Effect of linear accelerator carbon fiber couch on radiotherapy dose.

This study aimed to explore the effect of carbon fiber couch on radiotherapy dose attenuation and gamma pass rate in intensity-modulated radiotherapy (IMRT) plans. A phantom inserted with an ionization chamber was placed at different positions of the couch, and the dose was measured by the chamber. Under the same positioning, the phantom dose was calculated using the real and virtual couch images, and the difference in the planned dose of radiotherapy was compared. Ten clinical IMRT plans were selected as dose verification data, and the gamma pass rates were compared between couch addition and non-addition conditions. When the radiation field was near 110° and 250°, the measured value attenuation coefficient of the ionization chamber at the joint of the couch was up to 34%; the attenuation coefficient of the treatment couch from the actual couch image calculated using the treatment planning system (TPS) was up to 33%; the attenuation coefficient of the virtual couch calculated using the TPS was up to 4.0%. The gamma pass rate of the dose verification near gantry angles 110° and 250° was low, and that of the joint could be lower than 85% under the condition of 3%/3 mm. The gamma pass rates of the radiation field passing through the couch were all affected. The dose was affected by the radiation field passing through the couch, with the largest effect when passing through the joint part of the treatment couch, followed by that of the main couch plate and extension plate. When the irradiation field passed through the joint and near 110° and 250° of the main couch, the dose difference was large, making it unsuitable for treatment.

Comparison of combinations of irradiation techniques and jaw conditions in intensity-modulated radiotherapy for lung cancer.

PURPOSE: To assist in the selection of a suitable combination of an irradiation technique and jaw condition in intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc radiotherapy (VMAT) for lung cancer treatment plans. MATERIALS AND METHODS: Thirty patients with lung cancer who underwent radiotherapy were enrolled retrospectively. They were categorized as having central lung cancer, peripheral lung cancer with mediastinal lymph node metastasis (peripheral E lung cancer), and peripheral lung cancer without mediastinal lymph node metastasis (peripheral N lung cancer). Four treatment plans were designed for each patient: fixed jaw and adaptive jaw IMRT technique (FJ-IMRT and JA-IMRT), and fixed jaw and jaw tracking VMAT technique (FJ-VMAT and JT-VMAT). The dose parameters of the four group plans were compared and analyzed. RESULTS: Compared to FJ-IMRT, JA-IMRT significantly reduced the mean dose (Dmean ) and volume percentage of 5 Gy (V5Gy ) of the total lung in central and peripheral N lung cancer. Similarly, compared to FJ-VMAT, JT-VMAT provided better protection to most organs at risk (OARs), particularly for total lung and heart. In comparison with IMRT, VMAT significantly improved the conformity index (CI) of the planning target volume for the three lung cancer classifications, and it reduced the dose of almost all OARs except V5Gy and Dmean of the total lung. Moreover, the mean monitor units of the VMAT groups were far lower than the IMRT groups. CONCLUSION: Based on the dosimetric findings and considering clinical data published on lung and heart side effects, we propose recommendations on the preferred treatment technique based on tumor location and pulmonary function. For central lung cancer with normal pulmonary function, we advise JT-VMAT techniques. Conversely, for central lung cancer with poor pulmonary function, we recommend JA-IMRT techniques. We advocate JA-IMRT for peripheral E lung cancer. For peripheral N lung cancer, JT-VMAT techniques are strongly recommended.