ESTRO 2022 - Abstract Book

S1480

Abstract book

ESTRO 2022

In the current system there is a delay of 3-5 seconds before the radiation will start after the breath hold command is given, which is partially due to the preparation state of Elekta linac. The noise in the measured signal of the system was about 1 mm. Conclusion The system detects when the DIBH is not within the gating window. The position of the chest wall is accurately monitored during the treatment and changes in chest wall position during treatment can be easily detected.

PO-1680 Verification method for Total Body Irradiation plans using TomoTherapy exit detectors

D. Tovmasian 1,2 , A. Loginova 1 , A. Chernyaev 2

1 Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology, Department of Radiotherapy, Moscow, Russian Federation; 2 Lomonosov Moscow State University, Department of Physics, Moscow, Russian Federation Purpose or Objective Total body irradiation (TBI) includes irradiation of entire body except for organs at risk such as lungs, kidneys, and lenses. In our department, TBI plans are created using TomoTherapy (Accuray, USA) with Helical mode delivery. The standard treatment plan verification includes the point absolute dose measurements in the phantom. However, with the increasing complexity of TBI delivery, there is a growing need for more accurate and informative plan verification. It seems to be not enough to use a few point measurements for whole TBI plan. In this study we present the phantomless verification method for TBI plans using TomoTherapy exit detectors data (ED) which ordinary used for visualization purpose. For each plan we performed the Static Couch procedure (plan delivery in the absence of a phantom and couch movement). The signal from ED was extracted using the TomoTherapy Quality Assurance tool. A hand-made software was designed for processing raw data from ED as well as the sinogram data from treatment planning station. The raw ED data were converted into synthetic sinogram by applying the correction factors such as: background radiation, the shape of the detector, the influence of neighboring collimators leaves and the leaf-channel dependence. Comparison of planned and synthetic sinograms using Gamma-analysis (5% 1mm, global) was performed for each plan with respect to different body regions. Each plan was also verified by standard method using Cheese Phantom and A1SL ion chambers. Planed and measured absolute dose difference was found in at least four points corresponding to different body regions. Materials and Methods TBI treatment plans were calculated for ten patients.

Results Result are reported in Table 1.

Table 1. Comparison of the results for two plan verification methods: maximum dose difference in point measurements and Gamma index between planned and synthetic sinograms for different body regions.

All plans pass the standard dosimetry criteria for phantom measurements: maximum dose difference did not exceed 3%. Regions including high dose gradient such as chest and abdomen show highest values of dose difference. This result correlated with the calculated gamma-index between planed and synthetic sinograms. Passing Gamma criteria for developed method can be determined with future data collection. Conclusion The data from ED store a large amount of information about the work of the collimator and individual leaves. Using these data for dosimetric purposes allows us to increase the quality and fullness of TBI plan’s verification. Our method can be used as additional plan verification tool for the cases with long targets and complex dose delivery.

PO-1681 Fully automated rigid image registration versus human registration in postoperative spine SBRT

Y. Koide 1 , H. Shimizu 1 , R. Miyauchi 1 , S. Haimoto 2 , H. Tanaka 3 , Y. Watanabe 4 , S. Adachi 5 , D. Kato 6 , T. Aoyama 1 , T. Kitagawa 1 , H. Tachibana 1 , T. Kodaira 1