Understand TG-51 Protocols and Saved Evidence

Quadrant saves the protocol identity, calculation revision, inputs, source evidence, coefficients, intermediate values, and result used for each new TG-51 calibration. The browser, PDF report, and Excel report present that saved calculation evidence.

Supported Calculation Paths

Calibration	Saved Identity	What It Means
Photon	TG-51 photon	Uses the photon calculation with the selected chamber coefficients and saved measurement values.
Electron	AAPM TG-51 (1999)	Uses the original cylindrical-chamber electron calculation, including measured Pgr. This is the default electron choice.
Electron	AAPM Report 385 (2024)	Uses the supported cylindrical-chamber Report 385 calculation. It uses chamber-specific Report 385 coefficients and does not use measured Pgr.

Select the electron path under Electron Protocol in the new-data-set wizard’s Calibration Conditions step. Photon and electron defaults are stored independently.

Caution

Equipment, coefficient, reference-condition, or reference-data changes can affect saved calibrations. Review the recalculation dialog and every affected energy before saving.

AAPM TG-51 (1999) Electron

Use AAPM TG-51 (1999) for the original cylindrical-chamber electron workflow. Quadrant records:

• distal R₅₀ and the calculated reference depth, d_ref;
• the chamber’s original TG-51 k_ecal coefficient;
• charges measured at d_ref and the effective point of measurement;
• the resulting P_gr gradient correction;
• correction factors, corrected chamber reading, dose at d_ref, clinical PDD conversion, and final dose.

New cylindrical-chamber calculations require R₅₀ greater than 26 mm. The original protocol requires a plane-parallel chamber at or below that boundary; plane-parallel chambers are not supported in this workflow.

AAPM Report 385 Electron

Use AAPM Report 385 (2024) only after a qualified medical physicist (QMP) has reviewed the chamber and measurement conditions for this use. Quadrant requires:

• a listed cylindrical chamber with a complete, exact Report 385 k_Qecal, a₀, b₀, and c₀ coefficient tuple;
• separate QMP confirmation that the individual chamber has reference-class behavior;
• a measured P_pol for the selected energy and mode;
• a distal R₅₀ from 17 through 87 mm;
• water-phantom confirmation and nominal energy from 4 through 22 MeV;
• a measured surface field of at least 100 × 100 mm;
• a 1000 mm beam-quality SSD and a 900–1100 mm reference-dose SSD;
• confirmation that the reference-dose SSD and clinical PDD geometry match the intended treatment planning system (TPS) setup;
• confirmation that R₅₀ is the distal 50% dose depth; and
• confirmation that the cylindrical chamber axis is positioned at d_ref without an effective-point shift.

The chamber model stores original TG-51 k_ecal separately from Report 385 k_Qecal, a₀, b₀, and c₀. The Report 385 tuple must be either complete or absent. Matching that tuple to the Report 385 coefficient tables establishes coefficient eligibility. It does not establish that a particular chamber is reference class. The separate QMP confirmation records that clinical judgment.

Report 385 applies the measured electron P_pol. Quadrant blocks the calculation when |P_pol − 1| is 0.02 or greater. The photon reference-class P_pol range is not applied to Report 385 electrons.

Quadrant stores all lengths in millimeters. For Report 385 Equation 7 only, it converts the saved R₅₀ to its numerical value in centimeters exactly once because the published Table 5 coefficients use that convention. The coefficients themselves are not changed.

P_leak and P_rp are shown in the saved equation evidence and reports. Both are fixed at 1.000 by Quadrant policy for this release; they are not measurement inputs. Report 385 does not use measured P_gr.

Beam-Quality and Clinical PDD Evidence

Quadrant accepts percent depth dose (PDD) data for electron scan analysis. It does not add percentage depth ionization (PDI)-to-PDD conversion or detector-position correction. Perform any required conversion or correction before importing the scan.

Electron calculations preserve two evidence roles:

Evidence Role	What It Supplies
Beam quality	The distal R50 and full-precision dref from PDD measured at the required beam-quality geometry.
Clinical normalization	PDD(dref) from PDD matching the reference-dose geometry used to convert dose at dref to the selected clinical normalization depth.

One imported PDD can fill both roles only when its energy, mode, field, and geometry satisfy both. Otherwise, keep the sources separate. A later reference-data change replaces only the matching evidence role; it does not substitute beam-quality evidence for clinical-normalization evidence.

How Saved Calculations Are Protected

Preview, save, recalculation, and reports use one complete, versioned result. The browser creates that result once. On save, the server validates its protocol identity and evidence without calculating a separate dose. A save can fail when equipment, coefficients, or evidence changed after preview; reopen and review the calibration instead of relying on the stale preview.

Each accepted recalculation creates a new read-only version of the saved calculation. Previous versions remain available in revision history. PDF and Excel exports use the selected saved version rather than current chamber-model coefficients or a current formula fallback.

Accepting or superseding a reproducible modern calculation does not automatically lock it. A lock indicates that historical evidence quality prevents safe recalculation; it is not the normal finalization state.

A locked record displays Historical record (read-only). Its older rounded values may be insufficient to reproduce dose, so Quadrant does not unlock or recalculate it in place. A protocol change requires a separate calculation context linked to the locked source and full-precision evidence for every required input.

Review the Result

Before clinical use:

1. Confirm the displayed protocol label and open the calculation details.
2. Review source-linked warnings and failures. Published requirements identify their document location; local Quadrant policies are labeled separately.
3. Review the equation details, coefficients, correction factors, units, substituted values, intermediate results, clinical PDD conversion, and final dose.
4. Confirm the PDF and Excel reports show the same saved protocol and values.
5. Before clinical release, obtain QMP approval of the canonical clinical test vectors and their generated PDF and Excel reports.

Continue with Add an Electron TG-51 Calibration or Export a TG-51 Report.