The new two-component conformity index formula (TCCI) and dose-volume comparisons of the pituitary gland and tonsil cancer IMRT plans using a linear accelerator and helical Tomotherapy

Abstract

Background/Aim

To examine the new dose-volume verification tool, called the two-component conformity index formula (TCCI), for tumours of the pituitary gland and tonsil cancer IMRT plans using helical Tomotherapy and a linear accelerator.

Material and Methods

10 medically inoperable patients – 5 with tumour of the pituitary gland and 5 tonsil cancers – were considered. Tomotherapy and Eclipse plans were compared by DVH analysis and new TCCI analysis including: 1/ the physician's intents for dose distribution in PRVs, 2/ more than one dose-volume constraint for dose distribution in PTV and healthy tissues, and 3/ separation between coverage and excess components.

Results

DVH analysis shows differences for the PTV received doses close to the prescription dose (PD): 1/in pituitary gland, Eclipse – 61% of PTV volume enclosed by PD and Tomotherapy – 50%, and 2/in tonsil cancer, Eclipse plans – 44% and Tomotherapy – 55%. These differences were clinically confirmed for tonsil cancer through TCCI analysis. Moreover, TCCI analysis shows better coverage of PTV volume through 90% and 95% isodose levels for Tomotherapy plans. Better high dose region reduction for brain stem and optic chiasm in pituitary gland and middle dose region reduction for parotids and spinal cord in tonsil and dose reduction in healthy tissues reported by TCCI analysis were observed for Tomotherapy plans.

Conclusions

The usefulness of the information provided means that TCCI could be used as a primary or alternative method of quick dose-volume verification finally supported by advanced DVH analysis.