ESTRO 38 Abstract book

S1001 ESTRO 38

and the bowel were 36.75Gy 3

, 27.87 Gy 3

and 66.41cc;

30.36 Gy 3 and 119.48cc, respectively. The median accumulated D max of the spinal cord was 6.42 Gy 3 . The median cumulative D mean and D 2/3 of the left and right kidney were 4.62 Gy 3 and 3.03 Gy 3 ; 2.67 Gy 3 and 2.10 Gy 3 , respectively. The median cumulative D mean and D 50% of the liver was 4.28 Gy 3 and 3.03 Gy 3 , respectively. The median summed dose to the radiation field was 93.38 Gy 3 . No grade 3-4 toxicity occurred. Partial response and a stable disease to the second irradiation was found in 4 and 33 patients. Conclusion The cumulative doses to OAR as dose constraints were acceptable and safe, which could be used as a reference in the decision for re-irradiation with SBRT after prior SBRT for pancreatic cancer but required further validations with radiobiological models in cohorts. EP-1845 Proton beam therapy vs best photons for the management of mediastinal Hodgkin lymphoma: step by step L. Abbassi 1 , F. Goudjil 1 , A. Arsène-Henry 1 , M. Amessis 1 , R. Dendale 1 , Y.M. Kirova 1 1 Institut Curie, Département Oncologie-Radiothérapie, Paris, France Purpose or Objective Reducing treatment-related toxicity among survivors of Hodgkin lymphomas (HL) has been the cornerstone of recent advances in the treatment of hematologic malignancies. The purpose of this presentation is to describe the practical procedure inspired by the recently published ILROG Guidelines of treatment decision, preparation and treatment, illustrated with the presentation of the first reported case of localized HL treated with Protontherapy (PT) in Europe. Material and Methods We present the case of 24 years old female patient with a mediastinal Bulky localized mixed cellularity classic HL who required an Involved-Site Radiation Therapy (ISRT) after complete response acquired with polychemotherapy. The 3D conformal radiotherapy (RT) was not acceptable due to high doses to breasts, heart and lungs. The first step was realizing a 4D CT-scan to evaluate target movements and another one with respiratory control (gating and breath-hold technique) by spirometer. Step 2: Delineation was realized on the 4D CT-scan as well as on the deep inspiration breath-hold CT-scan after images registration between initial PET-scan and the CT in treatment position, for photon RT and PT respectively. CTV/ITV and organs at risk (OAR) were delineated the same way for both technics, following ILROG Guidelines. Step 3: Realization of 2 dosimetric plans: one with rotational intensity modulated radiation therapy (IMRT) with a Helical Tomotherapy (HT) with the Tomotherapy Treatment Planning System (TPS) and one with conformational PT with Eclipse TPS. Results The step 4 consisted of the choice of the best plan treatment for this patient after discussion between 2 senior radiation oncologists with comparison of the treatment volume coverage and evaluation of doses to OAR. Step 4a: volume coverage was good with 95% of PTV covered by 98% and 99% of the prescribed dose with PT and HT, respectively. Step 4b: sparing of OAR was better with PT for lungs, in terms of the mean dose (3.7Gy vs 8.4Gy), median dose (0.002Gy vs 6.9Gy) and low dose (V5 Gy = 17.8% vs 54.18%). Mean dose to the heart was higher with HT (3.7Gy) compared to PT (2.6Gy). Breast sparing was better with PT, with a mean dose of 2.4Gy to the right breast and 1.9Gy to the left breast versus 4.4Gy and 4.6Gy. Total dose chosen was 30Gy in 15 fractions of 2Gy with PT with direct anterior field using Pencil Beam Scanning (PBS). Step 5: Treatment delivery and follow-up during PT. We observed only grade 1 skin erythema, no , 22.13 Gy 3 and 18.66cc; 35.76 Gy 3 , 28.06 Gy 3

Conclusion Actual MF values for BCW positive correlations with the gantry period, which indicates the treatment time could be potentially reduced by decreasing the planned MF value. Proper range of planned MF was present for HN, thorax, ABD, brain and pelvis regions based on the clinical data in our center. EP-1844 Re-irradiation with SBRT for pancreatic cancer: dose summation and toxicity X. Zhu 1 , C. Yangsen 1 , Z. Xianzhi 1 , S. Yuxin 1 , J. Xiaoping 1 , Q. Shuiwang 1 , C. Fei 1 , J. Zhen 1 , F. Fang 1 , G. Lei 1 , Z. Huojun 1 1 Changhai Hospital, Radiation Oncology, Shanghai, China Purpose or Objective A significant number of patients with pancreatic cancer may develop local recurrence after treatment. These patients may not be amenable for surgery due to its high complication rates. In addition to second-line chemotherapy regimens, re-irradiation with stereotactic body radiation therapy (SBRT) may be an alternative, which has been used in few studies. However, the techniques were conventional radiotherapy prior to re- irradiation with SBRT in previous studies and the dose constraints of organs at risk (OAR) were never reported. Therefore, the goal of the study was to determine the cumulative dose-volume parameters to OAR after two courses of SBRT. Material and Methods All patients received two courses of SBRT for the same region with a partial or complete overlap of two previous dose distributions were enrolled. The maximum dose of OAR was calculated as 50% more than the normal constraint. Secondly, we allowed a dose reduction of 50% for a re-irradiation 12 months after the last radiation. A dose reduction of 25% was allowed for a re-irradiation after 6–12 months. No dose reduction was used when re- irradiation was done within 6 months. Due to different doses to target regions and OAR and fractionation schemes, all treatment schedules were recalculated to an Equivalent Dose of 2 Gy per fraction (EQD 2 ). An α/β value of 10 Gy (Gy 10 ) was employed for the tumor dose and acute effects, and the value determined as 3 Gy (Gy 3 ) concerning late effects. Dose distributions, structures sets and CT scans of two treatment plans were extracted from Multiplan ® System (version: 4.0.2) and sent to MIM ® System (version: 6.6.8) for analysis. Firstly, two CT scans were aligned rigidly via automatic bone matches (translation and rotations). Therefore, for each plan before summation, each of the contoured OARs was registered rigidly. Subsequently, a non-rigid registration was followed in dose summations. After non-rigid registration, the dose distributions of the first plan were projected to the second treatment with both of doses converted to EQD 2 , which were summed up finally. Results A total of 41 patients were identified. The median accumulated D max , D 1 and V 10 of the stomach, duodenum