ESTRO 38 Abstract book

S30 ESTRO 38

V 20Gy (p<0.01). Moreover, CPAP decreased the intersection between whole heart and PTV volumes (p<0.01) and resulted in lower dose to heart (p<0.01), whole coronary arteries (p<0.01), left ventricle (p<0.01) and aortic valve (p<0.01). Breast V 4 was similar for FB and CPAP (p=0.20). Dose parameters are reassumed in the table. Significant lower RR for CAD (p<0.01) and CHF (p<0.01) were observed for CPAP, with a mean 22% and 8% risk reduction, respectively. LAR for lung cancer was lower with CPAP (p<0.01), while LAR for second breast cancer was similar for CPAP and FB (p=0.81). and V 5Gy

remission. Median OS for all patients was 75 months (1.64- 78.5). Median OS for patients with relapsed/progressive disease was 13 months (1.64-74.5). Deauville score (DS) prior to RT was predictive of relapse risk. 5/9 patients (55.6%) with DS 5 post chemotherapy have relapsed/progressed compared to 8/32 (25%) of those with DS 4. Response assessment PET-CT scans after RT were performed in 38/41 (92.6%) patients. 18 patients (47.4%) achieved a complete metabolic response (DS 2 or 3), 10 (26.3%) a partial metabolic response (DS 4) and 10 (26.3%) had DS 5. 9/10 (90%) patients with DS 5 post RT have clinically progressed. Only 1/10 (10%) patients with DS4 post RT has progressed. Conclusion Our experience suggests that the majority of patients with an incomplete metabolic response, will not relapse following radiotherapy to the PET positive site. Relapses/progressions were more common in patients with Deauville Score 5 at end of chemotherapy, but a proportion can be successfully salvaged by RT. OC-0067 Continuous Positive Airway Pressure (CPAP): an innovative respiratory gating in lymphoma patients M. Levis 1 , P. Solidoro 2 , S. Bartoncini 1 , E. Gallio 3 , F.R. Giglioli 3 , V. De Luca 4 , L. Focaraccio 2 , C. Cavallin 4 , G.C. Iorio 4 , R. Parise 4 , C. Palladino 4 , V. Di Martino 4 , G. Furfaro 4 , G. Rovere 2 , A. Mattei 2 , R. Ragona 4 , U. Ricardi 4 1 A.O.U. Città della Salute e della Scienza, Radiation Oncology, Torino, Italy ; 2 A.O.U. Città della Salute e della Scienza, Pulmonology, Torino, Italy ; 3 A.O.U. Città della Salute e della Scienza, Medical Physics Unit, Torino, Italy; 4 University of Turin, Department of Oncology, Torino, Italy Purpose or Objective Respiratory gating techniques, as deep inspiration breath holding (DIBH), are strongly encouraged for lymphoma patients with mediastinal involvement in reason of their ability in reducing the dose to normal tissues and to minimize the risk of long term complications. With this background, we aimed to investigate the potential role of Continuous Positive Airway Pressure (CPAP), as an alternative to DIBH, by comparing this innovative respiratory gating with free-breathing (FB) approach in Hodgkin lymphoma (HL) and primary mediastinal lymphoma (PMBCL) patients treated with an optimized volumetric arc therapy (VMAT) solution. Material and Methods After institutional review board approval, 23 patients (9 males and 14 females; mean age 28 years, range 16-38) affected with mediastinal HL (18) or PMBCL (5) were included. All patients underwent computed tomographic simulation twice: with FB and with CPAP. The CPAP pressure used was 18 cm H 2 O for each patient. Median prescription dose to the PTV was 30 Gy in 2-Gy fractions (range 30-40 Gy). Lungs, female breasts, heart and cardiac structures (coronary arteries, valves, atria and ventricles) were all contoured as organs at risk and included in the optimization process of the same VMAT solution in FB or with CPAP for each patient. Maximum and mean dose were compared for all organs and CPAP was used during treatment if judged beneficial. Second breast and lung cancer risks were estimated by calculating the lifetime attributable risk (LAR). Coronary artery disease (CAD) and chronic heart failure (CHF) risks were estimated by calculating the relative risk (RR). CAD risk was derived from the mean dose received by the sum of coronary arteries, while CHF was derived from the mean dose received by the left ventricle, as recently published. Results CPAP was well tolerated by all patients. Only one had no benefit from the addition of CPAP and received treatment in FB. CPAP increased mean lungs volume (4.21 vs 2.71 liters, p<0.01) and significantly reduced both lungs

Conclusion In this pilot study, we first demonstrated the contribution of CPAP to a reduction in lungs and heart structures dose, with a significant impact on long term complications. CPAP was well tolerated, simple to implement, reproducible and does not require breath-holding. In our opinion, CPAP should be further implemented as a novel strategy for motion management and respiratory gating in lymphoma patients. OC-0068 MR-guided adaptive radiotherapy for intra- abdominal lymphoma F. Spoelstra 1 , P. Cobussen 1 , M. Palacios 1 , A. Bruynzeel 1 , F. Lagerwaard 1 , B. Slotman 1 , S. Senan 1 1 VU University Medical Center, Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective Radiotherapy for intra-abdominal lymphoma may be impaired by geographic misses arising from variations in gastric filling, bowel movement, or respiratory motion. Larger PTV margins are therefore used, resulting in