Fraction # with CT

L-R shift (mm)

Av. L-R shift (mm)

A-P shift (mm)

Av. A-P Shift (mm)

1

4.1R

 

8.4P

 

2

2.3R

 

8.3P

 

3

1.9R

 

5.4P

 

4

4.0R

 

4.5P

 

5

1.9R

0

7.1P

7P

6

0.8R

 

4.1P

 

7

5.7R

 

7.0P

 

8

6.1R

 

0.93P

 

9

3.1R

 

5.5P

 

10

5.5R

4R

9.4P

5P

11

0.9L

 

0.33P

 

12

3.2R

 

0.56A

 

13

2.6R

 

1.5A

 

14

0.7R

 

0.5A

 

15

0.7R

4R

1.9P

5P

16

1.9R

 

0.3A

 

17

1.3R

 

0

 

18

1.2L

 

0.9P

 

19

0

 

1.1P

 

20

1.2R

 

0.3A

 
Table 2: Isoshift in the L-R and A-P directions in 15 consecutive treatment sessions. Each entry represents the magnitude and direction of shift required in order to match the pre-treatment CT scans with the corresponding planning CT image set. Fractions 1-15 are treatments with image guidance. Fractions 16-20 represent the weekly isochecks. The numbers in the columns labeled ‘av. L-R and Av. A-P shifts are used to set up the patient for the five subsequent fractions.