Room: Exhibit Hall
Purpose: To investigate the feasibility of using mobile MOSFET dosimeter to measure eye dose during 2D MV portal imaging for setup verification in radiotherapy treatment.
Methods: The Mobile MOSFET dosimeters were calibrated against PTW 0.6 cc ionization chamber for low doses ranging from 1 cGy to 10 cGy. The in-vivo dose measurements were performed by placing the mobile MOSFET dosimeters on the surface of eyes and at the central axis of the beam for 30 head and neck patients. Double exposure technique was used to acquire portal images with EPID on the Primus linear accelerator (Siemens, Germany). The field sizes for double exposures were 10 cm x 10 cm and 15 cm x 15 cm. For each of the exposure, 1 MU was delivered.
Results: The average dose to the right and left eyes for 10 patients when both eyes were completely inside the portal fields were found to be 3.1Â±0.2 cGy and 2.9Â±0.2 cGy respectively whereas when both the eyes were completely out of the portal fields, the averaged dose to the right and left eyes were observed to be 0.29Â±0.03 cGy and 0.25Â±0.02 cGy respectively. The average dose to eyes for 10 patients in which one eye was inside the portal fields and other eye was completely outside the portal fields were 3.6Â±0.2 cGy and 0.6Â±0.1 cGy respectively. The average dose in the central axis of the beam was found to be 6Â±0.3 cGy for both portal fields.
Conclusion: The doses received by the eyes have been arrived at during 2D MV portal imaging. The mobile MOSFET dosimeters have been found to be very suitable dosimeter for assessing the dose during MV imaging and the dosimetric data helps to optimize the imaging procedure. Also it helps to document the patientâ€™s dose due to imaging.