Abstract Book

S693

ESTRO 37

1 Institut Curie, Department of Radiotherapy, Paris, France Purpose or Objective Whether the localization of totally implantable venous devices (TIVD) in radiation field is an issue or not remains an unresolved recurrent question. Hence, we aimed to measure the attenuation of TIVD with common energies, and assess the clinical impact of TIVD in radiation volumes in patients with Hodgkin’s Lymphoma. Material and Methods On the first hand, we irradiated a TIVD (Heliosite, Vygon, Switzerland) on radiochromic film with orthogonal beams at a source-axis distance of 100cm with electrons beams of 6, 9 and 12 MeV and with beam of X photons of 4, 6, 10, 15 and 20 MV. On the second hand we reviewed patients treated by radiotherapy in our institution for Hodgkin’s lymphoma in adjuvant or salvage settings. Inclusion criteria included the localization of TIVD in the radiation field and the use of a CT-scan assisted dosimetry. We assessed the type of irradiation, energy used, quality of treatment measured by dosimetric indices and geometric indices and clinical outcomes. In patients treated on both sides of the thoracic wall, we compared the side of the TIVD with the other side. Ultimately, we compared patients treated with 3D conformational radiotherapy (3D CRT) with those treated with helicoidal IMRT (H-IMRT).

(CI) (p<0.0022) and a significantly lower healthy tissue coverage (HCO) (p=0.0008) than 3D CRT. There was not any other significantly differences between H-IMRT and 3D CRT regarding Dmax, Dmean, D near min, D98%, D95%, D90%, D2%, Coverage Index (CO) and Target Coverage (TCO).

Conclusion While TIVD can cause significant beam attenuation in electrons beam, this issue can be solved easily by the use of high energy photons or by creating an exclusion zone around the device in H-IMRT. We recommend a close collaboration between the surgical/anesthetic team and the radiation oncologist for choosing beforehand the site of implantation of the port in relation to anticipated treated areas. EP-1255 Target volume and dose to organs at risk for RT of Hodgkin's disease of adolescents. F.S. Lautenschlaeger 1 , G. Iancu 1 , R. Engenhart-Cabillic 1 , K. Zink 1,2 , V. Flatten 1 , H. Vorwerk 1 , F. Eberle 1 1 Universitätsklinikum Marburg, Klinik für Strahlentherapie, Marburg, Germany 2 Technische Hochschule Mittelhessen, Institut für Medizinische Physik und Strahlenschutz, Gießen, Germany Purpose or Objective Radiotherapy is frequently used in the therapy of lymphoma. Actual studies tried to further reduce the amount of patients treated with radiotherapy resulted so far in worse clinical outcome for the chemotherapy-only cohort. Lymphoma, especially hodgkins disease, often affect rather young patients, the induction of secondary cancers or other long-term adverse effects after irradiation are important issues to deal with. Especially for mediastinal manifestations numerous organs and substructures at risk play a role. The heart, it's coronary vessels and cardiac valves, the lungs, the thyroid gland and, for female patients in addition the mammarial glands are only the most important ones. Proton RT of mediastinal lymphoma can reduce as well the integral body dose as the dose to certain organs at risk. This might reduce the risk of secondary Cancers and other adverse effects. Material and Methods In this work we compared the dose delivered to the heart, it's coronary vessels and valves, the lungs, the thyroid gland and the mammarial glands by VMAT photon plans, 3D-CRT plans and proton plans consisting of one or two fields. All have been calculated for a dose of 28,8 Gy (according EURO-NET-PHL-C2-Study). Data from seven young female patients with mediastinal lymphoma have been evaluated. All investigated cases affected also the lower mediastinum. Target Volumes have been defined by 2-cycles post chemotherapeutic F18-FDG PET-positive areas, following a modified involved node approach. CTVs and PTVs extents were defined according to the EURO- NET-PHL-C2 protocol. For the calculation of the body dose the body-segment between C1 and T12 has been selected. For Plan-Evaluation Conformity- and

Results We found that the beam attenuations behind the TIVD were, with electrons: 79% for 6MeV, 59% for 9MeV, 46% for 12MeV; and with X photons: 9% for 4MV, 8% for 6MV, 5% for 10MV and 15 MV and 3% for 20MV. Between 2007 and 2016, 19 patients met our inclusion criteria. 18 had a stage 2 disease and 1 a stage 3. 7 were treated exclusively on the side of the TIVD and 12 bilaterally. 13 were treated with H-IMRT (6MV photons exclusively) and 6 with 3D CRT (mixed energies of 6, 10, 15, 20MV photons). Mean prescription dose was 31Gy. Acute toxicities did not exceed grade 2. At last news, 15 patients were in complete response, 1 in partial response, 1 in progressive disease, 1 died of other causes and 1 was lost to follow-up. There was not any significant clinical or dosimetric differences between the side of the TIVD and the other side in patients treated bilaterally. H- IMRT resulted in a significantly higher conformity index