Radiobiological aspects of IORT with

Intrabeam Carsten Herskind, Ph.D.

Dept. of Radiation Oncology, Universitätsmedizin Mannheim (UMM)

Medical Faculty Mannheim, Heidelberg University, D-68167 Mannheim, Germany

e-mail: carsten.herskind@medma.uni-heidelberg.de

TARGIT Symposium, Herlev Hospital, 21st January 2015

Very large dose fractions in radiotherapy

Hypofractionated HDR Brachytherapy

Radiosurgery, Stereotactic Body/Ablative Radiotherapy (SBRT/SABR)

Intraoperative Radiotherapy (IORT)

IORT with

50 kV X-rays

IORT with electrons

3

A Novel Mobile Device for Intraoperative Radiotherapy (IORT) U. Kraus-Tiefenbacher Onkologie 2003; 26:596-5998

The INTRABEAM Intraoperative Device low-energy X-rays: 30-50 kV

Characteristics of IORT with Intrabeam X-rays Differences from External Beam RadioTherapy

Low-energy X-rays (50 kV vs 6 MV)

point source: intensity decreases with distance ( 1/dist2)

stronger energy absorption (attenuation), less penetration most of the dose is deposited in a small volume radiation quality: enhanced relative biologic effectiveness (RBE)

Lower dose rate

Repair of damage during protracted irradiation (20-50 min)

Single dose, no fractionation dose must be reduced

Effect on residual tumour cells ? Sparing of late-reacting normal tissue (NT) ?

No delay between surgery and RT

No repopulation of tumour cells during wound healing (~ 5 weeks)

5

Radiation quality: ionisation density

Linear Energy Transfer (LET):

Mean energy deposited per track length

- measured in keV/µm

10-40 keV photons: 4-6 keV/µm

i.e. an order of magnitude lower

than

Heavy particles: high-LET

typically 50-200 keV/µm

photon

scattered

photon

electron

-particle

~1000 tracks/Gy

3-4 tracks/Gy

Photons, electrons: low-LET

typically 0.2-2 keV/µm

Adapted from Goodhead, Health Phys (1988)

Low-energy X-rays deposit

a larger proportion of their

dose in electron track ends

Electron track ends (<1 keV):

Schematic electron track produced by 50 kV X-rays

Schematic electron track produced by 6 MV X-rays

10 keV electron

LET=2.3 keV/µm

Distance (nm) H. Nikjoo,

IFMBE Proceedings, Springer 2009

Goodhead, in Meyn, Withers,1980

Goodhead et al., Int J Radiat Biol., 1993

Herskind, Wenz, Transl. Cancer Res. 2014

Target molecule: DNA

http://en.wikipedia.org/wiki/File:ADN_animation.gif

Double helix ( 2.3 nm)

Sugar-phosphate backbone:

deoxyribose-phosphate

Base pairing: A T, T A

C G, G C

Induction and repair of DNA damage

e¯

OH OH

OH

OH For low LET:

~25% direct action

ionisation directly in DNA

~75% indirect action

via aqueous free radicals (OH)

Double-strand breaks ~ 40 per Gy

Single-strand breaks ~ 1000 per Gy

Base damage ~ 3000 per Gy

Lethal lesions ~ 0.5 per Gy

very efficient repair of most lesions

Residual, complex damage is important

9

Relative Biologic Effectiveness (RBE)

Cell survival curves

Su

rviv

ing

Fra

cti

on

(S

F)

Low LET High LET

Unirradiated Irradiated

RBE: Dref(MeV photons)/Dtest

RBE = ratio of physical doses

producing same effect

Dref = RBE Dtest M.C. Joiner in: Joiner & van der Kogel (Eds)„

Basic Clinical Radiobiology, 4th ed., 2009

Hall & Giaccia„ Radiobiology for the Radiologist, 7th ed., 2012 50kV X-rays

Clonogenic survival: surviving fraction (SF)

Su

rviv

ing

Fra

cti

on

(S

F)

Low LET High LET Quadratic component:

Reparable lesions

Linear component:

Irreparable lethal lesions

-ln(SF)= D+ D2

Shape of the survival curve: Linear-Quadratic

(2nd-order polynomial)

Various

biophysical

models Repairable

lesions

Cell death

Survival

Irreparable

lesions

repair

Damage fixation

Misrepair/no repair

Dose (Gy)

0 2 4 6 8 10 12 14 16

SF

1e-5

1e-4

1e-3

1e-2

1e-1

1e+0

1e+1

G=1.0

G=0.5

G=0.1

RBE for protracted irradiation with 50 kV X-rays

Dose (Gy)

0 5 10 15 20 25 30

SF

1e-10

1e-9

1e-8

1e-7

1e-6

1e-5

1e-4

1e-3

1e-2

1e-1

1e+050 kV acute

50 kV, G=0.5

Ref, acute

Repair during

irradiation

RBEacute

RBEprotracted

Radiation quality affects .

Continuous production and

repair of sublesions affects .

Lea-Catcheside time factor

-ln[SF(D)] = D+G(T) D2

continuous

protracted

acute

Split dose irrad.

12

Experimental determination of RBE in tumour-bed phantom in vitro

Spherical breast applicator (4.0 cm diam.):

RBE=1.35 [c.i. 1.2;1.5] in 8 mm distance from

applicator surface (2.0 cm from source)

Liu et al.(2013), Int J Radiat Oncol Biol Phys 85:1127-33

13

Anz. Fraktionen

0 10 20 30 40

SF

1e-8

1e-7

1e-6

1e-5

1e-4

1e-3

1e-2

1e-1

1e+0

2 Gy/Fx

4 Gy/Fx

D2=

48 Gy

D1=

62 Gy

no. of fractions Dosis (Gy)

0 2 4 6 8 10 12

SF

0.001

0.01

0.1

1

Einzeitdosis

2 Gy/Fx

4 Gy/Fx

single dose

Effect of fraction size on the surviving fraction (SF) in the Lin.-Quadr. model: SF = exp[-( d+ d2)]

L-Q model for fractionation:

-ln(SF) = -n ln(SF(d) = n ( d+ d2) = D+ dD

D: total dose (Gy)

n: number of fractions

d: Fraction size (Gy)

: lin. coefficient (Gy-1)

: quadr. coeff. (Gy-2)

Total dose, D [Gy]

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 20 40 60 80 100

P (

en

dp

oin

t)

Total dose (Gy)

d=2 Gy

d=3 Gy

d=6 Gy

Single dose

Is the L-Q model for isoeffective fractionation valid

for dose fractions >8-10 Gy ?

YES: Brenner et al.

Mechanistic basis

Several mech. models lead to L-Q

Good fit of SF up to 15 Gy

Works well for late reacting tissue

NO: Kirkpatrick et al.

Linear slope of SF at high doses

Mechanistic basis is not all

Effects of stroma, vasculature

Different cell kill modes at high doses

Subpopul. cancer stem-like cells

?

Semin. Radiat. Oncol. 18, 2008

EQD2=10Gy

0 20 40 60 80 100 120 140 160

Local con

trol

0

20

40

60

80

100

Single (liver)

3 Fx. (liver)

Single (lung)

3 Fx. (lung)

3 Fx. (lu./liv.)

Very large dose fractions have proved efficient in stereotactic body radiotherapy (SBRT)

Herskind, Wenz (2014):

Transl. Cancer Res. 3:3-17

Data from studies reviewed in Siva et al. (2010), J Thorac Oncol 5:1091-9

and Hoyer et al. (2012), Radiother Oncol 82:1047-57

Doses converted to equivalent dose given in 2 Gy/fx (EQD2) using the L-Q model

16

Modelling the biological effect of tumour bed

irradiation with Intrabeam

DoseINTRABEAM Doseref Biol. effect

RBE

Clinical

dose-response

fract. L-Q

model

Single-dose Single-dose

Strategy:

17

Total dose (EQD2: Gy)

0 20 40 60 80 100

TC

P

0.0

0.2

0.4

0.6

0.8

1.0

30% foci

small tumours

solid tumours

Dose response for different types of targets

The number of tumour cells matters

Modified after Herskind et al.: WC2009

IFMBE Proceedings 25/III, Springer, 2009.

18

EQD2

0 20 40 60 80

local

tum

ou

r c

on

tro

l0.5

0.6

0.7

0.8

0.9

1.0

conv. fract.

w/o repop.

Distance from applicator (mm)

0 5 10 15 20 25

Do

se (

Gy)

1

10

100

Dphys

(50 kV)

Disoeff

(ref.)

EQD2 (ref.)

RBE

Fractionation

Modelling the risk of recurrence (breast)

DoseINTRABEAM Doseref Biol. effect

RBE Dose-response

EQD2ref

fract.

L-Q

model Herskind et al. Int J

Radiat Oncol Biol

Phys 72 (2008)

For IORT, the probability of recurrence

increases as the absorbed dose decreases

with depth in the tumour bed. For external

beam RT, the probability is constant.

20 Gy single dose at the

applicator surface

Equivalent Dose EQD2= 67.8-73.0 Gy

Exceeds 50 Gy given in a standard

course of external beam radiotherapy

Sphere of equivalence in relation to excised

tumour plus 10 mm margin. The relative

dose and probability of recurrence are

given on the y-axis as function of distance.

Risk of Local Recurrence:

- “Sphere of Equivalence”

20

Clinical dose-response: Therapeutic window of complication-free tumour control

0.0

0.5

1.0

0 20 40 60 80 100

Dose (Gy)

Pro

ba

bil

ity

Tumour

control (TC)

Normal tissue

complication

complication-

free TC

Holthusen 1936

Small dose fractions widen the therapeutic window by

protecting the normal tissue relative to the tumor cells

The curves are displaced away from

the applicator surface and the

displacement is greater for the

larger diameters. ED50 is reached at

5.9-7.8 mm. The risk becomes

negligible at larger distances (lung)

For different applicator diameters the

probability of developing subcutaneous

fibrosis is the same. This end point

requires higher doses than pneumonitis,

the volume at risk for developing fibrosis is

smaller than that for pneumonitis

Herskind et al., Radiat. Res. 163 (2005)

Modelling calculations including the effect of recovery

Late effect probability after a single high dose

Pneumonitis Subcutaneous Fibrosis Pneumonitis Subcutaneous Fibrosis

Estimated extent of late reaction

under different assumptions for RBE

Pneumonitis is limited to ~ 10-12 mm distance even if RBE = 1.5

Thus the thorax wall offers sufficient protection of the lung

Subcutaneous Fibrosis Pneumonitis

Herskind et al., Radiat. Res. 163 (2005)

23

Electron IORT (uniform) : 21 Gy

50 kV IORT

(non-uniform):

max 20 Gy x RBE

Radiosurgery (e.g. brain, liver, lung)

i

v(i)/Vk

5022 1)(D(i)/NTDNTDP1

High doses may be

tolerated if the irradiated

volume is small:

Does not apply to serial

tissues !

Limiting the volume of irradiated normal tissue

1-p probability without necrosis

V total volume of brain

NTD2(i) normalised total dose à 2 Gy/fx

v(i) volume receiving NTD2(i)

NTD2(D50) NTD inducing 50% risk of necrosis

Flickinger,

IJROBP 17, 1989

Volume effect

Nairz et al., Strahlenther.

Onkol. 6, 2006

24

Radiobiological aspects of high single doses

Cellular response to large single doses Influence of radiation quality, dose protraction

Effects on DNA repair, genomic instability

Non-targeted (cohort) effects

Influence of the stroma, micromilieu Microvasculature, platelets, endothelial cells

Microenvironment, cytokines

Immunological effects Release and presentation of tumour-associated antigens (TAA)

Non-targeted effects in medium-transfer experiments

Conditioned medium (CM) from irradiated cells

(2 Gy) induces DNA DSB repair foci ( H2AX)

Burdak-Rothkamm et al. Oncogene 26 (2007); Cancer Res 68

(2008)

15 Gy CM induces H2AX foci

over many hours in MCF7

breast cancer cells and reduces

colony formation. Veldwijk et al., PLoS One 9(1) 2013

26

Role of microvascular endothelial cell apoptosis for

tumour growth and radiation-induced growth delay

Acid sphingomyelinase (asmase) ceramide endothelial apoptosis

Garcia-Barros et al., Science 300, 2003

Ch‘ang et al., Nat. Med. 11, 2005

Truman et al., PLoS One. 5, 2010

Induction of

ceramide

synthase

20 Gy 10 Gy 15 Gy MCA/129

asmase-/-

mice

w.t.

mice

27

Radiation-induced clotting of blood platelets: Thrombus formation

Maeda et al., PLoS One 7 (2012)

D=30 Gy

Dorsal Skin Fold Window Chamber

Red blood cells

Platelets

Micromilieu – Cytokines in Wound Fluid

MCF-7 in MATRIGEL

MDA-MB 231

PRE-Sera WF UNTR.

WF TARGIT

PRE Sera

WF UNTR

WF TARGIT

NIH CM

SFM PRE Sera

Irradiation with

a high single

dose changes

cytokine profile

in wound fluid

Invasion assay

Transwell

chemotaxis

assay

Belletti et al., Clin. Cancer Res. 14, 2008

29

Immunological effects

Irradiation of large volumes of blood and tissue is

immunosuppressive (kills lymphocytes)

However

IR also induces an inflammatory environment

Cytokines (IL1 , IL-6, TNF- ), chemokines

Endothelial adhesions molecules: ICAM-1, E-selectin, P-selectin

attracts antigen presenting cells (APC)

recruits T-cells to tumour

Immunological effects

IL-1, IL-6, TNF

Hs proteins

Chemokines

Adhesion mol.

Demaria, Formenti, Int.J.Radiat.Biol. 83, 2007

Demaria et al., IJROBP 63, 2005

Lugade et al., J. Immunol. 174, 2005

Herskind et al., Strahlenther. Onkol.

180, 2004; 174 suppl.3, 1998

antigen presenting cells (APC)

(dendritic cells, macrophages)

CD8+ T-cell

MHC-I

stromal cells Tumour-draining

lymph node

Tumour

cell

death

antigens

+ „danger“ signals

Homing: e.g. CCL5

ICAM-1, E-, P-selectin

tumour cells

IR

Activation

CD4+ (Th1) IL-2

IL-12

MHC-II

MHC-I

Overview: model of biological effects versus dose

Dose range

3-6 Gy > 8-10 Gy 25-30 Gy

Repair saturation Increased irreparable damage

Non-targeted effects

Decreased

prolif./invas.

Increased CIN Increased cell death, release of

Tumour-Associated

Antigens

Endothelial

apoptosis

Cells

Stroma,

micro-

milieu,

systemic

Cytokines

Antigen

presentation Thrombus

formation

Targeted/non-targeted effects

SUMMARY: single large dose vs. fractionation

Biophysics; L-Q formalism

RBE is increased for 50 kV X-rays; dose dependence not verified

L-Q model for fx. is a reasonable approximation up to ~15-20 Gy

Biological effects on residual tumour cells

IORT eliminates tumour cell repopulation before ext.beam RT

Sphere of Equivalence: high dose at applicator surface

Minimize NT volume to counter smaller therapeutic window !

Biological effects of high doses per fraction

Cellular radiation response (repair quality, non-targeted effects)

Effects of irradiated stroma (vascular effects, cytokines)

Immunological effects (increased antigen presentation)

33

Acknowledgements

Lab:

Miriam Bierbaum

Juliane Bradl, M.Sc.

Linda Hartmann, Ph.D.

Anne Kirchner

Junqi Liu, M.D.

Xiaolei Liu, M.Sc.

Patrick Maier, Ph.D.

Marlon Veldwijk, Ph.D.

Previous members

Qi Liu, Ph.D.

Lin Ma, Ph.D.

Nicole Roth

Bo Zhang, Ph.D.

Clinic, Physics:

F. Giordano, M.D.

U. Kraus-Tiefenbacher, M.D.

F. Schneider, Ph.D.

E. Sperk, M.D.

V. Steil, head physicist

Director: Prof. F. Wenz, M.D.

34

References

Herskind C, Steil V, Kraus-Tiefenbacher U, Wenz F (2005). Radiobiological aspects of intraoperative radiotherapy (IORT) with isotropic low-energy X rays for early-stage breast cancer. Radiat. Res., 163, 208-15

Herskind C, Schalla S, Hahn EW, Höver K-H, Wenz F (2006). Influence of different dose rates on cell recovery and RBE at different spatial positions during protracted conformal radiotherapy. Radiat. Protection Dosimetry 122 (Nos.1-4) 498-505

Herskind C, Griebel J, Kraus-Tiefenbacher U, Wenz F (2008). Sphere of equivalence – a novel target volume concept for intraoperative radiotherapy using low-energy x rays. Int. J. Radiat. Oncol. Biol. Phys. 72:1575-81

Herskind C, Wenz F (2009). Is there more to intraoperative radiotherapy (IORT) than physical dose ? Int J Radiat Oncol Biol Phys 74:976-977

Herskind C, Ma L, Liu Q, Wenz F (2009). Biological Effect of Single, Very Large Dose Fractions as used in Intraoperative Radiotherapy (IORT), O. Dössel and W.C. Schlegel (Eds.): WC2009, IFMBE Proceedings 25/III, Springer, 18-21

Herskind C, Wenz F (2010). Radiobiological comparison of hypofractionated accelerated partial breast irradiation (APBI) and single-dose intraoperative radiotherapy (IORT) with 50 kV x rays. Strahlenther. Onkol. 186:444-51

Liu Q, Schneider F, Ma L, Wenz, F, Herskind C (2013). Relative Biologic Effectiveness (RBE) of 50 kV X-rays Measured in a Phantom for Intraoperative Tumor-Bed Irradiation. Int J Radiat Oncol Biol Phys. 85:1127-33

Veldwijk MR, Zhang B, Wenz F, Herskind C (2014) The biological effect of large single doses: a possible role for non-targeted effects in cell inactivation. PLoS One 9:e84991

Herskind C, Wenz F. (2014). Radiobiological aspects of intraoperative tumour-bed irradiation with low-energy X-rays (LEX-IORT). Transl Cancer Res 3:3-17

35

Replacing multiple fractions of conventional RT with

a single large dose

multiple fx single dose

Therapeutic window narrower (NT ?)

4 R‘s of radiotherapy

Repair less (tumour/NT ?)

Redistribution none (resistant cells ?)

Reoxygenation none (hypoxic cells ?)

Repopulation none (tumour/NT ?)

The biological effect of high doses per fraction

may differ from the effect of 2 Gy daily fractions