Using graph paper, one can easily check which of the following parameters of a linac?

Using graph paper provides a practical method for evaluating various parameters of a linear accelerator (linac), particularly field size and orthogonality of the jaws.

Field size can be accurately determined by outlining the treatment area defined by the jaw settings on the linac. By placing the linac's radiation field onto the graph paper, the exact dimensions can be assessed. This visual method enables dosimetrists to ensure that the established field size adheres to the prescribed treatment plan.

Orthogonality of the jaws pertains to the alignment of the collimator jaws with respect to each other and the treatment axis. By using graph paper, one can check if the jaws are positioned at right angles to each other simply by drawing lines and measuring angles. This ensures that the radiation beam is delivered precisely to the intended treatment area, minimizing any potential dose to surrounding healthy tissues.

Thus, since both field size and the orthogonality of the jaws can be effectively evaluated using graph paper, the correct conclusion is that both parameters are amenable to this checking method.