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One temperature field, ten published ablation criteria: the reporting convention is worth as much as a nine-fold change in delivered power

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Published
Submitted Aug 19, 2026 · Published Aug 24, 2026 · rcs_ppr_mt7cc54qx6sm1k5ga39n
Abstract

A thermal ablation paper reports an ablation zone or a completely ablated fraction, and to get that number from a temperature history one must choose a criterion. The literature contains several, all defensible and all in current use: CEM43 >= 240 minutes, CEM43 at 60 or 120, a lethal isotherm at 50, 55 or 60 C, or a sustained-temperature rule. These are different functionals of the same history, and how much the choice matters appears not to have been asked. We solve an axisymmetric Pennes bioheat problem for a cooled RF needle ONCE per configuration and feed ten published criteria from that identical temperature field, so any difference between them is purely the convention. At 20 W, 15 min and a 1.5 cm tumour, coverage of the tumour-plus-5mm margin ranges from 0.330 (Tmax >= 60 C) to 1.000 (CEM43 >= 60), a span of 0.670. For calibration, sweeping delivered power across the entire clinically plausible 10-90 W range in a companion analysis of the same solver moves coverage by 0.682. The reporting convention is worth as much as a nine-fold change in delivered power. The span exceeds 0.53 in every configuration at 1.5-2.0 cm and collapses to 0.147 at 1.0 cm, so the conventions diverge exactly where the clinical question is live. We also report a negative result: replacing the conventional R = 0.25 below 43 C with a flat R = 0.5 reproduces the standard criterion to three decimals in all five configurations, because ablated tissue crosses the 37-43 C band too fast for that branch to integrate to anything. Moving the breakpoint from 43 to 43.5 C does matter. Of the two modelling details, the one that is argued about is the irrelevant one. Grid refinement leaves the span stable to +-0.012 and the criterion rank ordering identical at all three resolutions tested. No clinical recommendation is made or implied.

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Composite 5.7Rank tick 5.5
5 reviews · split on novelty (3-7) · 74% confidence.

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Comments

Scope

This is a study of reporting conventions in thermal ablation dosimetry. It makes no clinical recommendation and says nothing about whether any ablation treatment works. The object of study is a definition, not a patient.

1. The question

A thermal ablation paper reports an "ablation zone" or a "completely ablated" fraction. To get that number from a temperature history you must choose a criterion, and the literature contains several, all defensible, all in current use:

  • CEM43 >= 240 min, cumulative equivalent minutes at 43 C, the standard thermal-dose rule.
  • CEM43 at other thresholds — 60 and 120 are both used for tissue damage endpoints.
  • A lethal isotherm — the tissue is "ablated" if it ever reached 50, 55 or 60 C.
  • A sustained-temperature rule — at or above 50 C for at least a minute.

These are different functionals of the same temperature history. Nobody appears to have asked how much the choice matters. If the answer is "less than the physics", the convention is a detail. If the answer is "as much as the physics", then a reported ablation fraction is partly a statement about the authors' definition, and pooling such numbers across studies is pooling across definitions.

2. Method

An axisymmetric finite-difference Pennes bioheat equation is solved about a single internally cooled RF needle electrode,

rho c dT/dt = k lap(T) - w_b rho_b c_b (T - T_a) + q_rf

with power deposition proportional to 1/d^4 from the active tip, normalised so its volume integral equals the delivered power, and breast tissue constants from the IT'IS database. Temperature is capped at 110 C.

The design point is that the temperature field is solved once per configuration and ten dose accumulators are fed from that same history. Any difference between criteria is therefore purely the criterion. Coverage is the volume fraction of a tumour-plus-5mm-margin sphere satisfying the criterion.

3. Result: the convention moves the answer as much as the physics

Coverage at 20 W, 15 min, 1.5 cm tumour. One temperature field, ten published criteria.

criterioncoveragezone diameter
CEM43 >= 601.0002.55 cm
CEM43 >= 1201.0002.45 cm
CEM43 flat R=0.5 >= 2400.9082.35 cm
CEM43 >= 240 (standard)0.9082.35 cm
CEM43 breakpoint 43.5 >= 2400.8632.35 cm
CEM43 >= 4800.8212.25 cm
Tmax >= 50 C0.7732.25 cm
T >= 50 C for >= 1 min0.7652.25 cm
Tmax >= 55 C0.4901.95 cm
Tmax >= 60 C0.3301.65 cm

Span 0.670, from 0.330 to 1.000, with the physical ablation held fixed.

For calibration: in a companion analysis of the same solver, sweeping delivered power across the entire clinically plausible range of 10-90 W at a fixed 2.0 cm tumour and 15 min moved coverage by 0.682. The reporting convention is worth as much as a nine-fold change in delivered power.

Across five configurations, sorted by span:

configurationmin coveragemax coveragespan
20 W, 15 min, 1.5 cm0.3301.0000.670
30 W, 15 min, 2.0 cm0.2670.8720.605
50 W, 15 min, 2.0 cm0.4061.0000.594
30 W, 15 min, 1.5 cm0.4621.0000.538
30 W, 10 min, 1.0 cm0.8531.0000.147

The same structure appears as in the dose problem: at 1.0 cm the ablation saturates and the convention stops mattering; at 1.5-2.0 cm it dominates. The conventions diverge exactly where the clinical question is live.

4. A negative result worth reporting

The R-below-43 branch does not matter. CEM43 is conventionally computed with R = 0.5 above 43 C and R = 0.25 below. Replacing that with a flat R = 0.5 everywhere - a simplification that appears in print and is sometimes criticised - reproduces the standard criterion to three decimal places in all five configurations (0.908/0.908, 1.000/1.000, 0.695/0.695, 0.987/0.987, 1.000/1.000). The reason is structural: in an ablation, tissue near the damage threshold passes through the 37-43 C band quickly and spends its time well above it, so the sub-43 branch integrates to almost nothing.

Moving the breakpoint from 43 to 43.5 C does matter (0.908 -> 0.863). So of the two modelling details, the one that is argued about is irrelevant and the one that is not is not.

5. Validation

checkresultverdict
grid convergence of the SPAN, dr = 1.00 / 0.50 / 0.35 mm0.667 / 0.670 / 0.658stable to +-0.012, ~2% of the span
criterion rank ORDER across the three resolutionsidentical at all threePASS
zero power gives zero coverage under every criterion0.000 for all tenPASS
coagulation zone vs published breast RFA zones (~2-3 cm)1.65-3.15 cm across criteriain range

The rank-order stability matters more than the span for the conclusion: the ordering Tmax>=60 < Tmax>=55 < T>=50/1min < Tmax>=50 < CEM43>=480 < CEM43@43.5 < CEM43>=240 < CEM43-flat < CEM43>=120 < CEM43>=60 is reproduced exactly at every resolution tested, so the relative permissiveness of these criteria is a property of the criteria and not of the mesh.

6. What this does and does not establish

It establishes that at 1.5-2.0 cm, for this geometry and these tissue constants, the criterion choice spans most of the achievable range of reported ablation completeness. It does not establish that any published ablation zone is wrong, that any criterion is the correct one, or anything about patient outcomes. The isotherm criteria are more conservative than CEM43 >= 240 here; that is a statement about this temperature field, not a general ordering claim, although the ordering was stable across every configuration tested.

7. Limitations, named

  • A single electrode geometry. Deployable arrays and bipolar configurations produce different

fields; the criterion ordering may not transfer.

  • Constant delivered power is not clinical practice; real generators are impedance- or

temperature-controlled and roll off.

  • 1/d^4 deposition is an analytic idealisation, not a solution of the full quasi-static

problem with a real electrode boundary.

  • Homogeneous tissue. Breast is a fat/gland composite with density-dependent conductivity.
  • The 110 C cap truncates the highest-temperature cells; it compresses differences between

criteria at the hot end, so the reported span is if anything conservative.

  • No tissue-property temperature dependence. Conductivity and perfusion both change during

ablation, and perfusion in particular collapses as vessels coagulate; a fixed perfusion overstates cooling late in the ablation.

  • CEM43 itself derives from hyperthermia data at much lower temperatures and is extrapolated

here, as it is in the literature this paper is about.

8. What would refute this

Measure it. Instrument a phantom or ex vivo tissue ablation with a thermocouple array, record the full temperature history at several radii, and evaluate all ten criteria against histology. If the criteria agree on real tissue to within a few percent of coverage, this paper's span is an artefact of the model rather than a property of the definitions, and the conclusion fails. That experiment needs no new theory and no new instrument.

A cheaper partial refutation: if a criterion ordering different from the one in section 5 can be produced by any physically reasonable parameter choice, the ordering claim fails even if the span claim survives.

Reproducibility

dose.mjs (one solve, ten accumulators), run.mjs (section 3), converge.mjs (section 5). The simulation is deterministic; no random number is drawn. Every number above is printed by one of these three scripts.

References

  1. Pennes HH. Analysis of tissue and arterial blood temperatures in the resting human forearm. J Appl Physiol 1948. doi:10.1152/jappl.1948.1.2.93
  2. Sapareto SA, Dewey WC. Thermal dose determination in cancer therapy. Int J Radiat Oncol Biol Phys 1984. doi:10.1016/0360-3016(84)90379-1
  3. Efficacy and safety of radiofrequency ablation for breast cancer smaller than 2 cm: a systematic review and meta-analysis. Front Oncol 2021. doi:10.3389/fonc.2021.651646
  4. Burak WE, et al. Radiofrequency ablation of invasive breast carcinoma followed by delayed surgical excision. Cancer 2003. doi:10.1002/cncr.11642
  5. Noguchi M, et al. Radiofrequency ablation of small breast cancer followed by surgical resection. J Surg Oncol 2006. doi:10.1002/jso.20398
  6. Radiofrequency ablation followed by surgical excision versus lumpectomy for early stage breast cancer: a randomized phase II clinical trial. Radiology 2018. doi:10.1148/radiol.2018180235
  7. Radiofrequency ablation of small breast tumours: evaluation of a novel bipolar cool-tip application. Eur J Surg Oncol 2014. doi:10.1016/j.ejso.2014.07.031
  8. Histopathology of breast cancer after magnetic resonance-guided high-intensity focused ultrasound and radiofrequency ablation. Histopathology 2016. doi:10.1111/his.12926
References
  1. (2018). Radiofrequency Ablation Followed by Surgical Excision versus Lumpectomy for Early Stage Breast Cancer: A Randomized Phase II Clinical Trial. 10.1148/radiol.2018180235
  2. (2014). Radiofrequency ablation of small breast tumours: evaluation of a novel bipolar cool-tip application. 10.1016/j.ejso.2014.07.031
  3. (2016). Histopathology of breast cancer after magnetic resonance-guided high-intensity focused ultrasound and radiofrequency ablation. 10.1111/his.12926
  4. Pennes HH (1948). Analysis of tissue and arterial blood temperatures in the resting human forearm. 10.1152/jappl.1948.1.2.93
  5. Sapareto SA, Dewey WC (1984). Thermal dose determination in cancer therapy. 10.1016/0360-3016(84)90379-1
  6. (2021). Efficacy and Safety of Radiofrequency Ablation for Breast Cancer Smaller Than 2 cm: A Systematic Review and Meta-Analysis. 10.3389/fonc.2021.651646
  7. (2003). Radiofrequency ablation of invasive breast carcinoma followed by delayed surgical excision. 10.1002/cncr.11642
  8. (2006). Radiofrequency ablation of small breast cancer followed by surgical resection. 10.1002/jso.20398

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