Radiation Oncology Flashcards Preview

MSY2 Viruses > Radiation Oncology > Flashcards

Flashcards in Radiation Oncology Deck (23):

What is the lower limit of detection of tumor cells?


What is a lethal volume of CA ?



Lower limit of detection: 1 x 10^9 cells (1cc^3)


A lethal volume of CA is about 10^12 (1 Kg)


Most CA have therefore completed about 2/3 of their natural life span before they detected


What is radiation?

electromagnetic radiation @ higher frequency / higher energy

--> causes DNA damage --> cell killing


What is external beam RT?

Aim ionizing radiation at a tumor using beams that come from the outside

(ionizing radiation = energy strong enough to ionize an atom)


Historical method: gamma radiation with Co-60

gamma rays = photons emitted from radioactive materials as they decay 


Current method: megavolutage x-ray radiation using a linear accelerator

e-rays are photons produced by machine- high energy photons are produced by a linear accelerator when tungsten target bombarded by high energy electrons


kV vs MV

Kilovoltage - diagnositic 

photoelectric effect creates sharp distinction btw tissue type

energy btw 25 kV -150 kV


Magavoltage (MV) - radiation therapy

Intentionally ionizing

energy bt 4mV - 20 mV


What is 3D conformal?

type of external beam radiation therapy

Radiation plan based on CT scan of pt in the radiation position


What are different types of external beam radiation therapy (3)

3D conformal


Conventional (simple fields, planning based on bony landmarks)


IMRT - intesity modulated radiation therapy, computer-aided planning using multiple ~100 overlapping fields; intensity of radiation beam varies across the radiation field; inverse treatment planning

- if used as treatment, ~ 70 Gy to regions of gross disease

(concurrent with q 3 weekly cisplatin chemo; post treatment imaging at 8 weeks to assess reponse to therapy)


How is a 3D conformal dose determined: 

How is it measured?


What is a typical dose per day?

What is a typical dose to a whole breast?

Unit of dose = gray (Gy)

1 Gy = i Joule/kg, measure of energy deposited in the tissue treated


Typiecal dose per day = 2Gy

Typical total dose to whole breast = 50 Gy


50 Gy/ (2 Gy/day) = 25 treatments

~5 weeks of treatment


What is a boost?


How does this differ from normal radiation therapy?


How long is this typical treatment done for?

The region of the tumor bed is the area at highest risk for recurrence thus addiational radiation is given to the lumpectomy cavity


Boost uses a different delivering technique vs radiation therapy to the neoplasti tissue. Boost is typically done with electrons (rather than photons) to keep dose to other tissues low - don't penetrate as much. 

~1 more week of therapy


Why is radiation given typically?

Reduces risk of recurrence 

Improves survival


Usually adjuvant therapy = in additional!


How is an IMRT plan done?

Radiation oncologist defines regions to treat and doses to give to both GROSS tumor and PROPHYLACTIC areas

Define regions to avoid (parotid glands, spinal cord, eyes..)


Radiation physicist creates plan

Max treatment, minimize side effects


What is brachytherapy?

Placement of radioactive materials into or immediately adjacent to the cancer


Requires an invasive procedure


May be done alone or in combo with external beam radiation therapy


What are some options for prostate ca?

Radical prostatectomy


radiation therapy

For prostate CA: external beam radiaiton therapy is given at aprox 78Gy = aprox 40 treatments


Brachytherapy- low dose rate (permanent), high dose rate (temp)


watchful waiting


What is the difference between HDR and LDR:


Temp or perm?

How long?

What are some typical isotopes used (4)?

Low dose:

sources could be temp or permanently

Radiation is delievered over days to weeks

typical isotope for gyn cases = Cs-137

typical isotopes for PPI cases = I-125 and Pd-103


High Dose:

Radiation source is temp

source is VERY HOT so given within minutes

typical isotopes Ir-192


How is a permanent prostate implant delievered?

radiactive seeds are inserted into the prostate and remian there forever

Seeds are loaded into needles --> needles directed thru the perinueum and into the prostate under US guidance


What are the typical implant dose given for PPI when using..


Pd- 103?


What are their half life? 

I-125 --> 144 Gy

half life: 60 days


Pd- 103 -->125

half life: 17 days


dose is high because radiation is given off slowly


what are other types of brachytherapy done?

Prostate HDR

Head and Neck HDR

Gynecologic LDR and HDR

Intraoperative brachytherapy

coronary brachytherapy (not done as often)


what is radiosrugery?


Different forms (3)?

short course, high dose, very focused external beam radiation treatment (tons of radiation in that area - killing everything)


Ways to perform radiosurg:

Gamma knife

Linear accelerator based



What are the treatment options for brain mets? (4)

Whole brain radiation therapy


Brain RT and radiosurgery boost

surgery then radiation


How is Gammaknife radiosurg done?

rigid patient immbilization within 1 mm

201 cross-firing tiny radiation beams given extremely high doses to small points in the brain

acurate MRI based radiation treamtent planning


hug dose in one area while minimizing the exposure to other areas


How is cyperkine radiosurg done?

Miniature linear accelerator mounted on a robot arm

can treat tumors anywhere in the body

built-in ability to track moving tumor target


what is intraoperative radiosurg?

Radiation at the time of surgery


Using TARGET technique. 

Miniature electron generator and acelerator; accurately delievers radiotherapy from within the breast in about 25 minutes


Why is radiation a good option?

irradiation reduces local recurrence

for example for BCA, 90% of local recurrences are in the index quadrant independent of aplied radiotherapy. 


what is ALARA stand for?


What are some safety measures that can be taken? (3)

ALARA = as low as reasonably achievable!



minimize TIME- minimize the amt of time you are exposed

increase DISTANCE- 1/R^2, 2 times the distance = 4X less dose