ESTRO 2023 - Abstract Book

S1428

Digital Posters

ESTRO 2023

Conclusion A large database of CSI pediatric cases was collected among three Italian institutes. Data comparison confirmed that RT practices are fairly homogeneous across the centers and multi-isocenter VMAT and HT delivery techniques can be considered diametrically equivalent. A preliminary KBP model based on 42 cases was built with encouraging prediction power. KBP model results were used to firstly describe Heart, Lungs, Kidneys and Lenses mean dose as a function of patient’s age.

PO-1713 MLC analysis using exit detectors on TomoTherapy

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

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 Verification of the technical characteristics of the device are an important part of the quality assurance (QA) procedures in radiation therapy. Small deviations in the operation of the device can lead to quite high changes in the dose delivered to patients. TomoTherapy uses multileaf collimator with 64 binary leaves. Daily QA procedures in TomoTherapy are the dose measurement in the Cheese Phantom using the A1SL ionization chambers at a few points. This may not be enough to detect errors such as a delay in opening/closing specific leaves. In this study, we present the procedures for daily MLC verification using exit detectors array. Materials and Methods We use an option on TomoTherapy of creating a new plan using sinogram. We made a few sinograms with different leaf open time – the goal was to analyze the accuracy of each leaf. First plan was made with each leaf opens at 25%, 50%, 75%, and 100% from projection time. Second plan included high modulation of all leaves. Third plan had couch and gantry movement and was used in transit dosimetry with Cheese Phantom. Each procedure was repeated daily for two weeks. Data from exit detectors was transferred off the TomoTherapy system after dose delivery for analysis using TomoTherapy quality assurance (TQA) module. The results were analyses in hand-made program in MATLAB, which allows to compare two data sets with gamma-analysis. In this study, we used parameters 0.6% and 0.6 mm. The value of the gamma index was obtained for the entire area of the sinograms, the first day data were taken as a reference. Results All three daily procedures showed similar results: the minimal gamma index of the whole sinograms area was 99.7%, which indicates stability in the leaves work. More thorough data analysis showed that almost every leaf had value of gamma index near to 100%. However, one of the leaf (number 38) had mean gamma index of 91.9 ± 1.2 %. It indicates that this leaf has opening time delay, which can lead to potential errors in dose delivery. This information was transmitted to the engineers and taken into account during further maintenance of the machine. The program was also used to analyze the movement of the leaves after the breakdown of the apparatus, where mechanical parts of the collimator were replaced, as well as the pressure in the system was changed. The results showed minor changes in the gamma index: the minimum gamma index between data before and after the accelerator failure had 96%. Conclusion The data from exit detectors store a large amount of information about the work of the collimator and individual leaves. Our method can be used as additional tool for daily QA as well as for leaves verification after the machine breakdown to increase the accuracy of the MLC work.

PO-1714 FMEA risk analysis of surface-guided DIBH breast radiotherapy by using a commercial software tool

S. Russo 1 , M. Esposito 1 , A. Bruschi 1 , A. Ghirelli 1 , P. Alpi 2 , F. Meacci 1 , C. Delli Paoli 2 , S. Scoccianti 2

1 AUSL Toscana Centro, Medical Physics Unit, Florence, Italy; 2 AUSL Toscana Centro, Radiotherapy Unit, Florence, Italy

Purpose or Objective To evaluate a new software tool for prospective risk analysis in DIBH surface-guided radiation therapy (SGRT) for left breast and to generate a template which could be used as starting draft by other institutions. Materials and Methods The tool is optimized for clinical applications, and it is aimed to solve common shortcomings of FMEA analyses performed using spreadsheets. The expected event rate of a failure mode calculation is based on occurrence and detectability evaluation, and on basic workflow statistics. This metric is used together with failure mode severity to assess risk tolerability in a risk matrix approach, and to quantify the benefit offered by safety measures, which is used for their cost/benefit analysis. Failure modes data can be organized either according to the process step where they occur (FMEA) or to the effect they generate (FTA) to perform a complete revision of the clinical workflow. Templates can be generated based on literature and common practice. They include a typical description of workflow, possible failure modes and common safety measures which could be adopted to reduce risks.