ESTRO 38 Abstract book

S493 ESTRO 38

PO-0921 Assessment of CT-based imaging biomarker of COPD in IGRT planning for lung cancer patient T. Shiinoki 1 , Y. Yuasa 1 , K. Fujimoto 1 1 Yamaguchi University, Department of Radiation Oncology- Graduate School of Medicine, Ube, Japan Purpose or Objective One of the most severe complications in radiotherapy of lung cancer is radiation pneumonitis (RP). Chronic obstructive pulmonary disease (COPD) is a recognized risk factor for RP. COPD is a heterogeneous disorder that arises from pathological processes including emphysematous lung tissue destruction, gross airway disease and functional small-airways disease (fSAD) in varying combinations and severity within an individual. It is widely accepted that fSAD and emphysema are two main components of COPD and that a spectrum of COPD phenotypes with varying contributions of these components exists in individual patients. The purposes of this study were to quantify relative lung function using a parametric response map (PRM) as the imaging biomarker of COPD and to assess the dosimetric impact of its integration in treatment planning in volumetric modulated arc therapy (VMAT). Material and Methods Seven patients who underwent stereotactic body radiotherapy (SBRT) for lung cancer with COPD were enrolled in this study. Four-dimensional CT data sets were acquired around the whole lung with 20-slice CT scanner under free breathing. Next, the entire lung was scanned under breath-hold with a full inspiration. The PRM of quantitative CT as expressed in HU, a measure of tissue density, was determined by imposing two thresholds: (i) - 950 HU on full inspiration scan, with values less denoting emphysema, and (ii) -856 HU on normal expiration scan, with values less denoting gas trapping. Therefore, deformable image registration (DIR) was performed from full inspiration to normal exhalation (50%). Classification of voxels with HU values characteristic of lung parenchyma representing normal, fSAD, or emphysema. PRM as imaging biomarker of COPD were calculated for each patient. The VMAT plan was designed based on the total lung. Dosimetric parameters (percent lung volume receiving 5 Gy [V5], V10, V20, and mean lung dose [MLD] to whole lungs (anatomical) versus functional lungs (normal and fSAD)) were compared. Results Figure 1 showed examples of PRM for two patients. PRM was able to visualize lung function. Red, yellow and green areas indicate emphysema, fSAD and normal lung regions. For all patients, the mean ± standard deviation (S.D.) of relative volume of emphysema, fSAD, and normal volume for total lung volume were 5.4 ± 8.8 % (0.2%–24.6%), 30.3 ± 15.2% (8.8%–50.2%) and 62.5 ± 20.6% (39.1%–90.8%). Figure 2 indicated an example of dose distribution for patient 3 in coronal and sagittal plane and the mean in V5, V10, and V20 for whole lung, normal, and fSAD, respectively. Mean differences between anatomical and functional lung (normal, fSAD) were 1.9% (0.2%–3.9%), 3.5% (0.3%–10.7%), 1.5% (0.5%–3.5%), 3.6% (0.3%–10.2%), 0.7% (0.2%–1.7%), 1.8% (0.3%–4.1%) and 39 cGy (5.6–67 cGy), 87.5 cGy (22.2–252.2cGy) in V5, V10, V20, and MLD, respectively.

Conclusion It is necessary to evaluate the weighted functional volume in the treatment planning with integration of PRM for functional lung-sparing VMAT. PO-0922 Knowledge-based optimization of an adaptive, early-regression-guided, technique for rectal cancer R. Castriconi 1 , C. Fiorino 1 , S. Broggi 1 , P. Passoni 2 , N. Di Muzio 2 , R. Calandrino 1 , G.M. Cattaneo 1 1 IRCCS San Raffaele Scientific Institute, Medical Physics, Milano, Italy ; 2 IRCCS San Raffaele Scientific Institute, Radiotherapy, Milano, Italy Purpose or Objective The aim of current study is to implement a knowledge- based (KB) optimization strategy to our adaptive (ART) early-regression guided boosting technique in neo- adjuvant radio-chemotherapy for rectal cancer. Material and Methods An ART approach for rectal cancer aiming to boost the residual tumor (GTV) in the last part of the treatment was developed and clinically implemented since 2009. The protocol consists of a first phase delivering 27.6Gy to tumor/lymph-nodes, 2.3Gy/fr (PTV 1 ); followed by the ART phase concomitantly delivering 18.6Gy (3.1Gy/fr) and 13.8Gy (2.3Gy/fr) respectively to the residual tumor (PTV ART ) and to PTV 1 : PTV ART is obtained by expanding GTV, as visible on MRI taken at fraction 9. Forty VMAT (Varian RapidArc) clinical plans were available and used to generate a KB-model for the first phase using the RapidPlan tool implemented in the Eclipse system (v13.5). Due to the large variability of the size and location of the residual tumor, a robust strategy in order to scale the KB- model of the first phase to the ART one was applied. Twenty clinical plans were retrospectively analysed in terms of PTV ART dose distribution: 2cm shell around PTV ART (1cm cranial-caudal) was generated for each ART plan. An automatic optimization template for the ART part was obtained by scaling the dose constraints of the first part and including constraints for the shell. An internal (closed-loop) and external (open-loop) validation were performed for both phases, in order to assess the potentiality of the method: all automatic plans ( RP ) were compared in terms of OARs/PTVs parameters against the original plans ( RA ). Results Before assessing best constraints for the shell, shell-DVHs of 20 ART plans were analysed and not found to be correlated with PTV ART volume or with the ratio between