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Evaluation of dosimetric parameters of small fields of 6 MV flattening filter free photon beam measured using various detectors against Monte Carlo simulation

Published online by Cambridge University Press:  09 March 2020

Gopinath Mamballikalam Open the ORCID record for Gopinath Mamballikalam [Opens in a new window] ,
S Senthilkumar ,
P. M. Jayadevan ,
R. C. Jaon bos ,
P. M. Ahamed Basith ,
Rohit Inippully ,
N. S. Shine  and
C. O. Clinto
Gopinath Mamballikalam*
Affiliation:
R & D, Bharathiar University, Coimbatore, Tamilnadu, India Aster Medcity, Kochi, Kerala, India
S Senthilkumar
Affiliation:
Rajaji Hospital & Madurai Medical College, Madurai, Tamilnadu, India
P. M. Jayadevan
Affiliation:
Aster Medcity, Kochi, Kerala, India
R. C. Jaon bos
Affiliation:
Aster Medcity, Kochi, Kerala, India
P. M. Ahamed Basith
Affiliation:
Aster Medcity, Kochi, Kerala, India
Rohit Inippully
Affiliation:
Aster Medcity, Kochi, Kerala, India
N. S. Shine
Affiliation:
Banasthali Vidyapith, Jaipur, Rajasthan, India
C. O. Clinto
Affiliation:
Aster Medcity, Kochi, Kerala, India
*
Author for correspondence: Gopinath Mamballikalam, Aster Medcity, Kochi, Kerala, India. E-mail: mgnmenon@gmail.com
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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 cm2 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 cm2 where the lateral charge particle equilibrium was not satisfied. Diamond detector was seen as most suitable for all measurements above 1 × 1 cm2. 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 cm2. 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 cm2 and microdiamond detector is suitable for above 1 × 1 cm2. Below these field sizes, perturbation corrections and volume averaging corrections need to be applied.

Keywords

FFF beamssmall field dosimetrydetectorradiotherapyMonte Carlo simulation
Type
Original Article
Information
Journal of Radiotherapy in Practice , Volume 20 , Issue 3 , September 2021 , pp. 332 - 339
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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Footnotes

*

This article was originally published with an error in the title. This error has now been updated and a corrigendum published.

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