Helical tomotherapy for single and multiple liver tumours

Dosimetric evaluations of single and multiple liver tumours performed using intensity-modulated helical tomotherapy (HT) were quantitatively investigated. Step-and-shoot intensity-modulated radiotherapy (SaS-IMRT) was used as a benchmark.

Sixteen patients separated into two groups with primary hepatocellular carcinomas or metastatic liver tumours previously treated using SaS-IMRT were examined and re-planned by HT. The dosimetric indices used included the conformity index (CI) and homogeneity index (HI) for the planned target volume (PTV), max/mean dose, quality index (QI), normal tissue complication probability (NTCP), V(30 Gy), and V(50%) for the specified organs at risk (OARs). The monitor units per fraction (MU/fr) and delivery time were also analysed.

For the single tumour group, both planning systems satisfied the required PTV prescription, but no statistical significance was shown by the indexes checking. A shorter delivery time and lower MU/fr value were achieved by the SaS-IMRT. For the group of multiple tumours, the average improvement in CI and HI was 14% and 4% for HT versus SaS-IMRT, respectively. Lower V(50%), V(30 Gy) and QI values were found, indicating a significant dosimetric gain in HT. The NTCP value of the normal liver was 20.27 +/- 13.29% for SaS-IMRT and 2.38 +/- 2.25% for HT, indicating fewer tissue complications following HT. The latter also required a shorter delivery time.

Our study suggests dosimetric benefits of HT over SaS-IMRT plans in the case of multiple liver tumours, especially with regards sparing of OARs. No significant dosimetric difference was revealed in the case of single liver tumour, but SaS-IMRT showed better efficiency in terms of MU/fr and delivery time.