Radiation-induced malignancies from simultaneous integrated boost-VMAT for oropharyngeal cancer delivered with four...

Late side-effects including carcinogenesis may appear following head-and-neck tumor irradiation. This study estimated the risk for developing second malignancies in heavily exposed tissues from simultaneous integrated boost (SIB) volumetric modulated arc therapy (VMAT) for oropharyngeal carcinoma.

Sixteen oropharyngeal carcinoma patients needing bilateral neck irradiation were included. A three-level SIB-VMAT technique with 6-MV photons was applied. Four different treatment plans were created per patient. The first plan (VMAT_70Gy) was generated based on conventional fractionation delivering total doses to three targets of 70/63/56 Gy in 35 fractions. The VMAT_66Gy, VMAT_60Gy and VMAT_56.7Gy plans gave target doses of 66/60/54 Gy in 30 fractions, 60/56/50 Gy in 25 fractions and 56.7/52.5/46.2 Gy in 21 fractions, respectively. Differential dose-volume-histograms and a non-linear model were employed to estimate the lifetime attributable risk (LAR) for cancer induction in critical tissues adjacent to the treatment volume. The model accounted for dose fractionation and tissue-dependent proliferation ability.

For 50-year-old males and females undergoing VMAT_70Gy, the average LAR for cancer induction in thyroid, salivary glands, mouth/pharynx and brain/CNS was up to 0.25%, 0.26%, 1.32% and 0.31%, respectively. The risk range for patients aged 60 years was 0.09-0.74%. These LARs were reduced up to 4.3%, 8.0% and 13.1% with VMAT_66Gy, VMAT_60Gy and VMAT_56.7Gy plans_, respectively. The three moderately hypofractionated radiotherapy techniques led to cancer risks of 0.08-1.27%.

The risks for radiation-induced malignancies following SIB-VMAT for oropharyngeal cancer were found to be comparable with the baseline risks for general population. Hypofractionated treatment restricted the probability for carcinogenesis.