Fully automated volumetric modulated arc therapy planning for locally advanced rectal cancer: feasibility and efficiency.

BACKGROUND: Volumetric modulated arc therapy (VMAT) for locally advanced rectal cancer (LARC) has emerged as a promising technique, but the planning process can be time-consuming and dependent on planner expertise. We aimed to develop a fully automated VMAT planning program for LARC and evaluate its feasibility and efficiency. METHODS: A total of 26 LARC patients who received VMAT treatment and the computed tomography (CT) scans were included in this study. Clinical target volumes and organs at risk were contoured by radiation oncologists. The automatic planning program, developed within the Raystation treatment planning system, used scripting capabilities and a Python environment to automate the entire planning process. The automated VMAT plan (auto-VMAT) was created by our automated planning program with the 26 CT scans used in the manual VMAT plan (manual-VMAT) and their regions of interests. Dosimetric parameters and time efficiency were compared between the auto-VMAT and the manual-VMAT created by experienced planners. All results were analyzed using the Wilcoxon signed-rank sum test. RESULTS: The auto-VMAT achieved comparable coverage of the target volume while demonstrating improved dose conformity and uniformity compared with the manual-VMAT. V30 and V40 in the small bowel were significantly lower in the auto-VMAT compared with those in the manual-VMAT (p < 0.001 and < 0.001, respectively); the mean dose of the bladder was also significantly reduced in the auto-VMAT (p < 0.001). Furthermore, auto-VMAT plans were consistently generated with less variability in quality. In terms of efficiency, the auto-VMAT markedly reduced the time required for planning and expedited plan approval, with 93% of cases approved within one day. CONCLUSION: We developed a fully automatic feasible VMAT plan creation program for LARC. The auto-VMAT maintained target coverage while providing organs at risk dose reduction. The developed program dramatically reduced the time to approval.

Plan Quality Comparison Between Hippocampus-Sparing Whole-Brain Radiotherapy Treated With Halcyon and Tomotherapy Intensity-Modulated Radiotherapy.

Objective: Hippocampus-sparing whole-brain radiotherapy using Halcyon, an instrument dedicated to volumetric modulated arc therapy, has not been studied till date; hence, we aimed to examine whether it can meet the RTOG0933 criteria. Based on this, we compared Halcyon to Tomotherapy, which also uses an O-ring-type linear accelerator. Methods: This exploratory, experimental, and retrospective study used 5 sets of computed tomography images in the head area to investigate the planning target volume, hippocampal doses, and irradiation time. Calculations were performed from 1 to 4 arcs to determine the optimal number of arcs in the Halcyon plan, which were compared to those of Tomotherapy. Results: The Radiation Therapy Oncology Group 0933 criteria could not be satisfied in Halcyon with 1 arc. With 2 arcs, the condition Dmax<16 Gy was not satisfied for 1 case in the hippocampus. Since there were no significant differences between 3 and 4 arcs, including the irradiation time, 3 arcs were considered the best. We compared Halcyon at 3 arcs with tomotherapy and found that tomotherapy was inferior to Halcyon at D98%; however, it was superior to Halcyon in other dose parameters. In contrast, the irradiation time in Halcyon was overwhelmingly superior, with the irradiation time for Halcyon being 1/ninth the time for Tomotherapy. Conclusion: Halcyon was effective in handling hippocampus-sparing whole-brain radiotherapy. We believe that 3-arc radiation is best suited for this procedure. Although Halcyon was inferior to Tomotherapy in terms of dose distribution excluding D98%, it was overwhelmingly superior in terms of irradiation time.

[A Preliminary Study of Optimal Imaging Acquisition Parameters for Fiducial Markers in Liver Stereotactic Body Radiotherapy].

In liver stereotactic body radiotherapy (SBRT) using fiducial markers, the accuracy of automatic image recognition of fiducial markers is important, and the imaging dose cannot be neglected in image-guided radiotherapy. Optimal imaging parameters of fiducial markers were investigated for automatic image recognition and imaging dose. We investigated automatic recognition with fiducial markers of different shapes and sizes. In addition, the optimum imaging conditions were examined based on the automatic recognition when the presence or absence of a filter, focal spot size, and phantom thickness were altered using the fiducial markers with a high automatic recognition. The results for different shapes and sizes of fiducial markers showed that larger markers were recognized more automatically, whereas shorter markers were recognized in the correct position. By using the filter, we were able to reduce the imaging dose by one third or one half compared to the case without the filter. The results for the focal spot size showed that using a larger size resulted in higher automatic recognition accuracy than using a smaller size. For the relationship between the automatically recognized imaging conditions and the air kerma when the phantom thickness was altered, it was necessary to keep the tube current-time product constant and increase the tube voltage in order to avoid poor recognition accuracy. The parameters we proposed are effective in shortening the treatment time and reducing the imaging dose because they allow us to acquire images with low doses and high accuracy of automatic recognition.

Frequency and predictors of detecting early locoregional recurrence/disease progression of oral squamous cell carcinoma with high-risk factors on imaging tests before postoperative adjuvant radiotherapy.

BACKGROUND: To clarify the frequency and predictors of detecting early locoregional recurrence/disease progression (LR/DP) during the interval between surgery and postoperative adjuvant radiotherapy with/without chemotherapy in patients with oral squamous cell carcinoma. METHODS: Data on 65 patients who had undergone the initial radical surgery for previously untreated oral squamous cell carcinoma which were scheduled to receive adjuvant radiotherapy with/without chemotherapy were reviewed. RESULTS: Of the 65 patients, 63 (97%) were margin-positive/close and/or extracapsular extension-positive (hereinafter, high-risk factors). Eighteen (28%) patients had abnormal findings suggestive of LR/DP on postoperative imaging. Fifteen (23%) patients were diagnosed with LR/DP and treatment policy was changed. Univariate and multivariate analyses revealed higher frequencies of abnormal findings suggestive of LR/DP (univariate/multivariate analysis, p = 0.020/0.036), diagnosing of LR/DP, and changing the treatment policy (univariate/multivariate analysis, p = 0.042/0.046), among the patients who underwent postoperative diagnostic imaging tests or radiotherapy-planning contrast-enhanced (CE) CT without diagnostic imaging tests as compared with those who underwent radiotherapy-planning non-CECT without such tests. CONCLUSION: The frequency of detecting of early LR/DP before postoperative adjuvant treatment in oral squamous cell carcinoma patients with high-risk factors was high. Furthermore, postoperative diagnostic imaging tests and radiotherapy-planning CECT may be useful to detect early LR/DP in oral squamous cell carcinoma patients before postoperative adjuvant therapy.