Abstract
PurposeAdaptive radiotherapy (ART) has potential to reduce toxicity and facilitate safe dose escalation. Dose calculations with the planning CT deformed to cone beam CT (CBCT) have shown promise for estimating the “dose of the day”. The purpose of this study is to investigate the “dose of the day” calculation accuracy based on CBCT and deformable image registration (DIR) for lung cancer radiotherapy.MethodsA total of 12 lung cancer patients were identified, for which daily CBCT imaging was performed for treatment positioning. A re‐planning CT (rCT) was acquired after 20 Gy for all patients. A virtual CT (vCT) was created by deforming initial planning CT (pCT) to the simulated CBCT that was generated from deforming CBCT to rCT acquired on the same day. Treatment beams from the initial plan were copied to the vCT and rCT for dose calculation. Dosimetric agreement between vCT‐based and rCT‐based accumulated doses was evaluated using the Bland‐Altman analysis.ResultsMean differences in dose‐volume metrics between vCT and rCT were smaller than 1.5%, and most discrepancies fell within the range of ± 5% for the target volume, lung, esophagus, and heart. For spinal cord Dmax, a large mean difference of −5.55% was observed, which was largely attributed to very limited CBCT image quality (e.g., truncation artifacts).ConclusionThis study demonstrated a reasonable agreement in dose‐volume metrics between dose accumulation based on vCT and rCT, with the exception for cases with poor CBCT image quality. These findings suggest potential utility of vCT for providing a reasonable estimate of the “dose of the day”, and thus facilitating the process of ART for lung cancer.
Highlights
Radiotherapy is a widely used treatment option for unresectable or inoperable non‐small cell lung cancer (NSCLC) patients
While adaptive radiotherapy (ART) is often done with repeat planning CT, utilizing cone beam computed tomography (CBCT) for estimating the “dose of the day” has been an attractive research topic since they are readily available along the treatment course
The approach of “dose of the day” calculation based on CBCT and deformable image registration (DIR)
Summary
Radiotherapy is a widely used treatment option for unresectable or inoperable non‐small cell lung cancer (NSCLC) patients. Significant progress has been made in radiotherapy for lung cancer in recent decades, improving clinical outcomes for NSCLC is still challenging.[1] Dose escalation is one of the potential strategies to improve outcomes, but it may increase normal tissues toxicities,[2,3] for example, pneumonitis, pulmonary fibrosis, and cardiac injury, among others. While ART is often done with repeat planning CT (rCT), utilizing cone beam computed tomography (CBCT) for estimating the “dose of the day” has been an attractive research topic since they are readily available along the treatment course. Previous studies have shown promising results for estimating the “dose of the day” based on deformed CT images.[15,17,18,19,25] Marchant et al.[15] found that less than 0.5% mean dose errors can be achieved with the deformed CT images for lung cancer patients, when compared with pCT. An open source deformation algorithm was used in this study, which may not be practical for clinical adoption
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