Influence of the contrast agents on dose-volume histograms in radiotherapy treatment planning based on CT-scan

In three-dimensional conformal radiation therapy (3D-CRT), contrast-enhanced CT (CECT) image is commonly used to assist radiation oncologists in diagnosing regions of interest, so that normal and target tissues can be better delineated. CECT causes the temporary increase in the CT number and the corresponding electron density (ρe). Administrated contrast agents (CA) during CT simulation and altering the ρe of structures can be effective on radiation calculations and dose-volume histograms (DVHs) in radiotherapy treatment planning. Therefore, present study was designed and performed to determine the influence of the administrated CA on DVHs.
Current study performed as a self-controlled clinical trial study with before/after method at Imam Reza Hospital, Kermanshah City, during the period from June 2015 till August 2016. Ten patients with pelvic cancer included in this study through simple sampling. Cases with prior reactions to CA, diabetes, renal diseases, and asthma were excluded. Two sets of CT-scans were taken for each patient in the same position and coordinates. Primary study sets contained pre-contrast images and secondary study sets were performed post-contrast. Both sets of CT images were transferred to the treatment planning system (ISOgray® software, Version 4.1.3.23 L, DOSIsoft®, Cachan, France). All treatment plans were generated on pre-contrast and subsequently copied to the post-contrast CT. Quantitative calculations were performed in treatment planning including the difference in ρe before and after CA administration.
The prostate (1.27%), the bladder (0.62-0.79%) and the rectum (0.43-0.56%) showed the largest changes in average ρe increase. The results confirm the expected relationship of increasing attenuation, CT number, and ρe with increased tissue density due to the CA. However, the DVHs showed insignificant difference between pre-and post-contrast CTs for 18 MV photon beam.
The results showed statistical insignificant difference between with and without CA CTs treatment plan in pelvic field for targets and OARs. These results may serve as a reference to justify the use of CECT data sets for 3D-CRT planning of pelvic region cancers using DosiSoft ISOgray system.