Author: Klaus Bacher, Tom Boterberg, Jeff Rutten, Barbara Vanderstraeten, Gwenny Verfaillie, Sarah Waelkens 👨🔬
Affiliation: Ghent University, Ghent University Hospital 🌍
Purpose: Lymphoma cancer patients frequently receive ionizing radiation during their treatment trajectory, including diagnostic CT, planning CT (pCT), recurrent CBCTs, radiotherapy (out-of-field) doses, and follow-up PET/CTs. Cumulative organ doses exceeding 100 mGy raise concerns about secondary cancer risks. This study evaluated cumulative imaging doses using Monte Carlo (MC) simulations for pCTs and CBCTs. Radiotherapy doses were calculated using TPS and Periphocal3D, an analytical out-of-field (OOF) dosimetry software, as the TPS significantly underestimates OOF doses.
Methods: Whole-body CTs of 10 chest lymphoma patients treated at Ghent University Hospital were used as voxel models. Heart, liver, lungs, kidneys, esophagus, spine, and thyroid were segmented for personalized dose calculations. Imaging doses were calculated with the Monte Carlo software ImpactMC, while radiotherapy doses used TPS (within the 5% isodose) and Periphocal3D (outside the 5% isodose). On average, the lymphoma patients received 1 pCT, 6 CBCTs, and follow-up 7 PET/CTs. The used pCT is a Siemens SOMATOM go.Open Pro CT and the CBCT is an Elekta X-ray Volumetric Imager (XVI).
Results: In lymphoma patients, imaging contributed up to 40% of cumulative doses due to high chest protocol exposure settings. All segmented organs received >500 mGy, with imaging doses contributing between 140–300 mGy to the total cumulative dose. On average, the lungs, heart, spinal cord, thyroid, esophagus, kidneys and liver received a mean cumulative dose of 3038.2, 1264.1, 757.4, 673.9, 658.2, 512.8 and 522.5 mGy, respectively.
Conclusion: This study demonstrates that lymphoma patients receive significant cumulative radiation doses throughout their treatment, with imaging contributing up to 40% of the dose for certain organs. This is attributed to the high exposure settings of chest imaging protocols and the frequent follow-up PET/CT scans. All critical organs received >500 mGy. The findings are clinically significant for optimizing imaging protocols, especially chest CBCT in the treatment of lymphoma patients.