A.215 BIOLOGICAL TARGET VOLUME SEGMENTATION FOR RADIOTHERAPY TREATMENT PLANNING A. Stefano * ,a,b , S. Vitabile c , G. Russo a,d , D. D’Urso a,e , M. Ippolito d , F. Marletta d , M.G. Sabini d , I.V. Patti d , S. Pittera d , D. Sardina d , O. Gambino b , R. Pirrone b , E. Ardizzone b , M.C. Gilardi a . a Istituto di Bioimmagini e Fisiologia Molecolare – Consiglio Nazionale delle Ricerche (IBFM-CNR), Cefalù, Italy; b Dipartimento di Ingegneria Chimica, Gestionale, Informatica, Meccanica (DICGIM), Università degli Studi di Palermo, Palermo, Italy; c Dipartimento di Biopatologia e Biotecnologie Mediche (DIBIMED), Università degli Studi di Palermo, Palermo, Italy; d Azienda Ospedaliera Cannizzaro, Catania, Italy; e Università degli Studi di Catania, Catania, Italy Introduction: The CT gross tumor volume (GTV) is the gold standard for target tumor delineation in head and neck cancer (HNC) radio-treatments (RT). Nevertheless, CT images may not show the viable extension of tumors. Vice versa, FDG-PET provides functional information, offering the oppor- tunity to radically change the patient treatment. In RT, within or without the GTV, it is possible to define the biological target volume (BTV) on PET image and to apply it to plan the radiotherapy treatment. BTV delinea- tion is challenging because of the low spatial resolution and high noise level in PET images. For these reasons, BTV varies substantially depending on the algorithm used. In this study, a fast, accurate, and scanner indepen- dent BTV segmentation method is proposed. Materials and Methods: The Random Walks (RW) method provides a target recognition in images in which the start seeds are specified by the user. An enhanced RW algorithm with automatic seed detection and with an adaptive probability threshold value, instead of the fixed one of the orig- inal RW method, is introduced. The proposed method has the benefit to make the algorithm not subjective and to take into account the intensity changes between slices along the tumor volume. Phantom experiments are performed to estimate the BTV segmentation accuracy. The same algo- rithm is then applied in 15 HNC patients to assess its clinical feasibility. BTV changes between pre and post RT are also evaluated. Results: High dice similarity coefficients (>85%) and true positive volume fractions (>87%), and low Hausdorff distance values (<3 mm) confirm the method accuracy. In addition, the method has real-time performance (0.3 sec) and it meets the physician’s requirements in a RT environment. Conclusions: The proposed method is very powerful in terms of BTV seg- mentation and time performance, and it may be used daily as a medical decision support system to enhance the current methodology performed by healthcare operators in RT. http://dx.doi.org/10.1016/j.ejmp.2016.01.219 A.216 A NEW 3D RADIOTHERAPY TECHNIQUE REDUCES SKIN TOXICITY FOR LARGE BREAST AND/OR HIGH BMI PATIENTS G. Stimato *, D. Gaudino, C. Di Venanzio, A. Mameli, E. Infusino, L. Bellesi, E. Ippolito, S. Silipigni, C. Rinaldi, R. D’Angelillo, S. Ramella, L. Trodella. Universita’ Campus Biomedico di Roma, Rome, Italy Introduction: The aim of this study was to develop an alternative 3DCRT standardized fields class solution for whole breast radiotherapy in pa- tients with large/pendulous breasts and/or high body mass index (BMI) to improve dose homogeneity and reduce hot spots and extra-target dose irradiation. Materials and Methods: Two treatment plans (tangential fields-TF and standardized five fields-S5F) were generated for patients with large breasts (PTV > 1000 cc and/or BMI > 25 kg/m 2 ), supine positioned. S5F plans consist of two wedged tangential beams, AP: 20° for right breast and 340° for left and PA: 181° for right breast and 179° for left. A field in field in medial-lateral beam and additional fields were added to reduce hot spot areas and extra-target irradiation and to improve dose distribu- tion. The total prescribed dose was 50 Gy/25 die. V95% PTV, V105% PTV, Dmax PTV, homogeneity index (HI) and conformity index (CI) were recorded. An opposite normal tissue structure (Body-PTV) was gener- ated. V105%, V107%, V5 Gy LUNG, V20 Gy LUNG, V40 Gy LUNG, V50 Gy LUNG, Dmax LUNG, V5 Gy HEART, V15 Gy HEART, V25 Gy HEART and Dmax HEART were recorded. Statistical analysis were performed using SYSTAT, v.12.0 (SPSS, Chicago, IL). Results: 38 patients were included in the analysis. S5F improved HI (8.4 vs. 10.1; p ≤ 0.001) and Dmax PTV and V105% PTV were significantly reduced, while CI and V95% PTV were not. However, the constraint V95% PTV > 95% was achieved for all S5F plans, not for TF. The extra-target tissue irradia- tion was significantly reduced using S5F for V105% (cc) and V107% (cc). These reductions were of particular interest because the difference in tissue ir- radiation was very high (46.6 cc vs 3.0 cc, p ≤ 0.001 for V105% and 12.2 cc vs 0.0 cc, p ≤ 0.001 for V107% for TF and S5F plans, respectively). No dif- ferences in lung and heart dosimetric parameters were recorded. Conclusion: S5F technique allows treatment of patients with large breasts or high BMI, increasing HI, decreasing Dmax PTV and by a factor of 15 hot spots in extra-target tissues. http://dx.doi.org/10.1016/j.ejmp.2016.01.220 A.217 IMPLEMENTATION OF A NEW STRATEGY FOR DOSE TRACKING AND OF NOVEL RADIOBIOLOGICAL MODELS FOR ADAPTIVE RADIOTHERAPY S. Strolin * ,a , E. Mezzenga b , A. Sarnelli b , V. Bruzzaniti a , S. Marzi a , S. Ungania a , G. Sanguineti a , L. Marucci a , M. Benassi b , L. Strigari a . a Istituto Nazionale Tumori Regina Elena, Roma, Italy; b Istituto Scientifico Romagnolo per lo Studio e la Cura dei Tumori IRST IRCCS, Meldola, Italy Introduction: The feasibility of the dose tracking approach in Head-and- neck (HN) cancer was tested by implementing and comparing two deformable image registration strategies. Material and Methods: For each of 15 patients with diagnosed Head-and- neck (HN) cancer a planning CT (pCT) and a total of 6 weekly CT (wCT) were acquired at our institute. The pCT, wCT, manually contoured structures and dose distributions were imported in Raystation TPS. Two approaches were implemented, both using the hybrid algorithm for region of interest (ROI) mapping. In the first approach (RH), the body contour was considered as focus ROI while manually contoured GTV, parotid gland and spinal cord were used as controlling ROIs. The second method (H) considers the body contour as focus ROI, without including any controlling ROIs in the anal- ysis. DICE similarity index was used to assess the agreement of propagated contours between the two approaches. Dose/volume statistics and radio- biological indices were computed and compared. Results: The RH approach provided the best results, with median DICEs values of 0.88, 0.94 and 0.94 for GTVs, parotid gland and spinal cord, re- spectively. The corresponding values in H strategy were 0.63, 0.82 and 0.88, respectively. Dose differences on GTVs showed a median variation within 1% with minimal values up to 8%; tumor control probability values for planned, RH and H approach were 63.7%, 69.7% and 61.9%, respectively. The average normal tissue complication probabilities in planned, RH-based and H-based accumulated dose-volume histograms (DVHs) were 36%, 46% and 34%, respectively, for homo-lateral parotids and 28%, 36% and 27% for contra- lateral parotids. Conclusion: The RH strategy generates structures with higher similarity to manually contoured ROIs thus proving the good accuracy of the gener- ated deformation matrix. This approach gives an appropriate strategy to perform dose tracking in HN cancer patients eligible for adaptive radiotherapy. http://dx.doi.org/10.1016/j.ejmp.2016.01.221 A.218 EVALUATION OF THE AUTOSEGMENTATION TOOL OF NORMAL TISSUE STRUCTURES IN PROSTATE CANCER: A MULTICENTRIC STUDY S. Strolin * ,a , L. Strigari a , V. Bruzzaniti a , S. Ungania a , R. Nigro b , S. Riccardi b , M. Casale c , A. Tonnetti d , M.T. Russo e , L. Chiatti e , R. Cassese b , N. Franza d . a Istituto Nazionale Tumori Regina Elena, Roma, Italy; b OGP S. Camillo de Lellis, Rieti, Italy; c Azienda ospedaliera Santa Maria, Terni, Italy; d Dosimetrica, Italy; e Ospedale Belcolle, Viterbo, Italy Introduction: In the treatment planning process, manual delineation of organs at risk (OARs) is tedious and time consuming. The aim of this study was to evaluate and clinically validate the feasibility and time saving of the autosegmentation algorithm of the prowess treatment planning system (TPS) using computed tomography (CT) images. e64 Abstracts/Physica Medica 32 (2016) e1–e70