Introduction: Intensity-modulated radiotherapy (IMRT) has been shown to reduce dose to organs at risk (OAR) while adequately treating tumour volume. This study quantitatively compares the dosimetric differences from step-and-shoot IMRT compared with helical tomotherapy (HT) for pancreatic head cancer.
Methods: Twelve consecutive patients with non-metastatic, stage T3 or T4, unresectable pancreatic head cancer were planned for step-and-shoot IMRT as well as HT. Radiotherapy was planned to deliver 45.9 Gy to the clinical target volume in 30 fractions with an integrated boost to 54 Gy to the gross tumour volume (planning target volume 5400 including a 1-cm set-up margin). The uniformity index (UI) and conformity index (CI) were used to compare the quality of target coverage, while the quality index (QI) compared the dosimetric performance for OAR.
Results: Both methods were effective at covering the tumour with no significant difference in UI or CI. However, HT dosimetry exhibited superior sparing of OAR with significantly less stomach (mean QI(StomV30) = 0.84, P = 0.006) and small bowel dosing (mean small bowel QI(SBV30) = 0.84, P = 0.005). HT reduced dose to the kidney receiving the highest dose but the overall volume of kidney receiving 18 Gy was not significantly different between the two systems, indicating that HT spread the dose more uniformly through the kidneys.
Conclusions: Target coverage is equivalent between the two systems; however, HT shows significantly better sparing of the stomach and small bowel. The decreased dose to OAR with HT is likely to improve the therapeutic ratio in the radiotherapy of pancreatic head cancers.
© 2012 The Authors. Journal of Medical Imaging and Radiation Oncology © 2012 The Royal Australian and New Zealand College of Radiologists.