What is the principal advantage of isocentric technique over non-isocentric source to surface distance techniques for a treatment using parallel opposed treatment portals?

Your patient is being treated supine using AP/PA ports. The dosimetrist asks you to make an anterior shift on the PA port of 1 cm. Which of the following is true?

7) Simplify the expression. Write the result with only positive exponents.  

A urinary bladder patient is being treated with an isocentric four-field box portal plan on a linear accelerator calibrated to 100 cm SAD . The AP/PA separation is 25.3 cm. The RT/LT lateral separation is 36.9 cm. The isocenter of the planned target volume is located at a depth of 18.7 cm from the anterior aspect of the patient and midline from the right and left lateral aspect of the patient. The treatment portal for the AP and PA portals are 7.2 cm x 9.8 cm to mirror each other. What would be the field size on the patient’s posterior skin surface?           

The prefix contra- means  

19) Multiply:

A patient is being treated for a spinal lesion where the primary collimator is set for a field size of 5.3 cm x 12.3 cm. The secondary collimator is set asymmetrically for a field size of 4.9 cm x 12.1 cm. What would be the calculated equivalent square needed for the MU setting? 

Identify the indicated structure.   

16)  Subtract from the sum of

26)  Simplify: