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S268

ESTRO 36 2017

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70.2% infratentorial, the tumor grade was anaplastic in

62.0%, the extent of resection was complete in 85.1% and

64.5% of patients received a dose >54 Gy. The median

PRTV was 43.8 cc (1.1-287.9), and the median CEPTV was

13.3 cc (0-71.4). The median PRTVF was 49.4 cc (0-336.7)

and the median POTVF was 4.6 cc (0-118.7). A statistically

significant benefit in survival was seen with a POTVF equal

to 0 cc in univariate analysis for the DFS and the OS (71.9%

versus 40.3% p=0.006) and (93.7% versus 72.37% p=0.023)

respectively. In multivariate analysis, POTVF was also

statistically significant for OS (p=0.05) and almost

significant for DFS (p=0.06).

Conclusion

In this retrospective study, POTVF was found to be

significant predictor of overall survival after ependymoma

radiotherapy. POTVF was the more significant predictor of

survival compared with PRTV, suggesting that this volume

and residual contrast-enhancing tumor may be a more

accurate and meaningful reflection of the pathobiology of

ependymoma.

OC-0513 Radiation necrosis following stereotactic RT

and immunotherapy for melanoma brain metastases

O. Kaidar-Person

1

, T. Zagar

1

, A. Deal

2

, S. Moschos

3

, M.

Ewend

4

, D. Sasaki-Adams

4

, C. Lee

3

, F. Collichio

3

, D.

Fried

1

, L. Marks

1

, B. Chera

1

1

University of North Carolina- Chapel Hill- North

Carolina- USA-, Department of Radiation Oncology,

Chapel Hill, USA

2

UNC Lineberger Comprehensive Cancer Center- Chapel

Hill- North Carolina- USA, Statistics, Chapel Hill, USA

3

University of North Carolina- Chapel Hill, Medicine,

Chapel Hill, USA

4

University of North Carolina- Chapel Hill, Neurosurgery,

Chapel Hill, USA

Purpose or Objective

Stereotactic radiotherapy (SRT) is the standard treatment

for patients with limited number of brain metastases. In

the past few years, newer immunotherapies (immune

checkpoint inhibitors) have been proven to prolong

survival in patients with metastatic melanoma. The safety

of the combination of SRT and immunotherapy for brain

metastases is unknown.

Material and Methods

We retrospectively identified patients with melanoma

brain metastases treated with SRT between 2007 and

2015. Patients who did not have at least 3 months of

follow-up with imaging after SRT were excluded from the

analysis. Outcomes were compared between patients who

were treated with or without immunotherapy.

Results

A total of 58 patients were included, of these 29 were

treated with SRT and immunotherapy. MAPK inhibitors

(BRAF, MEK inhibitors) were used more often in the

immunotherapy group (9 vs. 2 patients). There was a

higher incidence of intracranial complications in patients

treated with immunotherapy and SRT. Eight patients had

radiation necrosis, all occurred in patients who were

treated with immunotherapy. Nine patients had

hemorrhage, of which 7 occurred in patients who were

treated with immunotherapy (p=0.08). However, patients

treated with immunotherapy and SRT had a significant

overall survival advantage compared to SRT without

immunotherapy (15 vs. 6 months, p = 0.0013).

Conclusion

Patients treated with SRT and immunotherapy, have a

higher incidence/risk of intracranial complications but a

longer overall survival.

OC-0514 radiation necrosis after proton beam therapy

- when and where does it happen?

S. Harrabi

1,2,3

, C. Gudden

1

, S. Adeberg

1,2,3

, N. Bougatf

2,3

,

T. Haberer

3

, S. Rieken

1,2

, J. Debus

1,2,3

, K. Herfarth

1,2,3

1

University Hospital Heidelberg, Radiation Oncology,

Heidelberg, Germany

2

Heidelberg Institute of Radiation Oncology, HIRO,

Heidelberg, Germany

3

Heidelberg Ion-Beam Therapy Center, HIT, Heidelberg,

Germany

Purpose or Objective

Radiation necrosis after irradiation of central nervous

system tumors is a rare but severe side effect. The

differentiation on magnetic resonance imaging between

postoperative changes, gliosis and therapy associated

changes remains a challenge and is not always possible

with absolute certainty. Available data almost exclusively

refer to conventional radiotherapy with photons (XRT).

Since the use of proton beam therapy (PRT) is constantly

increasing – especially for the treatment of neurooncologic

diseases – we set out to determine the safety of proton

irradiation by evaluating the incidence of radiation

necrosis.

Material and Methods

We reviewed 430 patients with a median age of 37 years

(4 – 85 years) who received radiotherapy between 2009

and 2015 for meningioma or low grade glioma with either

protons (n=276) or photons (n=154). Median applied dose

was 54 Gy (50 – 60 Gy). Clinical and radiological

information of regular follow-up examinations were

analyzed resulting in nearly 3.000 available magnetic

resonance imaging (MRI) examinations with a minimum

follow up of 12 months (median 30 months, range 12 – 82

months). Findings on MRI were delineated in the

treatment plan system and correlated with parameters of

the treatment plan. Complementary calculations for dose

distribution, linear energy transfer (LET) and relative

biological effectiveness (RBE) for the original treatment

plan using different models (Monte Carlo, Wedenberg,

Carabe) were made.

Results

The cumulative incidence of radiation necrosis after PRT

in our cohort was 3.3 % with a median time to occurrence

of 12 months (6 – 32 months). No risk factor could be

identified with regard to treatment specific parameters

such as optimization algorithm (single beam optimization

vs intensity modulated proton therapy), number of used

beams (one vs multiple), concomitant chemotherapy or

applied dose (≤54 GyE vs >54 GyE). However, the observed

radiation necrosis affected significantly often the

periventricular border and were almost exclusively at the

distal edge of the spread-out Bragg peak (SOBP).

Conclusion

Radiation necrosis after PRT can be a severe side effect

but is as rare as after XRT. The accumulation of incidence

at the distal edge of the SOBP and at the periventricular

border warrants further radiobiological investigation.

OC-0515 Radiation necrosis in children with brain

tumours treated with pencil beam scanning proton

therapy

B. Bojaxhiu

1

, F. Ahlhelm

2

, M. Walser

1

, L. Placidi

1

, U.

Kliebsch

1

, L. Mikroutsikos

1

, P. Morach

1

, A. Bolsi

1

, T.

Lomax

1

, R. Schneider

1

, D.C. Weber

1

1

Paul Scherrer Institute, Center for Proton Therapy,

Villigen, Switzerland

2

Cantonal Hospital Baden, Department of Radiology,

Baden, Switzerland

Purpose or Objective

To assess the rate of radiation-induced brain necrosis (RN)

and related neurologic symptoms in paediatric patients

with primary brain tumours treated with Pencil Beam

Scanning (PBS) proton therapy (PT) with or without

concomitant chemotherapy at the Paul Scherrer Institute,

Switzerland.

Material and Methods

One hundred and seventy-one children and adolescent

young adults (AYA) (<18 years) with brain tumours were