Dose & Fields

Question 1

What marks are usually given to a breast patient?

Answer 1

Medial field border
AP mark
Central ray (probably a medial in this instance)
Lateral field border
Possibly a supraclavicular

Question 2

What is the total dose to the intact breast in EBRT?

Answer 2

About 50 Gy in 5 to 6 weeks using tangents to avoid underlying lung.

Question 3

What is used for uniform dose distribution within the breast?

Answer 3

Wedges or tissue compensators.

Question 4

Can wedges and tissue compensators be dynamic?

Answer 4

Yes, wedges and tissue compensators may be dynamic.

Question 5

What technique may be used to decrease skin toxicity?

Answer 5

Shrinking fields may be used to decrease skin toxicity and eliminate high dose areas at the inferior portion of the breast.

Question 6

What is the boost dose to the lumpectomy site?

Answer 6

An additional 10-20 Gy depending on tumor size and margins at surgery time.

Question 7

What determines the electron energy used in EBRT?

Answer 7

Electron energy depends on the depth of the tumor bed.

Question 8

What is the dose range for Tangents Breast and Chest wall?

Answer 8

4600-5000 cGy with a boost to 6000 cGy

Question 9

What is the dose for the Sunraclavicular Field?

Answer 9

4600-5000 cGy

Question 10

What is the dose for Scar Boost?

Answer 10

1000-2000 cGy for a total of 6000 cGy

Question 11

What are wedges used for in radiation therapy?

Answer 11

Wedges can be used to partially compensate for the curvature of the patient’s chest and or breast to give uniform dose distribution.

Question 12

What is needed for selecting wedge angle?

Answer 12

Contour through the central axis is needed for selecting wedge angle to give uniform dose distribution.

Question 13

When are wedges used in breast treatment?

Answer 13

Wedges are used on intact breasts or following a mastectomy to reduce hot spots from tangential treatment.

Question 14

What is the depth of treatment for supraclavicular?

Answer 14

Treated AP to depth of 3.0 cm

Question 15

What are the medial borders of the supraclavicular field?

Answer 15

Medial border at midline

Question 16

What is the recommended gantry angle for supraclavicular treatment?

Answer 16

Gantry angle (10 - 15°) may facilitate sparing of the larynx.

Question 17

What is the lateral border of the supraclavicular field?

Answer 17

Lateral border about two thirds of the clavicle

Question 18

What is the upper border for the supraclavicular field?

Answer 18

Upper border about 2 to 3 cm above the clavicle

Question 19

What should be used to block the humeral heads and larynx?

Answer 19

Use MLC’s to block humeral heads and larynx.

Question 20

What is the lower portion of the supraclavicular field blocked with?

Answer 20

Lower portion of field blocked with asymmetrical jaw

Question 21

How is the inferior border of the supraclavicular field matched?

Answer 21

Inferior border carefully matched to superior border of tangential field

Question 22

What is the prescribed dose for supraclavicular treatment?

Answer 22

to 45 Gy at 2 Gy per day

Question 23

How is matching achieved in single iso centric technique?

Answer 23

By half beam blocking the superior and inferior portions of the treatment fields with independent collimator jaws.

Question 24

What are internal mammary fields treated with?

Answer 24

Internal mammary fields are treated with a single anterior photon field, en face electrons, or a combination.

Question 25

Why are mixed beams often used in treatment?

Answer 25

Mixed beams are used to reduce exposure to the heart and lungs.

Question 26

What is the depth of IM nodes?

Answer 26

IM nodes are located at a depth of 3.0 cm.

Question 27

What is important in dosimetric planning for IM nodes?

Answer 27

Careful dosimetric planning is necessary to avoid overdose at the junction.

Question 28

What is the recommended patient position during treatment?

Answer 28

The patient should be positioned supine with the affected arm or both arms up, and the chin turned away from the affected side.

Question 29

What is the superior border of the IM field?

Answer 29

Match supraclavicular field ## Footnote Includes the first 3 intercostal spaces.

Question 30

What is the medial border of the IM field?

Answer 30

Midline on contralateral side

Question 31

What is the lateral border of the IM field?

Answer 31

5 - 6 cm past midline on the ipsilateral side to include internal mammary nodes

Question 32

What is the inferior border of the IM field?

Answer 32

1 cm margin inferior to the 3rd intercostal space

Question 33

What is the typical radiation dose for chest wall irradiation following lumpectomy?

Answer 33

About 45 to 60 Gy with photons.

Question 34

What additional method can be used for chest wall radiation?

Answer 34

Chest wall radiation may be delivered with electrons.

Question 35

What is used as a bolus in chest wall irradiation?

Answer 35

Bolus scar or entire chest wall.

Question 36

What is a boost treatment field?

Answer 36

A boost to the surgical bed is commonly recommended to eliminate microscopic tumor cells at the scar site.

Question 37

What methods can be used for boost treatment?

Answer 37

Boost may be given with interstitial implant, photons, or electrons.

Question 38

What radioactive material is used for HDR and/or interstitial implants?

Answer 38

Iridium 192 is used for HDR and/or interstitial implants.

Question 39

What is the typical dose range for boost treatment?

Answer 39

10-20 Gy

Question 40

What is the prescribed isodose line for the scar boost?

Answer 40

90% isodose line is normally prescribed for the scar boost.

Question 41

What is the prescribed isodose line for the chest wall?

Answer 41

80% isodose line should be on the chest wall.

Question 42

What should be considered regarding the lumpectomy site?

Answer 42

The lumpectomy site does not always lie directly under the surgical incision; allow a margin.

Question 43

How should the electron cone be positioned for treatment?

Answer 43

Electron cone is brought close to the patient to allow 100 cm SSD to the skin when bolus is being used of the breast.

Question 44

What is a bolus?

Answer 44

Flabby material that adds a layer to bring the dose up to the surface of the skin.

Question 45

What is the purpose of using a bolus?

Answer 45

Used to increase skin dose.

Question 46

How often may bolus be used?

Answer 46

May be used every other day to increase surface dose to skin and assure adequate irradiation of cancer cells in the skin.

Question 47

In what context is bolus often used?

Answer 47

Bolus is often used in the lumpectomy scar boost field to ensure adequate skin dose.

Question 48

What is accelerated breast irradiation?

Answer 48

Accelerated breast irradiation using iridium for 1 week using hyperfractionated twice daily.

Question 49

What is the purpose of accelerated breast irradiation?

Answer 49

Brachytherapy treatment for low recurrence risk cases instead of entire breast radiation.