A prototype anti-scatter detector for megavoltage X-ray imaging

In this work, a prototype anti-scatter detector based on Cherenkov radiation is developed by using glass rods. Scattering lends deleterious effects to the megavoltage x-ray portal imaging and anti-scatter detector can effectively reduce these effects. A 10 cm long glass rod with 1 mm in diameter is used as a Cherenkov detector prototype and it is studied for its response to x-ray scattering from, e.g., machine head and patient. It is subjected to 6 MV x-ray beam generated by linear accelerator (LINAC) with different field sizes (from 3 X 3 to 20 X 20 cm2) at different air gaps such as 10, 30 and 46 cm. The Cherenkov signal created by the detector is transmitted through optical fiber to photomultiplier tube (PMT) and measured by electrometer. The patient scattering is studied by placing a solid water phantom at isocenter. The response of single pixel Cherenkov detector is compared with the conventional ionization chamber detector. It has been observed that glass rod based Cherenkov detector is less sensitive to scatter radiation than ion-chamber for air gap of 10 cm. The Cherenkov signal created by glass rod is quite weak for larger air gaps and the uncertainties are quite high. Moreover, the coupling between Cherenkov detector and optical fiber is quite crucial for transmitting the Cherenkov signal from glass rod into optical fiber.