Verification of surface-guided radiation therapy (SGRT) alignment for proton breast and chest wall patients by comparison to CT-on-rails and kV-2D alignment.

BACKGROUND: Surface-guided radiation therapy (SGRT) systems have been widely installed and utilized on linear accelerators. However, the use of SGRT with proton therapy is still a newly developing field, and published reports are currently very limited. PURPOSE: To assess the clinical application and alignment agreement of SGRT with CT-on-rails (CTOR) and kV-2D image-guided radiation therapy (IGRT) for breast treatment using proton therapy. METHODS: Four patients receiving breast or chest wall treatment with proton therapy were the subjects of this study. Patient #1's IGRT modalities were a combination of kV-2D and CTOR. CTOR was the only imaging modality for patients #2 and #3, and kV-2D was the only imaging modality for patient #4. The patients' respiratory motions were assessed using a 2-min surface position recorded by the SGRT system during treatment. SGRT offsets reported after IGRT shifts were recorded for each fraction of treatment. The agreement between SGRT and either kV-2D or CTOR was evaluated. RESULTS: The respiratory motion amplitude was <4 mm in translation and <2.0° in rotation for all patients. The mean and maximum amplitude of SGRT offsets after application of IGRT shifts were ≤(2.6 mm, 1.6° ) and (6.8 mm, 4.5° ) relative to kV-2D-based IGRT; ≤(3.0 mm, 2.6° ) and (5.0 mm, 4.7° ) relative to CTOR-based IGRT without breast tissue inflammation. For patient #3, breast inflammation was observed for the last three fractions of treatment, and the maximum SGRT offsets post CTOR shifts were up to (14.0 mm, 5.2° ). CONCLUSIONS: Due to the overall agreement between SGRT and IGRT within reasonable tolerance, SGRT has the potential to serve as a valuable auxiliary IGRT tool for proton breast treatment and may improve the efficiency of proton breast treatment.

Measurements of fetal dose with Mevion S250i proton therapy system with HYPERSCAN.

PURPOSE: To characterize potential dose to the fetus for all modes of delivery (dynamic adaptive aperture, static adaptive aperture, and no adaptive aperture) for the Mevion S250i Proton Therapy System with HYPERSCAN and compare the findings with those of other available proton systems. MATERIALS AND METHODS: Fetal dose measurements were performed for all three modes of dose delivery on the Mevion S250i Proton therapy system with HYPERSCAN (static aperture, dynamic aperture and uncollimated). Standard treatment plans were created in RayStation for a left-sided brain lesion treated with a vertex field, a left lateral field, and a posterior field. Measurements were performed using WENDI and the RANDO with the detector placed at representative locations to mimic the growth and movement of the fetus at different gestational stages. RESULTS: The fetal dose measurements varied with fetus position and the largest measured dose was 64.7 µSv per 2 Gy (RBE) fraction using the dynamic aperture. The smallest estimated fetal dose was 45.0 µSv per 2 Gy (RBE) at the base of the RANDO abdomen (47 cm from isocenter to the outer width of WENDI and 58.5 cm from the center of the WENDI detector) for the static aperture delivery. The vertex fields at all depths had larger contributions to the total dose than the other two and the dynamic aperture plans resulted in the highest dose measured for all depths. CONCLUSION: The reported doses are lower than reported doses using a double-scattering system. This work suggests that avoiding vertex fields and using the static aperture will help minimize dose to the fetus.

Using failure mode and effects analysis (FMEA) to generate an initial plan check checklist for improved safety in radiation treatment.

PURPOSE: To apply failure mode and effect analysis (FMEA) to generate an effective and efficient initial physics plan checklist. METHODS: A team of physicists, dosimetrists, and therapists was setup to reconstruct the workflow processes involved in the generation of a treatment plan beginning from simulation. The team then identified possible failure modes in each of the processes. For each failure mode, the severity (S), frequency of occurrence (O), and the probability of detection (D) was assigned a value and the risk priority number (RPN) was calculated. The values assigned were based on TG 100. Prior to assigning a value, the team discussed the values in the scoring system to minimize randomness in scoring. A local database of errors was used to help guide the scoring of frequency. RESULTS: Twenty-seven process steps and 50 possible failure modes were identified starting from simulation to the final approved plan ready for treatment at the machine. Any failure mode that scored an average RPN value of 20 or greater was deemed "eligible" to be placed on the second checklist. In addition, any failure mode with a severity score value of 4 or greater was also considered for inclusion in the checklist. As a by-product of this procedure, safety improvement methods such as automation and standardization of certain processes (e.g., dose constraint checking, check tools), removal of manual transcription of treatment-related information as well as staff education were implemented, although this was not the team's original objective. Prior to the implementation of the new FMEA-based checklist, an in-service for all the second checkers was organized to ensure further standardization of the process. CONCLUSION: The FMEA proved to be a valuable tool for identifying vulnerabilities in our workflow and processes in generating a treatment plan and subsequently a new, more effective initial plan checklist was created.

Surface-Guided Patient Setup Versus Traditional Tattoo Markers for Radiation Therapy: Is Tattoo-Less Setup Feasible for Thorax, Abdomen and Pelvis Treatment?

PURPOSE: In this study, patient setup accuracy was compared between surface guidance and tattoo markers for radiation therapy treatment sites of the thorax, abdomen and pelvis. METHODS AND MATERIALS: A total of 608 setups performed on 59 patients using both surface-guided and tattoo-based patient setups were analyzed. During treatment setup, patients were aligned to room lasers using their tattoos, and then the six-degree-of-freedom (6DOF) surface-guided offsets were calculated and recorded using AlignRT system. While the patient remained in the same post-tattoo setup position, target localization imaging (radiographic or ultrasound) was performed and these image-guided shifts were recorded. Finally, surface-guided vs tattoo-based offsets were compared to the final treatment position (based on radiographic or ultrasound imaging) to evaluate the accuracy of the two setup methods. RESULTS: The overall average offsets of tattoo-based and surface-guidance-based patient setups were comparable within 3.2 mm in three principal directions, with offsets from tattoo-based setups being slightly less. The maximum offset for tattoo setups was 2.2 cm vs. 4.3 cm for surface-guidance setups. Larger offsets (ranging from 2.0 to 4.3 cm) were observed for surface-guided setups in 14/608 setups (2.3%). For these same cases, the maximum observed tattoo-based offset was 0.7 cm. Of the cases with larger surface-guided offsets, 13/14 were for abdominal/pelvic treatment sites. Additionally, larger rotations (>3°) were recorded in 18.6% of surface-guided setups. The majority of these larger rotations were observed for abdominal and pelvic sites (~84%). CONCLUSIONS: The small average differences observed between tattoo-based and surface-guidance-based patient setups confirm the general equivalence of the two potential methods, and the feasibility of tattoo-less patient setup. However, a significant number of larger surface-guided offsets (translational and rotational) were observed, especially in the abdominal and pelvic regions. These cases should be anticipated and contingency setup methods planned for.

FMEA-guided transition from microSelectron to Flexitron for HDR brachytherapy.

PURPOSE: To utilize failure mode and effects analysis (FMEA) to effectively direct the transition from the Elekta microSelectron to the Flexitron high dose-rate afterloader system. MATERIALS AND METHODS: Our FMEA was performed in two stages. In the first stage, the lead brachytherapy physicists used FMEA to guide the brainstorming sessions and to identify vulnerabilities during this transition. The second stage of FMEA was carried out 2 months after the clinical release of the Flexitron system. The process map was examined again to further refine and improve the entire process. RESULTS: In the first-stage FMEA, 81 process steps were identified. Moreover, 80 failure modes and their categorized causes were recognized. Checklists and data books containing the corresponding applicator information were verified and updated. Next, based on outcomes of our first-stage FMEA, we chose to implement the commissioning process in two phases. The second stage of FMEA identified error-prone steps in our newly updated processes. This second stage of analysis resulted in the development of new tools and checklist items. CONCLUSIONS: The two-stage FMEA approach successfully directed the transition to the Flexitron system by identifying the necessary changes in the checklists and workflows for all applicators utilized in our clinic. It also led to the decision to use a two-phase commissioning approach. This allowed for minimization clinical downtime, avoidance of an extra source change, and facilitation of efficient staff training. Additionally, multiple project-level failures were discovered. Our experience and outcomes from this FMEA-guided transition should provide valuable information to the brachytherapy community.

Evaluation of the effects of implementing a diode transmission device into the clinical workflow.

PURPOSE: This work investigated effects of implementing the Delta4 Discover diode transmission detector into the clinical workflow. METHODS: PDD and profile scans were completed with and without the Discover for a number of photon beam energies. Transmission factors were determined for all beam energies and included in Eclipse TPS to account for the attenuation of the Discover. A variety of IMRT plans were delivered to a Delta4 Phantom+ with and without the Discover to evaluate the Discover's effects on IMRT QA. An imaging QA phantom was used to assess the detector's effects on MV image quality. OSLDs placed on the Phantom+ were used to determine the detector's effects on superficial dose. RESULTS: The largest effect on PDDs after dmax was 0.5%. The largest change in beam profile symmetry and flatness was 0.2% and 0.1%, respectively. An average difference in gamma passing rates (2%/2 mm) of 0.2% was observed between plans that did not include the Discover in the measurement and calculation to plans that did include the Discover in the measurement and calculation. The Discover did not significantly change the MV image quality, and the largest observed increase in the relative superficial dose when the Discover was present was 1%. CONCLUSIONS: The effects the Discover has on the linac beam were found to be minimal. The device can be implemented into the clinic without the need to alter the TPS beam modeling, other than accounting for the device's attenuation. However, a careful workflow review to implement the Discover should be completed.

Skin dose estimation using virtual structures for Contura Multi-Lumen Balloon breast brachytherapy.

PURPOSE: To propose a workflow that uses ultrasound (US)-measured skin-balloon distances and virtual structure creations in the treatment planning system to evaluate the maximum skin dose for patients treated with Contura Multi-Lumen Balloon applicators. METHODS AND MATERIALS: Twenty-three patients were analyzed in this study. CT and US were used to investigate the interfractional skin-balloon distance variations. Virtual structures were created on the planning CT to predict the maximum skin doses. Fitted curves and its equation can be obtained from the skin-balloon distance vs. maximum skin dose plot using virtual structure information. The fidelity of US-measured skin distance and the skin dose prediction using virtual structures were assessed. RESULTS: The differences between CT- and US-measured skin-balloon distances values had an average of -0.5 ± 1.1 mm (95% confidence interval [CI] = -1.0 to 0.1 mm). Using virtual structure created on CT, the average difference between the predicted and the actual dose overlay maximum skin dose was -1.7% (95% CI = -3.0 to -0.4%). Furthermore, when applying the US-measured skin distance values in the virtual structure trendline equation, the differences between predicted and actual maximum skin dose had an average of 0.7 ± 6.4% (95% CI = -2.3% to 3.7%). CONCLUSIONS: It is possible to use US to observe interfraction skin-balloon distance variation to replace CT acquisition. With the proposed workflow, based on the creation of virtual structures defined on the planning CT- and US-measured skin-balloon distances, the maximum skin doses can be reasonably estimated.