Objective. The aim of this study was to reconstruct volumetric computed tomography (CT) images in real-time from ultra-sparse two-dimensional x-ray projections, facilitating easier navigation and positioning during image-guided radiation therapy. Approach. Our approach leverages a voxel-sapce-searching Transformer model to overcome the limitations of conventional CT reconstruction techniques, which require extensive x-ray projections and lead to high radiation doses and equipment constraints. Main results. The proposed XTransCT algorithm demonstrated superior performance in terms of image quality, structural accuracy, and generalizability across different datasets, including a hospital set of 50 patients, the large-scale public LIDC-IDRI dataset, and the LNDb dataset for cross-validation. Notably, the algorithm achieved an approximately 300% improvement in reconstruction speed, with a rate of 44 ms per 3D image reconstruction compared to former 3D convolution-based methods. Significance. The XTransCT architecture has the potential to impact clinical practice by providing high-quality CT images faster and with substantially reduced radiation exposure for patients. The model's generalizability suggests it has the potential applicable in various healthcare settings.

It is important to decrease the radiation exposure of normal tissue in intensity-modulated radiation therapy (IMRT). Minimizing planning target volume (PTV) margins with more precise target localization techniques can achieve this goal. This study aimed to quantify the extent to which organs at risk (OARs) are spared when using reduced margins in the treatment of nasopharyngeal carcinoma (NPC). Two IMRT plans were regenerated for 40 patients with NPC based on two PTV margins, which were reduced or unchanged following cone beam computed tomography online correction. The reduced-margin plan was optimized based on maximal dose reduction to OARs without compromising target coverage. Dosimetric comparisons were evaluated in terms of target coverage and OAR sparing. Improvements in target coverage occurred with margin reduction, and significant improvements in dosimetric parameters were observed for all OARs (P < 0.05) except for the right optic nerve, chiasm, and lens. Doses to OARs decreased at a rate of 1.5% to 7.7%. Sparing of the left parotid and right parotid, where the mean dose (Dmean) decreased at a rate of 7.1% and 7.7%, respectively, was greater than the sparing of other OARs. Significant improvements in OAR sparing were observed with margin reduction, in addition to improvement in target coverage. The parotids benefited most from the online imaging-guided approach.

Background: This prospective study was conducted to evaluate inter- and intra-fraction errors in nasopharyngeal carcinoma (NPC) patients undergoing volumetric modulated arc therapy (VMAT) using cone-beam computed tomography (CBCT) and to thus obtain planning target volume (PTV) margins to effectively guide treatment in the future. Methods: Fifteen NPC patients scheduled to undergo VMAT were prospectively enrolled in the study. For each patient, three CBCT scans were obtained; one after daily conventional positioning, one after online correction with 2 mm tolerance and one after 1 week of VMAT delivery. The scans were registered to the planning CT to determine the inter- and intra-fraction errors. Patient positioning errors were analyzed for time trends over the course of radiotherapy. PTV margins were calculated from the systematic (Σ) and random (σ) errors. Results: The average absolute values of the pre-correction, post-correction and intra-fraction errors (in order) were 1.1, 0.6 and 0.4 mm in the medial–lateral (ML) direction, 1.2, 0.7 and 0.5 mm in the superior–inferior (SI) direction and 1.1, 0.7 and 0.5 mm in the anterior–posterior (AP) direction. The corresponding Σ were 1.0–1.4 mm, 0.4–0.5 mm and 0.2–0.4 mm, while the corresponding σ were 0.7–0.8 mm, 0.6–0.7 mm and 0.5–0.6 mm. With time, gradual increases in both the inter- and intra-fraction three-dimensional displacements were observed (P = 0.019 and P = 0.044, respectively). The total PTV margins accounting for pre-correction and intra-fraction errors were 3.4–4.1 mm and those accounting for post-correction and intra-fraction errors were 1.7–2.2 mm. Conclusions: CBCT is an effective modality to evaluate and improve the accuracy of VMAT in NPC patients. Inter- and intra-fraction three-dimensional displacements increased as a function of time during the course of radiotherapy. In our institution, we recommend a PTV margin of 5 mm for NPC patients undergoing VMAT without CBCT and 3 mm for those treated with rigorous daily CBCT scans.

Background: This retrospective cohort study aims to study the changes of the exposed volume of the bladder and rectum under different filling states, and to clarify the influences of the morphing organs on themselves and each other, to provide the basis for reducing the risk of organ damage by intensity-modulated radiotherapy (IMRT) for cervical cancer. Methods: A retrospective analysis was performed on 24 patients with cervical cancer who received IMRT. Before radiotherapy, a comfortably full bladder and active defecation was ensured for all patients, and interative cone-beam computed tomography (iCBCT) was performed to delineate the bladder, rectum, and small intestine. The filling degree of the bladder, rectum, and small intestine and their intersection with the planned target volume were recorded. Results: 83.44% of patients exhibited reduced bladder volume during treatment. When the planned bladder volume was 400–500 cc, the bladder volume changed the least during treatment (F = 58.39, P < .001). The exposed volume of the small intestine was moderately correlated with the degree of bladder filling ( r = −.674, P < .01). For every 10% increase in bladder volume, the exposed volume of the small intestine decreased by 24.05% ( P < .01). Furthermore, 45.83% patients had an increase in rectum volume during treatment. The exposed volume increased by 9.47% for every 10% increase in rectum volume ( P < .01). Conclusion: Comfortable bladder and active defecation regimens may not keep bladder and rectal stability. Targeting a planned bladder volume of 400 to 500cc minimizes intrafraction variability. Strategic bladder filling optimization may mitigate small intestine exposure.

To compare the incidence of radiation-induced temporal lobe injury (TLI) between helical tomotherapy (HT) and conventional intensity-modulated radiotherapy

Objective: The objective of this study is to evaluate the impact of different belly board and daily changes in patient's body‐mass factor (BMF) on setup displacement in radiotherapy for rectal cancer.Methods: Twenty‐five patients were immobilized using the thermoplastic mask with belly board (TM‐BB), and 30 used the vacuum bag cushion with belly board (VBC‐BB), performing daily cone‐beam computed tomography (CBCT) scans 625 times and 750 times, respectively. Daily pretreatment CBCT scans were registered to the planned CT images for BMF change determination and setup displacement measurement. Independent t‐tests compared setup displacement between the two groups in left‐right (LR), superior‐inferior (SI), and anterior‐posterior (AP) directions, as well as the BMF changes. The impact of daily BMF changes on setup displacement was evaluated using multivariate logistic regression and 10‐fold cross‐validation.Results: The setup displacement for TM‐BB in the LR, SI, and AP directions were 0.31 ± 0.25, 0.58 ± 0.40, and 0.19 ± 0.18 cm, respectively, while VBC‐BB showed 0.19 ± 0.15, 0.26 ± 0.22, and 0.36 ± 0.29 cm in the corresponding directions, respectively. Margins of planning target volume (PTV) for TM‐BB were 8, 10, and 6 mm in LR, SI, and AP directions, while VBC‐BB showed margins of 5,7, and 8 mm, respectively. The daily BMF changes for both groups were ranked in descending order as follows: sacral rotation angle (RS), hip lateral diameter (HLD), and hip anterior‐posterior diameter (HAPD). HAPD was the main factor affecting setup displacement in both the AP and SI directions in TM‐BB, while RS was the primary factor for setup displacement in the AP direction in VBC‐BB.Conclusion: Compared with TM‐BB, VBC‐BB had a larger AP displacement but smaller in LR and SI displacement. Daily changes in BMF have distinct effects on setup displacement in different immobilization devices. Image‐guided radiation therapy (IGRT) is highly recommended and BMF changes should be given consideration during radiotherapy.