Journal of Medical Physics
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ORIGINAL ARTICLE
Year : 2020  |  Volume : 45  |  Issue : 4  |  Page : 215-220

Estimation of skin doses for retrofit prototype multileaf collimators designed for telecobalt therapy machine


1 Department of Physics, Osmania University; Department of Radiation Oncology, MNJ Institute of Oncology and Regional Cancer Center, Hyderabad, Telangana; Department of Radiation Oncology, International Cancer Centre, MGMMT, Bhimavaram, Andhra Pradesh, India
2 Department of Radiation Oncology, International Cancer Centre, MGMMT, Bhimavaram, Andhra Pradesh, India
3 Department of Radiation Oncology, Mahatma Gandhi Cancer Hospital and Research Institute, Visakhapatnam, Andhra Pradesh, India
4 Department of Physics, Osmania University, Hyderabad, Telangana, India

Correspondence Address:
Dr. Akula Roopa Rani
MNJ Regional Institute of Oncology and Regional Cancer Centre, Red Hills, Hyderabad - 500 004, Telangana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jmp.JMP_25_20

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Aim: The objective of this study was to evaluate skin dose based on retrofit prototype multileaf collimators (MLCs), designed for cobalt-60 teletherapy machine. Since patient's skin is sensitive to radiation, evaluation of skin dose is of utmost importance for investigating the risk of late effects. Materials and Methods: Measurements were performed with a Phoenix cobalt-60 teletherapy machine and the detector used was EBT3 radiochromic film. The experiments were performed in a solid water phantom with two prototype MLCs mounted to the machine. Dose readings were taken by placing the films at source-to-surface distance (SSD) of 60 cm, 65 cm, 70 cm, 75 cm, 80 cm, 85 cm, and 90 cm for various MLC-generated field sizes starting from 2 cm × 2 cm to 14 cm × 14 cm. The films were analyzed using custom made programs. The measured doses were normalized to the dose at dmax for that particular measurement of SSD. Results: The skin dose is expressed as a percentage of dose at dose maximum. In general, the skin dose increases with field size and decreases with SSD. The measurements indicate surface doses within 20%–60% for the investigated SSD range. Furthermore, there is no significant difference between the surface doses of two prototype MLCs studied. Conclusions: From the measurements, it can be concluded that there is good skin sparing even at close distance to the MLCs. The skin dose is <50% for SSDs >65 cm. A minimum gap of 5 cm is required to produce acceptable skin dose.


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