ESTRO 2021 Abstract Book

S1687

ESTRO 2021

location. Acute toxicity reviews were recorded according to Common Terminology Criteria for Adverse Events (CTCAE v.5). Follow -up is ongoing. For the descriptive analysis, analytical variables were represented using absolute and relative frequencies. All statistical analysis were conducted using software from SPSS (version 25.0, Chicago, IL). The hypothesis of our study is HRT will reduce radiotherapy sessions with a low rate of toxicity. Results The median age was of 67 years (IR 63,0;71,5). Population performance status was 0-1. A 60.5% of patients showed a pathological Gleason score of 7. 61.5% of patients had positive surgical margins. The median PSA pre-radiotherapy was 0.35 and median PSA doubling time was 7.1 months. Androgen deprivation was associated in 28 patients. Hormone therapy length was 6 months in 60.7%. IMRT was performed in 45.7% of the cases and VMAT in 54.3%. The image control was carried out with kilovoltage (84%) and megavoltage (16%) cone beams . Only one patient developed G3 genitourinary toxicity at the end of treatment and another patient 6 months after treatment. No patient had G3 gastrointestinal toxicity. Conclusion In our series, HRT after surgery was well tolerated with acceptable GU and GI toxicities, with low complication rates. PO-1985 Long-term results in CNS paediatric tumors: Stereotactic Radiotherapy and Reirradiation A.G. Rosa 1 , R. Carmen 1 , H. Ovidio 1 , C. Xin 1 , A. Leyre 2 , G.D.A. Paz 3 , G. Juan 3 , C. Raquel 1 , A. Beatriz 1 , V. Jeannette 1 , O. Marta 4 , M. Isabel 4 , M. Angel 1 , S. Emilio 1 , L. Mercedes 1 , G. Mariola 1 , N. Mónica 1 , G. Susana 5 , S. Mª Jesús 1,1 , P. Francisco 1,1 , L. Blanca 4 1 HM Hospitales, Radiation Oncology, Madrid, Spain; 2 HM Hospitales, Medical Physics, HM Hospitales, Spain; 3 HM Hospitales, Medical Physics, Madrid, Spain; 4 HM Hospitales, Pediatric Oncology, Madrid, Spain; 5 HM Hospitales, Antesthesiology, Madrid, Spain Purpose or Objective To describe our experience with Fractionated Stereotactic Radiotherapy (FSR) and re-irradiation in brain paediatric tumors (BPT) Materials and Methods From January-2007 to March-2021, we have treated 57 patients (p) diagnosed with different CNS tumors, with a median age of 7 years old (yo) (range 0-19). Tumors histopathology were; Astrocytoma (16), DIPG (12), Medulloblastoma (7) Oligodendroglioma (3), Atipical Teratoid-Rabdoid Tumor (3), PNET (3) Ganglioglioma (3), Germinal (3), Ependimoma (2), Craniopharingioma (1), Pinealoblastoma (1), Glioblastoma (1), Retinoblastoma (1), Teratoma (1). Fig. 1.

Radical-intent radiotherapy was delivered in 22p. 28p received adjuvant radiotherapy; 11p, 8p and 9p undergone R0, R1 and R2 surgical resections respectively. Four patients received initial palliative RT. Re-irradiation was performed in 13 patients. Planning CT and daily treatment were performed with general anesthesia in youngest patients (<7yo). For planning purposes, MRI image registration was used for tumor delineating in all patients. Besides, PET-TC images were used in 1p and PET-MRI in 10p. Treatments were planned with IMRT technique in 27p, VMAT in 21p and RTC3D in 9p. Treatments were delivered in Novalis and Elekta Linac with daily IGRT (Exactrac/CBCT). Results Radical median total dose was 52.2Gy (range 40-60Gy) in 1.8Gy-3.1Gy/fraction. Adyuvant median total dose was 45Gy (range 36-59Gy) in 1.8Gy-2.2Gy/fraction. Four patients with ATRT, PNET, Glioma and DIPG received palliative RT as initial treatment with a median total dose of 32.2Gy (range 28.8-40Gy).

Table 1. Median Dose Prescription

With a global median follow-up of 38,6months (range 0.2-151m), twenty six patients are alive with complete response (12p), partial response (3p), stable disease (9p), and loco-regional progression (2p). After RT treatment thirty one patients had CNS recurrence, (21p in local-field, 10p regional) and one distant progression. 13p received salvage re-irradiation, (11p with RT alone and 2p with Deep Regional Hyperthermia). Median dose 32.9Gy (range 25-50Gy) in 1.8-4Gy/fraction. In three patients the re-irradiation field included the whole neuroaxis (Median dose 30Gy (range 30-25Gy) in 2.5-3Gy/fraction. With a median follow up of 46.3 months (8-51), neurological symptoms