Evaluation of dosimetric parameters of small fields of 6 MV flattening filter free photon beam measured using various detectors against Monte Carlo simulation
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2020-03-09 |
| Journal | Journal of Radiotherapy in Practice |
| Authors | Gopinath Mamballikalam, S. Senthilkumar, P. M. Jayadevan, R. C. Jaon bos, P. M. Ahamed Basith |
| Institutions | Bharathiar University, Aster Medcity |
| Citations | 7 |
Abstract
Section titled “Abstract”Abstract Purpose: This study aims to evaluate dosimetric parameters like percentage depth dose, dosimetric field size, depth of maximum dose surface dose, penumbra and output factors measured using IBA CC01 pinpoint chamber, IBA stereotactic field diode (SFD), PTW microDiamond against Monte Carlo (MC) simulation for 6 MV flattening filter-free small fields. Materials and Methods: The linear accelerator used in the study was a Varian TrueBeam® STx. All field sizes were defined by jaws. The required shift to effective point of measurement was given for CC01, SFD and microdiamond for depth dose measurements. The output factor of a given field size was taken as the ratio of meter readings normalised to 10 × 10 cm 2 reference field size without applying any correction to account for changes in detector response. MC simulation was performed using PRIMO (PENELOPE-based program). The phase space files for MC simulation were adopted from the MyVarian Website. Results and Discussion: Variations were seen between the detectors and MC, especially for fields smaller than 2 × 2 cm 2 where the lateral charge particle equilibrium was not satisfied. Diamond detector was seen as most suitable for all measurements above 1 × 1 cm 2 . SFD was seen very close to MC results except for under-response in output factor measurements. CC01 was observed to be suitable for field sizes above 2 × 2 cm 2 . Volume averaging effect for penumbra measurements in CC01 was observed. No detector was found suitable for surface dose measurement as surface ionisation was different from surface dose due to the effect of perturbation of fluence. Some discrepancies in measurements and MC values were observed which may suggest effects of source occlusion, shift in focal point or mismatch between real accelerator geometry and simulation geometry. Conclusion: For output factor measurement, TRS483 suggested correction factor needs to be applied to account for the difference in detector response. CC01 can be used for field sizes above 2 × 2 cm 2 and microdiamond detector is suitable for above 1 × 1 cm 2 . Below these field sizes, perturbation corrections and volume averaging corrections need to be applied.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
Section titled “References”- 2016 - Analysis of small field percent depth dose and profiles: Comparison of measurements with various detectors and effects of detector orientation with different jaw settings [Crossref]