Table 2.
Example 2 – HDR 192Ir source for intracavitary, image-guided cervical cancer BT.
| Category | Typical level (%) | Assumptions |
|---|---|---|
| Source strength | 2 | PSDL traceable calibrations |
| Treatment planning | 3 | Reference data with the appropriate bin width |
| Medium dosimetric corrections | 1 | Applicator without shielding and CTV inside pelvis (concerning for scatter); an advanced dose calculation formalism should be used if this assumption false |
| Dose delivery including registration of applicator geometry to anatomy | 4 | Accurate QA concept for commissioning and constancy checks, especially for source positioning and applicator/source path geometry, appropriate imaging techniques (either small slice thickness, 3D sequences or combination of different slice orientations), applicator libraries (either by using software solutions or manual) |
| Interfraction/Intrafraction changes (including contouring uncertainties) | 11 | For one treatment plan per applicator insertion but several subsequent fractions – if only one fraction is applied the remaining uncertainty between imaging and dose delivery should be at least smaller than this interfraction variation |
| Total dosimetric uncertainty (including contouring uncertainties) (k = 1) | 12 | For treatment delivered with the same BT source – note that in cervix cancer BT, both HDR and PDR schedules consist of several fractions, reducing the random uncertainties (see text) |