ESTRO 38 Abstract book

S181 ESTRO 38

syndrome (6%). At last F-UP (median 70.8 mo, 14.3-207.9) 5 mild (30%), 1 moderate restrictive (6%) and 1 mild obstructive syndrome (6%) were recorded. No EF pathological reduction were observed. Mean trend of most significant PFTs (FVC, FEV1, DLCO) showed a ripid decline after BuMel-ASCT, reaching the lowest values (< 80% of basal value) after TLI, and they recovered gradually up to 90% of basal value over time. Only 1 reversible G2 interstitial pneumopathy was detected after BuMel-ASCT. Conclusion The combined strategy of BuMel-ASCT and TLI for treatment of lung and metastatic ES children seems to not compromise pulmonary and cardiac functions, demonstrating an acceptable toxicity profile. Neverthless, is mandatory to stricly and regularly assess pulmonary function before and after BuMel-ASCT to identify pts possibly ineligible for TLI, and during the F-UP. PV-0365 Adoption of expansion margins to reduce the dose received by coronary arteries in lymphoma patients V. De Luca 1 , S. Bartoncini 2 , M. Levis 1 , E. Gallio 3 , C. Cavallin 1 , G.C. Iorio 1 , R. Parise 1 , C. Palladino 1 , F.R. Giglioli 3 , C. Fiandra 3 , U. Ricardi 1 1 University Of Turin, Department Of Oncology- Radiation Oncology, Turin, Italy ; 2 A.O.U. Citta' Della Salute E Della Scienza Di Torino, Department Of Oncology- Radiation Oncology, Turin, Italy ; 3 a.O.U. Citta' Della Salute E Della Scienza Di Torino, Medical Physics Unit, Turin, Italy Purpose or Objective Many studies have demonstrated a linear correlation between the heart dose and the risk of coronary artery disease in lymphoma patients receiving mediastinal radiotherapy (RT). In order to reduce long term ischemic events, a detailed contouring of cardiac structures - particularly of coronary arteries (CA) – is needed. Anyway, heart motion impacts on the precise estimation of the dose received by small volumes as CA. An isotropic margin (PRV) for CA may compensate the uncertainties due to their displacement during the heart cycle. In this study, we aimed to evaluate the potential dosimetric benefit obtained by the coronary tree with the optimization of the treatment plan on each PRV volume rather than just on CA volumes. Material and Methods We enrolled fifteen patients (mean age 30, range 16-54) affected with Hodgkin lymphoma or primary mediastinal B cell lymphoma (4 males and 11 females) with high prevalence of bulky presentation at baseline (13/15 patients: 87%). Median prescription dose to the PTV was 31 Gy (range 24-40). The following CA were contoured as organs at risk (OARs): left main trunk (LM), left anterior descending artery (LAD), left circumflex artery (CX) and right coronary artery (RC). We designed a dedicated PRV for each CA by applying an isotropic margin of 3 mm to LM, 4 mm to CX and 5 mm to LAD and RC, as suggested by a recent publication (Fig. 1).

We then compared two care plans, either optimized on the original OARs (CA) or on their dedicated PRV in order to test potential dosimetric benefit conferred by the integration of PRV in the optimization process. Similar PTV coverage was deemed mandatory to proceed with the planning workflow. We included only those CA that were located in the close proximity of the target of treatment; we thus evaluated 33 CA and their relative PRVs. Seven patients (47%) had 3 CA, 4 (27%) had 2 CA and the remaining 4 (27%) had only 1 CA close to the PTV. Maximum and mean doses (Dmax and Dmean) were estimated for all the structures and were then compared with t-Student Test. Results The plan optimization on PRVs shows a significant dosimetric benefit, both in terms of Dmax and Dmean, for the CA volumes, with a mean dose reduction of 20% for Dmax (12.3 vs 15.4 Gy, p<0.05) and of 16% for Dmean (6.8 vs 8.1 Gy, p<0.05). Moreover, we obtained a significant dosimetric gain also for the PRV volumes: in fact, we observed a mean dose reduction of 15,5% for Dmax (18.0 vs 21.3 Gy, p<0.05) and of 15,3% for Dmean (7.2 vs 8.5 Gy, p<0.05), respectively (Fig. 2).