(Saturday, 4/7/2018)
Room: Foyer
Purpose: To investigate the dosimetric influence of oral contrast medium used for pancreatic cancer radiotherapy treatment planning, as well as the influence intension correlated to different levels of contrast density and different radiation techniques.
Methods: 10 candidates with locally advanced pancreatic cancer and no remote metastasis were enrolled in our study. 250ml of diluted solution consisting 3% iopamidol was given orally 15mins before CT scanning. Target volumes, normal tissues and astrointestinal contrast volume (CV) under irradiation implicated were countered on the oral contrast CT images respectively.In our study, we simulated 4 branches of treatment plans as 5/7/9-beam conformal radiotherapy (5/7/9b-CRT) and volumetric modulated arc therapy (VMAT) for each patient. For each plan, 8 QA-plans were designed keeping all parameters the same except the HU value of CV were forced filled with 8 bulk of HU value varied from 0HU(ED=1.0) to 1000HU (ED=1.54). Finally, dose distribution of isolate plan was compiled and compared.
Results: The analysis warranted that as CV HU enlarged from 0HU to 1000HU, the dose deviation of target volume was linearly overestimated but the percentage difference was relatively small.It shows a decline trend of dose deviation when higher modulated techniques was employed. Dose in target volume showed a relatively smaller deviation compared with that in OARs. All percentage difference was smaller than 1% and a whole picture gamma index analysis indicated 100% pass rate for 2%/2 mm criteria when CV HU<500, while in clinical the CV mean HU value is around 200.
Conclusion: The dosimetric influence of oral contrast medium for pancreatic cancer radiotherapy was clinically negligible if the enhanced electron density was controlled in a reasonable zone. The quantitative analysis indicated the dose deviation was smaller than 1% if enhancement level kept in a suitable level. Furthermore, higher modulation technique can reduce the deviation.
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