Monte Carlo simulation based study of a proposed multileaf collimator for a telecobalt machine

Sahani, G.; Sharma, Sunil Dutt; Sharma, Pramod Kumar; Sharma, D.N.; Hussain, Syed Md Akram

doi:10.1118/1.4773308

Cited by 10 publications

(3 citation statements)

References 22 publications

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“…In the first configuration, as shown in Figure 2a the source with cladding, the primary collimator with fixed opening, and the telescopic collimator with four sections were simulated. The telescopic collimator follows the beam divergence defined by the periphery of the source bottom as defined by Mora et al .,[2] and Sahani et al .,[8]…”

Section: Methodsmentioning

confidence: 99%

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Monte Carlo study of MLC fields for cobalt therapy machine

Ayyangar¹,

Rani²,

Kumar³

et al. 2014

J Med Phys

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An automated Multi-Leaf Collimator (MLC) system has been developed as add-on for the cobalt-60 teletherapy machines available in India. The goal of the present computational study is to validate the MLC design using Monte Carlo (MC) modeling. The study was based on the Kirloskar-supplied Phoenix model machines that closely match the Atomic Energy of Canada Limited (AECL) theratron-80 machine. The MLC is a retrofit attachment to the collimator assembly, with 14 non-divergent leaf pairs of 40 mm thick, 7 mm wide, and 150 mm long tungsten alloy plates with rounded edges and 20 mm tongue and 2 mm groove in each leaf. In the present work, the source and collimator geometry has been investigated in detail to arrive at a model that best represents the measured dosimetric data. The authors have studied in detail the proto-I MLC built for cobalt-60. The MLC field sizes were MC simulated for 2 × 2 cm2 to 14 × 14 cm2 square fields as well as irregular fields, and the percent depth dose (PDD) and profile data were compared with ROPS† treatment planning system (TPS). In addition, measured profiles using the IMATRIXX system‡ were also compared with the MC simulations. The proto-I MLC can define radiation fields up to 14 × 14 cm2 within 3 mm accuracy. The maximum measured leakage through the leaf ends in closed condition was 3.4% and interleaf leakage observed was 7.3%. Good agreement between MC results, ROPS and IMATRIXX results has been observed. The investigation also supports the hypothesis that optical and radiation field coincidence exists for the square fields studied with the MLC. Plots of the percent depth dose (PDD) data and profile data for clinically significant irregular fields have also been presented. The MC model was also investigated to speed up the calculations to allow calculations of clinically relevant conformal beams.†Radiation Oncology Planning System (ROPS) is supplied by Tirumala Jyothi Computer Systems described at https://sites.google.com/site/tjcsrops/‡IMATRIXX is supplied by IBA Dosimetry described at HYPERLINK http://www.iba-dosimetry.com

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Section: Methodsmentioning

confidence: 99%

“…Sahani et al .,[8] have extensively studied an MLC design for cobalt machine. Although there are many similarities, to the current investigation, there are some notable differences.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo study of MLC fields for cobalt therapy machine

Ayyangar¹,

Rani²,

Kumar³

et al. 2014

J Med Phys

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“…The 3-D conformal radiation therapy is performed with the availability of the treatment planning system and radiation field analyzer. The new treatment modalities such as intensity modulated radiotherapy and image guided radiotherapy are also now facilitated in the telecobalt unit [1] [2] [3]. The dosimetry and treatment planning in the telecobalt unit is straightforward as compared to the linear accelerator.…”

Section: Introductionmentioning

confidence: 99%

Radiation Beam Characterization and Dosimetry of Theratron Equinox-80 Telecobalt Machine Using BEAMnrc Monte Carlo Simulation Code

Patel¹,

Balasubramanian²,

Atri³

et al. 2016

IJMPCERO

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The BEAMnrc code was used for the simulation of the Theratron Equinox-80 telecobalt machine. The phase space of radiation beam was generated at treatment distance of 80 cm for various field sizes. The phase spaces in air were analyzed by BEAMdp data processing program. The electron energy fluence with respect to photon energy was 0.09% and 0.34% for field size of 05 × 05 and 35 × 35 cm 2 respectively and it was maximum at the central axis which gradually decreases beyond this. The profiles for photon fluence were in symmetry for all the fields. The full width at half maximum of profiles in photon energy fluence shows good agreement with the field size. The photon energy fluence was flat till the field size of 27 cm 2 , after which it decreases gradually till the edge in larger field sizes. The air-kerma output factor from the simulation was in good agreement with measured value. We analyzed the dose data scored in the voxels in a large water phantom by simulation using dosxyznrc code. The percentage depth dose for all field sizes was in good agreement with the BJR supplement 25 and the data supplied by the manufacturer of machine. Significant deviation of about 20% in isodose line near the edge of the profile was observed for 35 × 35 cm 2 field size. The penumbra widths of all field sizes were comparable except for 35 × 35 cm 2 , which has a penumbra width of 4.1 cm at 10 cm depth. The significant under dose near the edge as compared to central axis for larger field sizes may be the indication for its careful use in treatment.

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The phenomenon of drop in output at larger field sizes for telecobalt units

Singh

Semwal

et al. 2016

Radiol Phys Technol

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It is known that the output factors (OPFs) for external-beam radiotherapy units increase with field size due to increased scattered radiation from the collimator system. Saturation in the OPF value is generally reported beyond approximately 30 × 30 cm(2). For the first time, to the best of our knowledge, we report on a drop in OPF values, although marginal, measured for a telecobalt machine beyond the 38 × 38 cm(2) field size. We believe that reporting and explaining the results will lead to a better understanding of the scatter composition of the radiation from telecobalt machines. This also has the potential to impact the estimation of low dose regions in patients, in addition to being a purely scientific inquiry. We used Monte Carlo (MC) simulations to validate the measured values. The MC data showed that the decrease in OPF was due to decreased scatter from the machine head.

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Monte Carlo simulation based study of a proposed multileaf collimator for a telecobalt machine

Cited by 10 publications

References 22 publications

Monte Carlo study of MLC fields for cobalt therapy machine

Monte Carlo study of MLC fields for cobalt therapy machine

Radiation Beam Characterization and Dosimetry of Theratron Equinox-80 Telecobalt Machine Using BEAMnrc Monte Carlo Simulation Code

The phenomenon of drop in output at larger field sizes for telecobalt units

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