Abstract
Fluorodeoxyglucose positron emission tomography-computed tomography (PET-CT) and four-dimensional CT (4DCT) are used in several methods for defining the biological target volume (BTV) in primary non-small cell lung cancer (NSCLC). Disagreements between the assessments using these methodologies make the use of BTV for radiotherapy planning controversial. In this study, we compared existing methods with our proposed internal biological target volume (IBTV) metric, derived by combining internal target volume (ITV) and BTV metrics. We defined the IBTV from ITV (IBTVi) or BTV (IBTVb) based on ITV or BTV with symmetrical margin expansion. We detected large differences between IBTV, IBTVi and IBTVb (p < 0.001), but no difference between ITV and BTV. A margin expansion of about 13 mm was necessary for ITV or BTV to encompass > 95% IBTV. The conformity index correlated negatively with IBTV/ITV, IBTV/BTV, IBTVi/ITV, and IBTVb/BTV volume ratios (p < 0.05). VR also increased the margins of IBTVi and IBTVb. Indeed, IBTV was much smaller than IBTVi or IBTVb, suggesting that using IBTV for radiotherapy planning could improve treatment by minimizing the radiation exposure of healthy tissue and organs surrounding tumors.
Highlights
Positron emission tomography-computed tomography (PET-CT) is widely used in the clinical practice of non-small cell lung cancer (NSCLC)
There was no difference between internal target volume (ITV) and biological target volume (BTV), whereas the difference between internal biological target volume (IBTV), IBTV from ITV (IBTVi) and IBTVb was significant (p < 0.001)
Compared to IBTVi or IBTVb, IBTV was closer to ITV and BTV
Summary
Positron emission tomography-computed tomography (PET-CT) is widely used in the clinical practice of non-small cell lung cancer (NSCLC). PETCT has revolutionized the field [1, 2], improving the definition of target volumes for radiotherapy planning [3]. Simulation of PET-CT scanning before radiotherapy is commonly advised because it provides more information than CT only. Taking advantage of the enhanced glucose metabolism of cancer cells, fluorodeoxyglucose (FDG) PET scanning distinguishes between normal and cancerous tissues, thereby accurately defines the biological target volume (BTV) [4]. CT provides precise tumor localization, volume evaluation, and the extent of local tissue invasion [5]. The application of BTV in radiation therapy planning is controversial because of the poor spatial resolution of PET images, which adds uncertainty in tumor localization, and because of disagreements between the various methods used to define BTV
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