Author: Alejandro Cuadra, Paulina E. Galavis, Juan Leal, Enrique Lozano, Franklin Reggio, Gabriel Zelada 👨🔬
Affiliation: Clínica Iram, Clinica Alemana, Hospital Clínico de Magallanes, E&G Medical Systems Ltda, NYU Langone Health 🌍
Purpose: To investigate and compare the new method “Pulse Normalization” proposed by Sun Nuclear to correct ion chamber signal for fluctuations in the accelerator output while performing relative dosimetry during beam scanning.
Methods:
A Versa HD Linac was commissioned with photon energies of 6MV, 10MV, 6FFF, and 10FFF. PDD and inline profiles (10 cm depth) were acquired for all photon energies using field sizes 1x1, 2x2, and 3x3cm2. The Edge diode was used as a field detector, and the following methods and reference detectors were used:
a) Pulse Normalization (SunSCAN 3D phantom from Sun Nuclear).
b) T-REF (transmission chamber) from PTW.
c) Leakage detector, from Sun Nuclear.
d) A6 (radiation protection detector) from Standard Imaging
Elekta shared the standard Accelerated Go Live (AGL) dosimetric data in Sun Nuclear format. This data was used as a reference to perform a gamma analysis using the 1%/1mm and 2%/2mm criteria.
Results:
For all used energies the Pulse Normalization method shows a good agreement for Inplane profiles and PDDs with the gamma criteria γ≥97.69%.
The T-REF chamber shows similar results with a γ≥96.46%.
The Reference Detector shows similar results, but the gamma criteria fail for PDDs at 10 MV and 10 FFF, and gamma criteria of 1%/1mm
The A6 chamber has reasonable results for 6 MV, 10 MV, and 10 FFF inplane profiles. However, it is not recommended for PDD measurements
Conclusion:
The new pulse normalization method available in the SunScan 3D phantom is an excellent option for small beam scanning dosimetry. T-REF and The Reference Detector also showed acceptable and similar results. The A6 chamber can be used with caution for small field profiles and PDDs for 6MV and 10MV.