ESTRO 2023 - Abstract Book

S1517

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ESTRO 2023

The resulting corrected signal of each dosimeter was normalized to the averaged signal of the 1000 RPLDs (~1.8 × 106 counts), to determine the sensitivity correction factor (SCF) of each RPLD. It was found that the SCF ranged between 0.968 and 1.040. Figure 1 shows the frequency distribution of the SCFs of 1000 RPLDs where it is shown that around 851 dosimeters lay in the range of [0. 985 – 1.015]. The standard deviation was 1.1% and for each dosimeter’s SCF this parameter ranged between 0.15% and 2.15% with an average value of 0.9%.

Conclusion In this work, a batch of 1000 RPLDs were commissioned. The signal was corrected for magazine position, temperature, and dose. The sensitivity correction factors have been established and will be used in the future for providing postal dosimetry audits for photon and electron beams, as well as high dose rate brachytherapy.

PO-1794 Patient QA comparison between three different OCTAVIUS 4D arrays in radiotherapy treatments

C. Velasco Fernandez 1 , I. Mosquera Cereijo 2 , T. Lusa Agüero 2 , R. Gómez Pardos 2 , J. Bonaque Alandi 3

1 Hospital Clinico Universitario de Valencia, Medical Physics and radiological protection, Valencia, Spain; 2 Hospital Clinico Universitario de Valencia, Medical Physics and radiological protection , Valencia, Spain; 3 Consorcio Hospitalario Provincial de Castellón, Medical Physics and radiological protection , Castellón, Spain Purpose or Objective Detector arrays are widely used for patient QA and there are several available models for that purpose. The aim of this study is to compare and analyze gamma-criteria results of different QA plans for three PTW extended used arrays. Materials and Methods Three PTW arrays has been used: OCTAVIUS Detector 1600 SRS (OD1600SRS), OCTAVIUS Detector 1500 (OD1500) and OCTAVIUS Detector 1000 SRS (OD1000SRS). OD1500 has 1405 plane-parallel vented ionization chambers of 0.06 cm ³ and a maximum field of 27 cm x 27 cm. OD1000SRS and OD1600SRS have 977 and 1521 liquid-filled ionization chambers of 0.003 cm ³ and a maximum field of 11 cm x 11 cm and 15 cm x 15 cm, respectively. The OD1500 is used for plans that require a relative large area of measurement and its spatial resolution is the lowest of the three detectors analyzed. OD1000SRS has a smaller active area, but its spatial resolution is higher than OD1500. It is used for small volumes, typically the ones destined to be treated with SRS/SBRT techniques. The last available model, OD1600SRS, is built to be an improved mix of the two above in terms of spatial resolution. Several patient QA plans has been measured with the OD1500, OD1600SRS and OD1000SRS using an Elekta Versa HD. These patient QA plans are divided in two categories: relatively large target volumes (mainly prostates and rectums) measured with OD1600SRS, OD1500 and merging two measurements with an offset of 5 mm between them in G-T direction, in order to improve the spatial resolution of this array (that we name OD1500 HR); and smaller volumes measured using OD1000 and OD1600SRS. Results The results of the gamma analysis has been compared between them and summarized in Table 1 and Table 2. It has been applied a Global 2%/2mm criteria with a threshold of 10% of the maximum dose. Table 1: OD1600SRS vs OD1500HR and OD1500