Radiation Flashcards
What is control rate for 50Gy on LN > and < 10mm
Wakatsuki et al have described a
- 97% control rate with 50 Gy radiotherapy for lymph nodes <10 mm in patients with cervical cancer i
- 76% for nodes >10 mm.
Similar results were found by Oh et al in 310 patients with locally advanced cervical cancer with a follow-up of 83 months. In-field failure rates for pelvic, as well as para-aortic lymph nodes >10 mm, were significantly higher than for smaller lymph nodes.
How many Gy to the Ovaries are required to ablate the oocytes
POI occurs with a dose of 20Gy in women under 40. Less for women over 40
The mean lethal dose for human oocytes is estimated to be 2Gy.
What are the 3 main volumes in RT planning
The known actual tumour is the Gross tumour volume (GTV)
TO ensure that disease outside of the GTV is treated a clinical tumour volume (CTV) is created to cover sublinical spread.
The CTV is placed in a planning target volume (PTV) - this is the area that received the treatment dose.
What are organs at risk and how are they incorporated into RT planning
The OR have a planning volume placed around them to reduce toxicity. This is planning Organ at RIsk (PRV)
How does oxygen effect the effectiveness of RT
Oxygen is required to make DNA damage permanent. Hydroxy free radicals react with and damage DNA. In an anoxic environment the DNA is able to be repaired. In an oxic enviornment the damage is made permanent. the Oxygen Enhancement Ratio can be up to 3. meaning 3x dose required in hypoxic environment.
How does RT work?
Directly by damaging DNA and indirectly by creating OH free radicals that interact with and damage DNA.
What is image guided adaptive Brachytherapy
IGABT 3D technique uses CT or MRI based planning to escalate the dose to target and reduce dose to adjacent tissues.
What is tumour related Leukocytosis
Investigated as a marker of radiation sensitivity. Identified that the level of serum leukocytes correlated with response to radiotherapy.
2 levels > 9 in the absence of infection have a lower radiotherapy response rate.
What are 6 mechanisms for late RT toxicity?
AV FISH
A - Atrophy - loss of fibrocytes and collagen reabsorption
V - Vascular damage - either small vessel dilation or cons- Proliferation of surviving fibrocytes owing to growth factors released as a result of injury
F - Fibrosis
I- Infertility
S - Second Malignancies
H- Hormone deficiences
In the EMBRACE Trial what was the 5yr overall incidence of Gr 3 AE after radical treatment for cervix cancer?
Genitourinary: 4.7% Gastrointestingal: 4.3% Vaginal 4.0% Fistula 1.0% Overall 10.2%
From PORTEC 3
What was the rate of late GI toxicity in both RT and CCRT groups
Grade 2 - 12 months 7-8%, 60 months 5 - 8%
Grade 3/4 - 12 months 1-2% 60 months 1%
From PORTEC 3
What was the rate of late genitourinary toxicity in both RT and CCRT groups
Grade 2 - 12 months 4-6%, 60 months 6 - 8%
Grade 3/4 - 12 months 0% 60 months 0%
What is rate of acute and late toxicity for vulva radiotherapy in a cohort of 39 women with primary and adjuvant IMRT
Skin; Gr 1 - 23 % Gr 3 69% GI - Gr 1 5%, Gr 2 33% Acute GU Gr 1 - 5%, Gr 2 10% Late GI - Gr 1 5%, Nil Gr 2 or above Late GU Gr 1 5%, Nil Gr 2 or above.
What is a cell cycle survivial curve?
Cell survival curve describes the relationship between the surviving fraction of cells (i.e. the fraction of irradiated cells that maintain their reproductive integrity (clonogenic cells)) and the absorbed dose.
Cell survival as a function of radiation dose is graphically represented by plotting the surviving fraction on a logarithmic scale on the y axis against the dose on a linear scale on the x-axis.
What is a therapeutic index
Plot of the probability of tumor control in Y axis against radiation dose in X axis what we get is the tumor control probability (TCP).
Normal tissue complications similarly plotted we get the normal tissue complication probability (NTCP)
TCP and NTCP curves are sigmoid in shape.
The therapeutic index (TI) defines how the TCP relates to NTCP for different doses of radiation
May be called toxicity or dose reponse curves.
