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Principles of Science BVetMed 3 > Principles of radiation therapy > Flashcards

Principles of radiation therapy Flashcards

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1
Q

How does ionising radiation cause damage?

A 
Indirect damage (most important)
Direct damage (least important)
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2
Q

What is the unit for radiation therapy (RT)?

A

Grey(s) [Gy]

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3
Q

Outline basic effects of radiobiology

A

Mitosis delayed - 1 Grey
Cells cannot divide - 10-100 Gy)
Radiation damaged cell usually die after 1 or 2 attempts at mitosis

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4
Q

Which cells in the body are the most radiation sensitive?

A

BM
Intestinal crypt cells
Germinal layer of epidermis
Tumours

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5
Q

Why is fractionation important?

A 
Allows the 4 Rs of radiation therapy to be obeyed:
Repair
Repopulation
Reoxygenation
Redistribution
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6
Q

Define REPAIR in the context of the 4 Rs

A

Tumour cells are less able to repair DNA daage as they are often oxygen and nutrient deficient

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7
Q

Define REOXYGENATION in the context of the 4 Rs

A

Tymours have a necrotic, poor oxygenated centre. A single dose of RT would tend to kill off the healthy, oxygenated tumour cells but may not affect the hypoxic cells. The death of the vascularised cells will make more room for the surviving hypoxic cells.

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8
Q

Define REDISTRIBUTION in the context of the 4 Rs

A

Cells are more sensitive to RT in some phases: M>G2 > G1> ES > LS

The remaning cells willbe ‘synchronised and eventually will move into a more sensitive phase. This is the time to deliver the next RT fraction.

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9
Q

What type of radiation is used for RT in animals?

A

X-rays
Gamma rays
Particles - beta particles (electrons) in radioisotopes

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10
Q

Describe a Cobalt-60 therapy unit

A

Radioactive source
Photons
Fixed energy (1.24 MV)
Low technical requirements

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11
Q

Outline a linear accelerator unit

A 
Variable energies
Electrons/photons
No radioactivity
High technical maintenance
High accuracy
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12
Q

Describe an electron beam

A

Various energies possible (5-15 MeV)
Rapid dose reduction (depending on energy)
Therapeutically useful depth (1.5-5.6cm)
Single fields, simple dose calculations

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13
Q

Outline a photon beam

A 
High penetration
Slow dose reduction
Field arrangements necessary
Penetration of normal tissue
CT-based treatment planning
Sedation sufficient, no GA required
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14
Q

What is the best Tx option for nasal tumours?

A

Radiation therapy

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15
Q

Define gross tumour outline

A

what may be visible on a CT scan

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16
Q

Define microscopic disease outline

A

the peripheries of the disease that may not be clearly visible on a CT beyond the gross tumour outline

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17
Q

What are the 2 broad goals of RT?

A

Curative/definitive (cure or long term control)

Palliative (palliation, stabilisation, pain reduction/relief)

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18
Q

How many greys are generally used for curative/definitive RT?

A

Generally 40-60 but these are fractionated into small amounts

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19
Q

Why perform curative RT?

A

Absolute indications: RT has better results than other therapies

Relative indications: RT shows same tumour control, but other advantages (functional, cosmetic)

Combination therapy: RT+surgery +/-chemo (e.g. ISS for best MST)

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20
Q

For what tumours is RT the primary Tx modality?

A

Brain
Head and neck (oral, nasal)
MCT
Epulis

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21
Q

What is an epulis tumour?

A

Benign,

Require aggressive surgery (e.g. removal of underlying bone)

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22
Q

For which tumours is post surgery adjuvant RT indicated?

A

MCT
STS
FISS

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23
Q

What is en bloc resection (EBR)?

A

used in certain cancers to remove a primary lesion, the contiguous draining LNs and everything in between, as in a modified radical mastectomy

24
Q

Define negative margin

A

For tumour removal, no cancer cells are seen at the outer edge of tissue that was removed. AKA clean or clear. Sometimes the pathologist will tell you how wide this margin is but there is no uniform definition.

25
Q

Define positive margin.

A

Cancer cells extend to the edge of the margin. More treatment is indicated.

26
Q

Indications - RT

A 
Local therapy (local Dx, not systemic)
Incompletely resected umours - then this is the Tx of choice: non-resectable tumours (results depend on tumour type) and pain control (bone cancer or metastases)
27
Q

Describe nasal tumours

Describe MST with different Tx

A

2/3 are carcinomas
1/3 are sarcomas

MST without Tx = 3 months
Surgery alone = 3-6 months (NEVER DO THIS!)
RT alone = 8-20 months
RT + Sx = 47 months (BEST OPTION!!!)

28
Q

Outline pituitary tuours

A

85% animals show rapid improvement in clinical signs (with RT?)

CS, localisation and size DON’T have prognostic significance

Very few side effects
MST = 24 months

29
Q

Outline common canine oral tumours and their progression free intervals with RT.

A

ACANTOMATOUS EPULIDES = 90% tumour control. 86% 3 year PFI 4cm.

ORAL SCC: 45Gy 1 year PFI 75%

ORSAL FSA: 33-67% 1 year PFI

30
Q

Define PFI

A

Progression Free Interval

31
Q

Describe SCC - canine

A 
Middle-aged dogs
Rostral mandible
Often cauliflower-like
Local invasive
Metastases (non-tonsillar 20%, tonsillar 70%)

Prognosis: site dependent:
Rostral: local control –> cure
Tonsillar: <10% survive 1 year (usually 3-6 months)

32
Q

Tx - feline SCC

A

This is a very nasty tumour - 2 fractions RT/day

33
Q

EPULIS:
metastases?
treatment?

A

No metastases

90% cure rate with curative RT

34
Q

Treatment - canine STS

A

Surgery (+/- RT, use RT if incomplete margins)

+chemo if grade 3

35
Q

Outline FISS (VAS)

A

Relationship between VAS and vaccination
Incidence 1/1000 - 1/10,000 cats
Tumour volume on contrast -enhanced CT - twice the vlume measured using calipers on PE
Metastasis in 12-24%
Only 10% cure rate with surgery alone (high probability of recurrence even with clear margins)

36
Q

Survival after FISS treatment

A

Surgery, conservative: recurrence after 2 months (median)

Surgery, radical: recurrence after 9 months (median)
Surgery + RT: Recurrnce (600 days), 40% cure rate, chemotherapy>

Prognostic factors: number of surgeries, margins

37
Q

Describe oral fibrosarcomas

A 
Histologically low grade but biologically high grade
Golden retriever predisposed
Maxilla > mandible
Very invasive locally
Often intact epithelium
Metastasis in 20% (LNs, lungs)
38
Q

List some radiosensitive tumours with a high metastasis rate that are ideal candidates for palliative RT

A

Histiocytic sarcoma
Oral melanoma
HSA
MCT grade 3

39
Q

List some tumours with a mass effect that are ideal candidates for palliative RT

A

Large head and neck tumours
Brain tumours
Large sublumbar LNs
Prostatic tumour

40
Q

List some radiosensitive tumours with high local pain that are ideal candidates for palliative RT

A

OSA

Metastatic bone tumours

41
Q

When is palliative RT indicated?

A

Age
Organ-related disease
Metastases

42
Q

Describe malignant melanoma

A

Most common oral tumour in dogs
Mainly older dogs (mean age is 11.4 year)
Highly metastatic potential
1/3 amelanotic

43
Q

Outline malignant melanoma response to RT

A

Overall response: 83-94%

Complete response: 53-69%

44
Q

What are negative prognostic factors for malignant melanoma? 3

A

Macroscopic disease
Bone lysis
Caudal location

45
Q

What are the adverse effects of radiation Tx?

A

ACUTE EFFECT: will resolve
rapidly dividing tissue
tumour, skin, mucosa, GI epithelium

LATE EFFECT: permanent
slowly dividing/non-dividing tissue
Bone, muscle, brain, CNS, lens, retina etc.

46
Q

Describe the acute effects of RT?

A 
After 3rd week of radiaion
7-10 days post RT --> maximum effect
Normal tissue reactions: MM (mucositis), skin (alopecia, dermatitis), eyes (keratitis, conjunctivitis), CNS (transient demyelination)
Self-limiting
Only symptomatic Tx
47
Q

Outline the skins/dermis acute side effects to RT

A

Target cells: stratum basale –> erythema, scaly or moist dermatitis, alopecia

Tx options:
protect from mechanical traum
analgesia
black/green tea
NO CREAMS/OINTMENTS/GELS
48
Q

Outline the acute side effects at the mucous membranes of RT

A

Hypersalivation, nasal discharge, mucositis (fibrinous plaques)
Pain –> anorexia (rare in dogs, frequent in cats)

Tx options:
Pain medication
ABs
Feeding tube (PEG) or oesophageal tube
Metamucil/lactulose for colitis and proctitis
49
Q

Define proctitis

A

inflammation of the anus and lining of the rectum

50
Q

What is metamucil?

A

bulk-producing laxative and fiber supplement

51
Q

What are acute side effects of RT on the eyes?

A

Decreased tear production, conjunctivitis, blepharitis, cornea ulceration

Tx options:
Optimmune/Vit E eye ointment
Check tear production

52
Q

What are acute side effects of RT on the brain/spinal cord?

A

Edema (8-12 weeks post RT)
Transient demyelination
Transient recurrence of neurological symptoms

Tx options: corticosteroids

53
Q

List examples of late side effects

A

Damage in stroma and vasculature
Earliest onset = 6 months after RT

Fibroses, contractions, strictures
Non-healing ulcers
Necrosis (bone, skin, CNS)
Cataract, KCS
Infarctions, haemorrhagias

Therapeutic intervention - difficult, to be avoided

54
Q

What are late side effects of RT on the skin/dermis?

A

damage of vasculature and fibroblasts
fibrosis
alopecia, pigment changes

55
Q

What are late side effects of RT on the eyes?

A

Cataract (clearing of fibres of lens not possible)

Chronic keratoconjunctivitis sicca (KCS)

56
Q

What are late side effects of RT on the brain/spinal cord?

A

Necrosis of white matter (6-18 months)
Vasculopathy (1-4 years)

Differentiation with diagnostic imaging is difficult - side effect or recurrent disease?

Try treatment with corticosteroids

Principles of Science BVetMed 3 (110 decks)

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