Treatment Delivery and Verification
Treatment delivery and verification tests whether you can reproduce the planned position, deliver the planned dose, and detect deviations before they become errors. It covers set-up, image guidance, record-and-verify systems, in vivo dosimetry, and adaptive action.
Delivery workflow
Before treatment, confirm patient identity, prescription, site, side, fraction number, and any plan change. A time-out with the team reduces wrong-site and wrong-plan errors. Set-up uses immobilization, lasers, and reference marks; imaging verifies bony or soft-tissue position. 2D kV or portal imaging is useful for bony landmarks and fiducials; CBCT gives soft-tissue information but adds imaging dose. Surface guidance tracks external motion but not internal tumour position. Record-and-verify systems check field parameters and dose, but they do not prove the patient is in the right position.
Verification and action
Image review compares the patient to the planning reference. A displacement is corrected by a couch shift, then re-imaged when the protocol requires. Action levels define when to treat, re-image, or escalate. MLC logs, beam-on time, and in vivo dosimetry can detect delivery errors. Adaptive radiotherapy is considered when anatomy changes materially, such as weight loss or tumour shrinkage.
Worked example
A prostate CBCT shows the prostate displaced 4 mm anteriorly relative to the planning position. The radiographer applies a 4 mm posterior couch shift, because moving the couch posteriorly moves the patient posteriorly into alignment. They repeat imaging to confirm, then treat within the departmental tolerance. If the shift exceeds the action level, or if the direction is ambiguous, they stop and ask the clinician or physicist. The reasoning is to correct the patient, not the planned isocentre.
Traps
Do not treat on a verbal looks fine without documented image review. Do not apply a couch shift in the wrong sign: anterior patient displacement needs a posterior couch move. Do not assume CBCT is always necessary; it adds dose and time. Do not use portal imaging to assess soft-tissue prostate position. Record-and-verify prevents parameter errors, not anatomical errors. Do not continue after a mismatch just because the fraction is due.