Ординатура / Офтальмология / Английские материалы / Primary Optic Nerve Sheath Meningioma_Jeremic, Pitz_2008

108

B. Jeremić, M. W. Wasik, S. Villà, F. Paulsen, G. Bednarz, D. Linero and M. Buchgeister

MRI scans of the brain every 6 months, then every 12

Contrast-enhanced CT data are obtained in the frame

months.

with a localization cage attached. The patient is removed

Gross Tumour Volume (GTV) was defined on MRI

from the frame and a gadolinium enhanced MR scan is

images, fused to the orbital CT scans. GTV comprised

obtained next. Both imaging datasets are electronically

the tumour alone and not the entire optic nerve. No

transferred to the treatment planning workstation where

margin was added to the GTV to create CTV or PTV.

they are fused into one composite image for treatment

Normal structures which were routinely contoured in-

planning purposes. Due to the high spatial fidelity of

cluded the optic nerves, optic chiasm, eye globes and

CT data, the CT dataset is an obligatory imaging dataset

lenses. The maximum allowed dose to the optic chiasm

for treatment planning. The patient is discharged home

was in the range of 54–57 Gy, depending on the circum-

and returns for treatment inception usually a week to 10

stances. Dose Volume Histograms (DVH) were always

days later. In the X-Knife system the dose is delivered by

used to assess the dose distribution to the GTV and

using the arc rotation of the linac radiation beam around

normal organs.

the linac isocenter. Beam collimation is accomplished

using circular collimators (cones) ranging from 0.5 cm

10.3.1.1.1

to 5 cm in diameter. For single isocenter treatment, the

treatment planning relays on selecting the cone size,

X-Knife-based SRT with Relocatable Frame

which covers the target and placing a number of arcs

and Multiple Isocenter Technique

to deliver the radiation dose (Fig. 10.2). For irregular

For X-Knife-based SRT, the pre-treatment patient prep-

targets multiple cones, each placed at a new isocenter,

can be combined to cover the target (Fig. 10.3). Adjust-

aration involves the customized design of a lightweight

ing the placement, lengths and weights of the arcs and

relocatable frame – the Gill-Thomas-Cosman (GTC)

the weights of the isocenters, can shape the dose cloud

frame (Kooy et al. 1994) , which is a large “halo” de-

(Fig. 10.4).

vice that is attached to the patient with custom molded

Because of the linear shape of ONSM, the X-Knife

devices that fit into the oral cavity (based on dental

treatmentPROOFSplanning and delivery necessarily involved

impression of patient’s upper dentition) and conform

multiple overlapping isocenters. This created dose inho-

to the shape of the occipital region at the back of the

D

Emogeneity along the axis of the optic nerve. With the

head (Fig. 10.1). Day-to-day accuracy of the GTC frametadvent of the Novalis unit, we have since adopted treat-

can be verified using a special device called the “depthC

ments based on a single isocenter which are much more

conformation helmet”, a plastic hemispherical shellEthat

efficient and which yield much higher dose homogene-

allows for the measurement of the distanceRbetween

ity along the axis of the optic nerve with dynamic arc

the shell and the head surface at a numberRof locations.

technique.

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Fig. 10.1. The Gill-Thomas-Cosman relocatable frame

Fig. 10.2. X-Knife treatment with single collimator and mul-

tiple arcs of various lengths and orientations

Stereotactic Radiation Therapy in Primary Optic Nerve Sheath Meningioma

109

Fig. 10.3. For irregular targets, such as ONSM, multiple cones,

Fig. 10.4. X-Knife treatment with multiple isocenters for

each placed at a new isocenter, can be combined to cover the

ONSM. The dose cloud is shaped by adjusting the isocenters

target

weight and arcs lengths, placements and weights

10.3.1.1.2

anteriorPROOFScomponents. In addition to the two anterior

The BrainLab/Novalis SRT System

parts, a special nose bridge is molded from thermoplas-

with Mini-multileaf Collimator

D

Etic beads to minimize head rotation during reposition-

ting. All components are mounted on a U-shaped metal

Patients can be treated on the Novalis system eitherCus-

frame and locked together with a set of plastic clips

ing the GTC frame or a multi-component thermoplasE

-

with adjustable spacers to allow for the mask shrinkage

tic head mask (BrainLab, Germany), which Ris custom-

(Fig. 10.5a). The Novalis treatment-planning worksta-

fitted to the shape of the patient’s head (GeorgR

et al. tion provides a number of planning options ranging

2006). The mask consists of one posterior shell and two

from dynamic arc treatment, to conformal static arcs or

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N

a

b

110

B. Jeremić, M. W. Wasik, S. Villà, F. Paulsen, G. Bednarz, D. Linero and M. Buchgeister

stereotactic IMRT (Solberg et al. 2001). At our insti-

tution, most treatment plans involve a single isocenter

treatment with five non-coplanar arcs utilizing the dy-

namic arc method. With micro-multileaf collimation,

this technique allows for both high target conformality

and high dose homogeneity (Fig. 10.5b).

We published our initial results of SRT for ONSM

involving 33 optic nerves in 30 patients in 2002 (An-

drews et al. 2002). The median prescription dose was

51 Gy (range: 50.4–54 Gy) and the median follow-up, 21

months. Of 22 optic nerves with vision before SRT, 20

nerves (92%) demonstrated preserved vision and 42%

manifested improvement in visual acuity and/or visual

fields. Four patients (13%) had post-treatment morbidi-

ties, including visual loss (two patients), optic neuritis

(one patient) and transient orbital pain (one patient). At

Fig. 10.7. Early improvement in visual acuity in a patient with

the time of publication, no tumour progression was re-

right ONSM treated with SRT

ported on MRI scans. Six patients were monitored with

111In-octreotide scintigraphy which demonstrated sig-

nificant metabolic responses following SRT.

10.3.1.2

Most recently, we updated our experience (up

to 2006) to include a total of 50 patients with ONSM

BrainLAB technique (Barcelona, Spain)

(manuscript in preparation). Follow-up data were avail-

Since 2000 this technique has been available at de-

able for 38 patients (one treated to both eyes), with 12

lost to follow up. Five patients had no light perception

D

partmentsPROOFSof Radiation Oncology of Centro Médico

in the involved eye on presentation (one lost to FU).

Teknon-CMT, and Catalan Institute of Oncology-ICO,

Among the remaining 34 patients with vision on pre-

Eboth in Barcelona, Spain.

sentation, 20 (59%) experienced improvement in visualt

Radiation therapy planning was done in several

acuity and/or visual fields and 11 (32%) had stableCvi-

phases:

sion, for a total of 31/34 (91%) preserving vision.EThree

1. Immobilization with triple thermoplastic mask

patients (9%) had worse vision, in one case attributedR

to

(Figs. 10.8a,b–10.11a,b). Material for positioning is

tumour progression. One of the two remainingR received

composed by head resting-place that includes head-

SRT with the BrainLab system.

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rest, mask ring, screws for fixing vertical posts and

N

cam locks to put into cube for checking coordinates.

Two cases below illustrate an improvement in visual

fields (Fig. 10.6) and an early visual acuity improvement,

The non-invasive triple mask (top, rear, and middle

u

mask) enables precise and easy repeatable patient

occurring during the SRT course and within 3 months

from SRT completion (Fig. 10.7). Such an early effect is

fixation. The mask of thermo-transformable material

not rare and it is difficult to explain biologically.

is individually moulded for each patient and secured

to the mask ring (BrainLAB 2000; Villà et al. 2000;

Brell et al. 2006). Mask should be heated in water

to 70–80 °C. Different steps are needed to mould

the entire mask. Patient’s head is left and snap the

mask onto the upper side of the vertical posts and

put down onto the headrest. In approximately 1 min

mask material is hardening. After that, middle mask

is placed in the centre of the middle’s face, carefully

stretched. A T-shaped form nose bridge mould is

added to the middle mask using rolled loose pellets

after heating to optimize head fixation. The next step

is to place the top mask centrally over the patient’s

Fig. 10.6. Humphrey automated perimetry (24-2 central

face ensuring that the curve in the mask is placed

threshold) of left visual field in patient with left ONSM at pre-

towards the patient’s mouth, but does not cover it.

treatment (left) and at 11 months after SRT (right)

Top mask is secured by clips. Different clips and

Stereotactic Radiation Therapy in Primary Optic Nerve Sheath Meningioma

111

a

b

Fig. 10.11. a Head fixation using a triple thermo-plastic mask

detected. b Lenses defined on each control CT scan (drawn in

at time of treatment. Arrow shows a plastic clip (with five dif-

different colours) and the respective lenses defined on the plan-

ferent thickness from 0 mm to 4 mm). It permits a comfort-

ning CT after CT-to-CT skull registration (Miralbell et al.

able positioning for every patient regarding change of weigh

2007)

(for corticosteroids or malnutrition). No errors in precision are

spacers are needed to adapt size and head anatomy

and projected on to the respective CT sets. CT scans

for every patient and fix rear mask to top mask. An

are used for dosimetric calculations.

additional dental support strip for superior maxil-

D

PROOFSDefinition of target volumes (GTV=CTV, and

lary fixation is added to improve its quality.

PTV) could be done in any of images (only CT scan

Position of ocular balls. Eyes should be closed

E volume definition is very useful in some patients;

for simulation and treatment. Patients are requiredt

see Fig. 10.12). GTV and CTV are defined as the

to close gently both eyes on MRI scan and onCCT

whole optic nerve due to the difficulty to separate

scan, and for every session thereafter. WithEthis

tumour itself of the rest of nerve in many cases. PTV

simple movement, we reported that marginsR

of

is defined with a margin of 3 mm (Miralbell et al.

3 mm around the target may be necessaryR to safely

2007). As a rule, all the following OARS have to be

CO

defined: retina, contra-lateral optic nerve, chiasm,

treat these tumours under ideal set-up conditions.

N

lens, brain-stem, lachrymal gland, and pituitary.

Experience from ocular melanoma was translated

to ONSM (Miralbell et al. 2007). As can be seen

3.

Dosimetry. Any of the facilities from TPS could be

u

used such as conventional circular arc radiosurgery

in Fig. 10.11, lenses for ipsilateral affected eye was

used to be defined on each control CT scan and the

(RS), dynamic arc RS, conformal RS using multiple

respective lenses defined on the planning CT after

static shaped beams (Fig. 10.13), and IMRS imple-

CT-to-CT skull registration.

mented by either static or dynamic micro multi-leaf

2. Co-registration of CT and MRI. After cranial immo-

collimator (mMLC) techniques (Fig. 10.14). The

bilization, all patients underwent a planning CT scan

so-called m3 mMLC “moulds” target shape in any

with fiducial rods attached to the head frame. CT im-

angle and field (beam eye view).

ages are obtained from the scalp vertex through the

4. Dose. Prescribed total dose ranges between 50 and

brain using 2–3 mm thick slices (acquisition time is

54 Gy at ICRU point, 25–30 fractions, 1.8–2 Gy per

of 30–40 s) and transferred to the treatment plan-

fraction, once a day (Fig. 10.15).

ning system (TPS), BrainScan 5.1 (BrainLAB A.G.,

5.

OARS. Contra-lateral optic nerve, chiasm, lens,

Heimstetten, Germany). Contrast for CT is used in

lachrymal gland, pituitary, brain-stem, and retina

some cases. CT to MRI registration is performed for

are systematically drawn (Fig. 10.15).Optimal or-

each patient by automatic alignment of bone struc-

gan dose constraints are as follows: retina: 50 Gy;

tures on the two image sets. Target volumes and or-

lens: 9 Gy; optic nerve and chiasm: 55 Gy; lacrymal

gans at risk (OARs) are defined on the MR images

gland: 30 Gy

Stereotactic Radiation Therapy in Primary Optic Nerve Sheath Meningioma

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Stereotactic Radiation Therapy in Primary Optic Nerve Sheath Meningioma

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10.3.1.3

mobilisation systems deal with the whole treatment

university of tuebingen, Germany Approach

unit including a visualisation tool (CT) at the LINAC

At Tuebingen, conformal radiotherapy of optic nerve

and a robotic table also being able to compensate for

rotational errors.

sheath meningioma has been performed with 6-MV

For the approach described in the following section,

photons and a conventional fractionation scheme at a

a rigid relocatable immobilisation mask system with a

linear accelerator (LINAC) employing a non-invasive

mean accuracy of 0.8 ± 0.6 mm is used. In an analysis of

rigid mask immobilisation system designed at the Ger-

our first patients 95% of all absolute measures were less

man Cancer Research Center, Heidelberg, since 1993

than 2.8 mm for transition to the LINAC and 4.6 mm

(Schlegel et al. 1992; Becker et al. 2002a). Treatment

during treatment (Kortmann et al. 1999). The isocen-

planning precedes an interdisciplinary board discussing

ter setup is performed with a stereotactic localization

the indication and target extension for treatment. The

system described in Becker et al. (2002a) using ste-

target volume comprises the gross visible optic nerve

reotactic coordinates. Stereotactic coordinates are used

sheath tumour. If this is not clearly distinguishable, the

for the transfer of the isocenter to the patient within the

whole optic nerve (GTV) covering the anatomical re-

immobilisation mask. The process of treatment plan-

gion of ophthalmological functional deficits, enlarged

ning starts with the building of the special removable

by necessary safety margins of the used mask immo-

immobilisation mask system. The mask is made of cast

bilisation system represents the planning target volume

material. For its creation the patient lies supine on a

(PTV). Organs at risk (OARs) in close vicinity such as

treatment couch with his head resting in an extension

chiasm, optical nerve, eye globes, lenses, brain stem or

made of two curved wooden plates around which the

the brain itself are segmented in the planning computed

cast material is rolled (Fig. 10.20). The extension is

tomography (CT) slices. The treatment planning is

necessary to avoid dosimetric disturbances due to the

performed with a commercial planning system (Helax

treatment couch for posterior entry portals or collision

TMS) employing non-coplanar, wedged and individu-

between gantry and couch. This enables a wide range

ally shaped small treatment portals. A fractionation of

of non-PROOFScoplanar beams. After hardening of the material

5 × 1.8 Gy/week up to 54 Gy is used. The immobilisation

(about 30–45 min) the mask is cut from chin to above

of the patient to treat this vulnerable region has to be

D

Ethe ear region to allow the patient to leave and re-en-

optimised for the correct daily beam application. Sevt-

ter the mask (Fig. 10.21) with reasonable comfort. For

eral principles can be used to achieve this goal. A Crela-

planning and treatment the mask is closed with simple

tively simple method is the usage of a rigid maskEsystem

fixation locks at each side. The patient holds an emer-

with well known immobilisation errors thatRare taken

gency trip wire to be able to release the mask fixation

into account in the definition of the PTV. TheRindividual

locking (Fig. 10.20).

set-up control is described below. More advanced im-

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N

u

Fig. 10.20. Mask made of casting material rolled around wood-

Fig. 10.21. Jaw of the mask and patients’ entrance into the

en plates, removable fixation for the patients’ emergency exit

mask

116

B. Jeremić, M. W. Wasik, S. Villà, F. Paulsen, G. Bednarz, D. Linero and M. Buchgeister

During treatment planning a diagnostic MRI and

the beams’ eye view function of the RTP. The treatment

the planning CT are fused (e.g. by mutual information

plan is iteratively optimized to achieve a dose distribu-

algorithms) in the radiation treatment planning system

tion according to the guidelines defined by the ICRU

(RTP) and checked by an experienced radiation oncolo-

50 report. PTV and OARs define the geometry of each

gist. A stereotactic localisator, that is mounted over the

field such that 95% of the prescribed dose surrounds

fixation mask (Fig. 10.22) defines the stereotactic coor-

the PTV. An experienced treatment planning team usu-

dinate system for the patients’ anatomy inside the mask.

ally achieves a homogeneous dose distribution for the

The planning CT includes the whole head from the top

PTV. The dose to brain stem, chiasm or optical nerves

of the scull to the neck to allow for the planning of non-

should not exceed 54–55 Gy in 1.8-Gy fractions, the

coplanar treatment beams and to estimate the beam

dose to the other OARs being as described above in this

direction inside the body (Fig. 10.23). The slice thick-

chapter. Usually 5–6 wedged fields are used. The posi-

ness is in the range of 2–3 mm in the region of the PTV

tion of the isocenter for treatment is defined within the

to get adequate resolution of the different small sized

stereotactic localisator at the CT. Three translations are

organs. As the planning CT and a high resolution MRI

given to move the patient from the stereotactic coordi-

is co-registered for target volume definition, a contrast

nate (0;0;0) to the coordinates of the isocenter (X;Y;Z)

media enhanced planning CT is not also necessary. Sec-

(Fig. 10.25) at the set-up for treatment. The z-coordinate

ond, due to the rigid mask system, there is a higher risk

is defined by the distance “A” of the metal markers at the

for severe complications in case of allergic reactions

surface of the stereotactic localisation tool (Figs. 10.22

3.6 Gy, the PTV is reduced by adding only 2 mm safety

trolled PROOFSbefore treatment by comparison of the block’s

to the contrast media when such a CT is taken. After

and 10.25). Two orthogonal verification beams of stan-

co-registration of the planning CT and the MRI, tar-

dardized field size of 8 × 8 cm2 are created and digital

get volumes (GTV, organs at risk) are delineated. The

reconstructed radiographs (DRR) are printed for fol-

PTV is generated by adding 5 mm to the GTV for the

lowing setup verifications at the LINAC. Individualized

treatment plan that is used for the first 28 fractions up

shielding is achieved by usage of conventional shielding

to 50.4 Gy (Fig. 10.24). For the boost of an additional

blocks made of MCP96. Every shielding block is con-

margin around the GTV.

D

light field shape at the LINAC with the scaled beam’s

Optimal beam angles are determined during the

Eoutline printed on paper (Fig. 10.26). The deviation of

C

radiation treatment planning process with the help oftthe resulting field has to be in a clinical acceptable range

E

R