Thanks, Larry, and thanks for the introduction. Before I begin, let me echo Larry's comments. It's been a privilege working with Larry these past several months. We've already forged a very productive and highly collaborative relationship.
I expect this partnership to directly benefit shareholders over the coming quarters. I'd also like to thank investors on the phone today with many of whom we've had the opportunity to discuss our business and the opportunities we see for the company. We appreciate your support and look forward to working hard on your behalf to continue building a great company.
Finally, I want to thank all of Mirion's nearly 2,500 employees who have worked entirely this year to continue delivering strong performance across all of our businesses. While our journey is nowhere near complete, I'm very proud of our transition to becoming a public company.
Moving to Slide 4, as you can see, we have been quite busy. We closed the deal with GS Acquisition Holding Corp II on October 20, and followed the closing with a great day on October 21st by ringing the closing bell on the New York Stock Exchange. Those events were a great joy for our team and continue to elevate the Mirion brand in the marketplace.
We formed an excellent Board of Directors chaired by Larry Kingsley. We've also refinanced our debt, reducing net leverage to 4x pro forma and the related interest burden on the heels of a fantastic fiscal year '21 financial performance. Lastly, our M&A campaign continues to evolve as planned with 3 accretive bolt-on acquisitions in the Medical segment, expanding our presence in complementing the Mirion portfolio. Important to note that our acquisition of CIRS is currently pending and has not yet closed.
Now let's turn to Slide 5 to review our financial results for the quarter ended September 30, 2021. First of all, let me say I'm extremely pleased with the company and team's performance during the September quarter. We have seen a number of supply chain challenges and logistical delays throughout the COVID period. We have been successful in mitigating the majority of these by supporting suppliers and sourcing critical components, extending our sales and operational planning forecast windows and leaning on our strong strategic inventory positions.
While global supply chain conditions appear to be worsening, we expect the attendant impact on us to be relatively muted. We believe we've been successful in asserting pricing offsets to rising material labor input costs. We expect to be fully compliant with U.S. federal government vaccine mandates with minimal employee attrition, that harbor some concerns regarding the potential impact on external logistics. This is an area of significant focus for me and the entire Mirion team, and we are sustaining a vigilant posture toward the evolving challenges.
For the quarter, our team delivered total revenue growth of 29%, an adjusted EBITDA growth of 28%, each compared with the prior year periods. We delivered organic adjusted revenue growth of negative 0.1%, a strong performance against the year ago comp of 8.5% growth.
In the Medical segment, 10.8% organic growth was driven by solid end markets and a bounce back from COVID-related headwinds. A better medical mix also helped drive adjusted gross margin expansion of over 300 basis points for the company overall. Industrial segment organic growth was negative 2.4% for the quarter compared to an 11.3% year-ago comp. Brian Schopfer will provide more color on our segment performance shortly.
I'd like to now turn to discuss execution against some of our key strategic initiatives, new products, strategic cost objectives and an update on our M&A process and pipeline. After significant testing in select nuclear power plants, we launched Orion, an innovative ecosystem that facilitates real-time integration of positional information with performance telemetry data in highly attenuated environments.
We also launched lab haul Services, which reduces the downtime of critical scientific instruments through the cloud-based transmission of performance data to our field services teams. The integration and footprint consolidation activities within newly acquired businesses is progressing well despite modest delays associated with certain facility consolidation objectives.
Our M&A pipeline continues to be both active and robust. We recently announced 2 medical dosimetry acquisitions, which will bolster our position in that segment. Yesterday, we announced the acquisition of CIRS, and I am pleased to welcome the CIRS team to the Mirion family. We're excited to augment our medical segment focus through the integration of CIRS' products, software and services capabilities.
Together, we will strive to improve patient care and outcomes in both the therapeutic and diagnostic markets. This acquisition is part of our broader inorganic growth strategy to add accretive, complementary businesses to enhance our product portfolio and to better serve our customers. As we've explained consistently over the past 6 months, we remain confident in the opportunities for acquisitive growth across our portfolio of businesses, both in the near and long term.
I want to close with some specific comments regarding the company's performance in the quarter and our outlook for the year. Performance was in line with our expectations in the quarter, and we are reiterating our guidance for the 12 months ended June 30, 2022 of $723 million in adjusted revenue and approximately $179 million of adjusted EBITDA.
As Alex mentioned, this guidance excludes the incremental impact of CIRS on our results. Demand for our products and services continues to be strong and is accelerating despite continued supply chain pressure.
To provide a deeper look into our performance and outlook, I'd like to hand the call over to Brian Schopfer, Mirion's CFO.