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Flashcards in Basic concepts of Radiation Therapy Deck (45):
1

cancer in pet animals

Common, increasing prevalence
Every 2nd dog is euthanized due to „cancer“
Radiation therapy: second most used treatment modality in man
Model for research

2

resection "en bloc"

can't remove just the tumour as tumour cells remain in the surrounding tissue

3

roles of radiation therapy

INCOMPLETELY RESECTED TUMORS (treatment of choice)
Non resectable tumors (results depending of tumor type)
Pain control (Bone cancer/bone mets)

4

ionising radiation

Direct damage
Indirect damage (free radicals)
Unit for RT: Grey

5

reproductive death

DNA damaged - cell dies or lives but is unable to divide further

6

damage to DNA by ionising radiation effects

Mitosis delayed (10-100Gy)
Radiation damaged cells usually die after 1 or 2
attempts at mitosis
Tissues with high proliferation rate express radiation damage relatively quickly

7

most radiation sensitive cells

undifferentiated
high mitotic rate
bone marrow
intestinal crypt cells
germinal layer of epidermis
tumours
Tumoral mecanisms of DNA repair not as efficient as in normal cells

8

fractionation

The total dose of radiation used to treat a tumour is
usually divided into a number of fractions
spares normal tissues because it allows repair of sublethal damage and repopulation
increases damage to tumour because of reoxygenation + redistribution of cells into radiosensitive phases of cell cycle

9

4 R's of radiation therapy

repair
repopulation
reoxygenation
redistribution

10

repair

tumor cells less able to repair DNA damage (Tumor cells are often oxygen + nutrient deficient)

11

repopulation

RT will often stimulate cell division.
Cells may respond to the death of adjacent cells by "accelerated repopulation"
In normal tissue this is kept under control by normal homeostatic mechanisms, but this is not true for the tumour.
need to give another dose to counteract repopulation + kill the cells

12

reoxygenation

The tumor contains a mix of aerated and hypoxic cells.
Immediately after RT, most cells in the tumor are hypoxic, but they tend to return at the pre-RT pattern because of reoxygenation

13

redistribution

Cells are more sensitive to RT in some phases: M-G2-G1-ES-LS
The remaining cells will be “synchronized” + eventually will move into a more sensitive phase
this is when to give next RT fraction

14

types of radiation used for radiotherapy

X-rays - Orthovoltage, 120-300kVp (not used much), Megavoltage, >1MeV "Linear accelerator"
Gamma rays - Cobalt-60, 1.2MeV
Particles - particles (electrons) in radioisotopes - Strontium-90: plesiotherapy, Iridium-192: brachytherapy

15

treatment machines

Cobalt-60-therapy unit
Linear accelerator

16

Cobalt-60-therapy unit

Radioactive source
Photons
Fixed energy (1.24 MV)
Technical requirements ↓

17

linear accelerator

Variable energies
electrons / photons
No radioactivity
High technical maintenance
High accuracy

18

electron beam

Various energies possible (e.g. 5-16 MeV)
Rapid dose reduction (depending on energy)
Therapeutically useful depth: 1.5-5.6 cm
Single fields, simple dose calculation

19

photon beam

High penetration
Slow dose reduction
Field arrangements necessary
Penetration of normal tissue
CT-based treatment planning

20

goals of radiation therapy

curative/definitive (long term tumour control)
palliative (palliation, stabilisation of disease, pain reduction)

21

curative radiation therapy

Absolute Indications - RT shows better results than other therapies
Relative Indications - RT shows same tumor control, but other advantages (functional, cosmetic)
Combination therapy - RT + surgery +/- chemo

22

primary Tx modality

Brain tumor, tumor of head and neck (oral, nasal), MCT, epulis

23

post Sx adjuvant RT

Mast cell tumor, Soft tissue sarcoma, Feline vaccine-associated sarcoma, etc.

24

nasal tumours

2/3 carcinomas; 1/3 sarcomas
median survival without treatment ~ 3 months
surgery alone ~ 3-6 months
radiation therapy alone: ~ 8-20 months
RT + SX: 47 months

25

brain tumours - pituitary tumours

85% of animals show rapid improvement of clinical signs
clinical signs, localization and size could not be shown to have prognostic significance
Very few side effects

26

oral tumours

acantomatous epulides - 90% tumour control, 86% 3y PFI 4cm
oral scc - 45Gy, 1y PFI 75%
oral fsa - 33-67% 1y PFI

27

squamous cell carcinoma - dog

Middle aged dogs
Rostral mandible
Often cauliflower-like
Local invasive
Metastases - nontonsillar ~ 20%, tonsillar ~70%
Prognosis -> site-dependent
rostral: local control -> cure
tonsillar: < 10% survive 1 year

28

epulis

no metastases
90% cure rate with curative RT

29

soft tissue sarcoma - dog

treat - surgery (+/- RT)
(chemo)

30

feline injection-site sarcomas

Relationship between VAS and vaccination Incidence unknown 1/1000 – 1/10 000 cats
Tumor volume on contrast-enhanced CT ~ twice the volume measured using calipers on PE
Metastasis in 12-24%

31

ISS therapy - surgery alone

10% cure rate with surgery alone (high probability of recurrence even with clean margins)
Surgery, conservative: recurrence after 2 months (median)
Surgery, radical: recurrence after 9 months (median)

32

ISS therapy - surgery + RT

Recurrence: 600 days (median)
40% cure rate
Chemotherapy?
Prognostic factors - no. of surgeries, margins

33

oral fibrosarcoma

Histologically low-grade but biologically high-grade fsa
Golden retriever predisposed
Maxilla > mandible
V. invasive locally
Often intact epithelium
Metastasis in ~ 20% (lymph nodes, lungs)

34

palliative radiation therapy

radiosensitive tumours w/high mets rate - histiocytic sarcoma, oral melanoma, hemangiosarcoma, Mast cell tumor grade III
mass effect - Large head and neck tumors, brain tumors, large sublumbar LN, prostatic tumor, etc
pain control - Osteosarcoma, metastatic bone tumors, etc

35

malignant melanoma

Most common oral tumor in dogs
Mainly older dogs (mean 11.4 y)
Highly metastatic potential
1/3 amelanotic
RT: Overall response: 83%-94%, Complete response: 53%-69%
Negative prognostic factors - macroscopic disease, bone lysis, caudal location

36

adverse effects of radiation TX

Some normal cells will die when they try to divide
RT effect may not be apparent until the irradiated cells attempt mitosis
Normal tissue included in radiation field
acute effect - will resolve rapidly dividing tissue: - Tumor, skin, mucosa, GI epithelium
late effect - permanent - Slowly dividing/non-dividing tissue: - Bone, muscle, brain, CNS, lens, retina, etc.

37

acute side effects

After the third week of radiation
7-10 days post RT → maximum
Normal tissue reactions
mucous membranes - mucositis
skin - alopecia, dermatitis
eyes - keratitis / conjunctivitis
[CNS - transient demyelination]
Self limiting
Only symptomatic treatment

38

acute side effects - skin/dermis

Target cells: stratum basale => erythema, scaly or moist dermatitis, alopecia
Treatment options - Protection from mechanical trauma (collar), Analgesia, no creams/ointments/gels

39

acute side effects - mucous membranes

Hypersalivation, nasal discharge, mucositis (fibrinous plaques)
Pain - anorexia (rare in dogs, frequent in cats)
Treatment - Pain medication, antibiotics, feeding-tube (PEG) or esophageal tube, Metamucil / lactulose for colitis and proctitis

40

acute side effects - eyes

Decreased tear production, conjunctivitis, blepharitis, cornea ulceration
Treatment - Optimmune / Vit. A eye ointment, Check tear production

41

acute side effects - brain/spinal cord

Edema (8-12 weeks post RT)
Transient demyelination - transient „recurrence“ of neurological symptoms
Treatment - Corticosteroids

42

late side effects

Damage in stroma and vasculature
Earliest onset: 6 months after RT
Fibroses, contractions, strictures
Non healing ulcerations
Necrosis (bone, skin, CNS)
Cataract, KCS
Infarctions, hemorrhagias
Therapeutical intervention difficult

43

late side effects - skin/dermis

Damage of vasculature and fibroblasts
Fibrosis
Alopecia bzw. pigment changes

44

late side effects - eyes

Cataract (clearing of fibres of lens not possible)
Chronic keratoconjunctivitis sicca

45

late side effects - brain/spinal cord

Necrosis of white matter (6-18 months)
Vasculopathy (1-4 years)
Differentiation with diagnostic imaging difficult (side effect or recurrent disease?)
Try treatment with corticosteroids