Abstract
The reproducibility of patient setup is an important issue for head and neck cancers treated with intensity-modulated radiation therapy (IMRT). In this study, an image-guided radiation therapy (IGRT) system has been used to minimize the uncertainty of patient setup while standard thermoplastic masks were used to provide adequate immobilization for the head and neck. However, they do not provide sufficient immobilization of the shoulders, which is an important requirement in comprehensive nodal irradiation. Therefore, we investigated the setup and rotational shifts in head and neck cancer patients undergoing IMRT for which this immobilization device had been used together with an IGRT system. The setup and rotational shifts of patients were analyzed using the ExacTrac X-ray 6D IGRT system. The patients were classified as having head and neck tumors in the upper or lower regions. The upper neck nodes included lymph nodal level II while the lower neck nodes included lymph nodal levels III and IV. Clinical data from 227 treatment sessions of 12 head and neck cancer patients were analyzed. The random translational error in inter-and intra-fraction errors of the anterio-posterior (AP) direction might influence the rotational errors of pitch and roll in the upper region. At the same time, the random translational error in the inter-and intra-fraction errors of the AP direction might influence the rotational error of roll in the lower region. We believe that these random translational errors should be considered during treatment. We found variability in random translational errors for different regions in the anatomy of head and neck cancer patients due to rotational shifts. Depending on the location of the primary lesion or the selected nodal treatment targets, these relative positional variations should be considered when setup and rotational shifts are corrected with IGRT systems before treatment.
Highlights
The primary goal of radiation therapy is to deliver the desired radiation dose accurately to the desired target volume throughout the course of treatment
We investigated the setup reproducibility in head and neck cancer therapy for two different regions using from ExacTrac X-ray 6D image-guided radiation therapy (IGRT) data acquired while patients were immobilized in the treatment position
Recent work by Court et al [5] and Zhang et al [6] indicated that bony landmarks C2, C6, and the palatine process of maxilla (PPM) were independently chosen as alignment targets to represent these landmarks in most head and neck cancer patients
Summary
The primary goal of radiation therapy is to deliver the desired radiation dose accurately to the desired target volume throughout the course of treatment. Technological advances in conformal radiation therapy have made it possible to tailor treatment to match the shape and position of the target, and thereby minimizing normal tissue damage to a greater extent than previously possible. Intensity-modulated radiation therapy (IMRT), has yielded significant gains in tumor control and toxicity reduction [1,2,3]. Another technique, image-guided radiation therapy (IGRT), has focused on the characterization and control of patient movement, organ motion, and anatomical deformation, which introduce geometric uncertainty and limit the effectiveness of high-precision treatment. Target localization performed with appropriate technologies and frequency is a critical component of treat- Open Access IJMPCERO A.
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