RADIOTHERAPY

Question 1

how radiation causes genetic mutations

Answer 1

• ionizing radiation strikes electrons in the body, freezing them from the atoms they were attached to
• the free electrons may hit and damage DNA directly
• free electrons may hit a water molecule, producing a free radical, a group of atoms that have an unpaired electron and is highly reactive. the free radical may then react with DNA and damage it

Question 2

the effects of ionising radiation

Answer 2

• radiation effects range from complete breaks of DNA, to point mutations, radiation induced chemical changes in the nucleotides
• single strand DNA lesions do not cause chromosome aberrations
• DNA double breaks are the cause of chromosomal aberrations - very hard to repair

Question 3

radiation therapy

Answer 3

• uses high-energy radiation to kill cancer cells by damaging their DNA
• can damage normal cells as well as cancer cells

Question 4

types of radiation therapy

Answer 4

• machine outside the body (x-ray radiotherapy)
• radioactive material placed in the body near tumour cells (brachytherapy)
• radioactive molecules (radiopharmaceuticals) injected into the blood stream

Question 5

dose fractionation

Answer 5

• radiation delivered in bundles
• fractionation allows normal cells to repair and survive but cancer cells can’t
• reduced radiation induced toxicity to non-cancer cells

Question 6

radiation therapy dose

Answer 6

patients treated curatively with radiotherapy generally receive around 2 Gy per day, 5 days a week, for 5-7 weeks

Question 7

intensity modulated radiation therapy (IMRT)

Answer 7

• a specialised form of 3D-CRT
• involves the use of varying intensities of hundreds of small radiation beams “beamlets” to produce dosage distributions
• beam is fitted to the tumour to avoid tissue toxicity

Question 8

2 types of brachytherapy

Answer 8

interstitial therapy
contact brachytherapy

Question 9

interstitial therapy

Answer 9

radiation sources are placed directly in the target tissue of the affected site, such as the prostate or breast

Question 10

contact brachytherapy

Answer 10

radiation sources are placed in a space next to target tissue

Question 11

radiotherapy side effects - acute phase

Answer 11

acute mucosal inflammation
- oesophagitis
- enteritis
- proctitis
- radiation dermatitis
- procedural pain - inserting brachytherapy

Question 12

radiotherapy side effects - late phase

Answer 12

radiation fibrosis syndrome
- oesophageal stricture
- abdominal pain - bowel spasms
- non-bacterial cystitis
- strictures - bowel, anus, urethra

fatigue everyday

Question 13

therapeutic differential in radiotherapy

Answer 13

• kill more tumour cells than normal tissue at lower doses
• but some cells are more resistant than others

Question 14

radiosensitiser

Answer 14

• a drug that makes tumour cells more sensitive to radiation therapy
• down-regulated free radical scavengers so cancer cell bombarded with DNA damaging free radicals - sustains too much damage and dies

Question 15

nuclear medicine

Answer 15

• application of radioactive substances in the diagnosis and treatment of disease
• allows detection of problems without invasive procedures
• to diagnose cancer a radioactive drug goes to the tumour, properties of the radiation allow a PET scan to be taken and show the cancer

Question 16

scans to diagnose cancer

Answer 16

PET scan
MRI
CT scan
SPECT

Question 17

theranostics

Answer 17

term used to describe the combination of using one radioactive drug to identify (diagnose) and a second radioactive drug to deliver therapy to treat the main tumour and any metastatic tumours

Question 18

targeted radionuclide therapy

Answer 18

• selective radiation dose delivery
• as high a dose for the tumour ONLY
• as a tumour grows it changes, it upregulates some markers, makes new proteins or transporters which are not on the normal cells
• use molecules which have an affinity only for tumour cells

Question 19

radionuclides

Answer 19

• can be produced artificially
• usually by the bombardment of stable nuclei by high-energy particles
• radionuclides can be chemically incorporated into another compound and injected into the body for diagnostic purposes - radiopharmaceuticals

Question 20

radiopharmaceuticals contain

Answer 20

1. a targeting part - seeks out the tumour
2. the warhead - has the isotope on it

Question 21

diagnostic imaging and treatment with 131I-MIBG

Answer 21

neuroblastomas express this transporter

Question 22

what is radioimmunotherapy

Answer 22

• RIT uses an antibody labelled with a radionuclide to deliver cytotoxic radiation to a target cell
• in cancer, an antibody with specificity for a tumour-associated antigen is used to deliver a lethal dose of radiation to the tumour

Question 23

how is immunotherapy specific towards tumour cells

Answer 23

RIT requires a tumour cell to express an antigen that is unique to the neoplasm or is not accessible to normal cells

Question 24

2 radio labelled antibodies used to treat non-Hodgkin’s lymphoma

Answer 24

Ibritumomab tiuxetan (Zevalin)
Bexxar

Question 25

Zevalin

Answer 25

• approved in B-cell non-Hodgkin’s lymphoma
• the antibody recognizes and binds to a protein (CD20 molecule) found on the surface of B lymphocytes
• conjugated to either the radioactive isotope indium-111 or Yttrium-90
• targeted therapy - CD20+ cells (B cells and lymphoma) are killed by beta emissions from radioisotope

Question 26

side effects of Zevalin

Answer 26

common s/e: fever, chills, rash, itching, dizziness, swelling

serious s/e: myelotoxicity

Question 27

possible mechanisms of radio-immunotherapy tumour killing

Answer 27

1. apoptosis - triggered by the antibody
2. complement-dependent cytotoxicity (CDC) - antibody fixes complement that kills the tumour cells
3. anti-dependent cellular cytotoxicity (ADCC) - where immune cells kill the tumour cells
4. ionizing radiation from the radioisotope damages the tumour cells, leading to cell death
5. vaccine-like effect - leading to adaptive immunity against cells that may initially survive

Question 28

how long are patients radioactive after receiving intravenous MIBG (radiopharmaceuticals)

Answer 28

4 days

Question 29

where are radiopharmaceuticals administered to patients

Answer 29

lead lined rooms

not in hospital ward because patient is radioactive

Question 30

radio pharmacology

Answer 30

the study and preparation of radiopharmaceuticals

Question 31

2 processes in the production of radiopharmaceuticals

Answer 31

• the production of a radionuclide on which the pharmaceutical is based
• the preparation and packaging of the complete radiopharmaceutical