ESTRO 2023 - Abstract Book

S927

Digital Posters

ESTRO 2023

Conclusion IMRT effectively lowered the risk of decrease in ALC compared to 3D-CRT. We may be able to prevent RT-induced lymphopenia by lowering Brain V15, which is a significant predictor of ALC. In addition, shrinking PTV as much as possible might be beneficial for preventing neutrophilia. Taken together, our findings support that using IMRT and modifying dosimetric dose may achieve the declined NLR that is associated with a favorable prognosis.

PO-1157 Fractionated stereotactic radiotherapy as a primary therapy for cerebral arteriovenous malformation

J. LEE 1 , W.C. Kim 1 , H.J. Kim 1,2 , H.S. Park 3

1 Inha University School of Medicine, Department of Radiation Oncology, Incheon, Korea Republic of; 2 Gacheon University School of Medicine, Department of Radiation Oncology, Incheon, Korea Republic of; 3 Inha University School of Medicine, Department of Neurosurgery, Incheon, Korea Republic of Purpose or Objective To explore the therapeutic outcomes of Cyberknife fractionated stereotactic radiotherapy (CKFRT) for patients with cerebral arteriovenous malformations (AVM). Materials and Methods Between January 2008 and October 2011, 45 patients underwent CKFRT for cerebral AVMs as a primary treatment. The delineation of AVM targets included AVM nidus. The mean target volume was 4.07 cm ³ and 9 lesions (20%) were larger than 10.0 cm ³ . CKFRT was delivered in median three fractions (range, 2~5 fractions). The mean marginal dose was 24 Gy (range, 20-35 Gy). Generally, AVM obliteration following CKFRT was confirmed by magnetic resonance imaging or angiography. Results During a mean follow-up of 46 (5-147) months, complete obliteration and partial obliteration of AVM after CKFRT were obtained in 23 (51.1%) and 13 (28.9%) patients, respectively. Median time to complete obliteration was 39 (15-63) months. The cumulative probability of complete obliteration rate at 3 years was 47%. Complete obliteration rate of AVM was associated with Radiosurgery-based AVM score, which was consisted of AVM volume, patients age, and AVM location. One (2.2%) patient had hemorrhage during the follow-up period. Continuous neurological deficit after CKFRT was observed in 11(24.4%) patients. 1 Leiden University Medical Center, Radiation Oncology, Leiden, The Netherlands; 2 HollandPTC, Radiotherapy, Delft, The Netherlands; 3 Leiden University Medical Center, Radiology, Leiden, The Netherlands; 4 HollandPTC, Radiology, Delft, The Netherlands; 5 Erasmus MC Cancer Institute, Radiation Oncology, Rotterdam, The Netherlands Purpose or Objective Chordomas and chondrosarcomas of the skull base are rare, slowly growing malignant bone neoplasms. Despite their radioresistant properties, proton therapy has been successfully used as an adjunct to resection or as a definitive treatment. In this study, we present the clinical results of robustly optimized intensity modulated proton therapy (IMPT) of twelve skull base chordoma and chondrosarcoma patients treated in HollandPTC, Delft, The Netherlands. Materials and Methods We retrospectively reviewed clinical data, treatment details, and acute toxicity of all patients with chordomas and chondrosarcomas of the skull base treated with adjuvant IMPT between July 2019 and August 2021 in our institute. CT and 3.0T MR imaging examinations for treatment planning were performed in supine position in a thermoplastic mold. Robustly optimized proton therapy (PT) dose planning was performed with RayStation software (version 10B, RaySearch Laboratories, Stockholm, Sweden) and delivered with the Varian Probeam pencil beam scanning proton system (Varian Medical Systems, Palo Alto, CA, USA). A cumulative dose of 70-74Gy (RBE) was administrated to the CTV with 3 or 4 beams, in 35-37 fractions. Acute toxicity was scored weekly during the treatment, at the end of the treatment, and 3 months after the end of the treatment according to the CTCAE v4.0 scale. Results Four male and 8 female patients, 9 with chordoma and 3 with chondrosarcoma of the skull base were included. Nominal coverage of the high dose CTV was 97.83%, and 95.2% in the voxel wise minimum dose distribution. Plan optimization was mostly performed for the brainstem surface and core, and for the spinal cord surface and core. (Table 1) Evaluation CT scans during the treatment were made in eleven patients; nine patients had more than 3 evaluation CT scans, one patient had 2, and one patient had 1 evaluation CT scan. A total of 4 plan adaptations were made. Middle ear inflammation, dry mouth, radiation dermatitis, taste disorder, speaking disorder, and/or alopecia of grades 1-3 were noted at the end of the treatment among 6 patients without similar complaints at the inclusion. (Tabel 2) However, these symptoms disappeared 3 months following the treatment. Only for one patient dry mouth and alopecia complaints were still present 3 months after the treatment. One patient developed a temporary grade 4 hearing impairment at the end of treatment. Three months following the treatment one patient developed grade 1 hearing impairment and one patient developed grade 2 dry eye. Conclusion CKFRT is an effective primary treatment for patients with cerebral AVMs with a low hemorrhage risk. PO-1158 Single-institution clinical experience using robust IMPT in skull base chordoma and chondrosarcoma V. Miladinovic 1,2 , Y. Klaver 1,2 , S. Krol 1,2 , M. Kroesen 2 , B. Verbist 3,4 , S. Habraken 5,2 , I. Coremans 1,2