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Cobalt-60 (Co-60) teletherapy units are most commonly used radiation device in low and middle income countries. The reasons for that are (1) low costs in purchase and maintenance, (2) simplicity of operation and (3) no need for non-interference electric power supply. The treatment with Co-60 still remains the main radiotherapy technique since developing countries include 85% of the world human population. Therefore, teletherapy with Co-60 needs further development and improvement. The purpose of the current study is to show the feasibility of MLC-based IMRT treatment planning on a Co-60 machine.

The treatment planning was performed with the Prowess Panther system using collapsed cone dose calculation algorithm. The plans were created for the treatment on a Best Theratron Equinox Co-60 machine equipped with a Best Theratronics Multileaf Collimator. Each plan consisted of 7 IMRT fields with user pre-defined gantry angles. Three different anatomical sites and treatment schedules were selected: (1) Head and Neck with simultaneous integrated boost (SIB) 70Gy/56Gy/35fx, (2) Prostate with Pelvic Lymph nodes with SIB 70Gy/50.4Gy/28fx, (3) Prostate 70Gy/28fx. The planning goals were to achieve acceptable target coverage (D_95%>95%) while fulfilling the OARs constraints and to maximize the prescription dose conformality.

Dose-volume statistics and “beam-on” times for the created treatment plans are presented in Fig.1. The example of isodose levels and DVH are showed in Fig.2.

We demonstrated the feasibility of MLC-based IMRT planning on a Co-60 machine with acceptable target coverage and OARs sparing. Although these plans cannot compete with the plans for modern linear accelerators, mainly due to low dose gradient and high entrance doses, the implementation of MLC-based IMRT treatments should noticeably improve the quality of treatment plans and potentially reduce side effects compared with the non-IMRT techniques implemented on Co-60 machines nowadays.