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Characterisation of small photon field outputs in a heterogeneous medium using X-ray voxel Monte Carlo dose calculation algorithm

Published online by Cambridge University Press:  23 August 2017

Karthikeyan Nithiyanantham ,
Ganesh K. Mani ,
Sambasivaselli Raju ,
Senniandavar Velliangiri ,
Maniyan Paramasivam ,
Karrthick K. Palaniappan  and
Sandeep Jain
Karthikeyan Nithiyanantham
Affiliation:
Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru 560029, Karnataka, India
Ganesh K. Mani*
Affiliation:
Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru 560029, Karnataka, India
Sambasivaselli Raju
Affiliation:
Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru 560029, Karnataka, India
Senniandavar Velliangiri
Affiliation:
Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru 560029, Karnataka, India
Maniyan Paramasivam
Affiliation:
Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru 560029, Karnataka, India
Karrthick K. Palaniappan
Affiliation:
Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru 560029, Karnataka, India
Sandeep Jain
Affiliation:
Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru 560029, Karnataka, India
*
Correspondence to: Ganesh K Mani, Ph.D, Radiation Physics, Kidwai Memorial Institute of Oncology, Hosur Road, Bengaluru 560099, Karnataka, India. Tel: +91 9481289421; E-mail: [email protected]
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Abstract

Aim

To characterise small photon beams using the Monte Carlo dose calculation algorithm for small field ranges in a heterogeneous medium.

Materials and method

An in-house phantom constructed with three different mediums, foam, polymethyl methacrylate and delrin resembling the densities of lung, soft tissue and bone respectively, was used in this study. Photon beam energies of 6 and 15 MV and field sizes of 8×8, 16×16, 24×24, 32×32 and 40×40 mm using X-ray voxel Monte Carlo (XVMC) algorithm using different detectors were validated. The relative output factor was measured in three different mediums having six different tissue interfaces; at the depth of 0, 1, 2 and 3 cm. The planar dose verification was undertaken using gafchromic films and considered dose at the lung and bone medium interfaces. For all the measurements, 104×104 mm was taken as the reference field size. The relative output factor for all other field sizes was taken and compared with planning system calculated values.

Results

From field size 16×16 mm and above, the relative output factors were analysed in bone and soft tissue medium having lung as first medium. The maximum deviations were observed as 1·8 and 1·3% for 6 MV and 2·5 and 1·1% for 15 MV photon beams for bone and soft tissue, respectively. For lung as measurement medium, the maximum deviation of 14·8 and 19·2% were observed and having bone as first medium with 8×8 mm for 6 and 15 MV photon beams, respectively. The fluence verification of dose spectrum for the lung–bone interface scenarios with smaller field sizes were found within 2% of deviation with treatment planning system (TPS).

Conclusion

The accuracy of dose calculations for small field sizes in XVMC-based treatment planning algorithm was studied in different inhomogeneous mediums. It was found that the results correlated with measurement data for field size 16×16 mm and above. Noticeable deviation was observed for the smallest field size of 8×8 mm with interfaces of significant change in density. The observed results demands further analysis of work with smaller field sizes.

Keywords

heterogeneityMonacoMonte Carlosmall field dosimetryXVMC
Type
Original Articles
Information
Journal of Radiotherapy in Practice , Volume 17 , Issue 1 , March 2018 , pp. 114 - 123
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Copyright
© Cambridge University Press 2017 

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