Purpose: To compare conformal radiotherapy (CRT), intensity-modulated radiotherapy (IMRT), and respiration-gated radiotherapy (RGRT) planning techniques for pancreatic cancer. All target volumes were determined using four-dimensional computed tomography scans (4D CT).
Methods and materials: The pancreatic tumor and enlarged regional lymph nodes were contoured on all 10 phases of a planning 4D CT scan for 10 patients, and the planning target volumes (PTV(all phases)) were generated. Three consecutive respiratory phases for RGRT delivery in both inspiration and expiration were identified, and the corresponding PTVs (PTV(inspiration) and PTV(expiration)) and organ at risk volumes created. Treatment plans using CRT and IMRT, with and without RGRT, were created for each PTV.
Results: Compared with the CRT plans, IMRT significantly reduced the mean volume of right kidney exposed to 20 Gy from 27.7% +/- 17.7% to 16.0% +/- 18.2% (standard deviation) (p < 0.01), but this was not achieved for the left kidney (11.1% +/- 14.2% to 5.7% +/- 6.5%; p = 0.1). The IMRT plans also reduced the mean gastric, hepatic, and small bowel doses (p < 0.01). No additional reductions in the dose to the kidneys or other organs at risk were seen when RGRT plans were combined with either CRT or IMRT, and the findings for RGRT in end-expiration and end-inspiration were similar.
Conclusion: 4D CT-based IMRT plans for pancreatic tumors significantly reduced the radiation doses to the right kidney, liver, stomach, and small bowel compared with CRT plans. The additional dosimetric benefits from RGRT appear limited in this setting.