Practical Dosimetry and the Future of Molecular Radiotherapies

You and your patients can achieve personalized and accurate dosimetry for Molecular Radiotherapy (MRT), also known as Radiopharmaceutical Therapy. All you need are the right tools.

Authors

• David Mirando, Senior Clinical Engineer, MIM Software Inc.
• Yuni K Dewaraja, PhD, Research Professor, University of Michigan
• Aaron S Nelson, MD, Chief Medical Officer, MIM Software Inc.

The Need for Practical and Accurate Dosimetry

Will your patients experience radiation-induced toxicity or tumor response during the course of MRT? Are they receiving suboptimal injected activities because of “one size fits all” fixed-activity treatment schemes?

These are the kinds of questions that personalized and accurate radiation dosimetry promises to answer. A long-used biomarker for external-beam radiotherapy (EBRT) planning, it has become increasingly used for treatment planning and response prediction for ⁹⁰Y microsphere therapies. Evidence is mounting for the utility in MRTs as well, as fixed-activity schemes have been shown to lead to highly variable absorbed doses and patient responses.

After all, just as for EBRT and ⁹⁰Y, MRTs such as ¹⁷⁷Lu-DOTATATE and ¹⁷⁷Lu-PSMA can be considered radiation delivery devices. The radioisotope (¹⁷⁷Lu) determines the type of irradiation, and the targeting molecule (DOTATATE or PSMA) determines the location of the irradiation. But the cell-killer is radiation, and it should be quantified, just as it is for nearly every other population at risk due to radiation exposure.

The future of MRT dosimetry depends on a central question: Can it be performed regularly on a wide scale in a way that doesn’t compromise accuracy? If so, hospital administrators will have comfort knowing resources are being used efficiently. Likewise, patients and physicians alike will gain crucial insight into these therapies, and dose-response relationships can be expected to follow in quick succession. The future of patient-specific planning will be jump-started.

The single most powerful advantage of MRT over other systemic therapies is in its potential for informed personalization.

Voxel-level dosimetry provides crucial information, such as tumor uptake heterogeneity, in addition to mean absorbed doses. But its adoption has been constrained by resources and logistical issues, including access to quantitative SPECT/CT scanner time, new tumor and organ segmentation needs that can require substantial time commitments, and dosimetry processing requirements.

MIM SurePlan™ MRT has been helping sites drastically reduce the clinical requirements for dosimetry by including AI-based auto-segmentation tools and support for quantitative SPECT reconstruction with existing SPECT/CT cameras, in addition to integrating automation into every facet of its design. This remains a primary focus for continued development.

Single SPECT/CT Dosimetry

The University of Michigan (U-M) and MIM Software have partnered on a collaborative grant to develop a highly practical treatment planning platform for ¹⁷⁷Lu-DOTATATE. The grant is ambitious, seeking to improve every aspect of the dosimetry process and generate dose-response information that can feed into future treatment planning.

One of the early accomplishments of this partnership has been the release of clinical single timepoint dosimetry tools within MIM SurePlan MRT, the first of their kind in a commercial platform. These tools further reduce the barriers to patient-specific dosimetry. Patients who have to travel far no longer have to return for scanning multiple times, SPECT/CT scanner time is preserved, and reimbursement may be easier.

While multi-timepoint SPECT/CT dosimetry remains the ideal “gold standard” method, the clinical constraints may vary from patient-to-patient, or from week-to-week. Having access to single timepoint and multi-timepoint dosimetry tools within the same platform provides the flexibility to achieve the best dosimetry possible for any circumstance.

The release of these tools was the culmination of testing showing that absorbed doses generated using a single SPECT/CT are accurate for ¹⁷⁷Lu-DOTATATE. That is, the differences between single SPECT/CT and multi-SPECT/CT methods may be acceptable for dosimetry-guided treatment. Support for other therapies is planned.

Practical Dosimetry Has Arrived

When combining single SPECT/CT techniques with AI-based auto-segmentation and automation built into every step of the MIM SurePlan MRT dosimetry process, a clinical workflow emerges that’s highly attainable and flexible for any institution with the right imaging equipment. At the SNMMI 2021 Annual Meeting, MIM Software and U-M showed how such a system can lead to absorbed dose calculation with just five minutes of manual input.

As absorbed dose and outcome data from an increasing number of patients is available, it will be important to pool this information within and between institutions to generate robust dose-response and dose toxicity relationships. The sooner this information is available, the sooner patients will benefit from optimized and personalized MRT.

Check out The Journal of Nuclear Medicine December 2021 supplement (“Dosimetry for Radiopharmaceutical Therapy: From Resources to Reimbursement” for additional practical information to help you best incorporate dosimetry into your practice.

Learn why MIM SurePlan MRT has quickly become the standard application used for radiopharmaceutical therapy in Centers of Excellence across North America.