Abstract Book

ESTRO 37

S498

PO-0924 4DCT and VMAT planning for lung patients with irregular breathing N. Sisson 1 , R. Caines 1 , C. Rowbottom 1 1 The Clatterbridge Cancer Centre, Medical Physics, Liverpool, United Kingdom Purpose or Objective This study aimed to evaluate suitability of 4DCT and VMAT planning for lung patients with irregular breathing. Prior 4DCT studies advise caution when imaging such patients, but no studies have evaluated dosimetric quality of treatment. Locally these patients currently receive 3DCT and conformal planning. Our objectives were to determine if for irregularly breathing patients 3DCT or 4DCT: 1. better represents the range of tumour motion 2. better represents the average densities in the patient 3. allows for VMAT plans that can be delivered with acceptable dosimetric accuracy Material and Methods Recorded breathing traces were identified for 10 patients for whom 4DCT was contraindicated (e.g. Figure 1). Traces were fed to a programmable moving platform (maximum sup-inf amplitude 2.85 cm) on which a CIRS lung tumour phantom was mounted, containing two spherical tumours of 2 and 3 cm diameter. Expected tumour motion range and average density profiles were calculated directly from the breathing traces together with HU values from a static scan.

(p=0.005). Dosimetry

Dosimetric agreement between TPS and mean measurement for three fractions is summarised in Figure 2. 9 of 10 4DCT plans were measured to be within 2.5% of the expected dose, compared with 5 of 10 3DCT plans. The 4DCT outlier was for an extremely slow breathing trace exceeding pitch limits of our CT scanner. Median agreement was not significantly different between modalities.

Figure 2 Box plot for VMAT plans, 3DCT (left) and 4DCT (right), showing dosimetric agreement between TPS and measurement. Dashed lines indicate nominal 2.5% tolerance level. Conclusion For the irregular breathing traces studied tumour motion range and average density was better represented with 4DCT compared with 3DCT. 4DCT images allowed for delivery of VMAT plans with acceptable dosimetric accuracy. Our findings have given us confidence to introduce 4DCT and VMAT planning for patients with irregular breathing. PO-0925 Monte Carlo Quality Assurance platform for particle therapy W. Kozłowska 1,2 , T. Böhlen 3 , C. Cuccagna 4,5 , A. Ferrari 1 , D. Georg 2,6 , A. Mairani 7,8 , V. Vlachoudis 1 1 CERN, Geneva, Switzerland 2 Medical University of Vienna, Department of Radiation Oncology, Vienna, Austria 3 EBG MedAustron GmbH, Department of Medical Physics, Wiener Neustadt, Austria 4 TERA Foundation, TERA, Geneva, Switzerland 5 University of Geneva, Nuclear and Corpuscular Physics Department, Geneva, Switzerland 6 Christian Doppler Laboratory for Medical Radiation Research - Medical University of Vienna/AKH, Department of Radiation Oncology, Vienna, Austria 7 Heidelberg Ion-Beam Therapy Center, Medical Physics Department, Heidelberg, Germany 8 CNAO, Medical Physics Department, Pavia, Italy Purpose or Objective While Monte Carlo (MC) codes are considered as the gold standard for dosimetric calculations, the availability of user friendly MC tools suited for particle therapy Quality Assurance (QA) is limited. In this study, we present an implementation and evaluation of the newly developed framework for particle therapy treatment planning (TP) and QA simulations based on the FLUKA MC Code and its GUI - Flair.

Figure 1 Example clinical irregular breathing trace. Dashed lines indicate middle 95% of the amplitude distribution. 3D and 4D (phase-binned) scans were acquired for each breathing trace. Tumours were delineated on 3D and 4D- MIP images by HU thresholding and apparent tumour motion range measured. HU tumour profiles were extracted from 3D and 4D-AIP images, and agreement with expected profiles quantified using area-under-curve scoring. PTVs were created on 3D and 4D-AIP images from the 2 cm tumour using locally established 3D and 4D margins. Clinically representative VMAT plans were created for each image, delivered to the moving phantom, and measured with a pinpoint chamber at the tumour centre. 3 fractions were delivered for each plan to minimise interplay effects. Results Tumour motion range Median difference in tumour motion range (expected – measured) was 2.5 [1.6 – 3.6] cm (3D) and 1.1 [0.1-1.9] cm (4D) (p=0.005). Density representation Median AIP HU profile agreement scores (ideal = 0) were 0.25 [0.14 – 0.49] (3D) and 0.12 [0.05 – 0.42] (4D)