Plan evaluation in RADIOTHERAPY

MANAGEMENT OF DIFFUSE GLIOMAS
4/5/2022 1
DR KANHU CHARAN PATRO
MD,DNB(RADIATION ONCOLOGY),MBA,FAROI(USA),PDCR,CEPC
HOD,RADIATION ONCOLOGY
Mahatma Gandhi Cancer Hospital And Research Institute, Visakhapatnam
drkcpatro@gmail.com M-9160470564
Plan evaluation in high technique radiotherapy

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Basics of plan evaluation - Steps

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Basics of plan evaluation – standardizing names

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Basics of plan evaluation – Immobilization

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Basics of plan evaluation – errors

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Basics of plan evaluation – GTV-CTV-ITV-PTV

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Basics of plan evaluation – OAR

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Basics of plan evaluation - Different plans

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Basics of plan evaluation – Adaptive radiotherapy

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Basics of plan evaluation – 3D vs beamlet

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Basics of plan evaluation – BEV vs REV

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Basics of plan evaluation
– isocentric vs nonisocentric

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Basics of plan evaluation
2d verification vs 3d verification

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Basics of plan evaluation – hexapod couch
ROLL
YAW
PITCH

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Basics of plan evaluation – FFF vs no FFF

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Basics of plan evaluation – review your contour

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Basics of plan evaluation – Notes to physics

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Basics – DVH

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Basics of plan evaluation – Michael Goitein

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Basics of plan evaluation – PIXEL and VOXEL
In 3D computer graphics, a voxel represents a value on
a regular grid in three-dimensional space. As with pixel in a 2D

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Basics of plan evaluation – Voxel And Pixel

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Basics of plan evaluation – Differential DVH
1. The generic form of any histogram, displaying the volume of the
organ that receives dose within each bin (1% or 0.5 to 1 Gy is a
typical dose bin width.
2. It is useful for display of the dose to target volumes, because one
can easily visualise the minimum dose, the maximum dose, and
the most representative of the dose to the entire target volume.

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Basics of plan evaluation – Grid
1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8
1.8 1.8 2 2.1 2.1 2.1 2.1 2.1 1.8 1.8
1.8 2 2 2.1 2.1 2.1 2.1 2.1 2 1.8
1.8 2 2 2.1 2.1 2.1 2.1 2.1 2 1.8
1.8 2 2 2.1 2.1 2.1 2.1 2.1 2 1.8
1.8 2 2 2.1 2.1 2.1 2.1 2.1 2 1.8
1.8 1.8 2 2 2 2 2 2 1.8 1.8
1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8

0
5
10
15
20
25
30
35
40
0-1.5 1.8 2 2.1
Chart Title
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Basics of plan evaluation – differential histo
Dose bin Counts
0-1.5Gy 0
1.8Gy 36
2Gy 18
2.1Gy 26
Total 80
V
O
L
U
M
E
In
CC
Dose in Gy

0
10
20
30
40
50
60
70
80
90
0-1.5 1.8 2 2.1
Chart Title
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Basics of plan evaluation – Cumulative Histo
Dose bin Counts Cum
0-1.5Gy 0 80
1.8Gy 36 80
2Gy 18 44
2.1Gy 26 26
Total 80 0
V
O
L
U
M
E
In
CC
Dose in Gy

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Basics of plan evaluation – CUMULATIVE DVH
1. Volumes receiving at least a given dose value are ploted.
2. The cumulative DVH integrates the direct histogram, so it
always begins at 100% (100% of the organ receives at least 0
dose)
3. It ends at maximum dose

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Basics of plan evaluation – Analyzing DVH

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Basics of plan evaluation – ICRU

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Basics of plan evaluation – DVH

• D50% (Median Dose)
• Most representative of prescribed dose
• Dmean is nearly identical to D50%
• D98% (Near Minimum Dose)
• Dose received by 98% of PTV
• D2% (Near Maximum Dose)
• Dose received by 2% of PTV
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Basics of plan evaluation – Defining the dose

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Basics of plan evaluation – Defining the dose

PUSHING BACKWARD AND FORWARD AT A TIME
DIFFICULT BUT NOT IMPOSSIBLE
OAR
TARGET
36

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Basics of plan evaluation – DVH pitfalls
1. Insensitive to hot spot and cold spot
2. Shape of DVH alone can be misleading
3. DVH is the most direct and informative representation of a treatment
plan available
4. 3D dose distribution are large and cumbersome to analyse quantitatively
5. User interactivity is essential to extract the most information from dose
distribution.
6. Clinical studies have shown that DVH metrics correlate with patient
toxicity outcomes.
7. A drawback of the DVH methodology is that it offers no spatial
information; i.e., a DVH does not show where within a structure a
dose is received.
8. Also, DVHs from initial radiotherapy plans represent the doses to
structures at the start of radiation treatment.
9. As treatment progresses and time elapses, if there are changes
(i.e. if patients lose weight, if tumors shrink, if organs change
shape, etc.), the original DVH loses its accuracy

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Basics of plan evaluation – plan evaluation

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Basics of plan evaluation – mlc and cone

Basics of plan evaluation – RVR
1. For plan optimization, additional
dose may be
dumped in RVR.
2. High absorbed dose in RVR

Basics of plan evaluation – FLASH vs BOLUS

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Basics of plan evaluation – dose displaying
1. Isodose Contours: Set of closed contours linking voxels of equal
dose
2. Color Wash: The coding of CT and Dose in the same voxel through
the modulation of both intensity (CT) and color (Dose)
3. Isodose Surfaces: The Shaded surface (pseudo 3D) representation
of the dose level and selected VOI

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Basics of plan evaluation – CBCHOP
Mary Dean/Applied Radiation Oncology/2017

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Basics of plan evaluation – COSID INDEX
Patro K C/Journal of Current Oncology/2022(UNDER REVIEW)
C
COVERAGE INDEX
O
OAR INDEX
S
SPILLAGE INDEX
I
IMAGING INDEX
D
DELIVERY INDEX

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Basics of plan evaluation – Coverage Index
PTV/CTV/GTV
D2/D98
95-107

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Basics of plan evaluation – OAR INDEX
Max dose in series organ
Mean dose in parallel organ
Volumetric analysis

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Basics of plan evaluation – Spillage Index
Conformity index
Homogeneity index
Gradient index

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Basics of plan evaluation – Imaging Index
Axial view
Coronal view
Sagittal View

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Basics of plan evaluation – Delivery index
Complexity of plan
MU
Complexity of Delivery

SL NO PARAMETER VALUE
1 D MAX 36.43Gy
2 D95% 31.01Gy
3 D100% 28.23Gy
4 V95% 99.99%
5 V30 Gy[V100%] 99.56%
6 V110% 44.45%
7 V120% 0.03%
8 V130% 0%
1. Prescription Isodose level is usually not 100% PD covering 100% PTV
2. Often 95% PD covering 95% PTV or higher
3. Or 100% PD covering 95% PTV or higher.
Michael Torrens,/J Neurosurg (Suppl 2)/2014
PTV coverage index

• Is your desired defined dose is confined to PTV ?
• FORMULA
• VOLUME OF PRESCRIPTION ISODOSE/PTV VOLUME
• 43.798/37.491=1.17
• DESIRABLE=1
[Sonja Petkovska
Proceedings of the Second
Conference on Medical Physics and
Biomedical Engineering]
RTOG conformity index

• FORMULA
(VOLUME OF PRESCRIPTION ISODOSE IN AREA OF INTEREST)2
PTV VOLUME X VOLUME OF PRESCRIPTION ISODOSE
• =39.764 x 39.764 /37.494 x43.798 =0.96
• IDEAL= > 0.85. AND <1
Michael Torrens,/J Neurosurg (Suppl 2)/2014
Paddick conformity index

• How homogeneous your dose inside the PTV?
• FORMULA
• MAXIMUM DOSE/PRESCRIPTION DOSE
• 36.43Gy/30Gy=1.21
• DESIRABLE = 1.1-1.3
HOMOGENITY index

• Dose fall off observation is very much needed in
this evaluation under headings
• Gradient index
• Difference between various isodose lines
• e.g between 80% and 60%- ideal- <2mm
• Between 80% and 40%- ideal- < 8mm
• For that reason, we must calculate equivalent
radius
Dose fall off

• To evaluate dose gradient, we must find out
difference between radius of various isodose
line
• But none is iso spherical
• We must find out equivalent radius from
formula
• First find out the specified isodose volume
• Then calculate the radius
• V=4/3 πr3
• r= (3V/4π)1/3
Equivalent radius

SL NO PARAMETER VOLUME RADIUS
1 100% ISODOSE 43.79CC 2.19mm
2 80% ISODOSE 64.45CC 2.49mm
3 60% ISODOSE 101.19CC 2.89mm
4 50% ISODOSE 130.84CC 3.15mm
5 40% ISODOSE 177.96CC 3.49mm
r= (3V/4π)1/3
Equivalent radius

• FORMULA
• Difference of equivalent radius of prescription isodose
and equivalent radius of 50% isodose
• 2.19mm-3.15mm=0.96mm
• It should be between 0.3 to 0.9
Gradient index

• BETWEEN 80% AND 60%- IDEAL-<2mm
• HERE- 0. 4mm
• BETWEEN 80% AND 40%- IDEAL- <8mm
• HERE- 1mm
EORTC-22952-26001
Distance between various isodose lines

Isodose line
COLOUR ISODOSE LINE
Dark green 100%
Light green 80%
Sky green 60%
Pink 50%
Blue 40%
ISODOSE LINES

SL NO ORGAN DESIRABLE ACHIEVED
1 RT. EYE MAX <22.5Gy 1.97Gy
2 LT. EYE MAX <22.5Gy 4.4Gy
3 RT. OPTIC NERVE MAX <22.5Gy 2.3Gy
4 LT. OPTIC NERVE MAX <22.5Gy 5.5Gy
5 OPTIC CHIASM MAX <22.5Gy 7.5Gy
8 BRAIN STEM MAX 23-31Gy 10.01Gy
9 RT. COCHLEA MEAN <25Gy <1Gy
10 LT. COCHLEA MEAN <25Gy <1Gy
GG HANNA/CLINICAL ONCOLOGY/2016
OAR coverage

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Basics of plan evaluation – junction volume
Accept under dosage in one of the Subvolumes

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Basics of plan evaluation – Low dose bath

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Basics of plan evaluation – Beam arrangements

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Basics of plan evaluation – BEAM entry exit point

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Basics of plan evaluation – misleading DVH

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Basics of plan evaluation – Check list

TRAIN YOUR BRAIN TO
DECREASE THE DOSES TO OARS
STRACTURES BUT NOT AT THE
COST OF PTV
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Take care of OAR otherwise rare
will not be rare

RESTRAIN YOURSELF FROM GIVING
STRICT CONSTRAIN OTHERWISE
TUMOR WILL SUSTAIN.
4/5/2022 70

Plan evaluation in RADIOTHERAPY

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