Ch 30 - Radiation Oncology - special procedures

what are 3 ways to treat cancer

- surgery

- chemotherapy

- radiation therapy

cancericidal

cancer-killing dose

fractionation

delivery of a small dose daily until the entire treatment dose is reached - reduces toxic effects of radiation

what percent of cancer patients are still being treated with radiation

75%

What is the role of a medical dosimetrist

creates a plan for delivering the treatments in a manner to best meet the physician's goals of irradiating the tumor while protecting normal vital structures

what is the role of a radiation therapist

obtain radiographs or CT to localize area to be treated

keep accurate records of the dose delivered each day

administer the treatments

monitor patient's wellbeing

what are the 3 steps to prepare a patient for treatment

- simulation

- develop an optimal treatment plan in dosimetry

- treatment delivery

cancer

unregulated, uncontrolled replication of cells

metastasis

spread of cancer from the original site to different parts of the body

most common cancers in men

- prostate

- lung

- colorectal

- bladder

- skin

most common cancers in women

- breast

- lung

- colorectal

- uterine

- thyroid

carcinogen

A cancer-causing substance

what is the classification system used for cancer

TNM - tumor, node involvement, metastasis

What are LET and RBE

linear energy transfer

relative biologic involvement

if you increase LET you increase RBE

Linear energy transfer

as radiation goes through the body, some of its energy is transferred

law of bergonie and tribondeau

the effectiveness of radiation depends on the state of the biologic system

cells are most sensitive to radiation when they are immature, undifferentiated, and rapidly dividing (during mitosis)

Why are cancer cells more sensitive to radiaiton

they have a higher metabolic rate

more active = more sensitive

What is CIS

carcinoma in situ

not cancer but abnormalities are present

external beam therapy

patient lies under and external source of radiation - most common form of treatment

brachytherapy

technique where radioactive materials are implanted into the the patient - achieves a higher dose to the tumor

what is the most commonly used machine for cancer treatment

linacs (linear accelerator)

photon beam is produced by accelerating a stream of electrons toward a target

the radiation beam can be composed of what two things

photons or electrons

what is the advantage of using electrons

the are more superficial and deposit their energy at a certain depth and go no deeper

isocentric/isocenter

maintains the same distance from the patient at all times - 360*

isocenter - point of intersection of the three axes of rotation

skin-sparing effect

phenomenon that occurs as the energy of the beam of radiation is increased

the greater the energy of the beam, the more deeply the maximum dose is deposited - sparing the radiosensitive organ of the skin

multileaf collimation

most complex beam-defining system

45 to 80 individual collimator blades that can be adjusted to shape the radiation field to conform to the target

VMAT

IGRT

intensity-modulated gated radiation therapy

tolerance dose

dose each organ can receive and still function normally

what does three-dimensional conformal radiotherapy allow

allows the dosimetrist to plan and design beams that are coplanar and noncoplanar - tightly conforming to the target/tumor volume

Bragg peak

the burst of energy deposited at a specific depth (80% of energy is deposited into targeted tissue and quickly drops to 0 in mms)

property of a proton beam

can be adjusted by changing the energy of the proton beam and adding beam modifiers

PBS

pencil beam scanning

what is the most current method of proton beam delivery

PBS - pencil beam scanning

delivers a more conformal dose distribution to the tumor than passively scattered particle therapy and allows for modulation of the intensity

what are some advantages of pencil beam scanning

- almost no exit dose - preferred for pediatric imaging

- lower dosage to normal tissues

- less risk of secondary malignancy

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