Abstract

Background: Radiation therapy for advanced head and neck cancer has developed from the Three-Dimensional Conformal Radiotherapy 3DCRT to intensity modulated radiation therapy IMRT and Volumetric Modulated Arc Therapy VMAT. Remaining Volume at Risk RVR is clinically important in plan evaluating process. RVR is useful for assisting and estimating the risk of late effects.

Aim: The aim of the present work is to compare dosimetric evaluation factors and dosimetric data remaining volume at risk for both IMRT and VMAT in the treatment of large volume head and neck cancer patients.

Patients and methods: Eleven retrospective patients with advanced head and neck tumors were selected for the planning study. The patients’ treatments are planned by using the two different techniques (IMRT and VMAT) and optimized to evaluate highly conformal target coverage and sparing organs at risk OAR. Standard fractionation is 33 fractions with 5 fractions weekly, the prescribed doses 70Gy, 59.4Gy and 54Gy for the high, intermediate, and low risk targets by simultaneous integrated boost.

Results: The study showed that VMAT and IMRT are comparable in target volumes homogeneity index HI, while VMAT is more superior (0.76, 44.4and 589) and (0.68, 55.6 and 1989) in conformity number CN, gradient index GI and Monitor Units (MU), respectively. Furthermore, VMAT has an advantage over IMRT in RVR volumes that received 15Gy, 10Gy and 5Gy, which are (4327, 5281 and 6703cc) and a 1019cGy mean dose in the VMAT technique, while in IMRT are (4435, 5311 and 6543cc) and a 1051cGy mean dose.

Conclusion: The results of comparing dosimetric evaluation factors of both techniques showed that VMAT had a priority over IMRT in 3 factors of RVR evaluation parameters. Additionally, to other comparison points, especially the time on the machine, makes VMAT a first choice in the treatment plan selection.

Keywords: Head and Neck; IMRT; VMAT; RVR

Abbreviations: 3DCRT: Three-Dimensional Conformal Radiotherapy; IMRT: Intensity Modulated Radiation Therapy; VMAT: Volumetric Modulated Arc Therapy; RVR: Remaining Volume at Risk; HI: Homogeneity Index; CN: Conformity Number; GI: Gradient Index; MU: Monitor Units; HNC: Head and Neck Cancer; OAR: Organs at Risk; GTV: Gross Target Volume; CTV: Clinical Target Volume; PTV: Planning Target Volume