TACTIC Challenge

Organized by challenge-organizer - Current server time: June 6, 2023, 10:26 a.m. UTC

First phase

Phase 0 - Request Data
Jan. 19, 2023, midnight UTC


Competition Ends
May 17, 2023, 11:59 p.m. UTC


TACTIC (Understanding Time-Activity Curve and Time-Integrated Activity Variations in Radiopharmaceutical Therapy Challenge) is a challenge sponsored by AAPM that is concerned with the calculation of time-integrated activity in radiopharmaceutical therapy dosimetry. The results of the challenge will be announced publicly at the Grand Challenge Symposium of the 2023 AAPM Annual Meeting in Houston, TX.

 Important Dates

  • Dec 15, 2022: Public announcement date

  • Jan 19, 2023: Phase 0 – Request Data opens and participants may request 1-5 timepoints

  • Feb 15, 2023: Phase 0 – Submit Results opens and participants can make submissions based on the TAC values they requested.

  • Mar 16, 2023: Phase 1 begins and participants can download 5 predefined TAC values for 3 organs of 5 patients.

  • Apr 16, 2023: Phase 2 begins and participants can download 5 predefined TAC values for 3 organs of 15 additional patients.


Dosimetry for radiopharmaceutical therapy (RPT) is a complex task. In contrast to external beam radiotherapy, where radiation is deposited through a well-defined external radiation source, the dose distribution in RPT depends on the time-varying distribution of the radiopharmaceutical inside the patient after administration, which is highly dependent on the radiopharmaceutical’s kinetics as well as the individual patient’s metabolism.

In addition to the geometry and composition of relevant source and target regions and S values describing the physical process of radiation deposition, it is therefore essential for RPT dosimetry to monitor the time course of the radiopharmaceutical distribution in each relevant region. In practice, this translates to a need for accurate activity measurements at different time points post-injection (e.g., by blood samples and/or SPECT/CT imaging) in combination with a fast and repeatable methodology for source or target region delineation, which is illustrated in Figure 1. This results in time-activity curves (TACs) for all relevant structures, based on which time-integrated activities (TIAs) can be calculated.

Goal of the Challenge:

Results from the SNMMI 177Lu Dosimetry Challenge 2021 [Uribe et al., JNM 2021] have recently demonstrated that RPT dosimetry is overwhelmingly user- and software-dependent: there is a wide variation in the RPT dosimetry methodology, and understanding the contributions of individual steps within the workflow is crucial for standardization. The TACTIC challenge zooms in on one of the most important sub-aspects of RPT dosimetry: TAC determination. Participants will be presented with a series of snapshots of precisely known time-activity curves at clinically relevant sampling time points. Based on their submitted TAC functions and TIA values, the Challenge Team will assess the degree of variation between different means of TAC/TIA estimation. Among all submissions, we will identify the best-performing methods including their uncertainties and thus take a decisive step towards improved robustness of TAC/TIA determination for RPTs.


  • Dr. Marta Cremonesi, European Institute of Oncology, Italy
  • Prof. Dr. Gerhard Glatting, Ulm University Hospital, Germany
  • Dr. Elisa Grassi, AUSL-IRCCS of Reggio Emilia, Italy
  • Dr. Oleksandra V. Ivashchenko, University Medical Center Groningen, the Netherlands
  • Dr. Eero Hippelainen, University of Helsinki and Helsinki University Hospital, Finland
  • Dr. Deni Hardiansyah, Universitas Indonesia, Indonesia
  • Dr. Jan W. T. Heemskerk, Leiden University Medical Center, the Netherlands
  • Dr. Jim O’Doherty, Siemens Medical Solutions/Medical University of South Carolina, USA
  • Dr. Johannes Tran-Gia, University Hospital Würzburg, Germany the AAPM Working Group on Grand Challenges


News and Announcements:

Phase 0 has finally started! Participants can now register and download their first “warm-up” dataset. Please follow the instructions under the Participate tab (Participate->Instructions).

After a „warm-up“ Phase 0, which will not flow into the evaluation, the challenge will be divided into two complexity levels, where participants will be asked to perform TAC fitting and calculate TIA:

Phase 1: only based on a provided scoring data set
Phase 2: based on the scoring data set (same as in Phase 1), which can additionally be improved using an auxiliary data set provided for this phase

Based on the 20 patients selected for the challenge, a ground truth for kidney, tumor, and blood was determined for each of the patients. This ground truth consists of the fit function and the fit parameters for each organ. From the ground truth, measurements were simulated, including noise, which realistically describe actually measured time-activity curves of real patients.

Phase 0 (15th February – 15th March) - Part 1:

Optional warm-up exercise. Participants may select between 1 and 5 time points from a synthetic predefined dataset of 140 time points < 140 hours post injection of 177Lu-PSMA. A download will be initiated, providing the participants with percent (%) activity data for 3 organs (blood, tumor and kidneys) from 5 separate patients for the time points they selected. A maximum of 3 (organs) x 5 (patients) x 5 (time points) = 75 data points will be available for download. A submission template can be found in the Starting Kit under Participate->Files.

Phase 1 (16th March – 13th April): 

All participants will download an identical predefined set of time-activity data corresponding to a typical clinical data acquisition scheme, consisting of 5 time points for 3 organs (blood, tumor and kidneys) for 5 patients (other than those used in Phase 0).

Participants will then:

● Fit the TAC functions that best represent the given data points

● Calculate the TIA values based on each fitted TAC function

● Enter their results in the submission template, which can be found in the Starting Kit under Participate->Files

● Submit the results back to the Challenge webpage

 Phase 2 (14th April – 15th May): 

All participants will download a new predefined set of time-activity data corresponding to a typical clinical data acquisition scheme, consisting of 5 time points for 3 organs (blood, tumor and kidneys) for 15 additional patients (other than those used in Phase 1). 

 Participants will then:

● Fit the TAC functions that best represent the given data points

● Calculate the TIA values based on each fitted TAC function

● Enter their results in the submission template, which can be found in the Starting Kit under Participate->Files

● Submit the results back to the Challenge webpage


All valid submissions will be scored and ranked by the Challenge Team according to minimum normalized root-mean-square error (NRMSE) and maximum deviation of the results from the ground truth TIA values.

The participants with the best scores in Phase 1 and Phase 2 will be announced as the two winners. These winners will be awarded complimentary registration to attend the AAPM Annual Meeting 2023 in Houston, TX, where they will present on their methodology in a dedicated Grand Challenge Symposium (in-person attendance mandatory).

Publication plan:

The results of this Grand Challenge will be summarized to reflect the variability and information-content dependence in TAC fitting and TIA values in RPT dosimetry, including suggestions on how to harmonize their calculation. These findings will be published, with participants listed as co-authors, in suitable journals such as Medical Physics or the Journal of Nuclear Medicine, within 2 years from completion of the challenge.

Terms and Conditions

The TACTIC challenge is organized in the spirit of cooperative scientific progress. By participating in this challenge, each participant agrees to abide by the following rules:

  • Anonymous participation is not allowed, each participant/team will disclose the name(s), professional title(s) and affiliation(s).

  • Participants may only be part of one participating group.

  • One member from each top-ranked team (Phase 1 and Phase 2) will be awarded complimentary meeting registration to attend AAPM's 2023 Annual Meeting in Houston, TX (July 23-27, 2023). In-person attendance is mandatory. They will present their results and methodology during a Grand Challenge Symposium and participate in an Awards & Honors Ceremony.

  • Participants from the host institution(s) and colleagues of the organizers may participate, but they will not be eligible for prizes or recognition as ranking participants. Please refer to the Challenge Organizer Guidance document of the AAPM Working Group on Grand Challenges (https://www.aapm.org/GrandChallenge/documents/ChallengeOrganizerGuidance.pdf).

  • Participants may only use the data provided.

  • Once participants submit their outputs to the challenge organizers, they will be considered fully vested in the challenge, so that their performance results will become part of any presentations, publications, or subsequent analyses derived from the challenge at the discretion of the organizers.

  • Participation in the TACTIC Challenge acknowledges the educational, friendly competition, and community-building nature of the challenge and commits to conduct consistent with this spirit for the advancement of the medical physics community. See this article (link: https://www.spiedigitallibrary.org/journals/Journal-of-Medical-Imaging/volume-2/issue-02/020103/Special-Section-Guest-Editorial--LUNGx-Challenge-for-computerized-lung/10.1117/1.JMI.2.2.020103.full?SSO=1) for a discussion of lessons learned from the LUNGx Challenge, sponsored by SPIE, AAPM, and NCI.

Phase 0 - Request Data

Start: Jan. 19, 2023, midnight

Phase 0 - Submit Results

Start: Feb. 15, 2023, midnight

Phase 1

Start: March 16, 2023, midnight

Phase 2

Start: April 16, 2023, midnight

Competition Ends

May 17, 2023, 11:59 p.m.

You must be logged in to participate in competitions.

Sign In