Introduction to Radiation Oncology Flashcards
what isRadiation therapy?
• Radiation therapy (RT) is the treatment of
cancer with ionizing radiation
• RT is one of the 3 main types of cancer
treatment:
– RT is a loco-regional treatment
– Surgery is a local treatment
– Chemotherapy is a systemic treatment
• About 50% of all incident cancer cases require
RT at some point during the management of
the disease
who are Radiation Oncologist?
• Radiation Oncologists are physicians
specialized in treating patients with RT
• Radiation Oncologists:
– develop and prescribe the patient’s treatment plan
– oversee the care of patients undergoing RT
– monitor the patient’s progress and identify and
treat any side effects of RT
– work closely with other members of the radiation
oncology team (radiation therapists, dosimetrists,
medical physicists, nurses, etc.)
Mechanism of Action
how it works
Most modern RT uses high energy x-rays
• High energy x-rays are converted to photons in a linear accelerator
• These photons are used to treat patient
• Photons interact with tissue, resulting in displacement of electron from its orbit around nucleus of an atom
• The atom is left with a net positive charge, and is thus an ‘ion’ (hence the name “Ionizing Radiation”)
• The recoil electrons interact with water in tissue to create free radicals, which cause damage to DNA …
• The main target of ionizing radiation: the cell’s nuclear DNA
• When enough DNA damage accumulates, cells can no longer divide = cell death
• Cancer cells cannot repair DNA damage as effectively as normal tissues, so they are preferentially killed by RT
Types of Radiation Therapy
External Beam RT
• The most common type of RT
• Uses machines (linear accelerators) to focus radiation on a
cancer site
• The higher the energy of the beam, the deeper the radiation
can penetrate into the target tissue
Brachytherapy
• Internal radiotherapy (“brachy” = “short distance”)
• Places radioactive implants directly in a tumor or body cavity
• May be permanent (ie: prostate seed implants) or removable
(ie: cervical cancer treatment)
• Intent: to deliver a high radiation dose to the tumor while
limiting the absorbed dose to surrounding healthy tissues
Definitions
• 1 RT treatment/day, 5 days/week
• Each RT treatment = 1 ‘fraction’
• Units of radiation = “Gray” (Gy)
• 1 Gy = 100cGy = 100 rad
How often is radiotherapy (RT) usually given?
How long does one RT treatment usually take?
Is RT given over the weekend?
Daily
Several minutes, 3-4 mins
Depends - only emergency settings, spinal compression or bleed, otherwise just weekdays
Do patients become radioactive from External
Beam RT?
No
radioactive iodine for thyroid cancer pt radioactive
radioactive seeds
will set off alarms in airport
others will not
Where can a patient receive
RT in Alberta?
Edmonton
Calgary
Lethbridge
Red Deer
Grande Prairie
Cross Cancer Institute: Edmonton
Tom Baker Cancer Centre: Calgary
Jack Ady Cancer Centre: Lethbridge
(opened June, 2010)
Central Alberta Cancer Centre: Red Deer
(opened January, 2014)
Grande Prairie Hospital (Opened October
2021)
Why is RT used in cancer patients?
Choices:
To improve survival
To improve local control
To decrease symptoms
To improve quality of life
All of the above
All of the above
top 2 is curative RT
bottom 2 is palliative RT
Indications for curative RT:
• Prostate Cancer
• Breast Cancer
• Lung Cancer
• Head and Neck Cancers
• Gastro-intestinal Cancers
• Lymphomas
• And many more….
• Chemotherapy may be used
– prior to RT (neoadjuvant)
– with RT (concurrent)
– after RT (adjuvant)
• The addition of chemotherapy improves cure
rates in some cancers, but also increases
toxicity (chemo side effects + RT side effects)
combie with chemo
synergist often with chemo, more side effects
Radiation Sensitizers
• Radiosensitizers: chemicals that increase the biologic effects of RT
• Some chemotherapy agents are radiosensitizers
• 5-FU:
– M of A: incorporated into RNA and DNA, and inhibition of
thymidylate synthetase function (and therefore DNA synthesis)
– ie: used with RT for rectal cancer
• Cisplatin:
– M of A: inhibition of DNA synthesis and transcription; inhibition of
DNA repair
– ie: used with RT for cervical cancer, head and neck cancers, bladder
cancer, lung cancer
Breast Cancer RT
• Post-lumpectomy, lymph node negative
– RT to breast only
• Post-lumpectomy, lymph node positive
– RT to include breast and regional lymph nodes
(intramammary chain, supraclavicular LN, +/- axillary LN)
• Post-mastectomy, lymph node positive
– RT to include chest wall and regional lymph nodes
(intramammary chain, supraclavicular LN, +/- axillary LN)
Prostate Cancer RT
• Low risk
– RT to prostate only
• Intermediate risk
– RT to prostate and proximal seminal vesicles
• High risk
– RT to prostate, proximal seminal vesicles and pelvic LN
• Uses Rapid Arc treatment planning, a form of IMRT
(intensity modulated radiotherapy)
– Allows a high dose of conformal RT to the target volume, while sparing the surrounding normal tissues
What percent of RT is given with palliative
intent?
about 50%
depedns on tumor group
head neck cancer 80% curative, 20% palliative
lung cancer 20% curative, 80% palliative
Indications for palliative RT
• Bone metastases
• Spinal cord compression (emergency)
• Brain metastases
• Advanced lung cancer
• Superior vena cava syndrome
Bone Metastases
Goals of RT:
• Decrease pain
• Preserve mobility, function
• Preserve quality of life
• Prevent complications
(fracture, spinal cord compression)
• Decrease need for opioids
a lot of times can treat bone that’s missing
works 75% of the time, good pain control in that area
Spinal Cord Compression
* One of the few RT emergencies! *
Goals of RT:
• Preserve neurological function
(walking, bladder and bowel function)
and prevent deterioration
• Decrease pain
• Preserve mobility
• Preserve quality of life
Brain Metastases
Goals of RT
• Improve symptoms, and
prevent further
deterioration of
neurological function
• Preserve quality of life
• Improve survival
• Minimize steroid side
effects by allowing
Decadron to be reduced or
stopped
can cause cognitive problems later
better control everywhere with drug tx except the brain due to BBB
• Improve symptoms, and
prevent further
deterioration of
neurological function
• Preserve quality of life
• Improve survival
• Minimize steroid side
effects by allowing
Decadron to be reduced or
stopped
Initial Consultation with Radiation Oncologist
- The patient is assessed by the radiation oncologist, and if appropriate for RT, the logistics, goals, and side effects of RT are discussed…
- CT simulation: a scan is taken of the area of the body to be treated, so that the radiation can be planned
- For brain tumors and head and neck cancers, a “mask” is made to keep the head still during treatment
Referral to other disciplines if needed
(Social Work, Rehab Medicine, Clinical Nutrition)
CT Simulation (Radiation Therapist)
RT Planning (Radiation Oncologist, Dosimetrist)
Calculation/QA (Medical Physicist)
RT treatment (Radiation Therapist)
Planning, Calculation,
and Preparation
• Planning on CT scan by radiation oncologist
• Calculations and prep performed by radiation
therapists, dosimetrists
• QA performed by medical physicists
RT Side Effects
• Radiation toxicities affect the area of the body
being treated
• Only generalized side effect: fatigue
• Early side effects
– develop during RT/shortly after RT
– common, but self-limited (last only days to weeks
after RT)
• Late side effects
– develop months to years after RT
– less common, but permanent
Early RT Side Effects
Depends on area being treated….
• Skin: redness, irritation
• RT over abdomen, pelvis: possible nausea, loose
stools, diarrhea
• RT to chest: esophagitis (dysphagia, odynophagia)
Late RT Side Effects
Depends on area being treated….
• Skin: fibrosis, pigmentation changes, telangiectasia
• Bone: osteopenia, radionecrosis
• Chest: lung fibrosis, esophageal stricture/fistula
• Abdomen: nephritis, small bowel stricture/fistula
• Pelvis: cystitis, proctitis
• Second malignancy
Criteria for radiation-induced malignancy:
1) within or at border of RT field
2) previously normal tissue
3) latent period exists (≥ 3 years)
4) histologically proven different from primary cancer
