Image-guided volumetric arc radiotherapy of pancreatic cancer with simultaneous integrated boost: Optimization strategies and dosimetric results

Abstract

PurposeTo introduce volumetric modulated arc therapy treatments (VMAT) with simultaneous integrated boost (SIB) for pancreatic cancer and describe dosimetric results on a large patient series. Methods and materials45 patients with pancreatic malignancies were treated with 18 MV single-arc VMAT. Image guidance was performed with daily online kilo-volt cone-beam computed tomography (CBCT). The conformity index (CI) and homogeneity index (HI) to the target volumes, PTV45Gy and PTV54Gy, and dose–volume indices to OARs from the QUANTEC task group were reported. The risk of clinical nephritis was evaluated using normal tissue complication probability (NTCP). Treatments were verified in-phantom with the Delta4 system. ResultsAverage CI was 1.06 with 95% confidence intervals (95% CI) of 0.97–1.22 for PTV45Gy and 1.17 (0.66–1.61) for PTV54Gy. HI of PTV54Gy was 1.06 (1.04–1.10). OAR constraints were achieved in all patients, except for kidneys V12Gy of 48 (35.4–72.3)%. NTCP of the kidneys was 0.98 (0.6–1.7)%. Kidneys V12Gy and V20Gy were inversely related to PTV54Gy CI and maximum dose. All in-phantom tests had gamma pass rates exceeding 95% with global 3% dose difference and 3 mm distance to agreement. Patient shifts measured with CBCT had 95% CI of −0.8, +0.8 in the RL, −0.7, +0.8 in the SI, and −0.8, +0.7 cm in the AP directions. ConclusionsDosimetric results of VMAT were excellent on PTVs and organs at risk. The kidneys represent the dose-limiting organ at risk for this technique. NTCP indicates that this technique is safe from radiation-induced side effects to the kidneys.