radiobiology of particulate irradiation...overview of the presentation • particulate radiation •...
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Radiobiology of Particulate Irradiation
Brian Marples PhDBeaumont Health Systems
Overview of the presentation
• Particulate radiation• LET of particulate irradiation• Microdosimetry/DNA lesion/repair• Linear quadratic (LQ) model • RBE, OER• DNA damage and repair, cell cycle• Fractionation• Conclusions and salient points
Contemporary & Particulate radiotherapy• X‐rays with high‐energy of 4‐25 MV
– Uncharged electromagnetic radiation: photons– Ionize molecules in tissues they penetrate– Roughly same biological effect per unit dose– Maximum dose at entry, independent of energy
• Light particles– e.g. protons, neutrons, α‐particles
• Heavy particles: Precise dose depth profiles – e.g. carbon, silicon, argon ions
• Major difference between photons and ions is spatial distribution of physical dose within tissue– Difference at entrance surface– Ions have steep dose gradient at beam margins
• Particles ‐ greater biological effect per unit dose
Particulate radiation: Optimization
Loeffler and Durante, Nat Rev Clin Oncol. 10(7):411‐24 (2013)
Anthropomorphic phantom with a virtual brain tumorscanning beams and have lower distal doses:Superior targeting
logical reduction in late effects
Particulate radiation:Linear Energy Transfer (LET)
• Describes density of ionization in particle tracks– 1.2 MeV 60Co =0.3 keV/μm; 250 kVp x‐rays=2 keV/μm– 10 MeV p=4.7 keV/μm; 150 MeV p=0.5 keV/μm– 2.5 MeV α=166 keV/μm; 4 MeV α=100 keV/μm
• As LET increases, more cell killing per Gray– High LET if >10 keV/μm; overkill effect ~100‐150 keV/μm
• For a given type of particle, the higher the energy, the lower the LET and lower biological effect
• Neutron; defined as high‐LET – nuclei p
MicrodosimetryLET: Linear Energy Transfer
A measure of average ionization density.
sparseintense
Repair more difficult- both strand rejoining and fidelity
Track ends
Goodhead Health Phys. 1988 55(2):231-40.
Low doses of -particles not all cells traversed
Human fibroblastsImmunostained for detection of ‐H2AX at 10 min
post‐RT. Each green focus corresponds to a DNA DSB
0.5 Gy of 176 keV/µm iron ions
0.5Gy 54 keV/µmsilicon ions2 Gy ‐rays
Desai et al., RADIATION RESEARCH 164, 518–522 (2005)
Calculated trackpatterns ‐ LET
H. G. Paretzke, Radiation Track Structure Theory, in Kinetics of Nonhomogeneous Processes, G. R. Freeman (Ed.), Wiley Interscience Publication, New York, 1987.
Electron tracks
50eV
2 keV
1keV500eV
200eV100eV
Proton0.3 MeV p
10 MeV p
30 MeV p
Calculated trackpatterns ‐ LET
H. G. Paretzke, Radiation Track Structure Theory, in Kinetics of Nonhomogeneous Processes, G. R. Freeman (Ed.), Wiley Interscience Publication, New York, 1987.
…for a given type of particle, the higher the energy, the lower the LET and lower biological effect.
Carbon
particle
1
2
4
6
8
MeV
MeV
1
3
overkill
Low LET
high LET
Barendsen, Curr Top Radiat Res Quart 4:293 (1968)
Linear Energy Transfer: Survival Curve
• Particulate (high‐LET) survival curves– Steeper, straighter, less of a shoulder– Higher ratio lethal to potentially lethal lesions– Damage is less likely to be repaired correctly
• LQ: higher α/β– In cells β increases with a lesser extent than α1
– In tissues skin reaction β increased same as α2
– Discrepancy between tissue culture and tissues3
• Biological effectiveness defined by RBE1. Britten et al. Int. J. Radiat. Biol. 61 805–12 (1992) 2. Ando et al. J. Radiat. Res. 46 51–7 (2005)3. Carlson et al. Radiat. Res. 169 447–59 (2008)
Relative Biological Effectiveness (RBE) • Equal doses of different radiations not equally effective– 1 Gy high LET more biologically effective than 1 Gy low LET– difference reflects pattern of energy deposition – LET
• Same dose = same energy deposition – but difference distribution– RBE is a relative system ‐ uses 250 kVp X‐rays
• RBE is a comparative measure– measured at a specific endpoint/biological system– survival level (shoulder)– LET (shoulder)– number fractions (shoulder)– dose rate (c.f. X vs N dose response curves)– endpoint and system (repair capacity)
Relative to 250 kVp x‐rays
Defined at isoeffect
Neutrons produce secondary knock-on protons from nuclear collisions, confers high LET status
RBE and LET
RBE for fractionated high LET increases with increasing dose
Same for LDR
RBE larger for small doses
Neutrons become progressively more effective (than x-rays) as the dose per fraction reduces and the number of
fractions increases
RBE larger after fractionation
Effect of dose and dose per fraction on the RBE
4 MeV particles
RBE decreases withincreasing dose for particles
T1g human kidney cells
RBE for high LET radiations vary with the dose (iso-effect)
Barendsen, Curr Top Radiat Res Quart 4:293 (1968)
SF = 0.8
SF = 0.1
SF = 0.01
60Co 250kVp
Pu particles
MegaV
RBE as a function of LET
Barendsen, Curr Top Radiat Res Quart 4:293 (1968)
Low-energy protonsNeutrons (~100 keV)
RBE higher ifmeasuredat lower doses
Particle RBE
Loeffler JS, Durante M. Nat Rev Clin Oncol. 2013 Jul;10(7):411‐24.
Measured at 10% survival
Proton RBE
The experimental in vivo and clinical data indicate that continued employment of a generic RBE value and for that value to be 1.1 is reasonable (recommended by IAEA/ICRU Working Group)
Paganetti et al. Int J Radiat Oncol Biol Phys 2002; 53(2):407–21.
“Biological overkill” – optimal LET
Overkill: per Gray
more densely ionizing radiations are just as effective per track, but less effective per unit doseProbability of a single
track causing a DNA DSB is low – single tracks have to interact:X-rays biologically inefficient
Highest Probabilityof causing a DNA DSB from a single particle:Biologically efficient
Low LEThigh LET
Direct and indirect effects: OER(oxygen enhancement ratio)
Oxygen fixation hypothesis
Free radicals produced in DNA can be repaired under hypoxia but fixed in the presence of oxygen
4MeV d-Be
OER = 3.1OER = 1.7
LET: Reduced effect of oxygen
hypoxic
oxic
V79 cells; varying N+X scheduling
As LET increases OER decreasesOxygen less important for high LET killing because of direct action
OER with LET
Barendsen, Curr Top Radiat Res Quart 4:293 (1968)
Variation of RBE and OER with LETRBE lowest at start of track: rationale for protons/pions
RBE and OER with LET
Cell survival curves for V79, HSG and T1 cellsexposed to carbon ions having different LETs
Particulate DNA damage
• Theoretical models– Monti Carlo based
• Measuring ‘foci’ for different DNA lesions– Formation and resolution
• Chromosome aberrations
Single strand breaks (SSBs): Model
A complex SSB is defined as a SSB accompanied by another SSB on the same strand or on the opposite strand but too far away to constitute a double‐strand break. (, ), Protons; (,), α particles.
Nikjoo et al. Radiat Res. 2001 Nov;156(5 Pt 2):577‐83.
Double strand breaks (DSBs): Model
Proportion of DSBs that are complex by virtue of additional strand breaks for protons and α particles as a function of LETdouble‐strand break. (, , +), Protons; (,, ) α particles.
Nikjoo et al. Radiat Res. 2001 Nov;156(5 Pt 2):577‐83.
DSB+ increases to more than 40% of the total
DSB++ increase greatly, from <5% to more than 30%
α particles 70% are complex
Particulate DNA damage
H2AX foci (DSB marker) as iron beams
XRCC1 in red (SSBs)TUNEL in green
colocalization of repair proteins RPA and 53BP1 (DBS via HR)
Particles and DNA breaks/repair• Damage occurs in clusters‐ large energy/small distance• More DSBs complex than ‐rays or X‐rays
– 90% of DSBs associated with other lessons1
• Protons are more potent than photons at recruiting H2AX2– Proton‐foci larger in size, but differences insignificant >6 hrs
• The size and frequency of radiation‐induced foci vary as a function of radiation quality, dose, time3– N ions (130 keV/μm), silicon (54 keV/μm) and Fe (176 keV/μm)– Enzymatic ‘cleaning’ of DNA break ends difficult after high LET
• X‐ray DSBs OER changes with time post RT; but not Carbon1. Goodhead, Radiat Prot Dosimetry 2006; 122: 3–152. Gerelchuluun et al. Int J Radiat Biol 2011; 87(1): 57–703. Costes et al. Radiat Res 2006; 165(5):505–15.Hada and Sutherland, Radiat Res 2006;165: 223–30
Charged Particle Microbeam: DSB repair
~50% of radiation‐induced damage was repaired first 1. 2 hrs X‐ray2. 6 hrs protons and3. 10 hrs 3He
3.5 MeV 3He particles (LET of 102 keV/μm) 2 MeV protons (LET of 17 keV/μm)240 kVp X‐ray
Ugenskiene et al. IJRB 85: 872‐882 (2009)
Kinetics of ATM/ATR signaling alteredpersistent phosphorylated ATM and ATR kinase, leading to Rad51 foci decay kinetics
Particles and clustered lesion repair
• DSBs, SSBs, and base lesions simultaneously– Surrogate markers: 53BP1, XRCC1 and hOGG1– Colocalization studies of repair foci for differing LET– 53BP1/XRCC1/hOGG1 to represent complex lesions, these increase in number with increasing LET
– Spatial and temporal distribution of DSBs is likely to critical factor in formation of chromosome aberrations –increased with particulate exposure
– Multiple DBSs per foci NHEJ‐mediated translocations• Linear increase in chromosome translations with dose c.f. curve‐linear for photons.
Asaithamby, Hu and Chen, Proc Natl Acad Sci U S A 2011; 108:8293–8.Saha, Wang and Cucinotta, DNA Repair (Amst). 2013 Dec;12(12):1143‐51
Exponentially growing HT1080 cells were irradiated with 1 Gy
Cells released from the G2/M checkpoint enter mitosis with unrepaired clustered lesions, which results in the formation of chromosomal aberrations (A) The total number of gross chromosomal aberrations per mitotic cell(B) The number of different types of chromosomal aberrations per mitotic cell after 1
Gy of ‐ray, O, Si, and Fe irradiation
DSBs, SSBs and base damage in human cells
Asaithamby Hu and Chen .PNAS. 2011 May 17;108(20):8293‐8
Particles & cell cycle phase sensitivity• Classic work of Sinclair: M G2/G1ESLS
– Photons and CHO cells; Radiat. Res 33: 620‐643 (1968)– Mid‐late G1 resistance in human cell lines
• High LET irradiations cell cycle variation reduced– Bird & Burki; Int J Radiat Biol Relat Stud Phys Chem Med 1975;27: 105–20.
• NHEJ was affected by high LET irradiation; along with DNA‐PKcs and Ku binding to sites of complex damage1,2
• G2‐checkpoint is impaired after extensive damage– More prolonged and longer to resolve3
– Extensive Chromosome aberrations
1. Anderson et al. Radiat Res 2010;174: 195–205.2. Zafar et al., Radiat Res 2010;173: 27–393. Moertel et al. Radiother Oncol 2004; 73(Suppl 2):S115–8.
sens
LET: Reduced effect of cell cycle phase
Bird and Burki, Int J Radiat Biol Relat Stud Phys Chem Med. 1975 Feb;27(2):105‐20.
19 keV/um to 2000 keV/umSynchronized V79 cells
Particles and cancer stem cells
• Cancer stem cells are resistant to photons• Recent in vitro studies have shown carbons ions more effect at killing then X‐rays– Stem cells in colon1 and pancreas2
• Neutron irradiation in glioma3 in vitro • Suggestion the same is true for low‐energy photons4,5
– Stem cells in colon and mammary
1. Cui et al. Cancer Res. 71: 3676 (2011)2. Oonishi et al. Radiother. Oncol 105: 258 (2012)3. Hirota et al. J Radiat Res. 2014 Jan 1;55(1):75‐83.5. Quan et al. Nucl. Instr. Meth B. 286: 341 (2012); 5. Fu . Nucl. Instr. Meth B. 286: 346(2012)
TISSUES AND FRACTIONATION:RBE AND HIGH LET
Isoeffect curves for photonsPre‐clinical studiesDashed line: acuteSolid line: late
Steeper responses for late‐responding tissues
Lower dose per fraction tends to spare late responding tissues
Withers, Thames & Peters, Radiother Oncol 1:187‐191 (1983)
Isoeffect curves for neutrons
Pre‐clinical studiesDashed line: acuteSolid line: late
Lesser effect of dose fractionation than seen with photons
Higher α/β
Withers, Thames & Peters, IJROBP 8:2071‐2076 (1982)
Change in isoeffect with dose fractionConclusionsLess effect of dose fractionation forhigh‐LET compared with photons
Photons: steeper late response reflects lower α/β
RBE minimum at high doses per fraction
Fig. 24.2 Basic Clinical Radiobiology (4th Edition Hodder Arnold) : Eds: Joiner and van der Kogel
Late effects in normal tissues• RBE of heavy ions for cataract induction is as high as 50 at doses less than 100 mGy1
• Data for induction of cancer in humans by protons or heavy ions is insufficient for the estimation of cancer– skin, harderian gland, mammary gland
• Skin: RBE values for single dose fractions (mouse and human) 1.3 for helium, 1.5 for carbon, 1.7 for neon, and 1.9 for argon peak ions2
• Mammary gland tumors in SD rats3
– Protons (250 MeV) were more effective than 60Co–rays1. Brenner et al. Radiat Res. 1991; 173: 73‐81 19912. Blakely and Chang, Cancer J. 2009; Jul‐Aug;15(4):271‐843. Dicello et al. Phys Med Biol. 2004; 49: 3817–3830
Carcinogenesis• Skin tumors in rats (Burns et al. 2007); tumors in hind limb (Ando et al. 2005), Hardarian gland in mice (Alpenet al. 1993), myeloid leukemia (Weil et al. 2009) and mammary tumors in rats (Dicello et al. 2004)
• Quantitative and qualitative differences in the RBE for different cancers, but RBE >1– Pathogenesis of specific tumor types– Initiation (mutations/chromosome aberrations or promotion (tissue inflammation)
– High LET produces chromosome aberrations but most are lethal
• Space studies: high HZE particles– Sridharan et al. Radiat Res. 2015 Jan;183(1):1‐26
ConclusionsBiological basis for high LET radiotherapy
• O2 differential radiosensitivity (OER) is reduced with high‐LET radiations due to “direct action” of damage– High‐LET more effective against hypoxic tumors
• Differential radiosensitivity of cell cycle reduced by high‐LET radiation– High‐LET more effective against slowly growing tumors
• Differential radiation response of cell types reduced with high‐LET compared with X‐rays– If tumor cells more resistant to x‐rays than critical normal tissues
– Comparative sensitization to a fixed level of damage