Radiation-Induced CT Texture Changes of Duodenum During Radiation Therapy for Pancreatic Cancer

Abstract

Acute and late Radiation induced duodenal toxicity is a factor limiting the delivery of curative radiation doses to pancreatic tumors. We investigated acute radiation-induced changes in CT textures and its potential to assess radiation effect on the duodenum during radiation therapy (RT) for pancreatic cancer. Daily diagnostic-quality CTs acquired using a CT-on-rails system during routine CT-guided chemo-RT (CRT) for 18 pancreatic head cancer patients were analyzed. All patients were treated with pre-operative radiation of 50.4 Gy/28 fractions with the maximum dose to duodenum limited to 53 Gy. Contours of the duodenum and pancreatic head were created on the 1st daily and every 5th daily CT for each patient. A series of CT texture features, including Hounsfield Units (HU) histogram features (e.g., mean CT number (MCTN), standard deviation (SD), skewness, entropy, and kurtosis) were extracted in these contours using an in-house algorithm. Changes in these features between the daily CTs in the duodenum and pancreatic head were calculated and tested with the GEE model. Association of the texture changes with the mean and maximum doses in the duodenum and with the texture changes in the pancreatic head were analyzed using Pearson correlation tests. The CT texture changes for the patients who experienced radiation-induced duodenitis were analyzed specifically. It was generally observed that the CT textures in the duodenum changed with increasing radiation dose, and these changes were highly patient specific. The duodenum MCTN in 12 patients decreased by up to 14 HU (range: -1.8 ∼ -14 HU; median: -6.1 HU) from the first to the last treatment fractions, while it increased in the remaining 6 patients (range: 0.2∼8.3 HU; median: 2.1 HU). The duodenum SD decreased in 11 patients by up to 7.2 HU (range: -0.2 ∼ -7.2 HU; median: -2.9 HU) and increased in 7 patients (0.1 ∼ 6.9 HU, median: 1.5 HU). For skewness, 13 patients had an increase (range: 0.04 ∼ 0.74; median: 0.28 HU) and 5 had a decrease (-0.04 ∼ -0.33, median: -0.1). For kurtosis, 13 patients had a decrease (range: -0.04 ∼ -3.4; median: -0.9) and 5 had an increase (0.01∼1.6, median: 0.3). For a given patient, the MCTN change in the duodenum is generally smaller than in the pancreatic head. The difference is not significant in all the patients studied (p=0.099). For the two patients experiencing duodenitis, neither mean nor maximum dose to the duodenum was associated with the MCTN changes. However, there were local abnormal changes observed in the high HU portions of the histograms for the two cases. Radiation can induce CT texture changes in the duodenum during CRT for pancreatic cancer. The change is patient specific and can be measured during the duration of RT delivery, indicating its potential as an imaging biomarker for radiation effect of the duodenum.