Investigating the safety of radiotherapy without simulation in patients with bone metastases

Palliative radiotherapy (RT) is an effective treatment method to manage disease symptoms such as pain, dyspnea and bleeding in patients with advanced and metastatic cancer. Approximately 35-40% of all palliative RT is directed to bone metastases. For RT planning, treatment planning is performed on cross-sectional images of patients using simulation computed tomography (CT-sim) available in clinics. In the elderly and infirm patient population, this step can be uncomfortable and may prolong the time until treatment is initiated. In such cases, the treatment process can be accelerated by planning on the available diagnostic CT images of the patients. The aim of this study was to investigate the efficacy and safety of simulation-free RT in patients with bone metastases. For this purpose, CT-sim images and PET-CT images taken with a median interval of 3 weeks with CT-sim images of 15 patients who were previously treated in our clinic were used. For each patient, the target volume of the L1-L4 vertebrae and the nearby organs at risk (OAR) including the kidney, spinal canal, renal hilus and renal vessels were recontoured. PTV was created with a 5-mm margin to the CTV created by contouring the L1-L4 vertebrae and a dose-fractionation scheme of 8 Gy/1 fraction was defined. Each patient was planned with 3D-CRT and VMAT techniques on CT-sim images and PET-CT images. A third treatment plan was made on PET-CT images and copied on CT-sim to reflect the treatment conditions. Together with the plans created to evaluate the contrast agent effect on both PET-CT and copied plans, 10 treatment plans were created for each patient and 150 treatment plans were created in total. PTVDmax, PTVD95 and OAR mean and maximum doses were calculated and statistically compared for 3D-CRT and VMAT techniques both within and between each other. For the target volume, no significant difference was observed when PTVD95 was evaluated as a result of the comparison of the plans made on PET-CT and CT-sim. For PTVDmax doses, both 3D-CRT and VMAT techniques were higher in the plans copied on CT-sim. Although this difference is statistically significant, it is at the cGy level and is quite small. When the mean and maximum doses of OARs were evaluated, no significant difference was observed in the plans performed on PET-CT and on CT-sim. In general, maximum dose values were higher in 3D-CRT plans and mean dose values were higher in VMAT plans. In our study, the doses received by the L1-L4 vertebrae and nearby RAOs were statistically compared in detail with both 3D-CRT and VMAT techniques. As a result, the findings of our study may help to make a patient-specific decision on which treatment plan to be made with 3D-CRT or VMAT techniques and may contribute to the literature on the difference in the doses received by OARs during treatment compared to the plans made on CT-sim. The fact that our study focused on vertebral metastases may limit the generalizability of our findings, although it provides an optimization specific to this region. In conclusion, the findings of our study demonstrated the usability and reliability of PET-CT in treatment planning. In line with these results, it can be used as a method to shorten the treatment planning process in the elderly and frail patient population. Further studies in a larger patient population may provide confirmation of our findings in a large patient population.