Evaluation and improvement of the safety of 3D-printed template assisted intracavitary/interstitial brachytherapy for cervical cancer using repeat FMEA.

BACKGROUND AND PURPOSE: 3D-printed templates are used in intracavitary/interstitial brachytherapy (3DP-IC/IS) for locally advanced cervical cancer (LACC). We applied failure mode and effects analysis (FMEA) twice in one year to improve 3DP-IC/IS safety. MATERIALS AND METHODS: A risk assessment group was established. We created a process map for 3DP-IC/IS procedures, identifying potential failure modes (FMs) and evaluating occurrence (O), detectability (D), severity (S), and risk priority number (RPN = O*D*S). High RPN values identified high-risk FMs, and quality control (QC) methods were determined by root cause analysis. A second FMEA was performed a year later. RESULTS: The 3DP-IC/IS process included 10 main steps, 48 subprocesses, and 54 FMs. Initial RPN values ranged from 4.50 to 171.00 (median 50.50; average 52.18). Ten high-risk FMs were identified: (1) unreasonable needle track design (171.00/85.50), (2) noncoplanar needle label identification failure (126.00/64.00), (3) template model reconstruction failure (121.50/62.50), (4) improper gauze filling (112.00/60.25), (5) poor needle position (112.00/52.50). QC interventions lowered all high-risk RPN values during the second assessment. CONCLUSIONS: A feasible 3DP-IC/IS process was proposed. Staff training, automatic needle path planning, insertion guidance diagrams, template checking, system commissioning, and template design improvements effectively enhanced process safety.

Sub-arc collimator angle optimization based on the conformity index heatmap for VMAT planning of multiple brain metastases SRS treatments.

Objective: The aim of this study was to investigate the impact of collimator angle optimization in single-isocenter coplanar volume modulated arc therapy (VMAT) stereotactic radiosurgery (SRS) for multiple metastases with respect to dosimetric quality and treatment delivery efficiency. In particular, this is achieved by a novel algorithm of sub-arc collimator angle optimization (SACAO). Methods: Twenty patients with multiple brain metastases were retrospectively included in this study. A multi-leaf collimator (MLC) conformity index (MCI) that is defined as the ratio of the area of target projection in the beam's eye view (BEV) to the related area fitted by MLC was applied. Accordingly, for each control point, 180 MCI values were calculated with a collimator angle interval of 1°. A two-dimensional heatmap of MCI as a function of control point and collimator angle for each full arc was generated. The optimal segmentation of sub-arcs was achieved by avoiding the worst MCI at each control point. Then, the optimal collimator angle for each sub-arc would be determined by maximizing the summation of MCI. Each patient was scheduled to undergo single-center coplanar VMAT SRS based on either the novel SACAO algorithm or the conventional VMAT with static collimator angle (ST-VMAT). The dosimetric parameters, field sizes, and the monitoring units (Mus) were evaluated. Results: The mean dose-volumetric parameters for the target volume of SACAO were comparable to ST-VMAT, while the conformity index (CI), homogeneity index (HI), and gradient index (GI) were reduced by SACAO. Improved sparing of organs at risk (OARs) was also obtained by SACAO. In particular, the SACAO method significantly (p < 0.01) reduced the field size (76.59 ± 32.55 vs. 131.95 ± 56.71 cm2) and MUs (655.35 ± 71.99 vs. 729.85 ± 73.52) by 41.11%. Conclusions: The SACAO method could be superior in improving the CI, HI, and GI of the targets as well as normal tissue sparing for multiple brain metastases SRS. In particular, SACAO has the potential of increasing treatment efficiency in terms of field size and MU.

Radiation dosimetry effect evaluation of a carbon fiber couch on novel uRT-linac 506c accelerator.

Recently, a diagnostic helical CT is integrated into a linear accelerator, called uRT-linac 506c, whose CT scanning dataset can be directly used to do simulation. This novel structure provides a possibility for online adaptive radiotherapy. For adaptive radiotherapy, the carbon fiber couch is an essential external device for supporting and positioning patients. And the effect on dose attenuation and distribution caused by a couch is inevitable and vital for precise treatment. In this research, the couch equipped with uRT-linac 506c was evaluated on the radiation dosimetry effect. The treatment couch equipped on the uRT-linac 506c accelerator was evaluated, and its effect on the attenuation, surface dose and dose buildup were measured for different phantom positions (offset = 0 cm, offset = + 10 cm and offset = - 10 cm, respectively) and different gantry angles. Since uRT-linac 506c is exclusively capable to provide diagnostic CT scanning data with real relative electron density (RED), this CT scanning data of the couch can be used directly in uRT-TPS to design plans. This scanned couch dataset was designated as the model A. The model B was a dummy structure of a treatment couch inserted with artificially preset RED. The dose calculation accuracy of these two models was compared using PB, CC, and MC on uRT-TPS. With the effect of carbon fiber couch, the surface dose was increased at least 97.94% for 25 × 25 cm2 field and 188.83% for 10 × 10 cm2 field, compared with those without. At different phantom positions (offset = 0, + 10, - 10 cm), the attenuation for 6 MV photon beam at gantry angle 180° were 4.4%, 4.4%, and 4.3%, respectively, and varied with changes of gantry angle. There do exists dose deviation between measurement and TPS calculation with the involvement of treatment couch, among the three algorithms, MC presented the least deviation, and the model A made less and steadier deviation than the model B, showing promising superiority. The attenuation, surface dose, and buildup effects of the carbon fiber couch in this study were measured similarly to most counterparts. The dose deviation calculated based on the couch dataset scanned by the diagnostic helical CT was smaller than those based on a dummy couch. This result suggests that an accelerator equipped with a diagnostic CT, which can help reduce the dose deviation of the carbon fiber couch, is a promising platform for online adaptive radiotherapy.

The safety and efficacy of a novel hypo-fractionated total marrow and lymphoid irradiation before allogeneic stem cell transplantation for lymphoma and acute leukemia.

PURPOSE: Total body irradiation (TBI) has been widely utilized as part of the conditioning regimen for hematopoietic stem cell transplantation (HSCT), but is associated with significant toxicities. Targeted TBI using helical Tomotherapy allows precise and homogeneous tumor coverage and excellent sparing of organs at risk. The purpose of this study was to evaluate the clinical outcomes of a novel hypo-fractionation strategy for patients receiving total marrow and involved lymphoid irradiation (TMLI) as part of the conditioning regimen before HSCT. METHODS AND MATERIALS: 61 patients (7 acute myelogenous leukemia (AML), 33 acute lymphoblastic leukemia (ALL), 18 non-Hodgkin's lymphoma (NHL), 3 mixed acute leukemia (MAL)) received conditioning radiation treatment with TMLI (8 Gy to bone marrow, 10 Gy to involved field in 2 fractions per day) in conjunction with chemotherapy before transplantation. RESULTS: The median age of 61 patients with TMLI was 24 (4-54) years. The prescribed dose covered the entire bone and involved target volume, and the dose of organs at risk (OAR) was reduced by 28%-78% of the prescription dose. Grade 1-2 nausea and vomiting occurred in 12 patients and grade 1-2 pain in 6 patients during radiotherapy. Fatigue occurred in 16 patients. 2 patients had diarrhea, enteritis, and 1 patient had fever. None of patient had grade 3-4 non-hematologic adverse reactions. Late (30 days after HSCT) grade 2 toxicities including reversible enteritis occurred in 3 patients. 5 patients developed infectious pneumonia. The 2 years progression-free survival (PFS) was 64.1% (95% CI: 0.16-0.22) and overall survival (OS) was 74.7% (95% CI: 0.19-0.24) for the 61 patients who had received their planned HSCT. The 2-year non-relapse mortality was significantly reduced to 5% in this patient cohort. CONCLUSIONS: This study demonstrates that hypo-fractionated TMLI (8 Gy to bone marrow, 10 Gy to involved field in a single day) as a conditioning regimen for lymphoma and acute leukemia was feasible and the clinical outcomes were acceptable.

Analyzation of the local confidence limits for IMRT and VMAT based on AAPM TG119 report.

The aim of this study was to generate a local confidence limit (CL) for intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) techniques for Clinac IX linear accelerator using the American Association of Physicists in Medicine (AAPM) Task Group (TG119) protocol. The results were compared with the published studies to test the capability and quality of the VMAT technique in our clinic. We used TG119 cases to create plans for IMRT and VMAT in Eclipse Treatment Planning System for Clinac IX using 6 MV and 10 MV photons. Two preliminary and 5 clinical test cases were created based on the dose prescriptions and planning objectives provided by TG119. Verification plans were created in a planning slab phantom, 2D matrix dosimetry system (MatriXX) with multicube phantom and a volumetric phantom (Delta4). Radiation absorption doses to high-dose points in the planning target volume region and low-dose points in avoidance structures were measured with a 0.125 cc semiflex thimble ionization chamber (PTW). The measured and planned doses were normalized with respect to their prescription doses and intercompared with each other. The gamma analysis was carried out for MatriXX and Delta4 adopting the acceptance criteria of 3% dose difference and 3 mm distance to agreement with 10% threshold dose, respectively. The local CLs with the bench mark set by TG119 were obtained for point, composite planar and field-by-field measurements for IMRT and VMAT with different energies. In this study, the CLs for the high-dose regions of IMRT with 6 MV and 10 MV were 0.025 and 0.014, respectively. For VMAT, they were 0.032 and 0.018. The counterpart CL was 0.045 in TG119. And in organs at risk region, the CLs of IMRT with 6 MV and 10 MV beam were 0.022 and 0.019, respectively, with the counterpart CL indicated by TG119 was 0.047. For VMAT with 6 MV and 10 MV photon beams, the CLs were measured 0.030 and 0.027 with Delta4, respectively. The CLs of the maximum gamma passing for all values were 2.0 in 6 MV VMAT plan, which however recommended in TG119 was 12.4. The data presented here showed all the CLs in our clinic meet the criteria of TG119 report well. All these local CLs reached the goals mentioned in AAPM TG119, which indicated that the local clinic had commissioned IMRT and VMAT techniques with adequate accuracy. Prior to the clinical application practice, it is essential to verify with the TG119 test cases for IMRT and VMAT, which allows us to better understand the basic capability of VMAT technology.

Evaluation and improvement the safety of total marrow irradiation with helical tomotherapy using repeat failure mode and effects analysis.

BACKGROUND & PURPOSE: Helical tomotherapy has been applied to total marrow irradiation (HT-TMI). Our objective was to apply failure mode and effects analysis (FMEA) two times separated by 1 year to evaluate and improve the safety of HT-TMI. MATERIALS AND METHODS: A multidisciplinary team was created. FMEA consists of 4 main steps: (1) Creation of a process map; (2) Identification of all potential failure mode (FM) in the process; (3) Evaluation of the occurrence (O), detectability (D) and severity of impact (S) of each FM according to a scoring criteria (1-10), with the subsequent calculation of the risk priority number (RPN=O*D*S) and (4) Identification of the feasible and effective quality control (QC) methods for the highest risks. A second FMEA was performed for the high-risk FMs based on the same risk analysis team in 1 year later. RESULTS: A total of 39 subprocesses and 122 FMs were derived. First time RPN ranged from 3 to 264.3. Twenty-five FMs were defined as being high-risk, with the top 5 FMs (first RPN/ second RPN): (1) treatment couch movement failure (264.3/102.8); (2) section plan dose junction error in delivery (236.7/110.4); (3) setup check by megavoltage computed tomography (MVCT) failure (216.8/94.6); (4) patient immobilization error (212.5/90.2) and (5) treatment interruption (204.8/134.2). A total of 20 staff members participated in the study. The second RPN value of the top 5 high-risk FMs were all decreased. CONCLUSION: QC interventions were implemented based on the FMEA results. HT-TMI specific treatment couch tests; the arms immobilization methods and strategy of section plan dose junction in delivery were proved to be effective in the improvement of the safety.

Mapping patterns of metastatic lymph nodes for postoperative radiotherapy in thoracic esophageal squamous cell carcinoma: a recommendation for clinical target volume definition.

BACKGROUND: The clinical target volume (CTV) for postoperative radiotherapy for thoracic esophageal squamous cell carcinoma (TESCC) needs to be defined. The study aim was to map metastatic lymph nodes (LNMs) in a computed tomography (CT)-based atlas and delineate the postoperative radiotherapy target area. METHODS: Sixty-nine TESCC patients with first recurrent regional LNMs after esophagectomy were included. The LNM epicenters were registered onto corresponding anatomic axial CT images of a standard patient in the treatment position, with reference to the surrounding vascular and bony structures. The LNM sites were based on lymph node map of esophageal cancer, AJCC 8th. The lymph metastasis risk for different segments of thoracic esophagus was assessed. RESULTS: One hundred and seventy-nine LNMs were mapped onto standard axial CT images. The upper-middle mediastinum region (station 1 to 8 M) contained 97% of metastases in the upper segment of thoracic esophagus, 90% in the middle segment, and 66% in the lower one. Advanced pathological stage (≥IIIB) might be a predictive factor for upper abdominal region (UAR) relapse in lower TESCC. Lower cervical para-tracheal LNMs were within a 4.3-cm bilaterally expanded area from the midline of the body and a 2.2-cm expanded area from the anterior of vertebral body, from the superior border of the C7, to the inferior border of the first thoracic vertebra. CONCLUSION: A modified target from the upper border of C7 to the lower border of caudal margin of the inferior pulmonary vein level could cover the high-risk area of TESCC underwent postoperative radiotherapy. UAR seems to be an elective irradiation target for lower TESCC at pathological IIIB stage and higher.

[A review of progress of real-time tumor tracking radiotherapy technology based on dynamic multi-leaf collimator].

While radiation treatment to patients with tumors in thorax and abdomen is being performed, further improvement of radiation accuracy is restricted by the tumor intra-fractional motion due to respiration. Real-time tumor tracking radiation is an optimal solution to tumor intra-fractional motion. A review of the progress of real-time dynamic multi-leaf collimator(DMLC) tracking is provided in the present review, including DMLC tracking method, time lag of DMLC tracking system, and dosimetric verification.