Verification of a treatment planning system using an in-house designedtrunk phantom

This study is aimed at verifying the dosimetric performance of a treatment planning system (TPS) and to as well compare the accuracy of the measured absorbed dose of the solid water phantom against the inhouse phantom. In this study, a phantom for use in radiotherapy treatment planning of human trunk anatomical region has been designed with six hollows for inserting materials mimicking different biological tissues and the ionization chamber. For the trunk, pure Glycerolwas used for Muscle, 75% to 25% Glycerol-Water was used for liver, Carboxyl-Methyl-Cellulose (CMC)was used for Lungs, 50% to 50% Glycerol-Water was used for Adipose, Sodium Hypochlorite (soda bleach) for Bone and SodiumLaureth Sulphate (Texapon) was used for Kidney. The phantom was scanned with Hi-Speed CT-scannerand images were transferred to a Precise PLAN Treatment Planning System where appropriate beams were applied and verified before it was transferred to the Elekta-Precise Clinical Linear Accelerator.Measurements of the Monitor Units (MU) were conducted using 6 MeV photon beams from the Elekta-Precise Clinical Linear Accelerator with iso-centric set up and the corresponding doses were calculated. The test of the phantom was done using an Irregular Field Algorithm (Clarkson Integration). The maximum standard deviation with large field size of22 × 24cmfor all sixinhomogeneous inserts and bone only inhomogeneous inserts were −3.39% and 2.93% respectively. And maximum standard deviation with small field size of 5 × 5cmwas−3.16%. Also, the percentage deviation for the solid water phantom when compared with the in-house phantom with SSD of 85cm for both set-ups was −2.09%. Theseresultsshow that irrespective of the field sizes and tissue equivalent materials, Irregular Field Algorithm compensates for inhomogeneity.