Introduction to radiation therapy pp

how is radiation therapy multidisciplinary

combines surgical, medical, and radiation oncology team

what are the 3 roles of the radiation oncologist

1. carefully assess all conditions relative to pt and tumor

2. systematically review need for diagnostic and staging procedures

3. in consult with other oncologists, determine the best therapeutic strategy

when are the goals defined for RT

onset of tx

what are the two goals that are defined onset at tx

curative or palliative

what is another name for curative

definitive

what is the definition curative or definitive

probability of long-term survival, with some side effects of therapy accepted; extended life

what is palliative

no hope for survival for extended periods

what does palliative tx offer

pain relief

what postpones impending condition that may impair comfort or self-suffficiency

palliative tx

what are two classification of palliative tumors

additive or destructive

what does adjuvant mean

the use of another form of tx in addition to primary therapy (surgery + XRT, chemo+XRT)

what does neoadjuvant mean

the use of chem as the initial tx, before surgery or radiation

what does prophylactic

contributes to the prevention of disease

what does concomitant or concurrent mean

two modalities of tx taking place at the same time

what are the 8 basis of RT prescription

1. staging

2. patho characteristics of disease

3. definition of tx goal

4. selection of appropriate tx modalities

5. determining volume to be tx

6. determining optimal dose of irradiation

7. evaluate pt condition

8. develop tx plan

how can you determine volume to be tx

anatomic location, histologic type, stage, potential regional nodal involvment

what 3 things will always rest with the radiation oncologist

responsibility for tx decisions, technical execution of therapy, and consequences of therapy

what does higher doses of irradiation produce

better tumor control

what happens for every increment of irradiation dose

a certain fraction of cells will be killed

what is subclinical disease

to small to see or detect with our own senses

for subclinical disease, doses of what will result in disease control in more than 90% of patients

doses of 4500-5000cGy

for subclinical disease, doses of 4500-5000cGy will result in disease control in more than _% of patients

90%

what kind of dose microscopic tumors require

higher dose (6000-6500cGy)

what dose for microscopic tumors

6000-6500cGy

what dose do clinically palpable tumors require

6500-8000cGy

what are the daily doses for tx

180-250cGy per fraction

what is the goal of additional dose given small portals to residual disease

increase probability of control

what are 3 small portals called

boost, reduction, field-within-a-field

what is boost or reduction

treats tumor and zone around it; then stop large field, reducing and only area in area

what is field-in-field

tx both the large field and small field daily until total dose for each port has been reached

what does IMRT stand for

intensity modulated radiation therapy

what is moving in IMRT

MLCs

MLCs are moving and doing what in IMRT

making different doses in different areas

what are examples of non-IMRT treatments

open field or 3D conformale

describe the “shrinking-field” technique

reductions will be made as portals are reduced in size

when do you use shrinki

what does shrinking field do

gives a higher dose to the tumor where there are potentially large numbers of malignant cells present

what does shrinking field technique allow

allows you to reduce off of normal tissue, where a potential smaller number of cancer cells are located

what does radiation effect depends on

total dose, fraction schedule, volume treated

what percent is an acceptable complication rate in a curative setting

5-15%

what is a TD 5/5 chart

the dose which results in a minimum 5% severe complication rate within 5 years after tx

what is TD5

what is TD5/5 for lens

1000cGy

what is TD5/5 for kidney

1500cGy

what two factors is the tolerance affected by for TD5/5

volume irradiated and fraction size

what are the 3 normal tissue effects of radiation

acute, subacute, late

what is an acute normal tissue effect

within the first 6 months

what is an subacute normal tissue effect

within second 6 months

what is a late normal tissue effect

after 1 year

what happens when you combine radiation with surgery or chemo

reduces tolerance of normal tissues to the same dose of radiation

what does fractionation of radiation spare

acute reactions

a prolonged course does what to early acute reactions

decreases

a prolonged course does not protect the pt against what

serious late damage to normal tissue

is a 5 fx/week or 3 fx/week preferable

5 fx/week

what is hyperfraction

refers to tx using more than one fraction a day

what are two BID tx objectives

1. spare normal tissue by decreasing the size of dose per fraction

2. deliver higher daily dose for rapidly growing tumors

what is the overall tx time for hyperfractionation

6-7 weeks

what is different with the fractions in hyper fractionation

fractions are doubled and the total daily dose is increased slightly

what is the dose per fraction for hyperfractionation

120-130cGy max

how long is the time in between fractions needed for hyperfractionation

6 hrs

why is the time in between fractions 6 hours for hyperfractionation

must be long enough to allow complete repair of sublethal damage

tx may be have to put on hold due to what

an acute side effect of tx

what is the names of when tx needs to be put on hold because of an acute tx

split course, planned break, on-tx break

what is a preoperative rad therapy

they get therapy before surgery

what is the rationale for preoperative rad therapy

potentially eradicates subclinical or microscopic disease

what is the disadvantage of preoperative rad therapy

may interfere with normal healing of tissue affected by radiation

what is the rationale of postoperative rad therapy

eliminate residual tumor. greater dose is directed to volume of high risk or known disease

what is the disadvantage of postoperative rad therapy

delay in initiation of tx until would heals. vascular changes due to sx may also impair radiation effect

what does combining RT and chemo do

increases effect on tumor and normal tissues greater than observed with the modalities alone

use of chemo during RT may interact with what

local tx

what does doing chemo before RT produce

produces cell kill and reduces number of cells to be eliminated by radiation

what is the gross tumor volume

volume of known disease in the pt

t/f: the tumor be defined as GTV if sx removed

false

what are the imaging studies for a gross tumor volume

mri ,ct

what is the clinical target volume

the GTV plus an area of suspected subclinical microscopic disease

what is the planning target volume

takes into account geometric uncertainties and organ/pt motion

what does PTV plan for

the anatomy not being the same from the beginning of tx

what are some examples of needing PTV for the pt

weight loss, food, immobilization devices

what are the two types of jaws you can have

symmetrical or asymmetrical

what does BEV stand for

beam eye view

what is the BEV

overhead tx head looking down

why does the collimator rotate

to prevent leakage to keep happening in same spot of tumor

what are 3 goals of beam arrangements

1. ensure that the target specified by the physician receives the dose specified by the physician

2. minimize dose to normal structures while maximizing dose to tumor

3. minimize dose to critical structures

what are some examples of common beam arrangements

2-field, 3-field, 4-field, 5-field

2 field can be called what

parallel opposed ports

what two things does a wedge to

eliminates hot spots so the thinner part does not get the same radiation as thick part

what is an unilateral beam used for

electron, no exit dose

what is the whole brain beam shape look like

german helments

what is the whole brain beam arrangment like

it has flash on anterior, superior, and posterior (2cm fall off)

what is a beam arrangement field shape called for lspine and sacrum

spade

what is the beam arrangement field name for testicular cancer

hockey-stick

what is the hockey stick beam field used to treat

testicular cancer; lymph nodes and iliac nodes near descending aorta

what does the inverted Y and mantle used to treat

lymph nodes for lymphoma

what is excluded on the pt on mantle

excludes lungs and larynx, humoral head

what is the beam arrangement to tx lymph nodes or iliac nodes

hockey stick

what is the beam arrangement that can be used to treat lspine and sacrum called

spade

what is the beam arrangement name that can be used to try lymph node groups for lymphoma

inverted Y and mantle

arc rotation is less than what degree

not full 360 rotation

what are used on mantle beam arrangements

positive blocks