Lung Geometric Verification

Question 1

scanning margin

Answer 1

the lungs inferiorly and the skins shoulder superiorly

Question 2

with lung patient w/o surgery there will be

Answer 2

ITV , CTV and GTV

Question 3

CENTRAL TUMOURS

Answer 3

2cm within the bronchial tree
fractionation is 60 Gy/8fx due to the heart

Question 4

when is SABR used

Answer 4

-primary early stage disease where pateint is not suitable for surgery
-Lung Oligometastases

Question 5

when is non SABR used

Answer 5

definitive RT (60-70Gy - 2Gy#)
post-op (45-54 - 1.8-2Gy#)
pre-op (50-60 Gy in 1.8-2.0 Gy daily fractions)

Question 6

Possible Target volumes

Answer 6

GTV (T)
GTV (N) – mediastinal lymph nodes
Tumour - CTV, ITV and PTV

Question 7

Possible sources of geometric uncertainties in lung cancer RT

Answer 7

-intra-thoracic anatomical changes (pleural effusion, atelectasis, tumour regression/growth)
-general patient factors affecting set up reproducibility
-Respiratory motion

Question 8

On Target recommendations

Answer 8

-CBCT is standard of care for radical&palliative for lung RT and allows more accurate set up

-daily image guidance w soft tissue set up to tumour or other anatomical landmarks is recommended

Question 9

benefit of using daily CBCT and set up corrections

Answer 9

allow smaller use of CTV-PTV margins by reducing random and systematic errors

Question 10

CBCT acquisition:
-gantry rotation
-gantry rotation

Answer 10

half scan:
- RL=180° → 25º
-LL= 330° → 180°

use half filter

Question 11

CBCT acquisition :
1. Bony anatomy registration

Answer 11

-clipbox around the verterbrea
-if tumour is located ventrally include sternum in clipbox
-if tumour is located laterally include ribs in clipbox
-dont include too much of scapula or head of humerous

Question 12

CBCT acquisition
2. Dual Registration

Answer 12

-when there is only a primary tumour and no LN involvement
- clip box (bony reg)&mask method
-mask=created from GTV delineation w 0.5cm margin
-remove unwanted bone from inside the mask

Question 13

Auto-registration is not recommended because

Answer 13

patients are match automically to the wrong vert level and causes geographical miss

Question 14

SABR treatments
Early stage primary disease or high dose palliative

Answer 14

-daily online imaging is recommended.
-for soft tissue indications CBCT is gold standard
-include 4DCBCT for moving tumours (lower lobe tumours)

Question 15

non-SABR treatments
palliative

Answer 15

-daily online imaging is recommended
-for palliative tx for large margins/fields 2D KV orthogonal maybe sufficent
-

Question 16

non-SABR treatments
radical w no mediastinal LN

Answer 16

CBCT with Dual registration (clip box and mask around GTV)

Question 17

non-SABR treatments
For Radical Lung only – Mediastinal LN involvement

Answer 17

-dual registration (clipbox and mask around carina)

Question 18

Justification for frequent volumetric imaging

Answer 18

-many sources of intrathoracic changes
-can have a impact of dosimetry
-can be dangerous is problems are not addressed (plueral effusion)

Question 19

4DCBCT

Answer 19

-motion artefact
-for lower lobe tumours
-Acquistion time (4 mins vs 1-2 mins for 3D CBCT)