Superficial

Question 1

History

Answer 1

Available since 1900s
Can treat at a max depth of 5mm
50-150kV

Question 2

Who we treat

Answer 2

Older (60-80 years old)
Comorbidities - more flexible positioning

Question 3

What diseases we treat

Answer 3

SCC
BCC
Mets
Bowens disease
Mycosis fungoides
Lesions within 5mm of skin
Curved surfaces

Question 4

Basal cell carcinoma

Answer 4

• 93% of skin cancer treated with RT
  
  • Not as metastatic
  • Starts with small bump or flat red patch
  • Develops slowly over months and years
  • Non-healing sore
  • 3 types - modular, infiltrating, superficial
    Face, scalp, forearms

Question 5

Squamous cell carcinoma

Answer 5

• Looks like a scab
  
  • Ulcer or reddish skin plaque
  • Raised scaly lump on sun exposed sites
  • Can metastasise
    Slow growing

Question 6

Mycosis Fungoides

Answer 6

• Most common form of lymphoma
  
  • Class of non-Hodgkins- cancer of the immune system
  • Electrons can only be used if they are all flat
  • TBI can be used
  • If not flat, superficial done first to flatten the cancer ous spots

Question 7

Most common treatment for SCC/BCC

Answer 7

Surgery + Superficial

Question 8

Indications for superficial RT

Answer 8

• Patients medically unfit or refuse surgery
  
  • Cosmetic reasons - lesions on the nose, lips, ear, corners of mouth
  • Functional reasons - avoids nerve or function damage
  • Patients at risk of microscopic disease or where small volume has recurred
  • Older patients - less issues of telangiectasia, hypopigmentation and scarring
  • Multiple lesions
  • Patients prone to keloid scar formation

Question 9

Superficial dose fractions

Answer 9

Elderly/significant comorbidities - 500cGy/ 7#
Older but healthy - 300cGy/15#
Younger patients and/or lesions <2cm - 250cGy/20#
Younger patients and/or larger lesions - 200cGy/30#

Question 10

Electrons advantages

Answer 10

• Sharp dose fall off below the surface
• Less absorption in bone and cartilage
• Can treat 7cm below skin
• Good cosmetic results

Question 11

Electrons disadvantages

Answer 11

• More expensive - linac needed
• Greater radiation protection measures required
• % depth doses less accurate under 4cm, field size limitation - doses are inaccurate
• Dose inhomogeneity on curved surfaces
  Eyes: shields can cause scatter and bowing

Question 12

Superficial Advantages

Answer 12

• Can treat sizes less than 4cm
• Defined beam edge: good for soft tissue sparing
• Good cosmetic results with fewer fractions: not as good as electrons
• Effective shielding around eyes
• Suitable for curved surfaces

Question 13

Superficial Disadvantages

Answer 13

• Young patients - side effects can be disfiguring
  invasion into bone. 1mm AL HVL bone absorption is almost 4 times greater compared to MV

Question 14

Warm up process

Answer 14

Slow process
Heat dissipation in the target is very high
As it is tungsten, if the machine warm up is too fast, cracking occurs

Question 15

Duty of filters

Answer 15

Hardens beam - reduces rapid attenuation
Smooths the beams - prevents excessive energies contributing to dose
Makes the beam more homogenous therefore able to penetrate more

Question 16

Half value layer

Answer 16

Half Value Layer (HVL): thickness of material at which the intensity of radiation is reduced by half
Beam quality is expressed in terms of kV and HVL
Units of distance (mm)
Filter selection is done by checking material and depth. Usually 1-5mm HVL filters are used

Question 17

Beam monitoring methods

Answer 17

Timer and backup timer
Dose monitor

Question 18

Stand in

Answer 18

Convex surfaces

Question 19

Stand off

Answer 19

Concave surfaces