The Effect of Contrast Agents on Dose Calculations of Volumetric Modulated Arc Radiotherapy Plans for Critical Structures

Abstract

Radiotherapy dose calculation requires accurate Computed Tomography (CT) imaging while tissue delineation may necessitate the use of contrast agents (CA). Acquiring these two sets is a common practice in radiotherapy. This study aims to evaluate the effect of CA on the dose calculations. Two hundred and twenty-six volumetric modulated arc therapy (VMAT) patients that had planning CT with contrast (CCT) and non-contrast CT (NCCT) of different cancer sites (e.g., brain, head, and neck (H&N), chest, abdomen, and pelvis) were evaluated. Treatment plans were recalculated using CCT, then compared to NCCT. The variation in Hounsfield units (HU) and dose distributions for critical structures and target volumes were analyzed using mean HU, mean and maximum relative dose values, D2%, D98%, and 3D gamma analysis. HU variations were statistically significant for most structures. However, this was not clinically significant as the difference in mean HU values was within 30 HU for soft tissue and 50 HU for lungs. Variation in target volumes’ D2% and D98% were insignificant for all sites except brain and nasopharynx. Dose maximum differences were within 2% for the majority of critical structures and target volumes. 3D gamma analysis results revealed that majority of plans satisfied the 2% and 2 mm criteria. CCT may be acquired for VMAT radiotherapy planning purposes instead of NCCT, since there is no clinically significant difference in dose calculations based on either image set.

Dosimetric effects of embolization material artefacts in arteriovenous malformations stereotactic radiosurgery on treatment planning calculation

“…Many published studies have investigated the effect of contrast agents on radiotherapy dose calculations [10][11][12][13][14][15][16], however, fewer studies investigated the influence of embolic materials. The reviewed published articles on the subject can be divided into two groups, first group acknowledged the effect and recommended dosimetric corrections [17][18][19][20].…”

Dosimetric effects of oral contrast in the planning of conventional radiotherapy and IMRT, for rectal cancer treatment

“…Contrast agents are frequently used during CT to characterise both healthy and tumour tissues more accurately. 1,2 Treatment planning systems (TPS) convert the Hounsfield Unit (HU) values of different tissues or materials in the CT to electron or mass densities, depending on the algorithm used for planning. As contrast agents have elements with higher atomic numbers than most of the human tissues, they increase HUs, which could result in changes in calculated doses.…”

“…3 Therefore, if the dose calculation is performed in a contrastenhanced CT, there is a concern of dosimetric deviation because the treatment is administered in the absence of contrast. 1,4 In order to avoid this problem, it is a common practice to obtain two CT scans during the same simulation session: one unenhanced and one enhanced. 5 However, it has been described that performing two CT scans during the simulation not only exposes the patient to additional radiation but also reduces the optimisation of resources in the radiation oncology department by extending the simulation time.…”

“…3,7 These limits could explain why some researchers have described that, even if contrast agents cause noticeable increase in HU values, these changes are clinically insignificant. 1,[8][9][10][11] In spite of that, there are few studies assessing dosimetric differences in pelvis. 1,4,[12][13][14][15][16] The present study evaluates the effect of oral contrast on dose distribution calculation for rectal cancer patients, using threedimensional conformal radiation therapy (3D-CRT) and volumetric modulated arc radiotherapy (VMAT) planning.…”

“…1,[8][9][10][11] In spite of that, there are few studies assessing dosimetric differences in pelvis. 1,4,[12][13][14][15][16] The present study evaluates the effect of oral contrast on dose distribution calculation for rectal cancer patients, using threedimensional conformal radiation therapy (3D-CRT) and volumetric modulated arc radiotherapy (VMAT) planning.…”