The impact of orthogonal image-guided frequency on positioning error correction and dose in postoperative radiotherapy for breast cancer.

background and purposeThe incidence and mortality of breast cancer are increasing year by year. Image-guided radiotherapy (IGRT) after breast cancer surgery is one of the important ways of comprehensive treatment of breast cancer, but the frequency of IGRT and additional radiation damage are one of the key problems of clinical attention. To investigate the impact of different orthogonal image-guided frequencies on positioning error correction, plan target volume (PTV) margin expansion, and dose distribution in postoperative radiotherapy for breast cancer patients, providing a reference for the optimal orthogonal image-guided frequency in clinical practice for post-surgical breast cancer radiotherapy patients. MATERIALS AND

methodsFrom January 2021 to January 2022, 61 patients undergoing postoperative intensity-modulated radiation therapy (IMRT) for breast cancer at Fujian Medical University Union Hospital were selected. Prior to each radiation session, initial setup errors were measured as the control group (Group A) using real-time orthogonal images aligned with digitally reconstructed radiographs (DRR). Automatic couch adjustments were then performed based on alignment results within specified error tolerances to determine residual setup errors. Data collected were categorized into experimental Groups B1 to B5 based on different verification frequencies (every 1 to 5 days). Statistical analysis was conducted on the grouped data to calculate PTV expansion margins under different error conditions and assess their impact on dose.

resultsIn the study involving 61 patients, a total of 915 datasets were collected. The initial setup errors in three translational directions were (3.57 ± 3.48) mm, (2.76 ± 2.60) mm, and (2.65 ± 2.28) mm, respectively. With increasing verification frequency, residual setup errors gradually decreased. Under daily verification frequency, residual errors were (1.65 ± 0.90) mm, (1.60 ± 0.94) mm, and (1.56 ± 0.90) mm in the three translational directions. Pairwise comparisons between control and experimental groups indicated that differences were statistically significant except between B3 Vs B4, and B4 Vs B5. Based on setup error calculations under different verification frequencies, the reference PTV expansion margins decreased with increasing frequency. Specifically, under daily verification, the calculated PTV expansion reference values reduced from initial uncorrected setup errors of 6.53 mm, 5.07 mm, and 4.01 mm to 1.26 mm, 1.41 mm, and 1.29 mm, respectively. The differences between verification frequencies of every 3 days, 4 days, and 5 days were minimal. Finally, virtual error plans were designed in the treatment planning system based on average errors for each group of patients. Deviations in target area doses were statistically significant compared to the original plan across different imaging frequencies.

conclusionDaily image-guided setup verification (including correction) effectively reduces setup errors in postoperative breast cancer IGRT. Variations exist in the efficacy of error correction and its impact on PTV expansion and dose among different verification frequencies. Higher frequencies exhibit more significant error correction effects, necessitating smaller PTV expansions. At the same time, daily image guidance can reduce the dose of the heart and left lung. Further follow-up studies are required to track the impact of these deviations on dose and clinical efficacy.