A Study on Radiation Level at the Treatment Plane Due to Induced Activity in Linear Accelerator Head

The induced activity is produced in the target, monitor chamber, flattening filter (FF), collimating jaws, etc., when a high-energy photon beam is utilized for radiation therapy. This may result in add-on exposure to radiation professionals.

This study aims to measure the radiation level (RL) at the treatment plane due to induced activity in the linear accelerator head.

In this study, RLs were measured close to the isocenter (I), LINAC head (H), and 0.5 m lateral to the isocenter (L) inside the radiation bunker. The RLs were measured for field sizes (FS) 5 cm × 5 cm, 10 cm × 10 cm, 20 cm × 20 cm, 30 cm × 30 cm, and 40 cm × 40 cm, using 50, 100, 200, 300, 400, 500, and 1000 monitor units (MUs) at above said locations inside the bunker using 10 mega-voltage (MV), 10 MV FF free, and 15 MV radiation beam.

RL increases with an increase in FS and MUs at all mentioned locations inside the bunker, except for 40 cm × 40 cm FS. The present study shows that RL increases with an increase in radiation beam energy, and there was significant RL inside the bunker at the mentioned location, even after the 1 min of high-energy radiation exposure.

Therefore, treatment with a high-energy beam should be scheduled in the later evening of the working day and the jaw should be closed to a minimum before entering the bunker and a sufficient time gap should be followed to minimize the additional exposure due to induced activation in high-energy treatment.