ESTRO 37 Abstract book

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ESTRO 37

with hypoxic tumour. Menadione decreased the surviving fraction of cells treated with radiation under hypoxia but had no effect on normoxic cells. Gemcitabine decreased the surviving fraction of cells treated with radiation under normoxia and hypoxia. Gemcitabine was a more effective radiosensitiser in hypoxia compared to normoxia. Conclusion Targeting tumour hypoxia in prostate cancer patients could enhance tumour radiosensitivity and improve patient response and outcomes. The QUADrATiC connectivity mapping software was used to identify FDA approved small molecule compounds which could be effective against hypoxic prostate cancer cells. Preliminary results have identified menadione and gemcitabine as potential radiosensitisers in the setting of hypoxic prostate cancer. OC-0383 Reduced cardiac risk in Hodgkin lymphoma patients treated with a full arc VMAT compared to b- VMAT M. Levis 1 , A.R. Filippi 2 , C. Fiandra 1 , V. De Luca 1 , D. Vella 3 , S. Bartoncini 1 , R. Ragona 1 , U. Ricardi 1 1 University of Torino, Radiation Oncology, Torino, Italy 2 San Luigi Gonzaga Hospital- University of Torino, Radiation Oncology, Orbassano, Italy 3 Sir Anthony Mamo Oncology Centre, Radiation Oncology, Msida, Malta Purpose or Objective With the aim of assessing the dosimetric profile and the associated risk of developing second cancers and coronary artery disease (CAD), we tested two different volumetric arc therapy (VMAT) solutions, specifically optimized for mediastinal lymphoma presentations, among a cohort of patients treated with involved-site radiation therapy for mediastinal Hodgkin’s lymphoma (HL). Material and Methods Thirty patients affected with mediastinal Hodgkin’s lymphoma (15 males and 15 females) were included. Disease extent was mediastinum plus neck (n=10, 33%), mediastinum plus unilateral axilla (n=10, 33%) and mediastinum alone with bulky presentation (n=10, 33%). Prescription dose to the PTV was 30 Gy in 2-Gy fractions. The 'so-called” butterfly VMAT (b-VMAT) solution, consisting in non-coplanar multi-arcs, was compared with a full–arc VMAT (fa-VMAT; 360° coplanar plus a 60° no- coplanar VMAT arcs) approach. Lungs, female breasts, whole heart and heart sub-structures (coronary arteries, valves, atria and ventricles) were all contoured as organs at risk (OAR) and included in the optimization process. Maximum and mean dose were compared for all organs; second breast and lung cancer risks were estimated by calculating the lifetime attributable risk (LAR), using the LAR ratio (LAR b-VMAT -to- LAR fa-VMAT ) as a comparative measure. CAD risk was estimated by calculating the relative risk (RR), derived from the mean dose received by the sum of coronary arteries. The figure shows the three different anatomical presentations of the thirty patients included in this study. Proffered Papers: CL 7: Hematological Malignancies/Sarcoma/Palliation

Results fa-VMAT resulted in lower dose to whole heart (p = 0.0028), whole coronary arteries (p = 0.0001), left ventricle (p = 0.007), aortic valve (p = 0.0004) and in lower V 20Gy to the lungs (p = 0.008). Conversely, b-VMAT resulted in lower mean dose (p = 0.033) and V 4Gy (0.04) to the female breasts. Dosimetric parameters are reassumed in the table. A significant lower RR for CAD was observed for fa-VMAT, with a mean 20% risk reduction (p = 0.0002); the entity of dose reduction was marginally higher for patients with bulky disease (25% vs 15%, p = 0.06). Despite these dosimetric differences, LAR ratio for breast cancer (p = 0.146) and lung cancer (p = 0.148) were not statistically different between fa-VMAT and b-VMAT, respectively, regardless of gender and anatomic presentation of disease.

Conclusion Among a heterogeneous cohort of mediastinal HL patients, reflecting the most frequent clinical presentations, an innovative fa-VMAT planning solution, compared to b-VMAT (both optimized for multiple organs at risk according to specific lymphoma dose constraints), significantly decreased the RR for CAD, particularly in bulky presentations, with similar second breast and lung cancer risks. OC-0384 Relationship of mean heart dose and cardiac substructure dose over evolving radiation techniques in Hodgkin lymphoma B. Hoppe 1 , N.P. Mendenhall 1 , J.E. Bates 1 , C.G. Morris 1 , S. Flampouri 1 1 University of Florida College of Medicine, Radiation Oncology, Jacksonville, USA