Normal Tissue Objective Tool in Radiotherapy Planning for Endometrial Cancer: A Dosimetric Study

Abstract

OBJECTIVE This dosimetric study investigated the influence of the normal tissue objective (NTO) tool in the EclipseTM radiotherapy (RT) planning system on intensity -modulated RT (IMRT) for adjuvant RT planning in endometrial cancer. METHODS Twenty patients, diagnosed with stage -2 endometrial cancer according to the International Federation of Gynecology and Obstetrics, were enrolled from our Radiation Oncology department. For each patient, three IMRT plans were devised: Without NTO (NTO-OFF), with manually configured NTO (NTO-MAN), and with automatically configured NTO (NTO-AUTO). The plans were compared using parameters derived from dose -volume histogram analysis, including planning target volume and organs at risk (OARs). RESULTS The mean conformality index was superior with NTO-MAN (0.76 +/- 0.05) compared to NTO-AUTO (0.72 +/- 0.03, p=0.001) and NTO-OFF (0.62 +/- 0.02, p=0.000). IMRT with NTO-MAN provided enhanced OAR protection, particularly for the bladder (V45=32.84 +/- 2.03 vs. 37.03 +/- 1.55, p=0.000) and rectum (V30=56.18 +/- 2.05 vs. 60.50 +/- 3.86, p=0.000), compared to NTO-AUTO. The dose constraints for the bladder and rectum were not exceeded in any patient treated with NTO-MAN but exceeded in 19 (95%) and 9 (45%) patients, respectively, with NTO-AUTO. CONCLUSION The manual NTO tool resulted in greater conformality and OAR protection. Therefore, we recommend the use of manual NTO in adjuvant IMRT planning for endometrial cancer patients.