Choi response criteria calculator

Notes

Measurements

• Tumor size is represented by the sum of the longest cross-sectional diameters of target lesions, similarly to the RECIST system
• Attenuation of individual lesions should be preferentially measured within a region of interest manually drawn around the margin of the tumor
• Attenuation should be always measured in identical phases on all studies
• In the original study by Choi et al. the portal venous phase was used for measurement

Response categories in the Choi system

• The Choi response system uses the same categories as RECIST 1.1, the key difference being the introduction of tumor CT density as an additional parameter
• The aim is to avoid a misdiagnosis of progression where secondary effects such as intratumoral hemorrhage, edema, necrosis, or myxoid degeneration result in a tumor size increase without an actual increase of tumor burden
• This system is also capable of early diagnosis of recurrence within a previously treated lesion where the tumor size has not yet increased
• The system was originally designed to assess response to treatment with imatinib in patients suffering from gastrointestinal stromal tumor (GIST), but has been since then applied to a variety of other tumors and treatments

• The response categories are:
  • Complete response (CR)
    • disappearance of all lesions
    • no new lesions
  • Partial response (PR)
    • ≥10% decrease of the sum of target lesion diameters OR ≥15% decrease of mean tumor density
    • no progressing non-target lesions
    • no new lesions
  • Stable disease (SD)
    • criteria for CR, PR, or PD are not met
    • no symptomatic deterioration that can be attributed to tumor progression
  • Progressive disease (PD)
    • ≥10% increase of the sum of target lesion diameters AND tumor density does not meet criteria for PR
    • new or growing intratumoral nodules
    • new lesions

• ^{Choi H, Charnsangavej C, Faria SC, Macapinlac HA, Burgess MA, Patel SR, Chen LL, Podoloff DA, Benjamin RS. Correlation of computed tomography and positron emission tomography in patients with metastatic gastrointestinal stromal tumor treated at a single institution with imatinib mesylate: proposal of new computed tomography response criteria. J Clin Oncol. 2007 May 1;25(13):1753-9. doi: 10.1200/JCO.2006.07.3049. PMID: 17470865.}

Practical points

• Some authors have proposed modifications to the original Choi response criteria. E.g. for metastatic renal cell cancer treated with tyrosine kinase inhibitors a modified (mChoi) system where both at least 10% size decrease and at least 15% decrease of CT density were required for partial response
• This system was found to correlate better with time to disease progression in the study population
  • ^{Nathan PD, Vinayan A, Stott D, Juttla J, Goh V. CT response assessment combining reduction in both size and arterial phase density correlates with time to progression in metastatic renal cancer patients treated with targeted therapies. Cancer Biol Ther. 2010 Jan;9(1):15-9. doi: 10.4161/cbt.9.1.10340. Epub 2010 Jan 17. PMID: 20009542.}

• Since tumor CT attenuation is a critical part of the Choi response criteria absolute care must be taken to ensure that scans are actually comparable, and comparable scanning protocols were used

• Technical issues such as significant contrast media extravasation, or a substantially different dose of the contrast agent can significantly influence the measured attenuation of target lesions

Further reading

• Radiology Assistant has a thorough summary of RECIST 1.1 including a brief discussion of the Choi response criteria with imaging examples

Last updated: 2022-01-17