Objective: To investigate IMRT planning process using the combined application of failure modes and effects analysis (FMEA) and fault tree analysis (FTA) by reference to the report of Task Group 100 of the AAPM, and stablish and optimize the quality. Methods: A multidisciplinary team detailed the process mapping of IMRT planning using Eclipse TPS. The team evaluated the potential failure modes (FMs) of every process step. The evaluation was divided into two groups according to whether quality management (QM) was considered. For every FM, occurrence (O), severity (S) and detectability (D) by consensus were evaluated, and the product of O, S and D yielded the risk priority number (RPN), which permitted the ranking of the FMs. Finally, FTA was used to determine the root factors contributing to the riskiest failure modes. Results: The IMRT plan process consisted of 10 major sub-processes and 33 steps, which amounted to 47 failure modes. For the group without quality management, the RPN of FMs was between 13.2-271.8, 27 of which had RPN≥80, and 18 FMs had S≥8. For the group with quality management, the RPN of FMs was between 11.2-158.4, 11 of which had RPN≥80. The difference of RPN between the two groups was statistically significant (RPN of the group without QM=101.17±66.34, RPN of the group with QM=59.54±35.64, t=8.501, P<0.05). Finally, FTA was used to determine the root factors contributing to the FMs, i. e., prescription dose definition and importing images. Conclusions The FMEA and FTA methods are operable and practical, which can systematically and comprehensively analyze the potential failures and risks existing in the process of IMRT plan. And the FMEA and FTA can contribute to establish and optimize the quality management program in radiotherapy.

Objective:To explore the impact of tissue inhomogeneity correction on the accuracy of dose calculations in brachytherapy of cervical carcinoma by comparing the results of Monte Carlo (MC) dose simulation with those (TG43 algorithm) of treatment planning system (TPS).Methods:Firstly, the 192Ir source was modeled by using a MC code specially designed for brachytherapy, called egs_brachy. The accuracy of this model was verified by comparing it with the published data. Then, 8 brachytherapy plans of cervical carcinoma were selected which completed treatment at Sun Yat-sen University Cancer Center from January 2022 to May 2023, and their CT image data and treatment parameters were exported. Relevant plan information such as the source dwell positions and their corresponding dwell times were reconstructed on the patient's individualized CT images using a self-developed program. The MC dose distributions were calculated for each case and compared with the TPS calculations. When the anterior wall of the rectum was filled with gas, the differences between MC simulation and TPS calculation were compared. Additionally, 5 different calculation ranges were set for MC simulation, and the MC simulation results of different calculation ranges were compared with the TPS's, combining with the time of MC simulation, a reasonable MC calculation range was comfirmed. Then, the scipy.stats library of Python was utilized to perform independent sample t-test on dosimetric comparison results, including D 90% of high risk clinical target volume (HR-CTV) and D max, D mean, and D 2 cm3 of organs at risk (OAR). Results:The comparison between MC calculations and TPS results showed that the CTV's D 90%, the bladder's D mean and the small intestine's D mean were all within ± 1%, except for the D max difference of approximately 3% on the anterior wall of the rectum. The 2%/2 mm gamma pass rates were all>98%. When anterior wall of the rectum filled with gas, compared with MC, TPS overestimated the anterior wall of the rectum's D 2 cm3 and D mean by approximately 6.06% ( t=-6.80, P=0.002) and 5.35% ( t=-6.57, P=0.003), respectively. When the dose calculation range of MC was consistent with that of TPS, the MC calculation result underestimated the dose distribution in water by approximately 4%. When extending the MC dose calculation range by 2 cm beyond the TPS calculation range, the dose difference between MC and TPS in homogeneous water was approximately 1%, and the calculation time was saved by at least 8 h compared to MC dose calculation based on the whole CT. Conclusion:The existing TPS TG43 algorithm can ensure that the dose calculation of cervical carcinoma meets the basic accuracy requirements of clinical practice, but tissue inhomogeneity correction is recommended to improve the accuracy of dose calculation whenever possible.

Objective:To design and evaluate the application value of intracavitary-interstitial brachytherapy (IC-ISBT) applicator template for locally advanced cervical cancer.Methods:MRI data of 100 patients with ⅡB-ⅣA stage cervical cancer (International Federation of Gynecology and Obstetrics 2018 staging system) before and after external beam radiation therapy (EBRT) admitted to Sun Yat-sen University Cancer Center from March 2019 to September 2020 were collected. The range of primary cervical lesions was retrospectively analyzed and compared. Based on the residual mass of patients, the corresponding high-risk clinical target volume (HR-CTV) was delineated, and the IC-ISBT applicator template was designed and initially applied to cervical cancer patients. Dosimetry analysis and efficacy evaluation were compared between the applicator template-guided ( n=37) and free-hand implantation groups ( n=63). Chi-square test or Fisher exact test was performed for categorical variables, and t-test or U-test for continuous variables. Results:The median distance between the residual tumor margin (clockwise 3, 6, 9, 12 o'clock) and the center of 100 patients with ⅡB-ⅣA stage cervical cancer after EBRT was 16.5, 14.0, 17.0 and 13.0 mm, respectively. The corresponding HR-CTV was superimposed to reconstruct the three-dimensional diagram, and the cylindrical IC-ISBT applicator template with mushroom-like head was designed and manufactured: the longest and shortest diameter of the head was 35 and 20 mm, respectively; the central channel was adapted to the uterine tube, the C1-C12 channels was arranged in inner circle, and the peripheral B1-B5 and A1-A4 pin channels were expanded bilaterally. In terms of dose coverage, there was no significant difference between the HR-CTV D 90% [(635.12±22.65) vs. (635.80±25.84) cGy], bladder D 2 cm3 [(473.79±44.78) vs. (463.55±66.43) cGy)], rectum D 2 cm3 [(396.99±73.54) vs. (408.00±73.94) cGy] and sigmoid colon D 2 cm3 [(293.07±152.72) vs. (311.31±135.77) cGy] between the template-guided and free-hand implantation groups (all P>0.05), but the HR-CTV D 98% was significantly higher [(544.78±32.07) vs. (536.78±32.04) cGy, P=0.007] and the rectum D 1 cm3 and D 0.1 cm3 were significantly lower [(438.62±69.65) vs. (453.97±67.89) cGy, P=0.016; (519.46±70.67) vs. (543.82±81.24) cGy, P=0.001] in the template-guided implantation group. In addition, there was no significant difference in the complete response rate between two groups (86% vs. 83%, P>0.05). Conclusions:This IC-ISBT applicator template is reasonably designed, and the therapeutic efficacy of the template-guided implantation is equivalent to that of free-hand implantation. The dose coverage of the target area meets the clinical demand with a better protection of the organs at risk. The applicator template has the potential to be widely used as a conventional template in clinical practice as the applicator-guided implantation is convenient to operate and repeat.