Abstract Book

S681

ESTRO 37

Results Median age was 64 years (range: 32-78 years). 64% were men. Tumors were most commonly of non-small cell lung origin (61 %), breast (18 %), kidney (7%), 14% of other histology (melanoma, pancreas, colon, upper tract tumor). 11 lesions were surgical cavities with a mean PTV of 19.14 cc [3.36; 52.61]. Mean PTV of 33 brain metastasis was 5.89 cc [1.03; 17.73]. Prescribed dose was 3 fractions of 11 grays (75%), or 5 fractions of 7 to 5 grays (25%), depending of PTV and irradiated brain. Prescription isodose curve was 70% for 30 lesions and 80% for 14 lesions. Time between fractions was either 24 hours (64%) or 48 hours (36%). WBRT was delivered in 4 cases of multiple brain recurrence. Median overall survival from time of HFSRT was 7.4 months (range: 1.7-23 months). Median radiological follow up time was 5.7 months (range: 0.3-14.6 months). The estimated LC at 3 and 6 months were 58 % and 40 % respectively. On multivariate analysis surgical resection, daily fractionation scheme and prescription isodose curve 80% tend to be predictors of LC, but didn’t reach statistical significance.

clinic were included in the study. We delineated PTVs and the boost volumes on the planning CTs with image fusion with MRIs. Delineation of the target volumes was based on the gross target volume (GTV) which is defined as the contrast enhancing visible tumor on the T1 with gadolinium (Gd) images. The clinical target volume (CTV1), representing the subclinical tumor involvement, is defined as GTV1 + 15.0-mm expansion including the edema visible on the T2-weighted images. The planning target volume (PTV1) is defined as CTV1 + 5.0-mm margin. The CTV2 is defined as the GTV + 5.0-mm expansion including the contrast-enhancing tumor visible on the T1–Gd images. The PTV2 is defined as the CTV2 + 5.0mm margin. we planned each case by three VMAT plans of the (SB) technique and two (SIB) techniques of two dose regimens utilizing equivalent biologically effective doses for all plans. The first Plan using SB, PTV1 received 46 Gy over 23 fractions in 2 Gy as dose per fraction and PTV2 received 14 Gy in 7 fractions with 2 Gy as dose per fraction. The second Plan SIB (SIB1) , the PTV1 received 54 Gy over 30 fractions with 1.8 Gy as a dose per fraction, while the PTV2 received 60 Gy over 30 fractions but with 2 Gy as a dose per fraction. The third plan SIB (SIB2) was carried out using different biologically equivalent dose to deliver to PTV-1 dose of 48.6 Gy over 27 fractions in 1.8 Gy as dose per fraction while the PTV- 2 will receive 59.4 Gy over 27 fractions but with 2.2 Gy as a dose per fraction. Results We compared the dose distributions and DVH for OAR constrains for all three plans. we found that the mean percentage coverage of 95% of PTV1 volume (109% , 96.49% and 96.23& ) for (SB, SIB1 and SIB2) respectively. The mean percentage coverage of 95% of PTV2 volume were (98%, 96.8% and 94.26%) for (SB, SIB1 and SIB2) respectively.The mean maximum dose to optic nerve is (19.7 Gy, 20 Gy, 18.23 GY) for (SB, SIB1 and SIB2) respectively which is statistically non significate with P- value = 0.94. The mean maximum dose to optic chiasm (40.3 GY, 41.76 GY, 38 GY) for (SB, SIB1 and SIB2) respectively which is also statistically non significate with P-value = 0.9. We found no statistical difference into the mean maximum dose to brainstem (55.6 GY, 54 GY, 50.2 GY) for (SB, SIB1 and SIB2), respectively (P-value = 0.057). Conclusion Based on our data we recommend that utilization of SIB with less number of fractions of biologically equivalent to standard fractionation might be the best option for treatment of high grade glioma patients. EP-1228 Local control and toxicity of brain stereotactic radiation in a French non-academic hospital N.H. Hau Desbat 1 , Y. Benmati 1 , M. Romanet 1 , A. Lecomte 1 , P. Fourneret 1 1 Centre Hospitalier Chambery, Radiation therapy, Chambery, France Purpose or Objective To evaluate local control rate and toxicity of all patients treated with HFSRT in a French public and non-academic hospital. Material and Methods Between November 2015 and October 2017, 44 brain metastases in 28 patients were treated with Novalis truebeam STX hypofractionated stereotactic radiation. We retrospectively analyzed clinical and dosimetrical datas from patients’ records. Local failure was defined as an increase in lesion size after HFSRT (RECIST criteria). Local control was estimated using the Kaplan-Meier method. The Cox proportional hazard model was used for univariate and multivariate analysis.

All patients had steroids during HFSRT. 2 patients had asymptomatic toxicity diagnosed on MRI : one necrosis and one intratumoral bleeding. Conclusion 2 years after the first brain HFSRT in our radiation department, no symptomatic toxicity occurred. The technique is secure but LC is poor, reflecting poor prognosis and OS of treated patients in our department. EP-1229 Early response of melanoma brain metastases to radiosurgery as important indicator of tumor behavior I. Zubatkina 1 , P. Ivanov 1,2 1 Radiosurgery- Stereotactic Radiotherapy and General Oncology clinic MIBS, Radiosurgery, Saint-Petersburg, Russian Federation 2 Polenov Russian Scientific Research Institute of Neurosurgery- Branch of Federal Almazov North-West