Contribution of Imaging to Organs at Risk Dose during Lung Stereotactic Body Radiation Therapy

Background: The use of imaging is indispensable in modern radiation therapy, both for simulation and treatment delivery. For safe and sure utilization, dose delivery from imaging must be evaluated. Objective: This study aims to investigate the dose to organ at risk (OAR) delivered by imaging during lung stereotactic body radiation therapy (SBRT) and to evaluate its contribution to the treatment total dose.Material and Methods: In this retrospectively study, imaging total dose to organs at risk (OARs) (spinal cord, esophagus, lungs, and heart) and effective dose were retrospectively evaluated from ۱۰۰ consecutive patients of a single institution who had lung SBRT. For each patient, dose was estimated using Monte-Carlo convolution for helical computed tomography (helical CT), Four-Dimensional CT (۴D-CT), and kilovoltage Cone-Beam CT (kV-CBCT). Helical CT and kV-CBCT dose were evaluated for the entire thorax acquisition, while ۴D-CT dose was analyzed on upper lobe (UL) or lower lobe (LL) acquisition. Treatment dose was extracted from treatment planning system and compared to imaging total dose. Results: Imaging total dose maximum values were ۱۱۷ mGy to the spinal cord, ۱۲۷ mGy to the esophagus, ۱۷۶ mGy to the lungs and ۱۹۳ mGy to the heart. The maximum effective dose was ۱۹.۶۵ mSv for helical CT, ۱۰.۶۲ mSv for kV-CBCT, ۲۵.۹۵ mSv and ۳۸.۴۵ mSv for ۴D-CT in UL and LL regions, respectively. Depending on OAR, treatment total dose was higher from ۱.۷ to ۸.۲ times than imaging total dose. Imaging total dose contributed only to ۰.۳% of treatment total dose. Conclusion: Imaging dose delivered with ۴D-CT to the OARs is higher than those of others modalities. The heart received the highest imaging dose for both UL and LL. Total imaging dose is negligible since it contributed only to ۰.۳% of treatment total dose.

Keywords:

Lung , Organs at Risk Exposure , Computed Tomography , Four-Dimensional Computed Tomography , Cone-Beam Computed Tomography , Stereotactic Body Radiation Therapy