Dosimetric Comparison of Inverse Planning by Simulated Annealing

102 Pages·2014·2.1 MB·English

by  Bereket Ghebremichael

Dosimetric Comparison of Inverse Planning by Simulated Annealing (IPSA) and Dose
Points Optimized Treatment Plans in High Dose Rate (HDR) Brachytherapy of Skin
Lesions Using Freiburg Flap Applicator
by
Bereket Tewolde Ghebremichael

A Thesis submitted to the Faculty of
The Charles E. Schmidt College of Science
in Partial Fulfillment of the Requirements for the Degree of
Professional Science Master

Florida Atlantic University
Boca Raton, Florida
December 2014
Copyright 2014 by Bereket Tewolde Ghebremichael

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Acknowledgments
I would like to express my utmost gratitude to my Thesis Advisor Zoubir Ouhib,
MS, DABR, of Lynn Cancer Institute of Boca Raton Regional Hospital and Research
Affiliate Associate Professor in the Physics Department at FAU, for providing me expert
guidance in completing this research, for his mentorship and help in my clinical practices,
and also for the countless invaluable professional advises he imparted in me.
I would also like to express my sincere gratitude to my Thesis Co-Advisor Dr.
Theodora Leventouri, Professor of Physics and Director of the Professional Masters in
Medical Physics program at FAU, for providing me invaluable guidance in my studies in
the program. I am sincerely thankful for the tireless work she did in directing and
structuring the Medical Physics program from its inception just a few years ago to its
recent CAMPEP accreditation.
I am eternally grateful to Dr. Silvia Pella for her endless support during my
studies in the program. She knows no bounds in helping her students grow as medical
physicists. Many thanks also go to Georgios Kalantzis for his expert input in preparing
the final version of the Thesis.
Lastly, I would like to thank Charles Shang and Jeremy Cole of Lynn Cancer
Institute for selflessly offering me their time and mentorship whenever I stepped my foot
into the Institute to do clinical practice. My special gratitude extends to Jeremy for help
he offered during data collection for the research.
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Abstract
Author: Bereket Tewolde Ghebremichael
Title: Dosimetric Comparison of Inverse Planning by Simulated
Annealing (IPSA) and Dose Points Optimized Treatment
Plans in High Dose Rate (HDR) Brachytherapy of Skin
Lesions Using Freiburg Flap Applicator
Institution: Florida Atlantic University
Thesis Advisor: Zoubir Ouhib, MS, DABR
Degree: Professional Science Master
Year: 2014

A detailed dosimetric comparison between Inverse Planning by Simulated
Annealing (IPSA) and Dose Points (DP) optimized treatment plans has been performed
for High Dose Rate (HDR) brachytherapy of skin lesions using Freiburg Flap applicator
in order to find out whether or not IPSA offers better clinical dosimetric outcomes for
lesions categorized into four different curvatures. Without compromising target coverage,
IPSA reduced the volume of Planning Target Volume (lesion) that received at least 125%
of the prescription dose on average by 41%. It also reduced the volume of the healthy
skin surrounding the lesion that receives at least 100% of the prescription dose on
average by 42%. IPSA did not show any advantage over DP in sparing normal structures
underlying the lesions treated. Although DP optimization algorithm has been regularly
used at Lynn Cancer Institute for HDR brachytherapy of skin lesions, recent upgrades in
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IPSA software have made IPSA more amenable to rapid treatment planning and therefore
IPSA can be used either in place of DP or as its alternative.

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Dedication
To my parents and siblings who selflessly encouraged me to pursue my education.
Dosimetric Comparison of Inverse Planning by Simulated Annealing (IPSA) and Dose
Points Optimized Treatment Plans in High Dose Rate (HDR) Brachytherapy of Skin
Lesions Using Freiburg Flap Applicator
List of Tables ...................................................................................................................... x
List of Figures ................................................................................................................... xii
1 Introduction ................................................................................................................. 1
1.1 Purpose ................................................................................................................ 1
1.2 Skin Cancer ......................................................................................................... 1
1.3 Radiation Therapy ............................................................................................... 4
1.3.1 Brachytherapy ................................................................................................. 5
1.3.1.1 Classifications of Brachytherapy ........................................................... 9
1.3.2 Role of Radiotherapy in Skin Cancer Treatment .......................................... 11
1.3.2.1 Skin HDR Brachytherapy Using Surface Applicators ........................ 15
1.4 Treatment Plan Evaluation ................................................................................ 18
1.4.1 Dose-Volume Histogram (DVH) .................................................................. 19
1.4.1.1 Differential DVH ................................................................................. 20
1.4.1.2 Cumulative DVH ................................................................................. 21
1.5 Dose Distribution Optimization in HDR Brachytherapy .................................. 24
1.5.1 Dose-Point Optimization .............................................................................. 25
1.5.1.1 Placement of Distance Dose Points ..................................................... 26
1.5.1.2 Optimization on Distance Dose Points ................................................ 27
viii
1.5.2 Inverse Planning by Simulated Annealing (IPSA) Optimization ................. 30
2 Materials and Methods .............................................................................................. 35
2.1 Patient Data Selection ....................................................................................... 35
2.2 Treatment Planning Procedure .......................................................................... 36
2.2.1 Patient Setup ................................................................................................. 36
2.2.2 Computer Treatment Planning ...................................................................... 37
2.2.2.1 Dose Point Optimization ..................................................................... 37
2.2.2.2 IPSA Optimization .............................................................................. 39
2.3 Data Collection ................................................................................................. 41
3 Results and Discussion ............................................................................................. 48
3.1 Dosimetric Comparison of Dose Coverage of PTV ......................................... 48
3.1.1 Dosimetric Comparison of IPSA-V with DP-V ....................................... 51
90 90
3.1.2 Dosimetric Comparison of IPSA-V with DP-V .................................... 55
100 100
3.1.3 Dosimetric Comparison of IPSA-V with DP-V .................................... 57
125 125
3.2 Dosimetric Comparison of Tissue Sparing ....................................................... 62
3.2.1 Evaluation of Healthy Skin Sparing ............................................................. 62
3.2.2 Evaluation of Sparing of Nose Cartilage in Nose Lesions............................ 66
3.2.3 Evaluation of Sparing of Tibia and Fibula in Shin Lesions .......................... 68
3.2.4 Evaluation of Sparing of Skull bone and the Brain in Scalp Lesions ........... 71
3.3 Additional Comments ....................................................................................... 73
4 Conclusion ................................................................................................................ 78
References ......................................................................................................................... 80

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List of Tables
Table 1: Common radionuclides used in brachytherapy.13 ................................................. 9
Table 2: Local control after brachytherapy for skin cancer. Results obtained are
comparable to those obtained with RT in Table 3. (FUP = Follow Up). ........... 13
Table 3: Local control after external beam radiation therapy (RT) for skin cancer. ........ 14
Table 4: Complications after brachytherapy for skin cancer. Results obtained with
brachytherapy are comparable to those obtained with RT in Table 5. .............. 14
Table 5: Complications after external beam radiation therapy (RT) for skin cancer. ...... 15
Table 6: Local control and complication rates for NMSCs after HDR brachytherapy
using surface applicators. Gauden, Guix, Kohler-Brock. .................................. 16
Table 7: Organs of interest (OIs) chosen for each lesion type. Skin refers to the cancer-
free skin (4mm in depth) surrounding the PTV. ................................................ 42
Table 8: Excel spreadsheet showing the dose-volume data collected from the treatment
plan DVH generated for Patient Case 01. Skin refers to the healthy skin
surrounding the lesion. ....................................................................................... 46
Table 9: Dose coverage results for the PTV from the coverage prioritized method.
V = 100% of the prescribed dose for all of the 20 cases. ................................ 50
80
Table 10: Values of coefficients of dependence, β, and their corresponding p-values for
dependence of V on optimization method used, PTV volume and curvature
90
of lesion. ............................................................................................................. 52

x