Automated conversion of Millennium-120 VMAT plans to HDMLC geometry: Software development and treatment of first patients.

PURPOSE: To provide plan backup resiliency for patients treated on a solitary high definition multileaf collimator (HDMLC) linac by developing a fully integrated Eclipse script, which converts patient plans initially optimized on Millennium-120 (M120) MLC to dosimetrically equivalent leaf motions for delivery on HDMLC. In the event of HDMLC machine downtime, affected patients can be transferred to Millennium-120 units, and their backup plan delivered without delay. METHODS: Write-enabled Eclipse scripting is leveraged to generate HDMLC treatment fields with control points parameterized to mimic apertures of an existing Millennium-120 VMAT plan. Non-parity between intermediate control point gantry angles of script generated arcs relative to VMAT is reconciled through an interpolation subroutine to correct for the apertures and monitor units that would have existed at intermediate angles. Differences in dosimetric leaf gap are corrected by displacing the subset of leaves undergoing dynamic motion. A nominal change to plan normalization corrects for remaining discrepancies between beam models. RESULTS: Over 220 non-SABR VMAT patients were treated on a solitary HDMLC linac with plans converted using the developed script. All have undergone streamlined RO review and physics quality assurance (QA), where the converted plan replicates the original leaf patterns, representing a minor dosimetric perturbation. Analyzing a subset of converted plans delivered at four anatomical sites, on average 99.3% of points pass the 1%/1 mm gamma criterion. Dose-volume histograms between the original and converted plans are in excellent agreement. ArcCheck measurements comparing delivery of the converted HDMLC plan to the calculated M120 dose distribution averaged a gamma pass rate of 99.4% (95.2%) at a 3%/3 mm (2%/2 mm) criterion. The conversion process takes 30 s to run, avoids errors in exporting/re-importing, and generates leaf motions deliverable within machine limits. CONCLUSION: The methodology developed for automated plan conversion helped maximize the utilization of a solitary HDMLC linac, while preserving backup interoperability with minimal overhead.

Implementation of Single-Fraction Lung Stereotactic Ablative Radiotherapy in a Multicenter Provincial Cancer Program During the COVID-19 Pandemic.

Background During the novel coronavirus disease 2019 (COVID-19) pandemic, cancer centers considered shortened courses of radiotherapy to minimize the risk of infectious exposure of patients and staff members. Amidst a pandemic, the process of implementing new treatment approaches can be particularly challenging in larger institutions with multiple treatment centers. We describe the implementation of single-fraction (SF) lung stereotactic ablative radiotherapy (SABR) in a multicenter provincial cancer program. Materials and Methods British Columbia, Canada has a provincial cancer program with six geographically distributed radiotherapy centers serving a population of 5.1 million, over 944,735 square kilometers. In March 2020, provincial mitigation strategies were developed in case of reduced access to radiotherapy due to the COVID-19 pandemic. SF lung SABR was identified by the provincial lung radiation oncology group as a mitigation measure supported by high-quality randomized evidence that could provide comparable outcomes and toxicity to existing fractionated SABR protocols. A working group consisting of radiation oncologists and medical physicists reviewed the medical literature and drafted consensus guidelines that were reviewed by a group of center representatives as a component of provincial lung radiotherapy mitigation strategic planning. Individual centers were encouraged to implement SF lung SABR as their resources and staffing would allow. Centers were then surveyed about barriers to implementation. Results On March 24, 2020, a working group was created and consensus guidelines for SF lung SABR were drafted. The final version was approved and distributed by the working group on March 26, 2020. The provincial lung radiotherapy mitigation strategy group adopted the guidelines for implementation on April 1, 2020. Implementation was completed at the first center on April 27, 2020. Barriers to implementation were identified at five of six centers. Two centers in regions with disproportionately high COVID-19 cases described inadequate staffing as a barrier to implementation. One center encountered delays due to pre-scheduled commissioning of new treatment techniques. Three centers cited competing priorities as reasons for delay. As of May 2021, two centers had active SF lung SABR programs in place, three centers were in the process of implementation, and one center had no immediate plans for implementation due to ongoing resource issues. Conclusion SF lung SABR was adopted by a provincial cancer program within weeks of conception through rapid communication during the development of COVID-19 pandemic mitigation strategies for radiotherapy. Although consensus guidelines were written and approved in an expedited timeframe, the completion of implementation by individual centers was variable due to differences in resource allocation and staffing among the centers. Strong organizational structures and early identification of potential barriers may improve the efficiency of implementing new treatment initiatives in large multicenter radiotherapy programs.