Comparison of the 3D-conformal, helical tomotherapy and multileaf collimators-based intensity modulated radiotherapy modalities using radiobiological measures

Purpose: Intensity modulated radiotherapy (IMRT) using multileaf collimators (MLC) and helical tomotherapy (HT) have become increasingly popular over the past few years. However their clinical efficacy and effectiveness continue to be investigated. In order toprovide a more thorough evaluation and comparison of treatment plans, the utilization of the biologically effective uniform dose (D) together with the complication-free tumor control probability (P₊) are examined. Materials and methods: In this study, a typical case of lung cancer was investigated by developing a 3D conformal treatment plan, a linac MLC-based step-and-shoot IMRT plan and a HT plan. The 3 different treatment plans were compared based on radiobiological measures by using the P₊ index and the D concept as the common prescription point of the plans and plotting the tissue response probabilities vs. D for a range of prescription doses. Results: The applied plan evaluation method showed that in this lung cancer case the MLC-based IMRT plan was best over the clinically useful dose prescription range. The 3D-conformal, MLC-based IMRT and HT treatment plans gave a P₊ of 55.4%, 72.9% and 66.9%, for a D to the internal target volume (ITV) of 57.0 Gy, 66.9 Gy and 64.0 Gy, respectively. Conclusion: In comparison to 3D conformal radiotherapy, both MLC based-IMRT and HT can better encompass the often large ITV required while minimizing the volume of the organs at risk receiving high dose. Taking into account the dose-response relations of the irradiated tumors and normal tissues, a radiobiological treatment plan evaluation can be performed, which may provide a closer association of the delivered treatment with the clinical outcome.