2Department of Public Health, İstanbul University-Cerrahpaşa, Cerrahpaşa Faculty of Medicine, İstanbul-Türkiye DOI : 10.5505/tjo.2023.4034 OBJECTIVE
Computed tomography images used in radiotherapy are automatically created by Treatment Planning Systems using the patient's body contour. However, due to irregularities in the head-and-neck region, some corrections are required, especially for auricular contours. Since the beam entrances are at all angles, a change in the auricular contour may alter the beam's entry angle and distance, which may cause changes in the target volume and surrounding critical structure doses in the volumetric arc technique (VMAT). We aimed to dosimetrically compare the treatment plans created with and without correction of auricular contours on the planning images.
METHODS
The data of 19 nasopharyngeal cancer patients treated using VMAT were evaluated. The VMAT treatment
plans made in the Eclipse Treatment Planning System using the same optimization values were
evaluated based on the ability to meet dose-volume constraints. Using the Student's t-test and Wilcoxon
signed-rank test, comparisons were made of planning doses, planning target volumes (PTV), conformity
index (CI), homogeneity index (HI), and critical organs involved.
RESULTS
We found a statistically significant difference between the corrected and non-corrected plans regarding
maximum dose (Dmax), dose to 2% of PTV (D2), CI, and HI. When evaluated in terms of normal tissue
doses, especially in patients with level 2 cervical lymph node metastases, particularly for the parotid
mean dose, a statistically significant increase in the planning dose was observed when the auricular
contour was corrected (p<0.001).
CONCLUSION
Thus, applying auricular contour correction on an individual patient basis seems appropriate, especially
in the presence of target volumes with close localization.