ESTRO 37 Abstract book

S1221

ESTRO 37

Martí-Climent 3 , C. Gámez-Cenzano 2 , C. Picón 1 1 Institut català d´Oncologia ICO- L'Hospitalet de Llobregat, Medical Physics and Radiological Protection, Barcelona, Spain 2 Hospital Universitari de Bellvitge, Nuclear Medicine Department, L'Hospitalet de Llobregat- Barcelona, Spain 3 Clínica Universidad de Navarra, Nuclear Medicine Department, Pamplona, Spain Purpose or Objective Positron Emission Tomography (PET) based Metabolic Tumor Volume (MTV) has an increasing role in the delimitation, evaluation and adaptation of radiotherapy volumes and plans. This volume could be affected by different factors, as could be the blurring induced by respiratory motion. The aim of this study is to evaluate how a respiratory correction method Q.Static (GE Healthcare, Milwaukee), used in diagnostic PET/CT, impacts in the definition of Five different respiratory cycles were acquired using the QUASAR 4D phantom (Modus QA, London). Ten different lesions from 8 lung cancer patients were also recorded; all of them were localized in the middle or lower lobes of the lungs. Phantom and patients were acquired on a Discovery IQ PET/CT scanner (GE Healthcare, Milwaukee) using a standard PET protocol (free breathing and 2 min per bed) and a Q.Static correction method (4 min per bed). The Q.Static method records PET data only during expiration, the most stable part of the respiratory cycle. Images were reconstructed using a standard algorithm VPHD-S (12 subsets, 4 iterations and a 4.8 mm Gaussian post-filtering). Images were compared qualitatively by an expert nuclear medicine physician, and quantitatively by means of MTV, SUVmax and SUVmean. MTV was defined as the volume segmented from a threshold of 41% of the SUVmax. Results The qualitative evaluation showed an improved fusion of PET and CT images for the Q.Static method. Quantitatively, results for the mean relative differences (Q.Static versus standard acquistion) of volume, SUVmax and SUVmean were, respectively, -7.8 ± 4.9 % (p=0.03), 2.2 ± 2.3 % (p=0.02), and 2.4 ± 2.5 % (p=0.02). Variations were small but statistically significant. Results show a decrease in volume size and a small increase on SUVmax and SUVmean values for the Q.Static technique, in agreement with the improvements observed in the images. Conclusion Q.Static proves to be a valid method to reduce image respiratory blurring, improving image fusion and slightly increasing the SUV-related metrics. However, as volume differences between tecniques are low or moderated, Q.Static does not need additional considerations regarding the MTV definition. EP-2205 An emerging SABR method with 4D dynamic HRCT for breast cancer in patients with MRI contraindication S. Velázquez Miranda 1 , D. Muñoz Carmona 2 , R. Haro Piedra 3 , M. Baeza Trujillo 1 , J. Peinado Serrano 3 , M.J. Ortiz Gordillo 3 , F. Luis Simón 1 1 Hospital Universitario Virgen del Rocio, Medical Physics, Sevilla, Spain 2 Hospital Universitario Virgen del Rocío, Radiotherapy, Seville, Spain 3 Hospital Universitario Virgen del Rocio, Radiotherapy, Sevilla, Spain Purpose or Objective SABR standard protocol in early stages of breast cancer includes acquisition of CT and MRI images of the patient. MRI allows the correct identification of the lesion. This work proposes, with the evolution of a wide-area MD CT the radiotherapy MTV. Material and Methods

scanners detector, that it is possible to properly identify the lesion using the 4D CT with high resolution and with the development of an ad hoc stereotactic system in patients with MRI contraindication Material and Methods In 2017 six early stage breast cancer patients were indicated for preoperative SABR treatment with MRI contraindication. In the CT simulation (Aquillion CT Big Bore) we used an special stereotactic multidampening device, developed in our hospital dedicated to breast immobilization. We first obtain a slowCT with FOV of 700mm over the whole thoracic area for dose calculation; secondly a 4DCT acquisition with FOV of 240mm focused on the lesion like a dynamic acquisition for cardiology , that is, without couch displacement and with the simultaneous use of 16-detector-row with the aim of tumor movement analysis ; and finally a breath- hold HRCT focused on the lesion for GTV definition. Multidampening system stops costal movements . The definition of the targets in HRCT allows the automatic contouring based on Hounsfield number histogram. Treatment planning is designed with Pinnacle using the negative margin technique for 4π treatment with 15 beams, which allows a high conformation to target, maintaining the dose in organs at risk below the established limits.Malignant breast tumors that measured < 40 mm (+4mm of PTV margin) in greatest dimension were treated by single-fraction SABR of 24Gy. For each patient, pre- and post-treatment cone beam computed tomography (CBCT) was performed for assessing geometrical intrafraction variability during radiotherapy. The total irradiation time is less than 12 minutes in order to increase biological efficiency. Results The volumes obtained from automatic contouring were accepted as GTV by three oncologists in all six cases.The dose length product (DLP) was for a high resolution study of 645mGy · cm, which gave us an effective estimate of 9.7mSv. A typical 4DCT for an anatomical location similar to a DLP between 700 and 1000 mGy · cm and an estimated effective dose of 12-16mSv.The mean overall correction values of post-treatment IGRT were lateral 1.0±1.8 mm ,longitudinal 0.8±1.4mm and vertical 1.2±1.7mm , time from star to end irradiation was 12.3±2.2 minutes and average relative increase in volume between GTV and ITV was 33.2%.The MULTIDAMPENING breast system has already been patentedThe 6 patients evolved with the difference of those simulated with MRI, although the follow-up is still short. Conclusion MRI is the Gold Standard for breast SABR, although this innovative procedure with HRCT that we propose is accepted by our oncologists for patients with MRI contraindication. We believe the high dose related to the HRCT used is aceptable in the context of SABR modality. EP-2206 Global findings of remote beam output audits; a review by the Global Harmonisation Group S. Kry 1 , C. Peterson 2 , R. Howell 1 , J. Izewska 3 , J. Lye 4 , C. Clark 5 , M. Nakamura 6 , C. Hurksman 7 , D. Followill 1 , P. Alvarez 1 , P. Taylor 1 , J. Leif 1 , A. Molineu 1 , R. Weathers 1 , J. Palmer 1 , T. Bokulic 3 , P. Kazantsev 3 , I. Williams 4 , A. Alves 4 1 UT MD Anderson Cancer Center, Radiation Physics, Houston- TX, USA 2 UT MD Anderson Cancer Center, Biostatistics, Houston- TX, USA 3 International Atomic Energy Agency, Nuclear Sciences and Applications, Vienna, Austria 4 Australian Clinical Dosimetry Services, Australian Clinical Dosimetry Services, Yallambie, Australia 5 Royal Surrey Country Hostpial, Medical Physics, Guildford, United Kingdom