How can the accuracy of the dwell position in a remote after loading 192Ir HDR unit be checked?

The accuracy of the dwell position in a remote afterloading 192Ir HDR (High Dose Rate) unit is primarily checked by taking an auto radiograph. An autoradiograph provides a visual representation of the radioactive source's position within the treatment area based on actual imaging. This method allows for precise verification of the source's location and distribution, which is crucial for ensuring that the intended dose is delivered to the target tissue while minimizing exposure to surrounding healthy tissues.

Using autoradiography, the dosimetrists can directly visualize the placement and alignment of the source against the planned treatment geometry. This method enhances quality assurance in the treatment process, confirming that the machine is functioning properly and that the parameters set by the treatment plan are accurate.

In contrast, visual inspection lacks the precision necessary to verify the dwell position accurately. Patient feedback does not provide the technical accuracy required to assess the source's actual position, as it is subjective and not based on measurable data. Manual calibration, while important for ensuring that the system is functioning correctly, does not provide a direct means of verifying the source's placement in relation to the treatment plan. Thus, autoradiography is the most effective method for verifying the accuracy of the dwell position in this context.