Tehran University of Medical Sciences Frontiers in Biomedical Technologies 2345-5837 0 0 2026 04 23 1329 1329 EN Shaghayegh Abroshan M.Sc in Medical Physics, Student Research Committee, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran. Farzaneh Allahveisi 0009-0002-4679-7839. Karim Khoshgard Department of Medical Physics, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran Bahar Moussas Ghaffari Department of Radiology, School of Medicine, Kurdistan University of Medical Sciences, Sanandaj, Iran. Mohsen Bakhshandeh Faculty of Allied Medical Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Siamak Derakhshan Department of Radiotherapy and Nuclear medicine, Faculty of Paramedical Medicine, Kurdistan University of Medical Sciences, Sanandaj, Iran. 2025 06 28 2025 10 03 Purpose: The main goal of radiotherapy is to deliver a lethal radiation dose to tumor tissue while minimizing the dose to healthy tissues. Treatment planning in radiotherapy requires precise determination of the treatment volume and specification of the radiation dose to both the tumor and healthy tissues. To define the treatment volume in radiotherapy, margins are considered around the tumor tissue, which may include a portion of normal tissue. Fusion of PET-CT images with CT images in the three-dimensional conformal radiotherapy for lung cancer may improve treatment by more accurately and precisely determining the Gross Tumor Volume (GTV). This study aimed to compare the treatment volumes and dosimetric parameters between conventional treatment planning (using CT images only) and treatment planning using PET-CT image fusion in 3D-conformal radiotherapy for lung cancer. Materials and Methods: All lung cancer patients who were referred to our Radiotherapy center over two years were examined. PET-CT images and simulation CT scans of 15 patients with non-metastatic lung cancer were analyzed. All patients were treated using the 3D-conformal radiotherapy method. The treatment planning and image fusion were performed using the ISOGRAY treatment planning software. The volumetric as well as dosimetric parameters, such as mean dose, maximum dose in the target volume, and other dose-volume parameters in organs at risk such as lung tissue including V5, V13, and V20 were compared between the two groups (including the conventional treatment planning group (only using CT data) and the treatment planning using the PET-CT image fusion group). Results: A total of 23 lung cancer patients were included during the study period; of these, eight patients were excluded due to having metastatic lung cancer. The variation in Gross Tumor Volume (GTV) among the different patients was significantly high. The fusion of PET images with CT scans increased the GTV in 11 patients (on average by 48±89.7%) and decreased it in 5 cases (46.4±98.0%). According to the results (considering all patients), no statistically significant difference was noted in the Contoured Tumor Volume (CTV) between the conventional method (based on CT images only) and the method based on the fused images with PET-CT images (P-value > 0.05). There was no statistically significant difference in maximum dose at healthy tissues/Organs At Risk (OARs), including the ipsilateral lung, contralateral lung, skin, and spinal cord, between treatment planning based on CT images and based on fusion with PET-CT data (P-value > 0.05). The mean dose in the lung (in involved side %43±.16.66) decreased (on average by %41±21.00) after fusion with PET-CT images (P-value > 0.05). Conclusion: The use of PET-CT data in radiotherapy treatment planning for lung cancer patients undergoing adaptive 3D radiotherapy can have an improving and impactful role. The fusion of PET-CT images with CT data had a significant effect on the tumor volume definition, resulting in changes in the gross tumor volume in most patients. It is recommended to utilize data from both anatomical (CT) and functional (PET) imaging modalities for a better assessment and definition of tumor volume, as each modality has its advantages and limitations. However, by combining them, the tumor volume can be determined with greater precision and accuracy. Additionally, improving the precision in defining tumor volume can reduce the radiation dose received by healthy tissues/organs at risk https://fbt.tums.ac.ir/index.php/fbt/article/view/1329 https://fbt.tums.ac.ir/index.php/fbt/article/download/1329/557