ESTRO 36 Abstract Book

S243 ESTRO 36 _______________________________________________________________________________________________

C. Bonnet 1 , A. Dr Huchet 1 , E. Blais 1 , J. Dr Benech-Faure 1 , R. Dr Trouette 1 , V. Dr Vendrely 1 1 Hopital Haut Leveque, Radiotherapy, Pessac, France Purpose or Objective Advances in intracranial stereotactic radiotherapy have led to high gradient dose between tumor and normal tissue and to dramatically reduced Planning Target Volume (PTV) margins. Accurate definition of the gross tumor volume (GTV) for stereotactic radiotherapy of brain metastases is an essential key for the treatment planning. However, its underestimation due to tumor growth during the delay between planning and stereotactic radiotherapy may lead to treatment failure. Our purpose was to evaluate the tumor growth kinetics and its impact during the delay before treatment of brain metastasis secondary to lung cancer (LC) or melanoma (ML). Material and Methods This retrospective monocentric study included all consecutive patients (pts) treated for brain metastases secondary to LC or ML between June 2015 and May 2016. Margins from GTV to PTV were 2 mm. Imaging at diagnosis of brain metastasis and preplanning imaging were compared; GTV corresponding to the contrast enhancement was analyzed. Linear extrapolation was used to determinate the n minimum theoretical time leading the diameter of the tumor to increase more than 4 mm (T4mm). Results Out of 103 pts treated for brain metastasis by stereotactic radiotherapy, 50 were treated for metastases secondary to LC (n=26) or ML (n=24). Six pts were excluded because of lack of imaging data. Median age was 68 years old (range: 25-92). RPA status was 1 for 1 patient (2%), 2 for 33 pts (79%) and 3 for 8 pts (19%). Systemic treatment was given at diagnosis for 19 pts (45 %). Radiotherapy was delivered according to a monofraction scheme for 8 pts (3 LC and 5 ML metastasis), 3-fraction scheme (23 LC, 18 ML) or 5-fraction scheme (2 LC, 3 ML). A hundred and eight brain imaging (84 MRI, 24 CT-scan) were analyzed. Comparison of imaging at diagnosis and preplanning treatment showed bleeding inside metastasis for one patient with primary LC; increased tumor volume for 40 pts (ML n=25 ; LC n=15) ; stability for 11 pts (ML n=1 ; LC n=10) and decreased volume for one LC patient. Median delay between brain imaging at diagnosis and pretreatment planning were: 28 days (range 8-107) for ML pts and 31.5 days (range 7-70) for LC pts. Median Volumes of GTV at diagnosis were 0.5 cm3 (range 0.05-8.6cm 3 ) for ML pts and 0.45cm 3 (range 0.05-6.1cm 3 ) for LC pts; median volumes of preplanning treatment GTV were 1.55 cm 3 (range: 0.2-9.9cm 3 ) for ML pts and 0.85 (range 0.2- 10.4cm 3 ) for LC patients. Linear extrapolation revealed a median increase of tumor volume of 0.16 cm3/wk (range 0-0.8 cm3/wk) for ML and 0.06 cm3/wk (range 0-0.5 cm3/wk) for LC. Shorter T4mm was 15 days for ML patients and 17 days for LC pts. Conclusion Maximal delay for treatment appeared to be 15 days for ML patients and 17 days for LC patients to ensure that tumor radius has grown less than to 2 mm. Above this delay, clinicians should reconsider planning of treatment. PV-0458 FMECA of Cyberknife process: two years’ experience for improvement S. Cucchiaro 1 , D. Dechambre 1 , T. Massoz 1 , N. Gourmet 1 , D. Boga 1 , N. Jansen 1 , P. Coucke 1 , M. Delgaudine 2 1 C.H.U. - Sart Tilman, Radiotherapy Departement, Liège, Belgium 2 C.H.U. - Sart Tilman, STA Quality Departement, Liège, Belgium Purpose or Objective Failure Modes Effects and Criticality Analysis (FMECA) is a risk analysis allowing the identification of causes and

Purpose or Objective The objective was to study the differences in target coverage and dose-volume parameters for heart and lung between Deep Inspiration Breath Hold (DIBH) 3D Conformal Radiation Therapy (3D-CRT), DIBH Volumetric Modulated Arc Therapy (VMAT) and free breathing Intensity Modulated Radiation Therapy (IMRT) in patients treated with synchronous bilateral breast cancer. Material and Methods This planning comparative study was conducted in nine patients previously treated for synchronous bilateral breast cancer. These patients were treated with either DIBH 3D-CRT or IMRT in free breathing. All patients were treated with whole breast irradiation and those requiring a boost were given a simultaneously integrated boost (SIB). Three treatment plans were constructed for each patient individually; a DIBH 3D-CRT plan, a DIBH VMAT plan and an IMRT plan in free breathing. DIBH IMRT is clinically not feasible due to the extended duration of treatment. Three patients were treated without a boost, three were treated with unilateral SIB and the remaining patients were treated with double sided SIB. DIBH 3D-CRT plans were created using tangential fields for both breasts and up to three boost fields for each breast, if a boost was required. IMRT plans were created using 14 fields around the patient, 24° apart, covering both breasts and simultaneously covering the boost target in one or both breasts. DIBH VMAT plans without boost targets were created using eight 30° arcs, four on each side, oriented in a tangential design. Four 60° arcs, in a tangential design, were used in patients with boost targets, two for each breast, with an additional semi-circle arc on either side covering the boost targets. The parameters reviewed were V95% (percentage of volume receiving 95% of the prescription dose) PTV1 and PTV2 coverage, with PTV1 being the elective target and PTV2 the boost target, the mean heart dose and heart left ventricle V5 (percentage of volume receiving 5 Gy), mean lung dose, lung V5 and lung V20. The parameters were compared using the paired T-test for normally distributed data and the Wilcoxon signed rank-test for not normally distributed data. Three statistical analyses were performed on each parameter, therefore the Bonferroni correction was applied. P ≤0.016 was considered statistically significant in this study. Results Target coverage of PTV1 and PTV2 were comparable between the three techniques (table 1), except the V95% PTV1 left. All dose volume parameters of the heart and lung were lower for the DIBH VMAT technique (table1) in comparison with the DIBH 3D-CRT and free breathing IMRT technique.

Conclusion DIBH VMAT is the most optimal radiation technique in the treatment for patients with synchronous bilateral breast cancer. Both PTV coverage and the sparing of the organs at risk give better results for DIBH VMAT in comparison with DIBH 3D-CRT and IMRT in free breathing. PV-0457 Delay between planning and stereotactic radiotherapy for brain metastases: margins still accurate?