ElShafie Handout SRS AVM for cAVM.pdf · MRA‐contour CBCT‐contour smaller than MRA‐contour...

05.11.2019

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Universitätsklinikum Heidelberg | RadioOnkologie und Strahlentherapie| Dr. med. Rami ElShafie

Dr. med. Rami El Shafie

Heidelberg Institute for Radiation Oncology(HIRO) Heidelberg University Hospital

Stereotactic Radiosurgeryfor intracerebral arteriovenous malformations

Agenda


• Indications for Radiosurgery

– Guideline recommentations

• Radiosurgery Techniques

– CyberKnife

– Proton Therapy

• Practical aspects of Radiosurgery

– Target Definition

– Dosimetric Evaluation

– Examples

INDICATIONS FOR STEREOTACTIC RADIOSURGERY


Interdisciplinary guidelines

– interdisciplinary AVM board

– consisting of neurosurgeons, neurointerventionalists, radiosurgeons, and neurologists experienced in the diagnosis and treatment of brain AVM

– primary strategy should be defined by the multidisciplinary team prior to the beginning of the treatment and should aim at complete eradication of AVM

– Balancing the risk of hemorrhage against the risks of treatment


Interdisciplinary guidelines

Frequent indications for stereotactic radiosurgery (SRS)

– risk factors for rupturing (e.g. history, deep location, deep venous drainage,…)

– symptoms, deficits

– unresectable, resection risky, patient wish

– embolization not possible

– complementing incomplete embolization


Efficacy of SRS

– Obliteration rates in literature:40‐90%

– strongly influence by prognostic factors

– average time to obliteration: 18months

– 90% chance of obliteration with a margin dose≥ 20Gy1

– between 12 and 22 Gy: approx. 25% increasein obliteration probability per Gy2

– larger nidus / larger margin dose= dose to healthy brain↑= complication risk↑

favorable prognostic factors:

• S‐M‐grade (I‐III)↓• nidus size↓• margin dose↑• (previous embolization)*• age↓• recent treatment

*complications ↑

unfavorable prognostic factors:

• S‐M grade↑• age↑• nidus size↑• ruptured AVM• eloquent location

largest publishedmeta‐analysis:– 142 cohors, 13.698 patients, of those 9.436 treated with SRS– median FU: 30 months

1 Lunsford LD, Kondziolka D, Flickinger JC, et al. Stereotactic radiosurgery for arteriovenous malformations of the brain. J Neurosurg. 1991;75(4):512‐524. doi:10.3171/jns.1991.75.4.0512.


2 Milker‐Zabel S et al. Proposal for a new prognostic score for linac‐based radiosurgery in cerebral arteriovenous malformations. IJROBP. 2012;83(2):525‐532.doi:10.1016/j.ijrobp.2011.07.008.

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RADIOSURGICAL TECHNIQUES / MODALITIES


A look at what‘s available…

CyberKnife+ robotic precision↑+ frameless

‐ treatment time↑‐ low dose↑

GammaKnife+ precision↑+ longestexperience

‐ frame‐based‐ treatment time↑‐ low dose↑

AdaptedLINAC+ availability↑+ cost↓

‐ frame‐based‐ precision↓‐ low dose↑

Protontherapy+ low dose↓+ large lesions

‐ availability ↓‐ cost↑‐ experience↓


robotic

patientcouch

stereoscopicX‐rays

(image guidance)

linearaccelerator

X‐ray detectors

Cyberknife M6 – stereotactic radiosurgery (SRS)

robot


The robotic approach

• Automated irradiation from multiple different angles “nodes” on a virtual sphere around the target.

• typically 200‐400 beams per session (vs. 10‐15 at conventional linac)

Images courtesy of Accuray Inc.


protons

photons

Why use protons?• inverted depth dose profile

• max. dose deposition at predefined depth „Bragg peak“

• less dose in entry‐ and exit trajectories

• problems:

– lateral scattering unsuitable for small lesions

– range uncertainties for matter with ↑↑or ↓↓ HU(e.g. air, metal, embolisate)1

.5cm


Proton SRS

– largest analyzed collective– n = 248, median FU = 35 mo– AVM‐volume (median) = 3.5 ml– Dose (median) = 15 GyRBE– Outcome: 64.6% CO, median time to CO = 31mo

– Pos. prognostic factors:• smaller volume, higher margin dose, higher

maximum dose– Neg. prognostic factors :

• deep location

Heidelberg experience with proton SRS:

– 22 Patienten with large cAVM treated since 2012, mostly since 2015

– AVM‐volume (median) = 7,7 ml

– Dose (median) = 17 GyRBE

– median Follow‐up at present < 18Monate

– Early obliteration for 6/22 Patienten (27%)

– longer follow‐up pending


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Are protons better?


publication n= media

n FU

median

AVM

volume

total CO

rate

median

time to CO

% COat

5 yrs

% CO at

10 yrs

Photon‐SRS

Milker‐zabel et al.,

IJROBP, 2012

293 50 mo 3,1 ml 48% 26,9 mo 55% ‐

Starke et al.,

JNS, 2013

1012 96 mo 3,5 ml* 69% ‐ n/a ‐

Colombo et al.,

Neurosurgery, 1994

153 43

mo*

‐ 86% ‐ 86% ‐

Pollock, Flickinger,

JNS, 2002

220 ‐ 4,1 ml* 66% ‐ ‐ ‐

Proton‐SRS

Hattagandi et al.,

IJROBP, 2014

248 35 mo 3,5 ml 65% 31 mo 70% 91%

Vernimmen et al.,

IJROBP, 2005

64 ‐ 16,3 ml 67%(<14ml)

43% (>14ml)

‐ ‐ ‐

Blomquist et al.,

Acta oncol., 2016

65 49 mo 3 68% ca. 54 mo 54% 69%

*mean

Conclusion:– no evidence for better or faster

efficacy of proton SRS

– but no directly comparativedata available

– relevant aspects, independentof efficacy:

• dose distribution(less low‐dose for large lesions!)

• patient age( protons advantageous forchildren!)

• treatment time(shorter with protons)

• location(e.g. radionecrosis risk ↑ with protons for periventricular lesions!)

TARGET DEFINITION


DynaCT, ConeBeam CT

significant reduction of the contoured nidus volume when using 3D rotational

angiography

CBCT‐contoursmaller thanMRA‐contour

CBCT‐contoursmaller thanMRA‐contour

lowsimilarity between contours

In Summe:


– no significant change in contour size

– median similarity only 52%

– relevant influence on dose distribution

– no influence on brain volume receiving more than 12 Gy (V12Gy)

Target definition

– 3D registration of all available imaging:

• treatment planning CT (for dose calculation)

• 3D‐CBCT / DynaCT

• MRT TOF (native + contrast)

• T1‐weighted sequence (a.e. MPRAGE, VIBE) for delineation of organs at risk

– Gross target volume (GTV):• visible nidus, excluding feeders

and veins– Planning target volume (PTV):

• GTV + 1 mm isotropic margin

– Dosepresciption:• 16 – 18 Gy @ 65%‐Isodose,

depending on size and location• prescription to the PTV


Zielvolumendefinition

Gross Target Volume (GTV) = green line

Planning Target Volume (PTV) = red line

margin dose = yellow line

PTV volume = 0.37ml

Gross Target Volume (GTV) = not visible

Planning Target Volume (PTV) = red line

margin dose = yellow line

PTV volume = 1.9ml


DOSIMETRIC EVALUATION


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Prospective treatment plan comparisonHeidelbergWorkflow:treatment planning for all AVM patients by prospective dosimetric comparison

target definition

structure set export

treatment plan calculation for CyberKnife and

protons

comparisonconsideringall

relevant aspects

decision ontreatmenttechnique

Decision criteria:

dosimetric criteria• conformity and dose gradient – High‐dose „spill“ surrounding targetvolume?• coverage – entire target covered? relevant for complex shapes andgeometries• mid‐ and low‐dose distribution – Comparison of V10Gy and V12Gy volumes• organs at risk –Which technique achieves better sparing of critical adjoining organs at risk?• beam trajectories – Are there relevant limitations? (e.g.embolisate,artefacts)

clinical criteria• treatment time – relevant for pa ents with clinical performance ↓, clasutrophobic patients• location – periventricular lesion? higher risk for necrosis with protons


Individual dosimetric comparison








Take home


• Stereotactic radiosurgery is an effective means of treating AVM, leading to obliteration rates of up to 90%.

• Precision is paramount to lower dose exposure of surrounding healthy brain and reduce risk of complications

• Choice of ideal treatment modality (e.g. CyberKnife, proton SRS) is influenced by different factors (size, shape, location,...) and done individually for each case.

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ElShafie Handout SRS AVM for cAVM.pdf · MRA‐contour CBCT‐contour smaller than MRA‐contour...

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