The role of EPID in vivo dosimetry in the risk management of stereotactic lung treatments.

BACKGROUND AND OBJECTIVE: In this work we report our experience with the use of in vivo dosimetry (IVD) in the risk management of stereotactic lung treatments. METHODS: A commercial software based on the electronic portal imaging device (EPID) signal was used to reconstruct the actual planning target volume (PTV) dose of stereotactic lung treatments. The study was designed in two phases: i) in the observational phase, the IVD results of 41 consecutive patients were reviewed and out-of-tolerance cases were studied for root cause analysis; ii) in the active phase, the IVD results of 52 patients were analyzed and corrective actions were taken when needed. Moreover, proactive preventions were further introduced to reduce the risk of future failures. The error occurrence rate was analyzed to evaluate the effectiveness of proactive actions. RESULTS: A total of 330 fractions were analyzed. In the first phase, 13 errors were identified. In the active phase, 12 errors were detected, 5 of which needed corrective actions; in 4 patients the actions taken corrected the error. Several preventions and barriers were introduced to reduce the risk of future failures: the planning checklist was updated, the procedure for vacuum pillows was improved, and use of the respiratory compression belt was optimized. A decrease in the failure rate was observed, showing the effectiveness of procedural adjustment. CONCLUSION: The use of IVD allowed the quality of lung stereotactic body radiation therapy (SBRT) treatments to be improved. Patient-specific and procedural corrective actions were successfully taken as part of risk management, leading to an overall improvement in the dosimetric accuracy.

Incorporating plan complexity into the statistical process control of volumetric modulated arc therapy pre-treatment verifications.

BACKGROUND: Statistical process control (SPC) is a powerful statistical tool for process monitoring that has been highly recommended in healthcare applications, including radiation therapy quality assurance (QA). The AAPM TG-218 report described the clinical implementation of SPC for Volumetric Modulated Arc Therapy (VMAT) pre-treatment verifications, pointing out the need to adjust tolerance limits based on plan complexity. However, the quantification of plan complexity and its integration into SPC remains an unresolved challenge. PURPOSE: The primary aim of this study is to investigate the incorporation of plan complexity into the SPC framework for VMAT pre-treatment verifications. The study explores and evaluates various strategies for this incorporation, discussing their merits and limitations, and provides recommendations for clinical application. METHODS: A retrospective analysis was conducted on 309 VMAT plans from diverse anatomical sites using the PTW OCTAVIUS 4D device for QA measurements. Gamma Passing Rates (GPR) were obtained, and lower control limits were computed using both the conventional Shewhart method and three heuristic methods (scaled weighted variance, weighted standard deviations, and skewness correction) to accommodate non-normal data distributions. The 'Identify-Eliminate-Recalculate' method was employed for robust analysis. Eight complexity metrics were analyzed and two distinct strategies for incorporating plan complexity into SPC were assessed. The first strategy focused on establishing control limits for different treatment sites, while the second was based on the determination of control limits as a function of individual plan complexity. The study extensively examines the correlation between control limits and plan complexity and assesses the impact of complexity metrics on the control process. RESULTS: The control limits established using SPC were strongly influenced by the complexity of treatment plans. In the first strategy, a clear correlation was found between control limits and average plan complexity for each site. The second approach derived control limits based on individual plan complexity metrics, enabling tailored tolerance limits. In both strategies, tolerance limits inversely correlated with plan complexity, resulting in all highly complex plans being classified as in control. In contrast, when plans were collectively analyzed without considering complexity, all the out-of-control plans were highly complex. CONCLUSIONS: Incorporating plan complexity into SPC for VMAT verifications requires meticulous and comprehensive analysis. To ensure overall process control, we advocate for stringent control and minimization of plan complexity during treatment planning, especially when control limits are adjusted based on plan complexity.

Characterization of EPID software for VMAT transit dosimetry.

Dosimetry check (DC) is a commercial software that allows reconstruction of 3D dose distributions using transit electronic portal imaging device (EPID) images. In this work, we evaluated the suitability of DC software for volumetric modulated arc therapy (VMAT) transit dosimetry. The volumetric gamma agreement index 3%/3 mm between twenty VMAT dose distributions reconstructed by DC and calculated with treatment planning system (TPS) were compared to those obtained using PTW OCTAVIUS®4D to assess DC accuracy in VMAT quality assurance (QA). The sensitivity of DC in detecting VMAT delivery and set-up errors and anatomical variations has been investigated by measuring the variation of the gamma agreement index before and after the introduction of specific errors in four VMAT plans related to different anatomical sites. The influence of dose computation algorithm in presence of density inhomogeneity was also assessed. The assessment of VMAT QA shows agreements with TPS maps comparable to OCTAVIUS® 4D (OCT) in homogeneous phantom (p < 0.001). DC mean gamma agreement index was 94.2% ± 3.4, versus 95.6% ± 2.5 of OCT, lower dose threshold was set to 10%. Introduction of deliberate errors resulted in lower gamma agreement index and in 38/56 cases the gamma agreement index was over the detection threshold. The dose computation algorithm of DC is accurate in all anatomical sites except lung. However in lung cases, the aqua vivo approach used in this work reduced the algorithm dependence of DC results. DC accurately reproduced VMAT 3D dose distributions in phantom and is sensitive to detect errors caused by delivery inaccuracy and anatomical variations of patients.

Image-guided Stereotactic Body Radiotherapy in Metastatic Prostate Cancer.

BACKGROUND/AIM: In the last years, the use of Image Guided Stereotactic Radiotherapy (IG-SBRT) in patients with metastatic prostate cancer has increased. In this study, we aimed to assess the role of IG-SBRT in terms of local control and safety in patients with metastatic prostate cancer. MATERIALS AND METHODS: Primary and secondary endpoints of this prospective observational study were local control and safety related to IG-SBRT. All lesions were treated with 24 Gy as a single fraction or 27 Gy in 3 fractions. After SBRT, Systemic therapies were administered only after the occurrence of more than three synchronous active lesions in oligometastatic patients (patients with less than 4 active synchronous lesions) or new lesions occurrence in patients with more than 3 synchronous lesions. RESULTS: From April 2011 to June 2017, 78 metastatic lesions (32 bone and 46 node) from 51 patients with prostate cancer were treated. After a median follow-up of 18.5 months (range=3-103 months), only 2 lesions (4%) relapsed inside the radiation field. All local recurrences were located on the bone. Estimated 12 and 24 months local control ratios were 98.7 and 97.4%, respectively. Except for one case, toxicity greater than G2 was not recorded. CONCLUSION: IG-SBRT is safe and can be considered as a valid therapy in patients with metastatic prostate cancer requiring a long-lasting metastases control.

A comparison study of radiation exposure to patients during EVAR and Dyna CT in an angiosuite vs. an operating theatre.

The aim of this study was to assess the patient dosimetric impact of endovascular abdominal aortic aneurysm repair (EVAR), both in an operating theatre (OR) and in an angiosuite (AS), with the facility of Dynamic CT (Dyna CT, Siemens AG, Berlin, Germany). One hundred and forty-six consecutive EVAR procedures dating from May 2011 to March 2013 were analysed. These were performed either in an OR (n = 97) using a mobile C-arm or in an AS (n = 49) equipped with a ceiling-mounted angiography system. Air kerma area product (P(KA)) and total air kerma at reference point (K(a,r)) values were reported for all procedures and Dyna CT. Radiation exposure during EVAR was quite low in the majority of patients but nearly 50 % higher if performed in AS vs. OR. Median Dyna CT K(a,r) was the same as an entire EVAR procedure in OR. The higher patient's radiation exposure recorded in the AS should be balanced with the technical advantages given to the EVAR procedure.