Evaluation of tumor control probability and normal tissue complication probability in IMRT and VMAT: A comparative study for assessment of efficacy of radiotherapy plans in tumors of the thorax.

Objective: The primary aim of radiation therapy planning is to achieve optimal tumor control probability (TCP) while minimizing the risk of normal tissue complications (NTCPs). Traditionally, the dose-volume histogram has been a reliable tool for evaluating volumetric dose distribution in treatment plans. This study aims to assess the radiobiological efficacy of volumetric modulated arc therapy (VMAT), step-and-shoot intensity-modulated radiation therapy (ss-IMRT), and dynamic IMRT (d-IMRT) in the treatment of thoracic tumors.

Materials and methods: This study involved 13 patients diagnosed with squamous cell carcinoma of the thorax. Thirteen patients with squamous cell carcinoma of the thoracic site were included in this study. For each patient, three treatment plans (VMAT, ss-IMRT, and d-IMRT) were created, and the corresponding radiobiological parameters, such as equivalent uniform dose (EUD), TCP, and NTCP, were computed using Niemierko and LKB model for all 39 treatment plans using BIOSUITE software.

Results: The estimated average TCPs for ss-IMRT, d-IMRT, and VMAT are 61.51%, 62.86%, and 63.09%, respectively. Moreover, the average NTCPs observed for the organ at risk, lung, for ss-IMRT, d-IMRT, and VMAT were 3.27%, 1.96%, and 1.29%, respectively. In terms of the spinal cord, the average NTCPs for ss-IMRT, d-IMRT, and VMAT were 0.07%, 0.0%, and 0.0%, respectively. For the heart, the average NTCPs for ss-IMRT, d-IMRT, and VMAT were 0.10%, 0.12%, and 0.13%, respectively.

Conclusions: The findings of this study suggest that VMAT might give equivalent TCP with less NTCP when compared to IMRT. The development of treatment planning techniques based on radiobiological factors aided in the prudent selection of physical parameters to attain high TCP and low NTCP.