Saxsons Group — India's trusted nuclear medicine, radiotherapy, oncosurgery, dosimetry and cyclotron supplier since 1986

MAX 4000 Plus · Reference Electrometer — what the literature says.

Four real anchor citations across the workflow the MAX 4000 Plus is bought for — reading out the reference ionisation chamber during TG-51 (photon), TG-51 addendum (electron) and TRS-398 absolute-dose calibrations. Covers the reference-class electrometer specification (McEwen 2014), the 2024 electron-addendum revision (Renaud 2024), the observed D_w difference between old and addendum protocols (McCaw 2017), and the case for continuous P_elec self-inspection on top of annual ADCL calibration (Kawashima 2023). Every DOI + journal reference verified.

± 0.1 %reference-class P_elec agreement with ADCL (Kawashima 2023)
0.91 – 1.2 %TG-51 / addendum combined D_w uncertainty (McCaw 2017)
Report 3852024 TG-51 electron addendum revising the electron formalism
Product specsProduct specs
Filter
TG-51 addendum · reference-class specification
≤ 1.6 %
IEC 60731 combined uncertainty ceiling
ADCL
independent electrometer charge calibration
Monte-Carlo
updated k_Q derivation
The addendum recommends users obtain independent charge-calibration data from an ADCL (Accredited Dosimetry Calibration Laboratory) rather than relying on manufacturer specifications alone. The reference-class electrometer sits at the entry point of that separately-calibrated chain.
Photon addendum2014
Reference-classThe addendum that establishes the reference-class electrometer specification: updated k_Q factors from direct Monte Carlo calculations, tightened uncertainty budget, ADCL-issued charge-calibration recommendation. This is the protocol the MAX 4000 Plus is engineered against

Addendum to the AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon beams

Medical Physics 41(4):041501 — McEwen, DeWerd, Ibbott, Followill, Rogers, Seltzer, Seuntjens (AAPM WGTG51)

TG-51 electron addendum · Renaud 2024
≤ 22 MeV
high-energy electron beam scope
k_Q
updated Monte-Carlo derivation
2024
first electron-formalism revision since TG-51 (1999)
Extends the reference-class electrometer + reference chamber pairing framework from photon reference dosimetry into modern electron reference dosimetry. Applies directly to any linac electron programme that measures reference output on a MAX-4000-class electrometer.
Electron addendum2024
Report 385The 2024 electron-beam addendum that revises the TG-51 electron formalism, updates k_Q data and clarifies electrometer + reference-chamber pairing requirements for high-energy electron reference dosimetry

Addendum to the AAPM's TG-51 protocol for clinical reference dosimetry of high-energy electron beams — AAPM WGTG51 Report 385

Medical Physics 51(9):5840 – 5857 (open-access PDF at Baptist Health) — Renaud, Sarfehnia, Siebers, Tantôt (AAPM WGTG51)

D_w cross-protocol difference — McCaw 2017
0.1 – 0.3 %
Flattening-filter photon beams
small chamber; both protocols agree
vs
≤ 0.8 %
FFF beams · Farmer chamber
volume-averaging correction up to 0.6 % on FFF
TG-51 vs addendum comparison2017
0.1 – 0.8 %Cross-protocol D_w differences: 0.1-0.3 % for flattening-filter photon beams; up to 0.8 % for FFF beams with a Farmer chamber. Combined uncertainty 0.91-1.2 % — the budget the reference-class electrometer needs to keep clear of

Comparison of the recommendations of the AAPM TG-51 and TG-51 addendum reference dosimetry protocols

Journal of Applied Clinical Medical Physics 18(4):128 — McCaw, Hwang, Jang, Huq (UPMC)

Reference-class electrometer P_elec · Kawashima 2023
± 0.1 %
agreement with ADCL P_elec
± 0.2 %
long-term stability, 3 months
0.26 %
combined uncertainty (k = 2)
One of the electrometers in the cohort drifted initially and stabilised after six months — the paper is the case for a self-inspection cadence on the reference-class electrometer, not just an annual ADCL calibration. The MAX 4000 Plus's sub-fA leakage + 0.1 % repeatability sit inside this envelope.
Self-inspection · P_elec2023
± 0.1 %Every measured P_elec correction factor for a set of reference-class electrometers agreed within 0.1 % of the ADCL calibration value; long-term stability held within 0.2 % across 12 weekly measurements over 3 months. Combined uncertainty 0.26 % at k = 2

Assessment of a self-inspection method and reporting measured electrometer correction factors for reference-class electrometers in radiotherapy

Journal of Applied Clinical Medical Physics 24(8):e14082 — Kawashima, Varnava, Ozawa, Okada, Higuchi, Hoshino, Tashiro

Back to MAX 4000 Plus product page

White Papers & Background Reading

PDF

IAEA TRS-398 — Absorbed Dose Determination in External Beam Radiotherapy

IAEA International Code of Practice for dosimetry based on standards of absorbed dose to water. The reference protocol the MAX 4000 Plus is used against on ionisation-chamber measurements in photon, electron, proton and heavy-ion beams world-wide.

Reference · IAEADownload
FILE

AAPM TG-51 — Photon and Electron Reference Dosimetry Protocol

AAPM Task Group 51 clinical-reference-dosimetry protocol for high-energy photon and electron beams. The North-American equivalent of TRS-398 for absorbed-dose-to-water determination; addenda published 2014 (photon) and 2024 (electron).

Reference · AAPMDownload
PDF

AAPM TG-51 Photon Addendum (Report 67 Addendum)

The 2014 photon-beam addendum establishing the reference-class electrometer + reference-class ionisation chamber specification, updated k_Q factors and tightened uncertainty budget.

Reference · AAPMDownload
FILE

IEC 60731 — Medical electrical equipment · Dosimeters with ionization chambers as used in radiotherapy

The international electrical-safety + performance standard governing radiotherapy dosimeters. Sets the ≤ 1.6 % combined-uncertainty ceiling that the TG-51 addendum tightens for reference-class use.

Reference · IECDownload
FILE

IAEA/WHO Network of Secondary Standards Dosimetry Laboratories (SSDL)

The SSDL network that traces the electrometer's calibration chain back to the IAEA/BIPM primary standards. Anchor of the international measurement-comparability programme covering therapy-level ionisation-chamber and electrometer calibrations.

Reference · IAEADownload
FILE

AERB Safety Code No. AERB/RF-MED/SC-1 — Medical Diagnostic X-Ray Equipment and Installations

Indian regulatory framework governing external-beam radiotherapy commissioning and periodic QA including reference-dosimetry uncertainty budgets.

Reference · AERBDownload

Literature Radar · auto-updated daily

Latest reference-dosimetry research

Fresh peer-reviewed papers on linac reference dosimetry — TG-51 / TG-51 addendum protocol implementation, TRS-398 comparability, reference-class electrometer performance, ADCL / SSDL calibration chain and uncertainty budgets. Auto-updated from Europe PMC.

See all in radar →
Loading recent papers…
Get the weekly digest →