radiobiology - hyperthermia and its effects on cell survival curves.

1. HYPERTHERMIA
PG – Dr.Pragatheeswari G K
Asst – Dr.Balaji S
Chief –Dr Jeeva S
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Dr.G K PRAGATHEESWARI MMC

2. synopsis
• Introduction
• History
• Effects of HT
• Arrhenius plot
• Factors influencing the effect of HT
• Methods of heating
• Thermal tolerance
• Dosimetry
• TER and therapeutic gain
• HT RT CT
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3. Introduction
• Elevation of temperature to supra- physiological level
• >39 degree c
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4. HISTORY
• 3500 years ago Egyptian papyrus – breast tumor treated with
hyperthermia
• Hippocrates 470 -377BC - those who cannot be cured by medicine
can be cured by surgery . Those who can not be cured by surgery can
be cured by fire. Those who can not be cured by fire are indeed
incurable.
• 1866 – german physician W.BUSCH patient with sarcoma of face
disappeared after a prolonged infection with erysipelas
• Erysipelas – infectious disease streptococcus pyogens , causes high
fever
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5. • Coley toxin – WILLIAM B COLEY mixed bacterial toxin, which induces
high fever with which he treated many patients
• 1898- westermark : Swedish gynaecologist published a paper –
marked regression of large uterine sarcomas when treated with local
hyperthermia
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6. Effects of hyperthermia
• Effects of hyperthermia is equal in both differentiated and undifferentiated
cells
• there is no major difference between normal and tumor cells, for response
to hyperthermia
• Heat kills cells ina predictable and repeatable way
• Main target for cytotoxicity due to hyperthermia are proteins
• Membrane components – changes in permeablity
• Cytoskeleton - changes in architecture and stability, signal transduction pathways
• DNA repair proteins - DNA damage and cell death , mech for heat induced radio and
chemo sensitization
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7. • Centriole damage – heat induced chromosomal aberrations
• Activation energy for protein denaturation and activation energy for
cytotoxicity are similar
• There is a increased expression of heat shock proteins after tumor
cells got heated
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9. HT AND CSS
• Cells exposed for various temperature for different duration
• Cell survival curve for heat are similar to those for xrays
• But different mechansims for cell killing by heat and xrays
• Energy involved in cell killing is 1000 times greater in heat than xrays
• for lower temperatures the curves flatten out after protracted
exposure, due to thermotolerance
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10. • HT kills cells in a log linear
fashion depending on the time
• Initial shoulder region indicates
that damage has to accumulate
to a certain level before begin to
die
• At lower temperature plateau is
due to thermo tolerance
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11. ARRHENIUS PLOT
• Defines temperature dependence on
the rate of cell killing
• Biphasic curve
• Obvious change in the curve is the
breakpoint
• Breakpoint – due to the
development of thermotolerance
during temp <43c and inhibition of
thermotolerance >43c
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12. Hyperthermia and other factors
• pH modification – acute reduction in extracellular pH can greatly
enhance sensitivity to hyperthermia
• Cell cycle stage – cells in late S phase of cell cycle & hypoxic cells are
radioresistant but are most sensitive to hyperthermia
• Cells deficient in nutrition are certainly heat sensitive
• Cells in tumor are nutritionally deprived and at acid pH , because of
their remote location from blood capillary may be particularly
sensitive to heat – large necrotic tumors shrink dramatically after heat
treatment
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13. At non cytotoxic temperatures
• Temperatures <43c , mor
particularly 40.5c to 41.5c
• It is now seen that mild
hyperthermia can promote tumor
reoxygenation
• The degree of reoxygenation
correlates with the degree of
radiosensitivity of tumor
• BRIZEL and collegues showed that
one HT led to reoxygenation
within 24 to 48 hours , in
conditions where no reoxygenation
with one week of standard RT
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14. IMMUNOLOGICAL EFFECTS OF HT
• Thermal stimulation of anti tumor
immune response
• Current evidence that supports this
possibility includes
1. Enhanced immunogenicity and heat
shock protein expression seen after
tumor cells are heated
2. Thermally enhanced immune
effector cell activation and function
3. Thermally enhanced vascular
perfusion and deliver or trafficking
of immune effector cells to tumors
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15. Methods of heating
• In labs ; heating by water baths
• Simplest and most reliable way to heat a petri dish or a tumor
transplanted to mice leg is by – immerse it totally in a
thermostatically controlled bath of water
• Tumors in patients cannot be heated this way
• It is challenging to produce uniform localised hyperthermia that can
be correctly measured
• Methods used are – microwaves , ultrasound, radiofrequency
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16. • Microwaves – good localisation can be achieved at shallow
depths.
• But at greater depth tumors ,even if the frequency is lowered
to allow deep penetration , localisatrion is poor and surface
heating limits the use , recurrent chest wall nodules are
treated with microwaves
• Ultrasound – adequate penetration and reasonably good
temperature distributions can be achieved in soft tissues ,
• The presence of bone and air cavities causes distortions of
the heating pattern, deep seated tumors below the
diaphragm are treated with focused array of ultrasound.
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17. Thermal ablation
• Destruction of tissue by extreme hyperthermia
• The temperature change is concentrated to focal zone in and around
the tumor
• At 50c it takes few minutes to kill a cell
• At 60c it takes only few seconds
• Ablative heating is produced by needle type radiofrequency or
microwave applicators ,1.5mm in diameter, which are inserted into to
tumor under CT or USG guidance
• Use – inoperable tumors in liver , osteoid osteoma, primary kidney
tumors, inoperable pulmonary nodules
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18. Thermotolerance
• The development of transient and non hereditary resistance to subsequent heating by initial
HT
• Two ways of heating induce thermo tolerance
1. At lower temp 39 to 42c – induced during heating period after an exposure of 2 to 3 hours
2. Temp >43c – takes sometime to develop after heating has been stopped, it then decays
slowly
• For cells in culture which developed thermotolerance it takes more than 160 hours to revert
back to normal or become heat sensitive
• Field and law and collehgues at hammersmith hospital showed that for normal tissues such
as gut skin and cartilage thermotolerance takes 1 or 2 days to reach maximum after heating
and takes 1 to 2 weeks to deacy completely
• Thermotolerance is limiting factor for clinical use of HT , because it imposes a limit of one or
at most two HT per week
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19. Thermal enhanmcement ratio
• To estimate the thermal radiosensitization
• The ratio of doses of xrays to produce given biological effect with or without hyperthermia
• experimental animal studies show that TER is
• 1.4 at 41c.
• 2.7 at 42.5c and
• 4.3 at 43c.
• Gillette et al and overgrid et al studied TER for canine and human tumors and it is observed that
in canine oral scc the TER is 1.15 when HT was administered twice weekly during fractionated RT
• Use – of HT is the dose of RT can be limited well within the values at which it cause the normal
tissue damage incase of oral scc it is taken as ORN of mandible.
• TER is 1.15 for several superficially located human tumors
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20. Therapeutic gain factor ÷
• Defined as ratio of TER in tumor to TER in normal tissues
• It is complicated in terms of heat, as tumor and normal tissues are not
necessarily at the same temperature
• For eg if a poorly vascularized tumor is heated with microwaves, It may
reach a temperature higher than that of a normal tissues because less heat
is carried away by the blood
• In addition overlying skin can also be cooled by the draft of air or even a
cold water pack.
• So exaggerates the differential response
• Hence therapeutic gain factor is not applicable for and not much of use in
hperthermia
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21. DOSIMETRY
A. DIRECT / invasive methods :
• For many years the only method of treatment monitoring, controland
thermal dose calculation
• Sensors should be able to measure temperatures to an accuracy and
precision of about 0,1c in a waterbath 0.2c in EM or ultrasound fields
1. Electrically conducting : thermistor, thermocouple sensors. These are
not suitable for EM fields
2. Minimally conducting : high resistivity thermistor with carbon
impregnated plastic leads , accurate measurement in EM fields
3. Non conducting : optical sensors at tip of fibres , used in EM fields
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22. Non invasive methods
• Several noninvasive thermal measurement approaches are under
investigation,
1. including infrared thermography and thermal monitoring sheet
2. fiber-optic arrays
3. electrical impedance tomography
4. microwave tomography
5. microwave radiometry
6. ultrasonic temperature estimation techniques,
7. magnetic resonance thermal imaging (MRTI)
8. Proton resonance frequency MRTI
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23. Dosimetry
• Sapareto & Dewey proposed concept of "Cumulative Equivalent Minutes" [CEM]
• Normalize thermal data from hyperthermia treatments using this relationship
• CEM 43°C = t R(43-T)
➤ where CEM 43°C is the cumulative equivalent minutes at 43°C , breakpoint temperature
• 43c ; above this temp 1c rise decrease time factor by 2 ,, below this temp 1c rise decrease need of time by 4 to 6 times ---
arrhenius plot
▸t is the time of treatment,
➤ T is this average temperature during desired interval of heating,
➤ R is a constant. (Above breakpoint R=0.5 and below=0.25)
For complex time-temperature history, heating profile is broken into intervals of time "t" length, where the temperature remains
relatively constant
CEM 43°C = [tR(43 -Tavg)
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24. Combining RT AND HT
• Cell in late S phase of cell cycle & Hypoxic cells are radio resistant but
are most sensitive to hyperthermia. Cells in all stages of cell cycle are
killed
• Hyperthermia can lead to Reoxygenation which improves radiation
response-Radiosensitization
• Inhibits the repair of sub lethal & potentially lethal damage
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25. Hyperthermia and chemotherapy
• There may be several different mechanisms that underlie the interaction of
heat with chemotherapeutic drugs
These include
1. increased drug uptake and/or retention in cells,
2. increased DNA damage and inhibition of repair processes,
3. increased oxygen radical formation, and
4. increased vascular delivery and tumor penetration.
5. It is also clear that the extent of hypoxia and the pH of the tumor may affect
the interaction between heat and chemotherapy
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26. • Potentiated by heat
Melphalan
Cyclophosphamide
BCNU
Cis-DDP
Mitomycin C
Bleomycin
Vincristine
Unaffected by heat
Hydroxyurea
Methotrexate
Vinblastine
Complex interaction
Doxorubicin
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27. THERMOSENSITIVE LIPOSOMES
• Liposomes consist of a lipid membrane that can be filled with a
cytotoxic chemotherapeutic agent such as doxorubicin.
• Enhanced permeability and retention (EPR) effect:Long circulating
liposomes that are covered with polyethylene glycol reduce recognition
by the reticuloendothelial system and can extravasate from tumor
blood vessels and accumulate in the extravascular space.
• hyperthermia can increase the size of these pores and enhance drug
delivery by four- to five fold over what can be achieved from just the
EPR effect.
• Further enhancement of drug delivery can be achieved by using
thermally sensitive liposomes that are engineered to melt at mild
temperatures (e.g., 41° to 42° C). These formulations yield further
improvement in drug delivery by an additional factor of 4 to 5 versus
nonthermally sensitive liposomes.
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28. • Indeed, these latter formulations
have been shown to enhance
doxorubicin delivery by 25- to
30-fold, compared with free
drug, resulting in impressive
antitumor effects in tumor that
were completely refractory to
free drug
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29. TRIALS
• CARCINOMA CERVIX - phase 3 in netherlands RT vs RT + HT , 361
patients - Complete response 57% vs 83% , 3yr sr - 27% vs 51%
• RECURRENT CHEST WALL TUMORS - collaborative study of 5 trials
• RT vs RT + HT , complete response in later , significant improvement in
previously irradiated site
• HEAD AND NECK CANCER - Valdagni Amichetti , stage III H & N
cancers , 58% CR in RT+HT vs 20% RT
• GBM - sneed et al ,also for
• ESOPHAGEAL CANCER , HIGH GRADE SARCOMA , it is seen that
HT + CT is more beneficial than CT alone
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30. • SUPERFICIAL MALIGNANCIES -
single institution randomized
trial by JONES ET AL , superficial
lesions <3cm . RT vs RT +HT - CR
42% vs 66% ,
• this was the study to
capitalise on the idea that for
hyperthermia act as a radio
sensitizer
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31. MAGNETIC HYPERTHERMIA
• experimental cancer treatment
• magnetic nano particles ,when subjected to alternating magnetic
field , generate a great deal of heat
• in studies , transplanted tumors in mice , iron nanoparticles were
injected iv, alloweed to circulate in blood,.
• when nano particles accumlate in tumors, alternating magnetic field
is applied ad it is seen that 60 c rise within few minutes
• human studies for - prostate ca and GBM , iron particles were injected
directly into the tumor than into blood
• temperature of 40 to 48c rise is observed, this HT combined with RT
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32. REFERENCE - ERIC.J.HALL textbook of
radibiology
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33. THANK YOU
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