Dose Calculation Accuracy and Algorithm Validation of Low Density Heterogeneities in Co

Telecobalt machine is one of the essential equipment needed in many cancer centers and still prominently used for the treatment of a variety of cancer cases in developing countries. This study aims to evaluate the impact of tissue heterogeneity corrections on 3D treatment planning system (Prowess). The human body contains a variety of tissues and cavities which vary widely in their physical and radiological properties. The presence of these heterogeneities in the path of telecobalt beam causes an altered dose distribution in the region of clinical interests. A computerized treatment planning system (TPS) is generally used for calculating the dose distribution in the patient. Experimental measurements were carried out in a telecobalt beam with the objectives to study the effects of low-density heterogeneities and to verify the ability of the Prowess radiotherapy TPS in predicting the altered dose distribution along the central axis and off-axis of the beam. All measurements were carried out in a PTW RW3 solid slab phantom by introducing heterogeneous waterlung equivalent phantom (full slab and lung geometry). A comparison of experimentally measured and TPS calculated dose values indicate that the TPS overestimates the dose by 12.7% in lung equivalent (Cork) heterogeneity along the central axis. For air heterogeneity of 1.0 and 2.0cm, a comparison of experimentally measured and TPS calculated dose values indicate that the TPS overestimates the dose by 3.9% and 5.9%, respectively. While testing the adequacy of TPS in off-axis region, it was found that the TPS calculation does not indicate the widening of the beam profile in the lowdensity heterogeneity region. This study suggests that the Prowess algorithm TPS is unable to achieve the recommended 3% accuracy of clinical dose calculation in heterogeneous media and air gap.