Wiener Filter Used in the EBT2 Film for Radiation Therapy

Abstract

EBT2 film has been widely used in the dosimetry application of radiation therapy with lots of benefits especially its self-development, water equivalent, energy independent and high spatial resolution. However, the higher inhomogeneity between the pixels of EBT2 image, needed to be averaged out according to the traditional method, but it could sacrifice the spatial resolution. The Wiener filter technique was introduced in this paper. The EBT2 film was calibrated by using the PDD method and the film calculate doses were compared with the measurement doses by the edge detector with the water phantom. The results demonstrate that the Wiener filter technique has higher accuracy than the traditional method and it would not sacrifice the high spatial resolution of EBT2 film. This method can also be applied to all the quality assurances of treatment planning of radiationtherapy by using EBT2 film. Index Terms—Wiener filter, EBT2 film, radiation therapy I. INTRODUCTION A rapid evolution of the available treatment methods has takenplace in radiation therapy during the last two decades, which includes those precise treatment techniques: intensitymodulated(IMRT), stereotactic (SRT) radiotherapy and several dynamic techniques.In order to achieve dose distributions with highlyconformal to the target volume and spare normal tissues (especially the organs at risk), the irregular fieldsand steep dose gradients are applied by the inverse treatment planning system with the advanced linear accelerator. For the effectiveness and success of the treatment prescribed,a high spatial and dosimetric accuracy during treatment delivery is of crucialimportance.Therefore, particular quality assurance (QA) procedureshave been developed together with those increasingly sophisticatedtreatment techniques (1)-(3), which wouldinclude the verification of absolute doses at one or more reference points as well as of twodimensionaldose distributions in different planes in awater-equivalent phantom. Those requirements could not be achieved by using the conventionaldosimeters, such as ionization chambers, semiconductor detectors and thermoluminescentdetectors (TLDs), since they could not offer high spatial resolution, twodimensionalinformation and determination of absolute dosessimultaneously.Film dosimeters offerpermanent records of the ionizing dose distribution measured at high resolutions with evident advantages for being 2D detectors. Due to the high-atomic-number material constituents, the