Abstract Book

S1239

ESTRO 37

while the 3D CRT technique is preferable to reduce breast low doses. Our study describes a novel IMRT template for early stage HL that delivers less dose to organ at risk than standard five fields equally spaced over 360° IMRT templates and 3D CRT techniques. Material and Methods The new template is a Sectorial Sliding Window (SSW) IMRT and consists of five fields spreading over a 100- degree sector, depending on Planned Target Volume (PTV) localization. Eleven females and four males with early stage Hodgkin’s Lymphoma diagnosis and PTV involving bilateral neck and mediastinum were treated with SSW template. On the same patients, a 3D-conformal plan and a standard 5- fields equally spaced 360° IMRT were also conformed. The target coverage was at least 95% of prescription dose (30.6 Gy in 1.8 Gy daily fractions) to 95 % of volume in all the three techniques applied. Results V 20 values for lungs and heart mean doses were lower in Dose Volume Histograms (DVH) obtained with SSW IMRT respect to both standard IMRT and 3D CRT techniques. V 5 values for breast resulted the lowest in 3D CRT plans, but the new SSW IMRT template showed a lower V 5 value compared to standard IMRT template: the mean volume difference for all patients was about 8%. Conclusion The results of the study confirmed the superiority of IMRT techniques in sparing normal tissues and the superiority of 3D CRT in sparing breast low doses in patients with Hodgkin’s Lymphoma. The new SSW template can be applied to treat target with different size, shape and anatomical position; our study shows that SSW template is able to deliver less dose to lungs, heart and breast respect to standard 5- fields equally spaced 360° IMRT techniques . Futhermore, the breast dose reduction could potentially reduce the risk of secondary malignancy in young patients. EP-2368 Dosimetric comparison between 3D-CRT and VMAT planning techniques in esophageal carcinoma. R. Pujol Badia 1 , J. Garcia-Miguel Quiroga 1 , M. Parcerisa Torne 1 , A. Ramirez Muñoz 1 , D. Amat De Los Angeles 1 , A.B. Lopez Muñoz 1 , G. Frontera Sola 1 , M. Colomer Truyols 1 , R. Gomez Pardos 1 , E.M. Ambroa Rey 1 , D. Navarro Gimenez 1 1 Consorci Sanitari de Terrassa CST, radiation oncology, TERRASSA, Spain Purpose or Objective Achieving a good coverage of the PTV at the same time as the constraints for organs at risk are accomplished is often challenging in the case of esophageal carcinoma. With the introduction of techniques such as VMAT, highly conformal dose distributions can be achieved. The aim of this work is the comparison of 3D-CRT and VMAT treatment planning analyzing the dosimetric data for PTV and organs at risk obtained from the DVH. Material and Methods 6 patients with esophageal carcinoma (4 of which had been treated with 3D-CRT and 2 of them with VMAT) were retrospectively planned using two different techniques: VMAT and 3D-CRT. Different locations in the esophagus were considered (proximal, middle and distal). 3D-CRT treatments were planned using 3 or 4 fields and VMAT treatments were planned using 2 arcs, one clockwise and one counterclockwise. All treatments were normalized so that the mean dose of the PTV was the prescription dose, which was 45 Gy in 25 fractions, in all cases. The restrictions considered for the

organs at risk were those used in our clinical practice: V25<10% for heart and V20<20%, V10<40% for lung. Different DVH values were analyzed and compared for both techniques: D98, D2 and V95 for the PTV; V25 and mean dose for the heart and V20, V10 and V5 for the lung. Results Dosimetric results obtained from the DVH for both techniques are summarized in Table1.

An improvement in PTV coverage with VMAT technique can be seen while dose maximum is reduced with respect to 3D-CRT. D98 and V95 were greater for VMAT in 4 out of 6 patients and D2 was reduced for all cases when VMAT planning was used. Regarding to organs at risk, we observed that heart doses were significantly reduced when treatments were planned using VMAT instead of 3D-CRT. In 3 out of 6 patients it was not possible to accomplish the V25<10% constraint due to the location and extension of the PTV, but in all cases there was a considerable reduction of V25 for VMAT with respect to 3D-CRT. In the case of the lung, great reductions were observed in the V20 values obtained with VMAT, accomplishing the V20<20% constraint in all cases (even in those where it wasn’t achieved with 3D-CRT). For low doses (V10 and V5) we observe larger irradiated volumes when VMAT was used, especially for V5, which was worse for all patients. Conclusion Based on the results obtained, we can say that a better and more homogeneous PTV coverage is obtained with VMAT, while a significant reduction in heart doses and lung V20 is observed. This fact makes VMAT a better technique for treatment planning of this pathology. However, an increment in the volume of lung irradiated with low doses is also produced, especially in those cases with a very large PTV, so an individualized analysis for each case is recommended. EP-2369 Dosimetric impact of imaging modality (CT versus MRI) for cervical cancer radiotherapy S. Burke 1 , V. Batumalai 1,2,3 , K. Lim 1,2 , D. Roach 2 , G. Dinsdale 1 , L. Mahoney 4 , M. Jameson 1,2,3 , C. Ochoa 1 , J. Veera 5 , L. Holloway 1,2,3 , S. Vinod 1,2 1 Department of Radiation Oncology, South Western Sydney Local Health District, New South Wales, Australia 2 South Western Clinical School, University of New South Wales, New South Wales, Australia 3 Ingham Institute of Applied Medical Research, Medical Physics, New South Wales, Australia 4 Faculty of Health, University of Newcastle, New South Wales, Australia 5 Department of Radiation Oncology, Peter MacCallum Cancer Centre, Victoria, Australia Purpose or Objective The use of magnetic resonance imaging (MRI) is becoming more prevalent in cervical cancer external beam radiotherapy (RT). To our knowledge, no planning study has been conducted to evaluate the dosimetric implications of imaging modality for cervical cancer RT.