ESTRO 2020 Abstract book

S93 ESTRO 2020

Mean dose of WBRT was 26.0 Gy for the patients achieved complete response (CR) (range, 18.0 to 30.6 Gy) and 27.8 Gy for those achieved partial response (PR) (range, 18.0 to 35.0 Gy). Mean total dose including dose from tumor bed boost was 45.4 Gy (range, 36.0 to 54.0 Gy) for the CR, and 50.4 Gy (range, 45.0 to 55.8 Gy) for the PR. CTV margin was varied within 0.5 to 1.5 cm, while PTV margin was mostly 0.3 cm. Two cycles of Ara-C were combined in 27 patients after RT. Patients who had grade 2 or more toxicity by CTCAE v5 in cognitive disturbance, memory impairment and dysarthria were considered to have neurotoxicity. A median follow-up was 3.62 years (range, 0.38 to 19.20 years). Results After chemotherapy, 36 patients achieved CR, and 45 achieved PR. The 3-yr overall (OS) and, progression-free survival (PFS) were 70.0%, 48.9% with rdWBRT and 63.2%, 43.2% with sdWBRT. The 3-yr OS and PFS for the PR after chemotherapy were 77.8%, 53.3% with rdWBRT and were 58.3%, 45.8% with sdWBRT. These survival differences between rdWBRT and sdWBRT were not significant (p>0.05). No significant difference of failure pattern was observed between rdWBRT and sdWBRT. Among the patients achieved CR during follow-up period, the 3-yr FFNT rate was 94.1% in rdWBRT and 62.4% in sdWBRT. For the patients with age ≥60, 3-yr FFNT rate was 87.5% in rdWBRT and 39.1% in sdWBRT (p=0.49). There was no neurotoxicity in pateitns with age <60 within rdWBRT group. 9 patients underwent hippocampus-sparing (hs) WBRT. 3-yr OS, PFS, FFNT rate were 77.8%, 55.6% and 87.5%, respectively. Conclusion rdWBRT ≤23.4 Gy combined with HD-MTX is as effective as sdWBRT, even in patients who achieved PR after chemotherapy. rdWBRT might be beneficial for patients with age <60. hsWBRT did not compromise OS and PFS, but further evaluation will be needed. PD-0172 Radio/immuno-therapies of brain metastasis disease: A meta-analysis of efficacy and safety outcomes V. Voronova 1 , S. Lebedeva 2 , M. Sekacheva 3 , G. Helmlinger 4 , K. Peskov 1 1 M&S Decisions LLC, department of mathematical modeling, Moscow, Russian Federation ; 2 I.M. Sechenov First Moscow State Medical University, Institute of Pharmacy, Moscow, Russian Federation ; 3 I.M. Sechenov First Moscow State Medical University, Computational oncology group, Moscow, Russian Federation ; 4 AstraZeneca, Clinical Pharmacology & Safety Sciences- BioPharmaceuticals R&D, Boston, USA Purpose or Objective In the treatment of brain metastases, multiple clinical studies have demonstrated the advantages of combining immune checkpoint inhibitors with radiation therapy (ICI- RT) over radiotherapy alone (mono-RT). In the present research, we sought to: (i) compare efficacy (1-year overall survival (OS) and 1-year local control (LC)) and safety (radionecrosis rate (RNR)) outcomes for ICI-RT and mono-RT, across all relevant published clinical studies; and (ii) identify factors affecting these outcomes, using a quantitative meta-analysis approach. Material and Methods A systematic literature search was performed, to identify studies with at least one ICI-RT arm and reporting information for the aforementioned outcomes. Whenever data on mono-RT arms were available, corresponding risk ratios were also calculated. A mixed-effects meta-analysis was then performed, to evaluate the importance of ICI and RT therapy administration sequencing, and of ICI agent class (PD-(L)1 vs. CTLA-4 Ab) and RT type on treatment outcomes. Results

> Conclusion Stereotactic radiotherapy leads to complete resolution of brain metastases during long-term follow-up, radioresistant histology was associated with slower regression. Volumetric analysis may have a role in identifying metastases at risk for subsequent progression. Volumetric regression ≥20% at 3 months post-SRT was predictive for subsequent local control and could therefore be suitable for the standardized assessment of volumetric response following SRT in clinical trials. PD-0171 Reduced-Dose Whole Brain Radiotherapy for the Primary Central Nervous System Lymphoma T.H. Lee 1 , J.H. Chang 1 , B.H. Kim 2 , C.W. Wee 2 , J.H. Lee 1 , T.M. Kim 3 , C. Park 4 , S. Ye 1 , I.H. Kim 1 1 Seoul National University Hospital, Department of Radiation Oncology, Seoul, Korea Republic of ; 2 SMG-SNU Boramae Medical Center, Department of Radiation Oncology, Seoul, Korea Republic of ; 3 Seoul National University Hospital, Department of Internal Medicine, Seoul, Korea Republic of ; 4 Seoul National University Hospital, Department of Neurosurgery, Seoul, Korea Republic of Purpose or Objective High-dose methotrexate (HD-MTX)-based chemotherapy with whole brain radiotherapy (WBRT) for primary central nervous system lymphoma (PCNSL) has main drawback of possibility of neurotoxicity from WBRT especially in elderly patients. Reduced-dose WBRT (rdWBRT) was introduced to overcome this problem . This study is to compare standard- dose (sd) WBRT and reduced-dose (rd) WBRT in terms of clinical efficacy and toxicity profile. Material and Methods A retrospective review of medical records was performed in patients who underwent HD-MTX-based chemotherapy then WBRT for histologically confirmed PCNSL between January 2000 and December 2016. Patients with previous cancer history or HIV were excluded. 5 patients present with ocular involvement. The dose was ≤23.4 Gy for rdWBRT (n=20) and >23.4 Gy for sdWBRT (n=68). RT was delivered as WBRT and tumor bed boost. RT dose was decided mainly based on response after chemotherapy.

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