ESTRO 2023 - Abstract Book

S1520

Digital Posters

ESTRO 2023

Conclusion 6. W1 is non-water equivalent at low and medium energy x-ray beams. The lower the kV, the larger the difference. 7. W1 response is energy-independent when absorbed dose is expressed as absorbed dose to polystyrene. 8. However, independent calibration for each modality is recommended to minimize uncertainties.

PO-1796 Evaluation of a novel plastic scintillator dosimeter for in vivo dosimetry in an Elekta Unity Linac.

C. Ferrer 1 , C. Huertas 1 , D. García 1 , M. Sáez 1

1 H.U. La Paz, Medical Physics Department, Madrid, Spain

Purpose or Objective With an Elekta Unity Linac, it is not possible to perform a previous treatment dosimetric QA for each session, as the patient is already positioned for treatment. This QA should be done after each adaptative treatment session. One possibility could be to do an in vivo measure of the dose while the treatment is delivered. Current ionization chambers cannot be used while acquiring magnetic resonance imaging. Other systems for in vivo dosimetry have to be analyzed after the treatment is delivered. Plastic scintillators seem to be suitable for in vivo dosimetry in a magnetic field. They are water equivalent, independent of the energy, dose rate, angularity and presence of a magnetic field. This work studies the performance of a novel plastic scintillator as in-vivo dosimeter. Materials and Methods A novel plastic scintillator, Blue Physics Model 10, has been used to in vivo measure the dose delivered while acquiring MR imaging. It consists in a plastic scintillator cylinder of 1 mm diameter and 1 mm long with 0.785 mm3 sensitivity volume, embedded in a plastic housing that mimics a semiflex 3D PTW ionization chamber. The scintillator was placed inside one of the inserts (Figure 1) of an anthropomorphic SRS head phantom. The phantom was scanned and images were sent to Monaco TPS (v. 5.40). In the TPS, the scintillator was delineated and considered as CTV. Then, the PTV was created with 1 cm margin from the CTV. 10 Gy in 5 fractions were planned to the PTV and the normal Unity treatment workflow was followed.