The normal tissue objective (NTO) is a tool used in inverse-planned intensity-modulated radiation therapy (IMRT) to minimize dose dispersion to surrounding tissues. The current study focuses on the NTO’s impact on RapidArc treatment plans for cervical cancer patients or its role in reducing doses to healthy surrounding tissues.

This study included 11 cervical cancer patients who underwent RapidArc treatment. We assessed plans both with and without the NTO objective by evaluating parameters such as homogeneity, conformity, gradient index (GI), IMRT factor, integral dose and the volume of normal tissues receiving low doses of 40, 30, 20 and 10 Gy. Further, differences between automatic NTO and manual NTO were evaluated using Wilcoxon signed-rank test.

There were no significant differences in the conformity index, homogeneity index, IMRT factor and integral dose between plans with automatic NTO and those with manual NTO RapidArc plans. However, we did observe a clear advantage in using manual NTO for controlling low-dose exposure to normal tissues. The comparisons between automatic and manual NTO resulted in a GI of 3·1 ± 0·3 versus 2·7 ± 0·68 (p = 0·008). Furthermore, we noticed a significant reduction in the volumes receiving low doses (V10, V20, V30 and V40) with the manual NTO settings.

The NTO plays a crucial role in optimizing RapidArc plans for treating cervical cancer. Based on the findings of this study, manual NTO settings of distance from PTV border xstart = 0·5 mm, start dose f0 = 105%, end dose f∞ = an average of 40%, dose fall-off 0·2 mm–1 were optimal. Further research involving a larger sample size and exploration of various NTO parameters is necessary to validate our results.