volumetric modulated arc therapy (vmat)

101 Pages·2012·1.27 MB·English

by  Swetha Oddiraju

VOLUMETRIC MODULATED ARC THERAPY (VMAT): ADVANCED DELIVERY
TECHNIQUES FOR STATIC AND MOVING TARGETS
_______________________________________
A Dissertation
presented to
the Faculty of the Graduate School
at the University of Missouri-Columbia
_______________________________________________________
In Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy
_____________________________________________________
by
SWETHA ODDIRAJU
Dr. Dharanipathy Rangaraj, Dissertation Supervisor
Dr. Lech Papiez, Dissertation Co-Supervisor
Dr. Sudarshan Loyalka, Dissertation Co-Supervisor

DECEMBER 2012
The undersigned, appointed by the Dean of the Graduate School, have examined the
dissertation entitled
VOLUMETRIC MODULATED ARC THERAPY (VMAT): ADVANCED DELIVERY
ALGORITHMS FOR STATIC AND MOVING TARGETS
presented by Swetha Oddiraju,
a candidate for the degree of Doctor of Philosophy,
and hereby certify that in their opinion it is worthy of acceptance.

Dr. Dharanipathy Rangaraj

Dr. Lech Papiez

Dr. Sudarshan Loyalka

Dr. Tushar Ghosh

Dr. Mark Prelas

Dr. Evan Boote

Dr. Lakshmi Santanam
ACKNOLEDGEMENTS

I would like to express my appreciation to my thesis advisor, Dr. Dharanipathy Rangaraj,
for his constant guidance, advice, and motivation to overcome any obstacles faced while
conducting this research. Furthermore, I extend my appreciation to my co-advisor, Dr.
Lech Papiez. I will forever consider myself fortunate to have his guidance through this
educational and life experience. I would also like to thank my co-advisor, Dr. Sudarshan
Loyalka for his endless support.

I would also like to thank my Ph.D. committee members: Drs. Tushar K. Ghosh, Mark
Prelas, Evan Boote and Lakshmi Santanam for their critical eye, support, advice, and
bountiful individual and collective knowledge. Finally, I would like to thank my family
and friends for always being there for me.

ii
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ................................................................................................ ii
LIST OF ILLUSTRATIONS ............................................................................................. iv
LIST OF TABLES ............................................................................................................ vii
Chapter
I. INTRODUCTION ....................................................................................................1
II. FUNDAMENTAL PROPERTIES OF THE DELIVERY OF VMAT TO STATIC
PATIENT AMATOMY ............................................................................................6
Medical Physics 37(8) 2010
III. GANTRY ACCELERATION CONSTRAINT FOR STATIC TARGETS ...........28
Medical Physics (Under review) 2012
IV. DELIVERY OF VOLUMETRIC MODULATED ARC THERAPY FOR
MOVING TARGETS ..............................................................................................45
Medical Physics 37(12) 2010

V. COMBINING MULTIPLE ARCS INTO A SINGLE ARC FOR DELIVERY .....58
Medical Physics (submitted) 2012

VI. DYNALOG BASED QA FOR RAPID ARC DELIVERY ....................................70
Journal of Medical Physics (submitted) 2012

VII. SUMMARY ............................................................................................................86
VIII. PUBLICATIONS ....................................................................................................92
VITA .......................................................................................................................93

iii
LIST OF ILLUSTRATIONS
Figure Page
2.1. Geometric representation of the relation amongst delivery parameters of a
VMAT plan for a given fixed g ............................................................................14
2.2. Gantry velocity profile comparing the Varian RapidArc delivery and the Optimal
VMAT delivery (with 467 MU) ...........................................................................18
2.3. Shows beam dose rate variation profile comparing the Varian RapidArc delivery
and the Optimal VMAT delivery of Plan 1 (with 467 MU as shown) .................20
2.4. Graph represents maximum leaf velocity among all leaves of MLC assembly for
the Optimal VMAT delivery ................................................................................21
2.5. The graph shows the dose rate profile for optimal constant gantry angular speed
(CGAS) delivery and dose rate profile for the Optimal VMAT delivery as
function of time .....................................................................................................21
2.6. The graph shows the gantry angular speed profile (pink solid line) for optimal
constant beam dose rate (CBDR) delivery and the gantry angular speed profile
for the Optimal VMAT delivery as function of time for plan 1 ...........................22
3.1. Logic flow of the gantry acceleration algorithm for VMAT delivery ..................34
3.2. Gantry speed profile with variable dose rate. Blue line indicates the gantry speed
without acceleration constraint and the green line indicates the same with the
constraint. Red dotted line represents maximum and minimum permissible gantry
acceleration ..........................................................................................................36
3.3. Gantry acceleration profile with variable dose rate. Blue line indicates the gantry
acceleration without acceleration constraint and the green line indicates the same
with the constraint. Red dotted line represents maximum permissible gantry
speed. The limitation for acceleration is set to 0.3degree/s2.................................37
3.4. Dose rate profile with variable dose rate. Blue line indicates the dose rate without
acceleration constraint and the green line indicates the same with acceleration
constraint. Red dotted line represents maximum permissible dose rate ...............38
iv
3.5. Gantry speed profile with constant dose rate. Blue line indicates the gantry speed
profile without acceleration limitation and the green line indicates the same with
acceleration limitation. Red dotted line represents maximum permissible gantry
speed. Maximum dose rate that is kept constant is 370 MU/min .........................39
3.6. Gantry acceleration profile for constant dose rate. Blue line indicates the gantry
acceleration without acceleration constraint and the green line indicates the same
with acceleration constraint. Red dotted lines represent maximum and minimum
permissible gantry acceleration ............................................................................39
3.7. Dose rate profile for constant gantry speed. Blue line indicates the dose rate for
variable dose rate delivery and the orange line indicates the same for constant
dose rate delivery. Maximum gantry speed is 3.7 degree/sec ..............................40
3.8. MLC opening area map with respect to gantry angle for optimal delivery with
and without acceleration constraint ......................................................................41
3.9. The graph illustrates the two stage computation of the admissible trajectories for
gantry rotation in arc therapy with acceleration constraint imposed on the gantry
motion ...................................................................................................................42
4.1. The target trajectory along the direction of the leaf motion .................................52
4.2. Gantry angular velocity as function of time .........................................................53
4.3. Dose rate as a function of time .............................................................................53
4.4. Speed of leaf travelling with maximal velocity ....................................................54
4.5. MLC aperture area as a function of gantry angle .................................................55
5.1. figure 1a shows the arc 1 with 4 degree gantry spacing, figure 1b shows the arc 2
which is offset by 2 degree and figure 1c shows the combined arc .....................63
5.2. Gantry Angle vs MU's for arc1, arc2 and combined arc ......................................64
5.3. Gantry angular velocity for the arc1, arc2 and combined arc ...............................65
5.4. Dose Rate with respect to time for the arc1, arc2 and combined arc ...................66
5.5. Gantry angular velocity profile for arc1, arc2 and combined arc with respect to
gantry speed ..........................................................................................................67
6.1. IMRT workflow ....................................................................................................73
v
6.2. Work flow of Dynalog QA using the Machine log files from the Linac console
and the DICOM-RT file from the treatment planning system ..............................75
6.3. Dose rate consistency plot ....................................................................................77
6.4. Gantry speed consistency plot ..............................................................................78
6.5. Fluence map comparison between planned and delivered fluence .......................79
6.6. MLC error of all the leaves with respect to the gantry angles ..............................80
6.7. MLC opening area with respect to gantry angles (planned vs delivered) ............81
6.8. Gantry angular velocity with respect to gantry angle. The dotted line represents
maximum permissible gantry speed which is 5.5 degree/sec ...............................82
6.9. Dose rate plot with respect to gantry angle. The dotted line represents maximum
permissible dose rate which is 600 MU/min ........................................................83

vi
LIST OF TABLES
Table Page
2.1. Delivery time comparison between Varian delivery with respect to optimal
delivery .................................................................................................................23
2.2. Treatment delivery time for 5 IMAT plans with optimal algorithm, Varian
delivery time, constant gantry speed and constant dose rate ................................23
3.1. Machine constraints for VMAT delivery .............................................................32
3.2. Treatment time for VMAT delivery. Column 3: no acceleration constraint and
Column 4: with acceleration constraint ................................................................35

vii
Chapter 1
Introduction

1
1.1. History of VMAT
Volumetric Modulated Arc Therapy (VMAT), formally known as Intensity
Modulated Arc Therapy (IMAT) was introduced by Cedric Yu (1995b)1. IMAT is a
rotational Intensity Modulated Radiation Therapy (IMRT) which can be delivered using
conventional linear accelerator with conventional multi leaf collimators (MLC). The
gantry is rotating continuously with the MLC leaves moving continuously while the
radiation beam is ON. Intensity modulation is created by overlapping arcs. Between 1995
till 20072, not much has been done with arc therapy. Linac manufacturers did not have
control systems to deliver IMAT. No treatment planning system was capable of offering
robust inverse planning tools for IMAT. Between 2008 till 20102, Elekta and Varian
came up with linear accelerators capable of delivering IMAT. Their main idea for IMAT
is that the dose rate, gantry speed and MLC leaf positions can be changed dynamically
during the delivery. The term VMAT has been adopted during this period and also first
commercial VMAT planning solutions were introduced.
VMAT is capable of producing conformal dose distribution in a short period of time
compared to conventional intensity modulated radiation therapy (IMRT). VMAT has
gained a greater popularity and interest in the recent times. The idea of IMAT is initially
explored by Brahme et al. Later more detailed analytical investigations at the level of
treatment planning had been carried out by Cormack and co-worker6-8, Tulovsky et al and
Ringor and Papiez9-11. In this work, he proposed the clinical use on linear accelerator to
produce conformal dose distribution. This method did not gain much interest until the
single arc version of the same, called VMAT, proposed by Otto has evolved because of
its simplicity and delivery efficiency compared to the method proposed by Yu et al12.
Along with these developments, commercial availability of VMAT such as Varian’s
RapidArc and Elekta’s VMAT products developed considerable momentum in clinical
applications. Rapid arc delivers treatments two to eight times faster than fastest dynamic
treatments today with increased precision which is a winning combination that enables to
improve the standard of case and treat more patients.
A VMAT plan is delivered by means of the gantry rotations: while the gantry is
rotating, beam aperture is changed continuously, and the dose rate and the gantry speed
are varied. VMAT can provide single or multiple arc delivery, coplanar or non-coplanar
2