ESTRO 37 Abstract book

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ESTRO 37

respectively. The mean (± 1 SD) GI was 3.1 ± 0.49. The target coverage was given higher priority than selectivity and PCI was at least 0.75 for all plans. The GI was < 4 for all cases except for 2 cases, one with PTV = 0.25 cc and the other where 2 mets were adjacent. Figure 1 and 2 shows GI vs. PTV and GI vs. PCI respectively. For small PTVs (diameter < 2 cm), DCA produced better GI than RA. For SRS plans, the mean (± 1 SD) normal brain V 12Gy = 9.94 ± 4.29 cc. The mean (± 1 SD) percentage variation of measured point dose to Eclipse calculated was -2.71 % ± 2.06%. Mean (± 1 SD) gamma pass percentage for film was 96.2 % ± 3.3 %(1 mm, 5 %) and 99.1% ± 1.4 %(2 mm, 5 %).

time between diagnostic MRI (dMRI) and planning MRI (pMRI), changes in dimension and/or number of lesions and time between pMRI and treatment delivery. Results Forty-one patients were identified. Median time between dMRI and pMRI was 28 days. Forty-six percent (n=19) of patients had stable disease on pMRI and 54% (n=22) had significant changes in dimension and/number of lesions. Median time between dMRI and pMRI for these two groups was 23 and 31,5 days, respectively. In 37% (n=17) there was a change in dimension which would lead to suboptimal tumour coverage or overtreatment of normal brain tissue. In 17% of patients (n=7) SRS was not performed: in 1 patient due to the disappearance of the suspicious lesion and in 6 patients due to a substantial increase in the number of lesions. These 6 patients were referred to WBRT. Median time between pMRI and SRS was 2 days. Thirty-four patients with 50 lesions were treated. Conclusion Important tumour changes can occur in a short time leading to suboptimal tumour coverage, overtreatment or geographical miss. Our study emphasizes the need to treat patients based on a planning MRI and to minimize the time between planning and delivery of SRS. EP-1983 Robust DIBH 3D conformal irradiation technique of left sided whole breast + supraclavicular region S. Russo 1 , F. Rossi 2 , M. Esposito 1 , S. Pini 1 , R. Barca 2 , S. Fondelli 2 , L. Paoletti 2 , P. Bastiani 2 1 Azienda USL Toscana Centro, SC Fisica Sanitaria - Firenze, Bagno a Ripoli - Firenze, Italy 2 Azienda USL Toscana Centro, SC Radioterapia- Firenze, Bagno a Ripoli - Firenze, Italy Purpose or Objective The aim of the study was to compare the deep inspiration breath-hold (DIBH) 3D conformal irradiation technique with Free-breathing (FB) 3D conformal and volumetric modulated arc therapy (VMAT) for left sided whole breast + lymph node radiation therapy and to verify the robustness of DIBH delivery Material and Methods An Elekta Synergy linac is used to simulate the treatment of five patients. Three plans were generated in Monaco 5.0 for each patient with FB and DIBH 3D conformal and FB VMAT technique with a dose prescription of 50 Gy in 25 fractions. Plan quality was assessed considering target coverage, sparing of the controlateral breast, the lungs, the heart and the normal tissue. The Wilcoxon test was used for statistical analysis with a significance level of 0.05. Optical surface tracking technologies were used to support the DIBH gated treatments. Prospective gating CT imaging was performed by Sentinel™ (C-RAD Positioning AB, Sweden) laser scanner system and a GE BrightSpeed CT scanner. Base line level and gating window amplitude of the respiratory signal was established during CT simulation procedure. DIBH treatments delivery was gated by the Catalyst™ system (C-RAD Positioning AB, Sweden) connected with an Elekta Synergy linear accelerator (Elekta AB, Sweden) via the Elekta Response™ Interface. Visual coaching through video goggles were provided to help the patient following the optimal breathing pattern. The robustness of DIBH delivery was assessed by set-up verification with electronic portal images (EPID) and intra-fraction monitoring via the optical system. EPID were acquired during the first three treatment fractions and one time week for and compared with the digitally reconstructed radiographs with a maximal acceptable tolerance of 5 mm. Intra-fraction and intra-beam set-up variability were quantified over all the treatment fractions.

Conclusion SRS/SRT planning using DCA or RA with 5 mm MLC adopting above methods can produce plans of quality similar to Gamma Knife or a Linac with 2.5mm MLC. This was corroborated by results from the recent national SRS QA programme in England. Cases involving complex target/OAR geometry will benefit from RA. For PTVs of diameter < 2 cm DCA is preferable. EP-1982 How does time affect radiosurgery treatment planning? J. Fonseca 1 , R. Colaço 1 , E. Netto 1 , G. Fernandez 1 , R. Pocinho 1 , C. Travancinha 1 , M. Labareda 1 , L. Carita 1 , M. Moreno 1 , F. Ribeiro 1 , F. Santos 1 1 Instituto Português de Oncologia de Lisboa Francisco Gentil- EPE, Serviço de Radioterapia, Lisboa, Portugal Purpose or Objective The aim of our study was to determine how changes in brain metastases over time can impact on radiosurgical treatment planning. Material and Methods Retrospective and unicentric study of patients with brain metastases who were evaluated for radiosurgical treatment (SRS) between March 2016 and September 2017. All patients underwent a planning MRI. We analysed