Verification of an irregular field algorithm of a treatment planning system using a locally designed pelvic phantom: A simple design low-cost phantom suitable for quality assurance and control test in radiotherapy

Abstract

BACKGROUND: Modern radiotherapy treatment machine today comes along side with sophisticated treatment planning systems (TPSs). The accuracy of any TPS depends on the mathematical algorithm it uses and can be well verified using a dedicated phantom. AIMS AND OBJECTIVES: To design a low-cost pelvic phantom and to use the designed phantom to verify whether the accuracy of an Irregular Field Algorithm of a Precise PLAN 2.16 TPS is within ±5% International Commission on Radiation Units and Measurements (ICRU) minimal limit. MATERIALS AND METHODS: Designed pelvic phantom was made of Plexiglas with six tissue equivalent inserts and an ion-chamber port. The mimicked organs for the inserts were: Prostate, bladder, adipose, muscle, rectum, and bone. A Hi-speed computed tomography (CT) simulator was used for acquiring images and CT numbers of the designed pelvic phantom, a Precise PLAN 2.16 TPS was used for image planning, an Elekta-Precise Clinical Linear Accelerator was used for prescription of the planned images and a precalibrated NE 2570/1 farmer-type ion-chamber with an electrometer was used to calculate the mean dose. Data analysis value was done using GraphPad Prism 5.0 statistics software. RESULTS: The maximum percentage deviation with large field sizes of 22 cm × 25 cm for six different inhomogeneous inserts was −3.95%, and bone only homogeneous inserts was 2.38%. The maximum percentage deviation with small field sizes of 5 cm × 5 cm with six different inhomogeneous inserts was −3.57%. The percentage deviation between the solid water phantom and the locally designed pelvic phantom was −3.46%. CONCLUSION: The irregular field algorithm showed an overall accuracy of approximately ±4% with the locally designed pelvic phantom for both large and small field sizes against ±5% ICRU minimal limit. Although there were significant differences in percentage deviation between inhomogeneity and homogeneous insert irrespective of field sizes.