Step-by-Step Stereotactic Radiotherapy Planning of Vestibular Schwannoma: A Guide to Radiation Oncologists—the ROSE Case (Radiation Oncology from Simulation to Execution)

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DOI:
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Address for correspondence: Dr. Kanhu Charan Patro,
Department of Radiation Oncology, Mahatma Gandhi Cancer Hospital and
Research Institute, Visakhapatnam, Andhra Pradesh, India.
E-mail: drkcpatro@gmail.com
Received: 25 October 2021; Revised: 10 November 2021;
Accepted: 17 November 2021; Published: 23 February 2022
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How to cite this article: Patro KC, Avinash A, Pradhan A,
Venkatramana P, Kundu C, Bhattacharyya PS, et al. Step-by-step
stereotactic radiotherapy planning of vestibular schwannoma: A guide
to radiation oncologists—the ROSE case (Radiation Oncology from
Simulation to Execution). J Curr Oncol 2021;4:68-75.
Original Article
Step-by-Step Stereotactic Radiotherapy Planning of Vestibular
Schwannoma: A Guide to Radiation Oncologists—the ROSE
Case (Radiation Oncology from Simulation to Execution)
Kanhu Charan Patro, Ajitesh Avinash1
, Arya Pradhan1
, Pamidimukkala Venkatramana2
, Chittaranjan Kundu, Partha Sarathi Bhattacharyya,
Venkata Krishna Reddy Pilaka, Mrutyunjayarao Muvvala Rao, Arunachalam Chithambara Prabu3
, Ayyalasomayajula Anil Kumar3
, Srinu Aketi3
, Parasa Prasad3
,
Venkata Naga Priyasha Damodara, Veera Surya Premchand Kumar Avidi, Mohanapriya Atchaiyalingam, Keerthiga Karthikeyan, Voonna Muralikrishna
Department of Radiation Oncology, Mahatma Gandhi Cancer Hospital and Research Institute, Visakhapatnam, 1
Department of Radiation Oncology, Acharya Harihar
Post Graduate Institute of Cancer, Cuttack, Odisha, 2
Department of Neurosurgery, Pinnacle Hospital, Visakhapatnam, 3
Department of Medical Physics, Mahatma
Gandhi Cancer Hospital and Research Institute, Visakhapatnam, Andhra Pradesh, India
Abstract
Background: Vestibular schwannoma (VS) is a slow-growing tumor that represents 90% of all tumors at the cerebellopontine angle.
One of the main modalities of the treatment is stereotactic radiotherapy (SRT). Here, we describe procedure details for stereotactic
planning of VS. Methods: The step-by-step procedure for stereotactic planning of pituitary adenoma has been described using a clinical
scenario of VS. Results: The stereotactic radiation planning of VS starts with the basic history and relevant evaluation of symptoms
such as tinnitus, dizziness, and facial symptoms. Magnetic resonance imaging (MRI) of the brain is the imaging modality of choice.
The radiation planning of VS starts with computed tomography (CT) simulation and MRI of the brain that should be performed in
prescribed format to achieve uniformity in radiation planning. After CT and MRI fusion, contouring of target, organs at risk (OAR),
and radiation planning should be performed. The plan evaluation includes target and OAR coverage index, conformity, homogeneity
and gradient index, and beam arrangement. After radiation plan evaluation, treatment is delivered after quality assurance and dry
run. Conclusion: The article highlights the sequential process of radiation planning for SRT of VS—starting from simulation to
planning, evaluation of plan, and treatment.
Keywords: Acoustic neuroma, radiotherapy planning, SRS, SRT
Introduction
Vestibular Schwannoma (VS), also known as acoustic
neuroma, is a benign neoplasm with an annual
incidence of one in one lakh. It accounts for 6%–7%
of all brain tumors.[1]
This neoplasm is usually seen
at the cerebellopontine angle. MRI of the brain is the
best imaging modality for the diagnosis of this tumor.
The treatment of VS includes observation, surgery, or
stereotactic radiation in the form of stereotactic radio
surgery (SRS) or SRT. In this article, the various steps
of radiation planning for SRT have been illustrated in
an easy way for the beginners who are planning for SRT
in a case of VS.
Methods
In this paper, the various steps of radiation planning for
SRT have been illustrated in an easy way for the beginners
who are planning for SRT in a case of VS with the help of
a clinical case as described below.
[Downloaded free from http://www.journalofcurrentoncology.org on Wednesday, February 23, 2022, IP: 10.232.74.27]

Patro, et al.: SRS ROSE case Vestibular Schwannoma
Journal of Current Oncology ¦ Volume 4 ¦ Issue 2 ¦ July-December 2021 69
A 40-year-old male presented with the chief complaints
of tinnitus for six months, a slight decrease in hearing,
dizziness, and facial fasciculation and twitching for three
months. There was no associated facial numbness.
A patient with symptoms of tinnitus, dizziness, facial
fasciculation, and twitching must be evaluated using
the Tinnitus Handicap Inventory, Dizziness Handicap
Inventory and House-Brackmann Scale for facial nerve
functioning, respectively.[2]
On evaluation of the present
case, the patient had grade II tinnitus using the Tinnitus
Handicap Inventory and grade II dizziness using the
Dizziness Handicap Inventory, as is depicted in Table
1. On speech audiometry, the patient had a speech
discrimination score (SDS) of 90% in the right ear and 95%
in the left ear. On Pure-Tone Audiometry examination, the
pure tone average was 35 dB for the right ear and 22 dB
for the left ear. With the above pure tone average (dB) and
the SDS, the patient was found to have grade II hearing
loss of the right ear, that is, the hearing of the right ear
was serviceable as per the Gardner-Robertson grade.
The facial nerve functioning was evaluated by House-
Brackmann Scale. The patient had a normal resting
tone with slight weakness in appearance, that is, grade II
whereas forehead, eyes, and mouth were normal, that is,
grade I as is shown in Table 1.
Imaging
On imaging by computed tomography (CT) scan of the
brain, there was a widening of the right acoustic porous
with an ice-cream on cone appearance. The lesion was
minimally enhanced, touching the brainstem without any
bony involvement [Figure 1A]. The FSPGR sequence of
magnetic resonance imaging (MRI) of the brain revealed
a fairly well-defined lobulated moderately enhanced
extra-axial lesion with altered signal intensity in the right
cerebellopontine angle cistern measuring 21 mm x 16 mm
Table 1: Tinnitus, dizziness grading system Gardner–Robertson grade, and House–Brackmann scale for vestibular schwannoma
Tinnitus handicap inventory
Grade Descriptions The present case has grade II tinnitus
I No tinnitus
II Intermittent or mild tinnitus, can only be heard when the ambient noise is low
III Persistent or moderate tinnitus, can be heard everyday
IV Persistent and severe tinnitus, interfere with work and sleep
Dizziness handicap inventory
Grade Descriptions The present case has grade II dizziness
I No dizziness or imbalance
II Occasional and mild dizziness or imbalance
III Persistent or moderate vertigo or imbalance
IV Persistent and severe dizziness or imbalance, disturbing daily life
Gardner–Robertson grade
Grade Hearing level Pure Tone
Average (dB)
Speech discrimination score (%) The present case had serviceable hearing
loss in the right ear, that is, grade II
I Good to excellent 0–30 70–100
II Serviceable 31–50 50–69
III Non-serviceable 51–90 5–49
IV Poor 91–maximum 1–4
V None/Deaf Non-testable 0
V None/Deaf Non-testable 0
House–Brackmann scale for evaluation of facial nerve function
Grade Appearance Forehead Eye Mouth The present case had grade II appearance,
grade I: forehead, eye, and mouth
I Normal Normal Normal Normal
II Slight weakness normal
resting tone
Moderate
to good
movement
Complete closure
minimal effort
Slight
asymmetry
III Nondisfiguring weakness
normal resting tone
Slight to
moderate
movement
Complete closure
maximal effort
Slight weakness
maximal effort
IV Disfiguring weakness
normal resting tone
None Incomplete
closure
Asymmetric
with maximal
effort
V Minimal movement
asymmetric resting tone
None Incomplete
closure
Slight
movement
VI Asymmetric None None None


70 70 Journal of Current Oncology ¦ Volume 4 ¦ Issue 2 ¦ July-December 2021
x 13 mm, with an intra-canalicular extension being 11 mm
x 9 mm [Figure 1B]. The lesion appeared hypointense on
both T1- and T2-weighted sequence; there was minimal
hyperintensity on FLAIR sequence and it was touching
the brainstem. Superiorly, the lesion was indenting the
cisternal component of the right V cranial nerve and
the right superior cerebellar artery. Laterally, the lesion
was indenting the right middle cerebellar peduncle and
the adjacent portion of the right cerebellar hemisphere.
The right VII and VIII cranial nerves were not separately
visualized from the lesion. There was no significant mass
effect on the right IX, X, and XI cranial root complex and
no significant effacement of the fourth ventricle. The Fast
Imaging Employing STeady-state Acquisition (FIESTA)
sequence showed the ice-cream cone appearance of
the lesion that was impending the fifth cranial nerve
[Figure 1C]. The features cited earlier were suggestive of
right-sided VS.
Grading of Vestibular Schwannoma
TherearevariousgradingsystemsforVS,suchasKoosgrading
system, House grading system, and Samii grading system.[2]
In the present case, as the tumor was reaching the brainstem
surface but not deforming the brainstem surface or shifting
the fourth ventricle, the tumor was grade III as per Koos
grading system, grade III as per House grading system, and
T3b as per Samii grading system as is seen in Table 2.
Line of Treatment
The treatment of VS includes observation, surgery, SRS,
or SRT.
Surgical Consultation
NeurosurgicalopinionfavoredhearingpreservationastheVII
and VIII cranial nerve roots not separated out on imaging.
Figure 1: CT and MRI images of Vestibular Schwannoma. (A) CT scan of the case depicting widening of the acoustic porous. (B) FSPGR sequence
of the same patient showing the lesion at the right cerebellopontine angle. (C) FIESTA sequence of the same patient showing the lesion impending
the fifth cranial nerve
Table 2: Tumor grading in vestibular schwannoma
Tumor description Tumor
size (CPA
maximum
diameter)
Stekers House Koos Smaii Present case
Confining to IAC 0 (intra-
canalicular)
Tube
type
Intra-canalicular I T1 Tumor size
10mm, House
Grade 3,
Koos grade III
and
Samii T3b.
Surpassing IAC ≤ 10mm Small Grade 1 (small) II T2
Tumor-occupying CPA ≤ 15mm Grade 2
(medium)
T3a
≤ 20mm Mild
Tumor-occupying CPA and contacting the brain stem
without compression
≤ 30mm Grade 3
(moderately
large)
III T3b
Tumor compressing the brain stem ≤ 40 Large Grade 4 (large) IV T4a
Severe brain stem displacement and deformation of the
fourth ventricle under tumor compression
40mm Huge Grade 5 (giant) T4b

Points in Favor of Choosing Radiation
The tumor was very small (maximum size 2.1 cm), solid and
the VII and VIII cranial nerves were not visualized separately.
The preservation of hearing and facial nerve functions were
the salient points that were the main reasons of choosing
radiation for this patient. As per the ISRS practice guidelines,
SRS was opted because it fulfilled the criteria of tumor
diameter 3 mm, no or mild brain stem compression.[3]
Treatment Decision by the Tumor Board
The patient details were put in the tumor board for a
decision regarding the line to treatment. After a group
discussion with the neurosurgeon, the radiation oncologist
and the board decided to plan for SRT.
Discussion with the Patient
The patient was explained about the bouquet of treatment
options, such as observation, surgery, and radiotherapy, and
the complications and outcome of each procedure. Further,
the radiation treatment procedures, hearing preservation,
imaging, and follow-up were also explained to the patient.
Counseling of the Patient
The patient was counseled regarding the tumor response
to radiation, the need for surgery in the future, and post-
radiotherapy pain.
Patient’s Preference
The patient opted for radiation, as his major concerns
were hearing preservation and trigeminal and facial nerve
weakness besides tumor control.
Dose Selection
As per ISRS practice guidelines, there is a strong consensus
to treat a newly diagnosed small size VS with single-
fraction SRS. In case of tumor abutting, the trigeminal
nerve fractionated SRT can be preferred.[4]
As per the
University Hospital of Wales protocol, a hypofractionated
SRT should be used in a VS case abutting the trigeminal
nerve.[4]
Thus, it was planned to conduct fractionated SRT
for this patient with a marginal dose of 25Gy in 5fractions
@ 5Gy/fraction as per the two guidelines cited earlier.
Decision of Radiotherapy Tumor Board
Fractionated radiotherapy was planned to a marginal
dose of 25Gy in 5fractions @ 5Gy/fraction as per the
ISRS practice guidelines.
Radiotherapy Planning
Here, we describe the steps of treatment of VS from
simulation to plan execution
Step 1: Computed tomography simulation
During simulation, the patient was set up in the supine
position with a neutral neck position and immobilization
was done using FRAXION thermoplastic mask and
a stereotactic frame [Figure 2A and B]. Fiducials were
placed on the thermoplastic mask after proper alignment
with the lasers. Intravenous contrast was given at a dose of
1ml per kg body weight. Then, a CT scan was taken from
the vertex to the neck with a CT slice thickness of 1 mm, as
is depicted in Table 3. After simulation, the DICOM CT
images were sent to our Oncentra server, which was then
imported for delineation of the target and organ at risk.
Step 2: Magnetic resonance imaging protocol
MRI of the brain of the patient was done using a 512 x 512
matrix in the neutral neck position similar to that of the CT
scan during simulation with no gap, no tilt, and a 1-mm slice
thickness as depicted in Table 3. The field of view included
the body contour along with nose, eyes, and skull. The MRI
should include the usual T1, T2, FLAIR sequences. In
addition, the 3D FSPGR was used for viewing the normal
anatomy. The cochlea, brainstem, and cranial nerves were
visualized in FIESTA sequence, and GRE sequence was
used to find out any cystic changes or hemorrhage. If a
dedicated MR simulator is available, MR simulation can be
done using this MRI protocol and the simulation process is
the same as the CT simulation mentioned earlier.
Figure 2: Immobilization of the patient using the stereotactic thermoplastic mask and frame during CT simulation in lateral view (A), the cranial view
(B), and Fusion of MRI of the patient with planning CT scan (C)


Step 3: Image fusion
These acquired MRI sequences were fused with the
planning CT scan by contouring the eyes, lens, basilar
artery, and sinuses, and calcification and matching was
done using the auto-fusion technique to help in the target
and organ at risk (OAR) delineation [Figure 2C].
Step 4: Target delineation
The gross tumor seen on the CT images that was fused
with the MRI images to consider the exact extension of the
tumor was delineated as GTV. The PTV was drawn, taking
1 mm around the GTV. Smoothing of the contour was done
from the adjacent bone. Multi-planar evaluation, that is, the
evaluation of both the GTV in all the three planes—axial
[Figure 3A], coronal [Figure 3B], and sagittal [Figure 3C]
and PTV—was done in all the three planes: axial [Figure
3D], coronal [Figure 3E], and sagittal [Figure 3F].
In the present case, the GTV volume was 1.682cc and the
PTV volume was 2.766cc.
Step 5: Organ at risk delineation
The OARs for delineation included the cochlea,
brainstem, trigeminal nerve, optic chiasma, and optic
apparatus.Thecochleawascontouredinthebonewindow
setting whereas other OARs, that is, the brainstem,
trigeminal nerve, optic chiasma, and optic apparatus,
were contoured using the MRI that was fused with the
planning CT.
Step 6: Radiotherapy technique
Radiation planning can be done using any of the RT
techniques, such as Intensity Modulated Radiotherapy
(IMRT), Volumetric Modulated Arc Therapy (VMAT),
Dynamic Conformal Arc Therapy (DCARC), or
3-Dimensional Conformal Radiotherapy (3DCRT)
according to the convenience of the radiation physicist
and physician.
In the present case, planning was done using the VMAT
technique.
Step 7: Plan evaluation
After the completion of planning by the physicist, the
evaluation for the treatment plan is done using the
following indices as noted next.
Table 3: CT simulation and MRI Protocol to be followed for
vestibular schwannoma
CT simulation protocols for simulation
Supine position
Immobilization using stereotactic thermoplastic mask
Intravenous contrast at a rate of 1 mg/kg
CT scan taken from the vertex to the neck
1-mm slice thickness
MRI protocol Utility
T1/T2/FLAIR sequence Usual sequence
3D FSPGR sequence Normal anatomy
FIESTA sequence Visualization of cochlea, brainstem,
and cranial nerves
GRE sequence To see any cystic changes/ hemorrhage
512 x 512 matrix
1 mm slice thickness
No gap
No tilt
Neutral neck
Field of view should include body contour, nose, eye, and skull
Figure 3: Delineation of the GTV (pink) of Vestibular Schwannoma in the axial (A), coronal (B), and sagittal plane (C) and PTV (cyan) generation
around the GTV taking 1 mm margin in the axial (D), coronal (E), and sagittal planes (F)

PTV coverage index
After the planning, we need to see the PTV coverage.
The prescription isodose level is usually not 100% of the
prescribed dose covering 100% of the PTV. Often, the 95% of
the prescription dose should cover 95% or higher percentage
of the PTV; otherwise, 100% of the prescription dose should
cover 95% or higher percentage of the PTV.[5]
Inthepresentcase,95%of theprescriptiondosecovers100%
of the PTV and 100% of the prescription dose covers 97.5%
of the PTV, which meets the earlier mentioned parameters
for the PTV coverage and is depicted in Table 4.
Intracranial stereotaxy organ constraints and organ at risk
coverage
Keeping in mind the desirable dose constraints to the
OAR, we need to check the dose to individual OARs.[6]
The dose desirable and dose achieved for all the OARs in
the present case is depicted in Table 5.
Conformity index
To note the conformity index of the SRS, here we used 2
types of conformity indices, that is, the RTOG conformity
index and the Paddick conformity index.[5,7]
RTOG Conformity index (CIRTOG
) is calculated using the
following formula:
CIRTOG
= Volume of Prescription Isodose / PTV volume
In this case of VS, the RTOG conformity index was 1.15
[Table 4].
Paddick conformity index (CIPaddick
) was calculated using
the following formula:
CIPaddick
= (Volume of prescription isodose in the area of
interest i.e. PTV)2
/ PTV volume x Volume of Prescription
Isodose
Here in the current case, Paddick conformity index was
1.02 [Table 4].
Homogeneity index
It is calculated using the formula:
Homogeneity Index = Maximum Dose/ Prescription Dose
In this case, the Homogeneity Index was 1.19 [Table 4].
Dose fall off
The dose fall off observation is very much needed in the
plan evaluation under the heading of gradient index. For
this we need to calculate the difference between various
isodose lines. In order to calculate the difference between
the isodose lines, we need to calculate the equivalent radius.
Equivalent radius calculation
To evaluate the dose gradient, we have to find out the
difference between the radius of various isodose lines.
However, none of the isodoses are spherical. So, we
use the following formula to calculate the equivalent
radius:
1st
: Find out the specified isodose volume
2nd
: Calculate the radius of the isodose volume by using
the formula:
V = 4/3 π r3
r = (3V/4 π)1/3
The calculation of the volume and radius of various
isodose lines in the present case is shown in Table 4.
Gradient index
The formula for calculating gradient index is as
given next.
Table 4: Various indices plan evaluation of vestibular
schwannoma in the current case
Parameter Value Desirable
Dmax 29.83Gy –
D95% 25.25Gy –
D100% 24.18Gy –
V95% 100% –
V25Gy (V100%) 97.5% –
V110% 18.26% –
V120% 0 –
V130% 0 –
PTV volume 2.776cc –
Volume of prescription isodose 3.214cc –
Volume of prescription isodose
within the PTV
3.03cc –
Maximum dose 29.83Gy –
Prescription dose 25Gy –
RTOG conformity index 1.15 1
Paddick conformity index 1.02 0.85–1
Homogeneity index 1.19 1.1–1.3
Parameter Volume Radius
100% isodose line 3.214cc 0.91 mm
Table 5: Individual OARS with its desirable dose and dose
achieved in the current case of vestibular schwannoma
Organ Desirable dose (Gy) Achieved
dose (Gy)
Right eye DMax
22.5 1
Left eye DMax
22.5 1
Right optic nerve DMax
22.5 1.2
Left optic nerve DMax
22.5 1
Optic chiasma DMax
22.5 2.8
Brainstem DMean
23–31 27.19
Right cochlea DMean
25 20.35
Left cochlea DMean
25 1.31


Gradient Index = Equivalent radius of 50% isodose –
Equivalent radius of prescription isodose. Ideally, the
gradient index should be between 0.3 mm and 0.9 mm.
In the current case, the gradient index is
1.83 mm–0.91 mm = 0.92 mm, which is close to the ideal
gradient index.
Distance between various isodose lines
The various isodose lines are depicted in Figure 4A.
The ideal difference between 80% and 60% isodose lines
should be 2 mm.[8]
In the current case, it is 1.65 mm–1.32 mm = 0.33 mm.
The ideal difference between 80% and 40% isodose lines
should be 8 mm.
In the present case, it is 2.06 mm–1.32 mm = 0.74 mm.
Beam arrangement
The arrangement of the beams [Figure 4B–D] was
done such that there is adequate coverage of the target
while giving a lower dose to the OARs. It should be
noted that the beams should not pass through the
ipsilateral eye.
Step 8: Quality assurance
A mechanical isocenter check was done using the Winston
Lutz test, and the point dose verification was done while
maintaining the tolerance as 1 mm.[9]
Step 9: Dry run
Treatment verification consists of setup reproduction,
isocenter verification, and clinically verifying each
treatment field: check beam clearance, check any
interlock, MLC interlock and potential Monitor Unit
(MU) problems, and then clearly mark the immobilization
devices after a successful dry run.
Step 10: Premedication protocol
Prior to the start of the treatment premedication was
delivered in the form of tablets as described next: all
starting the day before the start of RT treatment.
Figure 4: Isodose lines: 100% (red), 80% (green), 60% (yellow), 50% (blue), and 40% (pink) in (A) and beam arrangement in axial (B), coronal (C),
and sagittal view (D) for the current case of Vestibular Schwannoma

Tablet Dexamethasone 8 mg thrice daily
Tablet Ondansetron 8 mg thrice daily
Tablet pantoprazole 40 mg once daily
If thepatientisdiabetic,properdiabeticcareneedstobedone.
Step 11: Set up verification and treatment delivery
It includes cone beam CT correction [Figure 5A] and
hexapod corrections [Figure 5B]. After all the corrections
are done, the treatment is delivered.
Step 12: Postmedication
It is an optional protocol that usually includes antiemetics,
proton pump inhibitors, and tapering the dose of steroids
over a week.
Step 13: Advice and follow-up
After the completion of the treatment, the patient was
usually advised to follow up after six months for imaging.
Radiotherapy outcome grading for the VS was done as
per the consensus in the 7th International Conference on
acoustic neuroma.[2]
Supplementary File
Here, we also provide the VS SRS Plan Evaluation sheet as
a supplementary file that will help in proper and accurate
plan evaluation for every SRS case of VS.
Conclusion
This article conceptualizes and acts as an easy guide
for the beginners for the stereotactic radiation planning
for VS.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
References
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Figure 5: Treatment verification. (A) Cone beam computed tomography correction of the patient during the treatment. (B) Hexapod correction of the
same patient during the treatment

VESTIBULAR SCHWANNOMA SRS PLAN EVALUATION
1. NAME UMR
2. COMORBIDITY AGE
3. DIAGNOSIS SIDE
4. IMAGING A. SIDE AND SIZE
B.
INTRACANALICULAR PART LENGTH
C.
BRAINSTEM COMPRESSION
D.
TRIGEMINAL COMPRESSION
E. BONY EROSION ON CT
F. HYDROCEPHALUS
G. 7/8TH
NERVE STATUS
5. KOOS GRADING I II III IV
6. GARDNER-ROBERTSON HEARING
GRADES
I II III IV V
7. HOUSE-BRACKMAN SCALE OF
FACIAL FUNCTION
I II III IV V VI
8. TINNITUS GRADING I II III IV V
9. VERTIGO GRADING I II III IV V
10. ANY TRIGEMINAL / PAIN
DISTRIBUTION
PAIN
SCORE
11. SURGERY OPINION
12. PATIENT PREFERENCE
13. PRIOR SURGERY YES NO TYPE INTERVAL
14. PRIOR SRS YES NO DOSE INTERVAL
15. CTV VOLUME PTV MARGIN PTV
VOLUME
16. PLAN TYPE-[3DCRT/VMAT/DCR/
IMRS]
17. MONITOR UNITS
18. 1. PRESCRIBED MARGINAL ISODOSE
2. D MAX
3. D95%
4. D100%
5. V95%
6. V100%
7. V120%
8. V130%
9. DISTANCE BETWEEN 80% ISODOSE AND 60% ISODOSE-[2mm]
10. DISTANCE BETWEEN 80% ISODOSE AND 40% ISODOSE-[8mm]
11. CONFIRMITY INDEX [IDEAL 1] VOLUME OF PRESCRIPTION ISODOSE/VOLUME OF PTV
12. HOMOGENITY INDEX [BETWEEN 1.1–1.3] - MAX DOSE/ PRESCRIPTION DOSE
13. GRADIENT INDEX- [BETWEEN 0.3–0.9] [RAD OF PRESCRIPTION ISODOSE – RAD OF HALF PRESCRIPTION
ISODOSE]
19. BRAIN-GTV [12Gy volume] 10CC [4Gy volume] 20CC-MULTIPL FRACTION
20. OAR SINGLE FRACTION 5 FRACTIONS ACHIEVED
1. RIGHT EYE MAX8Gy MAX 22.5Gy
2. LEFT EYE MAX8Gy MAX 22.5Gy
3. RIGHT OPTIC NERVE MAX8Gy MAX 22.5Gy
4. LEFT OPTIC NERVE MAX8Gy MAX 22.5Gy
5. OPTIC CHIASM MAX8Gy MAX 22.5Gy
6. BRAIN STEM MAX 15Gy MAX 31Gy
7. RT. COCHLEA MEAN 9Gy MEAN 25Gy
8. LT. COCHLEA MEAN 9Gy MEAN 25Gy
Supplementary file

Step-by-Step Stereotactic Radiotherapy Planning of Vestibular Schwannoma: A Guide to Radiation Oncologists—the ROSE Case (Radiation Oncology from Simulation to Execution)

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