Photon dose-calculation in the treatment planning system (Eclipse) and its applications in cancer patients treatment planning

THis study is conducted & thesis submitted in partial fulfilment for requirements of the degree of M.Sc. in physics, College of Science, King Saud Univerisity, 2006G - 1427HAn extensive set of measured data was developed to verify the accuracy of a photon dose-calculation algorithm for the treatment planning system (Eclipse). Dose distributions from a linear accelerator were measured using an ion chamber in a water phantom and thermoluminescent dosimeters in a heterogeneous anthropomorphic phantom. Test cases included square fields, rectangular fields, fields having different source-to-surface distances, wedged fields, irregular fields, obliquely incident fields, asymmetrically collimated fields with wedges, multileafe collimator-shaped fields, and two heterogeneous density cases. The data set was used to validate the photon dose calculation algorithm in a radiation treatment planning system (Eclipse). Eclipse calculated photon doses to within the American Association of Physicists in Medicine (AAPM) Task Group 53 (TG-53) criteria for 99% of points in the buildup region, 93% of points in the inner region, 90% of points in the outer region, and 88% of points in the penumbra. For the heterogeneous phantoms, calculations agreed with actual measurements to within ±7%. The monitor unit tests revealed that the 6MV open square fields, rectangular fields, wedged fields, oblique incidence, SSD variation, mantle field, half beam block, and oblique incidence with wedge test cases did not meet the TG-53 criteria all the time. It was concluded that (i) The photon dose calculation algorithm (Pencil beam convolution algorithm) used by the treatment planning system (Eclipse) did not meet the TG-53 criteria 100% of the time. (ii) Some of the TG-53 criteria may need to be modified, regarding regions with high dose gradient (Build up and penumbra regions), regions at electronic equilibrium and build up in heterogeneous media. (iii) The generally stated goal of accuracy in dose delivery of within 5% cannot be met in all situations using this beam model in the treatment planning system (Eclipse). Hence, it is recommended to improve the accuracy of the TPS, e.g. with the incorporation of the Monte Carlo calculation method to the latest version of Eclipse