General principles: These are summary organ at risk tables to help make split second decisions in exams about acceptability of plans or give a gross indication of tolerances. Tolerance limit will vary according to the institution, fractionation and patient factors. This is NOT meant for clinical use or patient care. It is simply to help make a rapid judgement call in exams and based on dose constraints used in UK protocols/RCR protocols.

Target coverage

95% of the PTV volume should get >95% of the dose (or atleast 95% of the dose prescribed)
99% of the PTV volume should get >90% of the dose prescribed
5% of the PTV volume should get <105% of the dose
And avoid any hot spots – ie >107%
D50% is representative of the mean dose to the PTV

For SABR lung treatments

95% of the PTV volume should get 100% of the dose
Max dose to PTV should be between 110-140%
D50% of volume is not used in SABR to assess plan quality

PLAN EVALUATION:

1. Check isodose lines : Check 95% isodose line and check spatial coverage of PTV.
2. Check for any HOT SPOTS (defined as >107%)
3. Check spatial overlaps of treatment isodose lines with OARS – check general spatial coverage of organs at risk by 95% isodose – e.g. generally away from cord if 60Gy as treatment dose.
4. Check DVH statistics for OAR coverage and PTV coverage
5. Accept or Reject plan with reasoning.

Remember to check for: Max and min doses within PTV (to relevant volume, rather than point. Volume is more representative as the patient is not going to be in the exact same position during treatment. Volumes used are small e.g. 1cc or 0.5cc).
Remember series or parallel OAR when accepting doses (especially if above routine tolerance)
Revise ICRU definitions : https://clinicaloncologyregistrar.com/2019/10/06/dvh-and-icru-international-commission-on-radiation-units-reports-summary/