S933

Digital Posters

ESTRO 2023

Conclusion Despite the sample limitation, we can concluded that 10Gy fractionation has similar OS than higher dose schedules with acceptable tolerance.

PO-1167 Low dose radiotherapy in indolent lymphoma involving the orbit- a 21-year single centre experience

M. Rafi 1,2 , B. Sharma 3,4 , E. Alexander 1 , D. Cunningham 5,6 , J. Glaholm 7 , M. Ahmed 1 , M. Tan 1

1 The Royal Marsden NHS Foundation Trust, Radiotherapy, Sutton, United Kingdom; 2 Regional Cancer Centre, Radiotherapy, Trivandrum, India; 3 The Royal Marsden NHS Foundation Trust , Radiology, Sutton, United Kingdom; 4 The Institute of Cancer Research, Radiotherapy and Imaging, Sutton, United Kingdom; 5 The Royal Marsden NHS Foundation Trust, Medical Oncology, Sutton, United Kingdom; 6 Institute of Cancer Research, Clinical Research, London, United Kingdom; 7 The Royal Marsden NHS Foundation Trust, Radiotherapy, London, United Kingdom Purpose or Objective Low dose radiotherapy (LDRT), with 4Gy/2#, in indolent lymphoma has response rates of 88-95%. Although RCT data demonstrates inferior local progression-free rates when compared to the standard dose of 24Gy/12#, LDRT is an appealing approach when treating the orbit(s), where even 24Gy can cause acute & late toxicity. There is relatively limited long-term outcome data on orbital LDRT. We report here on patient outcomes following orbital LDRT for indolent lymphoma at our centre over a 21-year period. Materials and Methods In this single-centre retrospective analysis, patients with histologically confirmed indolent lymphoma receiving LDRT to the orbit(s) between 2000-2021 were identified. Those without response assessment post-LDRT, or receiving systemic treatment (ST) prior to assessment/within 8 weeks of LDRT were excluded. Response to LDRT was recorded as complete (CR) or partial (PR) response, stable disease (SD) or progressive disease (PD) as per RECIST or Lugano (if PET-assessed) criteria. Primary endpoint was overall response rate (ORR; CR+PR). Kaplan-Meier analysis for secondary endpoints of local progression-free survival (LPFS) & overall survival (OS) was performed in GraphPad Prism 9.4.1. Results 27 episodes of LDRT to the orbit(s) in 25 patients were assessable. 56% (15/27) had staging PET. 26% (7/27) were stage I/II, 74% (20/27) were III/IV. 41% (11/27) had follicular lymphoma, 41% (11/27) marginal zone, 11% (3/27) mantle cell & 7% (2/27) CLL/SLL. ORR was 92% (25/27) with CR in 63% (17/27) at a median of 96 days (IQR 34-177) post-LDRT. 4% (1/27) had SD & 4% (1/27) had PD. 15% (4/27) had local progression (LP) ie. PD within RT field, at a median of 1.1 years post-LDRT (range 0.3-1.6yrs). Initially, 50% (2/4) had CR, 25% (1/4) PR & 25% (1/4) PD. Half had further RT to the orbit; 1 achieved CR with LDRT but later developed distant disease. The 2nd patient was not assessed post-RT. Of the remaining 2 patients, one had ST for distant PD and the other was observed.

One patient with PR after initial LDRT had a further 10Gy/5# to CR. The total number of re-irradiated sites was 3/27 (11%).

76% (19/25) had PD outside the RT field (median 6.6 mths post-LDRT; IQR 2.8-12.3). 60% (15/25) received subsequent ST.

Of those with orbit disease only, 50% (3/6) had staging PET & 33% (2/6) had bone marrow biopsy. 33% (2/6) maintained