CALCULATION OF SPINAL CORD RECEIVED DOSE IN ESOPHAGEAL CANCER RADIOTHERAPY: A COMPARISON BETWEEN MONTE CARLO SIMULATION AND TREATMENT PLANNING SYSTEM

Spinal cord is one of the organs at risk in esophageal cancer radiation therapy. The difference between the dose distribution due to the Treatment Planning System (TPS) and the patient's body dose is dependent on the calculation of the TPS algorithm, which is more pronounced in heterogeneities such as the Spinal cord. In this study, the dose distribution of TPS algorithm was compared with monte Carlo calculations in both homogeneous and heterogeneous tissue.

In this descriptive-analytical study, three-dimensional planning composed of four fields were done on the CT using the CorPLAN TPS of a SIEMENS PRIMUS linac. EGSnrc monte Carlo simulation code was used for the same conditions. The dose distribution obtained from Monte Carlo simulation and TPS was compared using PDD curve and Dose Difference Percentage index that obtained from these two modes.

According to the results, the error rate from the TPS was less than 3% in the homogeneous tissue, whereas the error in the Spinal cord heterogeneity was significant (more than 5%).

Results shows that the accuracy of CorPLAN TPS at homogeneous tissue is more than in the Spinal cord heterogeneity and this should be considered in the clinic. The findings also indicate that the monte carlo code can be used to simulate and evaluate the dose distribution in radiotherapy, and in cases where the practical measurement of some dosimetric parameters is impossible or difficult, this code can be used for prediction and optimization of treatment plans.