Whole Pelvis

Question 1

Rationale for WPIRT/VMAT

Answer 1

More conformal
Reduce dose to small bowel - can escalate dose without harming OARs

Question 2

3DCRT whole pelvis beam arrangement

Answer 2

AP/PA
PA and opposed lateral
Four fields

Question 3

3DCRT limitations

Answer 3

Cannot deliver dose to paracervical or nodal tissue
Can increase bowel dose - bowel has high a/b ratio hence more sensitive to radiaiton
Cannot escalate dose

Question 4

Which sites are often treated with WPRT

Answer 4

Gynae
Rectum and LN
Anal canal and pelvic and inguinal LN
Prostate and LN

Question 5

EBRT dose fraction

Answer 5

50.4GY IN 28 (1.8gy per fraction) followed by boost of 5.4GY in 3#
Or
45Gy to nodal volumes
1.8Gy per fraction reduces severity of side effects

Question 6

Considerations for rectum WPRT

Answer 6

SIB plan - 54_51_47Gy
Primary GTV and Mesorectum and inguinal CTV
Complex plan - do not try to achieve dose to skin as it increases skin reactions
EXT_genitalia should be considered when planning
Folding in skin causes skin reactions

Question 7

WPRT techniques

Answer 7

✓3D-conformal radiotherapy (3D-CRT)
✓Intensity-modulated radiotherapy (IMRT)
✓Volumetric Modulated Arc Therapy (VMAT)
✓Intensity Modulated Proton Therapy (IMPT)
✓Helical Tomotherapy (HT)
✓Varian Halcyon

Most beneficial - VMAT

Question 8

Robust evaluation

Answer 8

Impact on patient’s safety due to possible difference in patient setup

Question 9

IMPT

Answer 9

Up to 3 beams - 2 ant oblique, 1 post
Intensity modulated proton therapy
Can be conformal but any movement can severely increase dose to OARs

Question 10

What is EXP ext 1CM USED FOR

Answer 10

Assess weight loss or gain

Question 11

Where should iso be located

Answer 11

In line with midline/ant tattoo
Close to BB markers
Middle of PTV

Question 12

IMRT beam arrangements

Answer 12

Non opposing gantry angles
Collimator should be sup inf oriented as it assist in shielding bowels and lowers MUs

Question 13

How many arc should be used in VMAT WPRT

Answer 13

2/3 depending on protocol on field size

Question 14

Gantry stop and start if there is a 4 degree spacing

Answer 14

178 - 182
182-178
Colli 15 on 1st arc, 345 on 2nd arc

Question 15

Which machine has less interleaf leakage and why

Answer 15

Elekta - lower jaw is primary collimator which means less interleaf leakage compared to Varian which has MLCs situated lower

Question 16

Max gantry rotation speed

Answer 16

6 degrees

Question 17

Why can’t we use a 45 degree collimator

Answer 17

Dose to OARs

Question 18

IGRT considerations

Answer 18

Could be:
KV Daily
CBCT daily
Kv+CBCT day 1,2,3 and then KV daily and CBCT weekly

Question 19

Imaging fields

Answer 19

Can be done on TPS or mosaiq
Copy IMRT fields and delete MLCs and change angles

Question 20

What structures to contour

Answer 20

Small bowel, bowel bag, bladder, femoral head and neck, bone marrow

Question 21

Bowel bag contour

Answer 21

Outlined on every slice which has visible bowel, extending 2cm above PTV
Includes bowels out to the edge of the peritoneum. Bowel bag contour to include small bowel, colon and sigmoid

Question 22

Rectum contour

Answer 22

Structure should extend from anal verge to recto-sigmoid flexure

Question 23

Bone marrow contour

Answer 23

The pelvic bone will be contoured as a surrogate for the bone marrow. Femoral heads included but not necks

Question 24

IMRT beam arrangements

Answer 24

7-9 beams
7 beams: 45, 90, 115, 180, 245, 280 and 310