Evaluation of Tumor Control and Normal Tissue Complication Probability in Head and Neck Cancers with Different Sources of Radiation: A Comparative Study

Introduction: The ultimate goal of radiation treatment planning is to yield a high tumor control probability (TCP) with a low normal tissue complication probability (NTCP). Historically  dose volume histogram (DVH) with only volumetric dose distribution was utilized as a popular tool for plan evaluation  hence present study aimed to compare the radiobiological effectiveness of the cobalt-60 (Co-60) gamma photon and 6MV X-rays of linear accelerators (Linac) in the radiotherapy of head and neck tumors.  Materials and Methods: TCP and NTCP were calculated using DVH through the BIOPLAN software developed by Sanchez-Nieto and Nahum . The treatment planning was performed for all the patients using both treatment modalities (i.e., Co-60 and 6 MV Linac). The TCP was also manually calculated using a mathematical formula proposed by Brenner’s et al. Results: The average TCP calculated by the BIOPLAN for Co-60 and 6 MV X-rays were 44.6% and 60.8%, respectively. Furthermore, the average NTCPs obtained for the organ at risk, namely optic nerve, for Co-60 and 6 MV X-ray were 0.24 % and 0.03 %, respectively. Regarding the spinal cord, the average NTCPs for Co-60 gamma photon and 6 MV X-ray of Linac were 0.05 % and 0.002%, respectively. Conclusion: As the findings of the present study indicated, Co-60 unit could provide comparable TCP along with minimal NTCP, compared to the high-cost technologies of Linac. The design of treatment plans based on the radiobiological parameters facilitated the judicious choice of physical parameters for the achievement of high TCP and low NTCP.

Keywords:

Tumor control probability , Normal tissue complication probability , Dose Volume Histogram