Medical Physicist's Notes · TBI dosimetry
Total body irradiation places unusual demands on the in-vivo dosimetry programme — many simultaneous points, long fractions, energy-dependent corrections at extended SSD. Five characteristics of the myOSL Chip line up directly with those demands. Each is sourced inline against the peer-reviewed literature or the manufacturer type-test data.
TBI in-vivo programmes routinely place 8 to 10+ detectors per fraction: head, neck, mediastinum, umbilicus, pelvis, knees, ankles, plus lung-block entrance/exit pairs. myOSL Chips are passive and independent — there is no reader-channel ceiling; the bench-side handheld reader sequences as many chips as the protocol requires. Adding a measurement point to the patient is adding a chip, nothing else.
Source: Manufacturer workflow specification — handheld myOSLchip reader.
TBI is delivered at extended SSD with photon energies typically 6–18 MV. The active element is beryllium oxide (Z_eff 7.21, density 2.85 g/cm³), sitting essentially next to soft tissue (Z_eff 7.35). The mass-energy-absorption ratio stays close to unity across the entire therapeutic photon range, so a single calibration factor handles the in-vivo points without per-anatomy energy corrections.
Source: Manufacturer material specification; characterised against tissue in Kowalski et al., J Appl Clin Med Phys 26(4):e70057 (2025).
TBI total prescriptions sit in the 8–14 Gy band, with single-point doses on the chip itself ranging from sub-Gy at shielded points to several Gy at midline. The type-test characterisation shows r² = 0.9999 linearity from zero to 10 Sv on a single dosimeter — well above any single-fraction TBI point dose — so saturation effects don't need to be considered in the dose calculation.
Source: myOSL Chip type-test data (extended-range linearity panel).
Most centres run a small number of TBI cases per year, but each case carries a long set-up and full in-vivo coverage. With characterised sensitivity drift of approximately −2 % across the first 0–15 Gy cumulative use and stable response to 32 Gy, the same chips are read, erased and re-issued across multiple TBI campaigns. The recurring per-patient detector cost is essentially the reader operator's time.
Source: Kowalski et al., J Appl Clin Med Phys 26(4):e70057 (2025) — characterisation, §sensitivity drift.
Two independent 2025 peer-reviewed groups validated the myOSL Chip against Landauer nanoDot (Al₂O₃:C). Kowalski et al. measured a TBI accuracy of +1.72 % ± 2.73 % against the Al₂O₃:C comparator. Davis et al. concluded equal or superior performance to nanoDot across TBI, TSET, en-face electrons and pacemaker / out-of-field measurements. Clinics moving off the discontinued nanoDot can substitute the chip into the same TG-191-style in-vivo workflow.
Source: Kowalski 2025 (PMC11969087); Davis 2025 (J Appl Clin Med Phys).
| Metric | myOSL Chip | Source |
|---|---|---|
| In-vivo points per fraction | Unlimited (sequential read on the handheld reader) | Manufacturer spec |
| Tissue equivalence | Z_eff 7.21 (vs soft tissue 7.35) | Material spec |
| Single-point linearity | r² = 0.9999 to 10 Sv | Type-test dossier |
| Sensitivity drift on reuse | ≈ −2 % across 0–15 Gy cumulative, stable to 32 Gy | Kowalski 2025 |
| TBI accuracy vs Al₂O₃:C | +1.72 % ± 2.73 % | Kowalski 2025 |
| TBI clinical validation | Equal or superior to nanoDot in TBI, TSET, electrons and out-of-field | Davis 2025 |
Sources cited on this page
myOSL™ Chip
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For Medical Physicist
Linearity to 10 Sv, fading at 3 months, energy & angular response — the manufacturer type-test data in one page.
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