Variations of the Dose Distribution Between CT- and CBCT-based Plans for Oropharyngeal Cancer

Abstract

Background/Aim: The parotid glands in the head and neck are organs at risks (OARs) adjacent to high dose region and dose of OARs might be increased during the course of radiotherapy. The influence factors of the dose distribution for the parotid glands were investigated in terms of weight loss and mandibular rotation for head and neck cancers treated with volumetric modulated arc therapy (VMAT). Patients and Methods: Ten oropharyngeal cancer patients (OPC) who underwent VMAT were enrolled. The dose volume histogram (DVH) parameters of the parotid glands and planning target volume (PTV) were compared between the planning computed tomography (CT) and the on board imager (OBI) at 1, 5, 10, 15, and 20 fractions. Results: The variation of dose distribution in PTV was not observed in both factors. The relationship between the mandibular rotation and dose difference for the right and left parotid glands (linear regression, r 2 =0.1577 and −0.689) showed a slighty stronger correlation with dose difference than the weight loss (linear regression, r 2 =−0.079 and −0.547). Conclusion: The mandibular rotation tends to have a large influence on dose distribution of the parotid glands for head and neck cancers treated with VMAT.

Assessment of dosimetric impact of interfractional 6D setup error in tongue cancer treated with IMRT and VMAT using daily kV-CBCT

“…They have substantial dosimetric effects on delivered doses to targets and OARs. Previous studies found that interfractional translational and rotational errors significantly alter the delivered dose to target volumes and OARs [22][23][24][25][26][27][28][29][30][31]. Many such studies have employed various methods to mimic the dosimetric impact of setup errors.…”

“…Many such studies have employed various methods to mimic the dosimetric impact of setup errors. These methods include dose simulation on planning computed tomography (pCT), cone-beam CT (CBCT), and dose accumulation using deformable image registration of pCT and CBCT [22][23][24][25][26][27][28][29][30][31][32]. Most previous studies simulated and evaluated the dosimetric impact of interfractional setup errors on pCT with weekly or lower imaging frequencies of setup verification [22][23][24][25][26][27][28][29].…”

“…Similarly, Otsuka et al evaluated the dosimetric impact of parotid and mandible rotation in oropharyngeal cancer using CBCT dose reconstruction. However, the dosimetric impact was evaluated with a limited CBCT dataset [31]. Most radiotherapy clinics perform verification imaging for the first three days and then weekly or less frequently (moderate setup error correction) for IMRT and VMAT [20,25,[27][28][29]31].…”

“…However, the dosimetric impact was evaluated with a limited CBCT dataset [31]. Most radiotherapy clinics perform verification imaging for the first three days and then weekly or less frequently (moderate setup error correction) for IMRT and VMAT [20,25,[27][28][29]31]. However, in tongue (head and neck) cancer, it is important to use daily CBCT to see how the daily interfractional setup error affects the dose.…”