Unintended overexposure of a patient during radiotherapy treatment at the Edinburgh Cancer Centre, in September 2015

Appendix 2:

The relevant section from the ECC's Employer's Written Procedure EP2\ ECC\3422 'RadCalc instructions' for parallel opposed pair at 100cm FSD calculations

For patients with POP calculation at 100cm FSD:

• A new calculation point must be created that sits midway between the 2 isocentres.
• In Points & Off Axis Assistance, copy the IsoCenter_1 point by clicking on the middle button "copy point".
• Tick "Enter 3D coordinates for point" and look at the x, y, and z coordinates for Isocentre_1 and Isocentre_2 to find out which value differs. If they are lateral fields, the x value will be different. If they are ant/post fields, the y value will be different.
• Set whichever value differs to zero for IsoCenter_3.
• With IsoCenter_3 selected, set the SSD for both beams to 100cm and then enter the prescribed dose per fraction in RTP Dose.
• On the photon beams tab, select Calc Pt as IsoCenter_3 for both beams.