Normal tissue objective (NTO) tool in Eclipse treatment planning system for dose distribution optimization

Abstract

Introduction: The purpose of this study was to determine the best normal tissue objective (NTO) values based on the dose distribution from brain tumor radiation therapy. Material and methods: The NTO is a constraint provided by Eclipse to limit the dose to normal tissues by steepening the dose gradient. The multitude of NTO setting combinations necessitates optimal NTO settings. The Eclipse supports manual and automatic NTOs. Fifteen patients were re-planned using NTO priorities of 1, 50, 100, 150, 200, and 500 in combination with dose fall-offs of 0.05, 0.1, 0.2, 0.3, 0.5, 1 and 5 mm-1. NTO distance to planning target volume (PTV), start dose, and end dose were 1 mm, 105%, and 60%, respectively, for all plans. In addition, planning without the NTO was arranged to find out its effect on planning. The prescription dose covered 95% of the PTV. Planning was evaluated using several indices: conformity index (CI), homogeneity index (HI), gradient index (GI), modified gradient index (mGI), comprehensive quality index (CQI), and monitor unit (MU). Differences among automatic NTO, manual NTO, and without NTO were evaluated using the Wilcoxon signed-rank test. Results: Comparisons obtained without and with manual NTO were: CI of 0.77 vs. 0.96 (p = 0.002), GI of 4.52 vs. 4.69 (p = 0.233), mGI of 4.93 vs. 3.95 (p = 0.001), HI of 1.10 vs. 1.10 (p = 0.330), and MU/cGy of 3.44 vs. 3.42 (p = 0.460). Planning without NTO produced a poor conformity index. Comparisons of automatic and manual NTOs were: CI of 0.92 vs. 0.96 (p = 0.035), GI of 5.25 vs. 4.69 (p = 0.253), mGI of 4.46 vs. 3.95 (p = 0.001), HI of 1.09 vs. 1.10 (p = 0.004), MU/cGy of 3.31 vs. 3.42 (p = 0.041). Conclusions: Based on these results, manual NTO with a priority of 100 and dose fall-off 0.5 mm-1 was optimal, as indicated by the high dose reduction in normal tissue.

Assessment of normal tissue objectives in RapidArc treatment for cervical cancer

“…This contrasts with the findings of a prior study by Indrayani et al, where a notable change in CI value occurred following optimization with NTO. 12 Another investigation by Bell et al aimed to establish the optimal NTO setting by assessing automatic and manual NTO with various priorities and dose fall-off values. 11 In the current study, the average CI value associated with manual NTO was more proximate to the optimal value than that associated with automatic NTO.…”

“…This contrasts with the findings of a prior study by Indrayani et al, where a notable change in CI value occurred following optimization with NTO. 12…”

“…Manual NTO settings with 500 priority and 0·15 mm fall-off produced significant results in lung SBRT planning 11 . Indrayani et al made an effort to find out the optimal NTO value for brain tumour radiation therapy 12 . According to their study, planning without NTO showed poor results.…”