angelica mirai

Radiobiologia delle
particelle pesanti
Angelica Facoetti
Fondazione CNAO
Corso teoricoteorico-pratico sull’adroterapia:
sull’adroterapia: l’alta tecnologia applicata alla clinica
CNAO, Pavia, 1717-18 Maggio 2013
Radiobiologia
“studio degli effetti delle radiazioni
ionizzanti sulla materia vivente”
• Interazioni iniziali
Radiaz. indirett. ionizzanti (raggi X, raggi γ)
10-24 - 10-4 s
Radiaz. dirett. ionizzanti (elettroni, protoni)
10-16 - 10-14 s
• Stadio fisico-chimico
10-12 - 10-8 s
• Danno chimico (radicali liberi)
10-7 s - ore
• Danno biomolecolare (proteine, acidi nucleici)
ms - ore
• Effetti biologici precoci (morte cellulare)
ore - settimane
• Effetti biologici tardivi (induzione di neoplasie,
effetti genetici)
anni, secoli
E. Fokas et al, 2009
X-ray
Protons
Carbon
ions
RBE (Relative Biological Effectiveness)
Effectiveness)
Schardt & Elsasser, 2010
BUT, RBE is a complicated radiobiological
concept that depends on:
•
•
•
•
•
•
•
•
•
Dose level
Measured endpoint
Particle charge and velocity
Dose rate or fractionation
Energy/LET of the particle
Cell/tissue type
Oxygen concentration
Cell cycle phase
Etc…
…and it gives a greatly simplified picture
of the high LET radiation effects
effects!!!
!!!
RBE is greater for lower doses
Protons have radiobiological properties that are close to those
of photons and electrons (RBE does not change very much
with the depth and a significant increase appears only in the
distal part of the Bragg peak) so that their main advatage
relies on the superior dose distribution compared to low LET
radiations
Carbon ions offer an even larger efficacy for tumour
treatments due to the enhanced biological effect at the end of
their range in the tumor.
7
RBE of C ions changes along the SOBP
Variation of RBE as a function of depth in the 290 MeV carbon-ion beam at HIMACChiba (Japan). The RBE is given at the four depths in water that are indicated.
The SOBP is 6 cm thick.
IAEA-TECDOC-1560
RBE in vivo
RBE values based on the dose for 50% complication probability for the
radiation tolerance of the rat spinal cord after 1, 2, 6, and 18 fractions of
carbon ions. Spread-out Bragg peak (125 keV/mm), plateau (13 keV/mm)
Schardt & Elsasser, 2010
Aim
•
to confirm the uniformity of biologic doses in PTV
positions with in vitro and in vivo experiments
•
to estimate biologic RBE values for in vitro and in
vivo endpoints in order to evaluate whether the
new carbon beam works in safe and optimal
conditions for the clinic.
Radiother Oncol. 2004
Microscopic understanding of RBE
Belli et al.
Low LET
High LET
ioni C (15 MeV/u)
Formation of fluorescent γ-H2AX clusters in irradiated human fibroblasts at 10 min
postirradiation with 2 Gy of gamma rays or 0.5 Gy of 176 keV/mm iron ions
Modificato da: JAEA R&D, 2007; Cucinotta and Durante, 2006
Clustered DNA Damage
It has been proposed that
Carbon ions radiation
produces multiple lesions
within a few nm in DNA
molecules, so-called
clustered DNA damage.
This densely localized
damage might distort the
tertiary structure of DNA and
consequently interfere with
the binding of repair
enzymes to the damage site.
http://jolisfukyu.tokai-sc.jaea.go.jp/fukyu/mirai-en/2008/6_5.html
The optimal LET
Diagram illustrating why
radiation with a LET of 100
keV/µm has the greatest RBE
for cell killing, mutagenesis,
or oncogenic trasformation.
Fot this LET, the average
separation between ionizing
events coincides with the
diameter of the DNA double
helix (i.e. about 2 nm).
Radiation of this quality is
most likely to produce a
double strand break from one
track for a given absorbed
dose.
Radiobiology for the radiologist, 7th edition
The larger size and the longer persistance of foci observed
after C ions compared to γ-rays can be due to multiple and/or
complex DSB which are difficult to repair
1.7 Gy of iron ions
fixed 5 h after
irradiation.
Comparison between H2AX phosphorylation-dephosphorylation
kinetics after irradiation with 1 Gy of γ-rays (closed circles) or
carbon ions (open circles).
Antonelli F et al, 2005; Desai N et al, 2005
Chromosomal aberrations induced by
Carbon ions
Chromosomal damage (mFISH) in first cycle cells after exposure to 0.2 Gy X-rays or 1 carbon
ion per nucleus (0.2 Gy). Fraction of aberrant cells.
Fournier C et al, 2012
1 hit
C ions per nucleus
Examples of karyotypes (mFISH)
mFISH) with clonal complex aberrations occurring in the progeny of
cells exposed to Carbon ions
Fournier C et al, 2012
5 hits C ions per
nucleus
Fournier C et al, 2012
FACTORS THAT
DETERMINE RBE
(BASIC RADIOBIOLOGICAL
PROPERTIES OF CHARGED
HADRONS))
HADRONS
Cell cycle phase radiosensitivity
The oxygen effect
The presence or absence of molecular oxygen
dramatically influences the biologic effect of X-rays.
Basic clinical radiobiology, Joiner & van der Kogel
The ratio of the dose required to kill the cells with the oxygen
divided by the amount to kill cells without oxygen is referred to
as the oxygen enhancement ratio (OER).
Oxygen-fixation
Oxygenhypothesis
E. Hall, Radiobiology for the Radiologist
OER is significantly reduced for ion
irradiation
Hirayama E et al, 2005
The OER decreases with increasing LET
Basic clinical radiobiology, Joiner & van der Kogel
CARBON IONS AND TUMOUR
CELLS GENETIC BACKGROUND
p53
x
The p53 tumor suppressor
limits cellular proliferation
by inducing cell cycle arrest
and apoptosis in response
to cellular stresses such as
DNA damage
About 50% of cancers harbor
mutation in the TP53 gene,
which result in a decreased
propensity to undergo
apoptosis.
These tumurs are more
resistant to treatment, both
by X-rays or chemotherapy
P53-dependent apoptotic
pathway
• Bcl-2 is an anti-apoptotic protein
• Bcl-2 overexpression has been associated with the resistance to
conventional photons and chemotherapeutic agents
High LET radiations
render BclBcl-2 cells more
vulnerable
Hamada N et al, 2008
Taking
into
consideration
that
Bcl
Bcl--2
overexpression and p53 mutations occur in
more than half of tumors,
tumors, high
high--LET heavy ions
appear to effectively kill a wide variety of
radioresistant tumors
tumors..
!
Human lung
adenocarcinoma (A549)
Human lung squamous
cell carcinoma(EBC-1)
Cell migratory
activity
Invasive activity
Akino Y et al, 2009
Particle Irradiation Suppresses Metastatic Potential
of Cancer Cells
X- rays
C ions
LM8 osteosarcoma cells
Ogata et al, 2005
X- rays
C ions
Therapeutic effects of cells irradiated with X-ray or carbon ion on
experimental pulmonary metastasis from mice inoculated intravenously
Ogata et al, 2005
“About 90% of the cells irradiated even at 0.1 Gy could be destroyed
compared with unirradiated cells.
On the other hand, sublethal X-ray irradiation promoted migration of
endothelial cells, and the capillary- like tube structure in three
dimensional culture progressed even after 16 Gy irradiation.”
BYSTANDER EFFECTS AND
HADRONTHERAPY
Morgan WF & Sowa MB, 2005
Radiation-induced bystander effect represents a paradigm
shift in the understanding of the radiobiological effects of
ionizing radiation in that extranuclear and extracellular
effects may also contribute to the final biological
consequences of exposure to low doses of radiation.
There is evidence that cells that are not directly hit by
radiation, whether nuclear or cytoplasm, but in the vicinity
of one that does, contribute to the biological response of the
cell population
The progeny of non-targeted cells shows an increase in
genomic instability as evidenced by an increase in delayed
mutations and chromosomal aberrations many generations
afterwards
Irradiated cells communicate
to neighboring nonnon-irradiated
bystander cells by transmitting
an irradiation signal
substance, which induces
radiation effect on bystander
cells as well.
Iwakawa, M et al, 2008
The expression profile of the bystander cells was completely
different from that of the irradiated cells.
Iwakawa, M et al, 2008
CANCER STEM CELLS AND
HADRONTHERAPY
Cancer stem cells
“A small subset of cancer cells within the tumor mass, which
constitutes a reservoir of self-sustaining cells with exclusive ability of
self-renewal and tumor maintenance” (from the Cancer Stem Cell Workshop of
the American Association for Cancer Research in 2006)
An anticancer therapy can cure a
tumour only if all cancer stem cells are
killed (without producing serious side
effects in surrounding normal tissues)
In the radiotherapy
context, a cancer
stem cell is a cell
which, when left
after irradiation to
its natural
environment, has
the capacity to
cause a tumour
recurrence.
Baumann M et al, 2008
Since cancer stem cells appear to be responsible for driving and
maintaining tumor growth in many tumors, it is critical to
understand the mechanisms by which these cells resist commonly
used therapies such as chemotherapy and radiotherapy
CSC: known (???) mechanisms of
radioresistance
A high frequency of CSCs are believed to be quiescent, and this
would make them more resistant to cycle active agents,
including radiation.
Their residence in a microenvironmental niche may provide
them with both direct physical contacts (eg, cell-cell or cellstroma) and growth factor/cytokine signaling that may provide
additional survival signals in response to the stresses induced
by radiation
Increased potential of defense against ROS mediated by high
levels of free-radical scavengers
The capacity to recover and repair sublethal damage between
irradiation fractions
X
X
X
X
Summary
Durante M & Loeffler JS, 2010