VMAT technique can deliver highly conformal dose distributions similar to those created by other forms of intensity modulated radiation therapy like the multiple static field multileaf collimator (MLC) technique , the dynamic MLC technique, static and henical tomotherapy ,the CyberKnife ,scannedbeam therapy.The purpose of this thesis is to provide general knowledge about this advance technique point out its advantages and disadvantages as compared to IMRT, so that find out the reasonable technique for each patient and help clinicians make decisions about patient radiotherapy treatments.
VIETNAM NATIONAL UNIVERSITY, HANOI VNU UNIVERSITY OF SCIENCE FACULTY OF PHYSICS Pham Anh Khoa VOLUMETRIC MODULATED ARC THERAPY Submitted in partial fulfillment of the requirements for the degree of Bachelor of Science in Nuclear Technology (Advanced program) Supervisor(s): Pham Thi Hong Van, MSc Hanoi - 2017 ACKNOWLEDGEMENT I would like to express my deep and sincere gratitude to my research supervisors, Master Pham Thi Hong Van and Master Nguyen Xuan Ku for their kind guidance and their enthusiastic mentor to me I greatly appreciate them for analyzing my thesis, giving me useful advices to complete my thesis and encouraging me to work and study, further more for giving me chance to experience the job of a research scientist Their advices on both my thesis and my future career is truly helpful and priceless Besides, my gratitude is also extended to all teachers, lecturers, researchers and other seniors in Faculty of Physics, particularly Department of Nuclear Technology, Vietnam National University, VNU University of Science, who have always given students a good conditions and enthusiastic helps for students to study and research I would like to give special thanks to my family and my friends They have supported and encouraged me in studying and researching They have become my emotional shelter and durable motivation throughout the hard time Student, Pham Anh Khoa LIST OF ABBREVIATION IMRT Intensity Modulated Radiation Therapy IMAT Intensity Modulated Arc Therapy IGRT Images guided radiation therapy VMAT Volumetric Modulated Arc Therapy 2D Two-dimensional radiation therapy 3D - CRT Three dimensions - conformal radiation therapy MU Monitor Unit MLC Multi Leaf Collimators TPS Treatment Planning System OAR Organ at Risk CBT Cone Beam Tomography LINAC Linear Accelerator DVO Dose Volume Objective SIB Simultaneous Integrated Boost DSS Direct Step and Shoot DVH Dose Volume Histogram GTV Gross Tumor Volume TABLE OF CONTENTS CHAPTER 1: OVERVIEW OF VMAT 1.1 Basic and developing history of VMAT 1.1.1 VMAT Definition 1.1.2 Developing history of VMAT 1.1.3 VMAT planning 1.2 Advantages and Disadvantages of VMAT 1.2.1 Advantages of VMAT 1.2.2 Disadvantages of VMAT 1.3 Achieved results 10 CHAPTER 2: APPLICATION OF VMAT IN A DUAL VENDOR ENVIRONMENT 1Error! Bookmark not defined 2.1 Background 12 2 Methods and Materials 14 2.2.1 Linear accelerator 14 2.2.2 Treatment planning system 15 2.3 Treatment planning feasibility study 16 CHAPTER 3: RESULT AND DISSCUSION 21 3.1 For the prostate case 21 3.2 For the case with cancer of the hypopharynx/larynx 22 3.3 For the patient with metastases in the lumbar vertebra 25 3.4 Results 26 3.5 Discussion 27 CONCLUSION 30 REFERENCES 32 LIST OF FIGURES Figure Structure of IMRT Figure SynergyS linear accelerator 12 Figure Dose distributions for prostate cancer 21 Figure Dose volume histograms for prostate cancer 22 Figure Dose distributions for hypopharynx/larynx cancer 23 Figure Dose volume histograms for hypopharynx/larynx cancer 24 Figure Typical MLC positions resulting from Dual Arc optimization 24 Figure Dose distributions for metastases in the lumbar vertebra 25 Figure Dose volume histograms for metastases in the lumbar vertebra 26 INTRODUCTION Radiation therapy is the therapy that uses ionizing radiation to kill cancer cells and normally delivered by a linear accelerator Radiation therapy developed since the characters of radionuclides have been discovered Radiation therapy has been promoted and has significant achievements base on the fabulous development of science and technology Nowadays, radiotherapy becomes the main and the most effective method in cancer treatment The advancement of radiotherapy techniques aim to distribute appropriately high dose to cancer cells while minimize dose to surrounding healthy tissues This is the important rule that explains the way radiation therapy techniques are developed There are numerous stages that formed radiotherapy techniques including: Two-dimensional radiation therapy (2D), three dimensions - conformal radiation therapy (3D - CRT), intensity modulated radiation therapy (IMRT), images guided radiation therapy (IGRT), Intensity Modulated Arc Therapy (IMAT), heavy particles radiotherapy Each stage has been gone through a long process to create the complete methods for modern radiotherapy techniques In Viet Nam, radiotherapy is chasing the world’s most modern techniques Most of rank of city and international hospitals are implemented advanced radiation therapy techniques Recently, intensity modulated radiation therapy (IMRT) and images guided radiation therapy (IGRT) are applied to real clinical cases Volumetric modulated arc therapy (VMAT), which is a type of IMRT and evolved from IMAT also has been put into applications for few years VMAT technique can deliver highly conformal dose distributions similar to those created by other forms of intensity modulated radiation therapy like the multiple-static field multileaf collimator (MLC) technique, the dynamic MLC technique, static and helical tomotherapy, the CyberKnife, scanned-beam therapy The purpose of this thesis is to provide general knowledge about this advance technique, point out its advantages and disadvantages as compared to IMRT, so that find out the reasonable technique for each patient and help clinicians make decisions about patient radiotherapy treatments The content of the thesis includes three chapters: Chapter 1: OVERVIEW OF VMAT Chapter 2: APPLICATION OF VMAT IN A DUAL VENDOR ENVIRONMENT Chapter 3: RESULT AND DISSCUSION CHAPTER 1: OVERVIEW OF VMAT 1.1 Basic and developing history of VMAT 1.1.1 VMAT Definition There are many radiation therapies in cancer treatment such as: twodimensional radiation therapy (2D), three dimensions - conformal radiation therapy (3D - CRT), intensity modulated radiation therapy (IMRT), images guided radiation therapy (IGRT) Each therapy has its own advantages but there still a lot of disadvantages exist For instance, IMRT has increased treatment time by requiring a larger number of beam directions, increased monitor units (MU), and, in the case of tomotherapy, a slice by slice delivery, overall treatment times have been increased by the improvements in patient care achieved through image-guided positioning and plan adaptation… VMAT appeared like an outstanding radiation therapy which can maintain a similar level of patient throughput it will be necessary to increase the efficiency of treatment delivery The solution of VMAT is a novel aperture-based algorithm for treatment plan optimization where dose is delivered during a single gantry arc of up to 360 degree [1] VMAT technique and tomotherapy have the common is a full 360 degree of beam directions are available for optimization but the basic difference is that in VMAT technique, the entire dose volume is delivered in a single source rotation More specific, VMAT is a radiotherapy technique that delivers intensity modulated radiation therapy and in the same time, the gantry rotates around the patient VMAT delivers conformal treatments by using continuous gantry rotation, dynamic beam modulation and variable dose rate 1.1.2 Developing history of VMAT VMAT evolved from a radiotherapy technique called intensity modulated arc therapy (IMAT), which first proposed by Cedric Yu in 1995 Basically, IMAT is conventional intensity modulated radiation therapy (IMRT), but in IMAT technique, the gantry moves in one or more rotating arcs, rather than delivers from a small number of fixed angles Therefore, most of IMRT’s concepts, benefits and drawbacks are applied to IMAT IMAT was developed as a conventional linac-based alternative to helical tomotherapy and as a more conformal / lower critical structure dose and faster version of static angle IMRT Figure Structure of IMRT The figure shows the IMRT hierarchy As we can see from the figure, IMAT is on the branch of cone-beam, dynamic gantry IMRT, while conventional IMRT is on the branch of static gantry In order to deliver IMAT, a linac must have some of the following capabilities: gantry motion with beam on, dynamic MLC (i.e leaf motion with beam on and gantry rotating), and variable dose rate IMAT was implemented on an existing and conventional linear accelerator and delivered treatments volumetrically Yu’s technique used a multi-leaf collimator to shape the beam dynamically while the gantry rotated and used multiple overlapping arcs Although Yu first proposed inverse planning for IMAT, forward planning was used for its actual implementation During planning, arcs were approximated as multiple fixed fields at gantry angles separated by 5-10° The plans mostly used three to five arcs and the final dose calculation approximated each arc as fixed fields at 10° gantry spacing Yu recognized that the forward planning techniques he implemented did not fully utilize the capabilities of IMAT to deliver conformal treatments However, there were several challenges to developing effective planning and dose calculation techniques Physical limitations of the linac, including leaf travel speed, dose rate, and gantry rotation speed, complicated planning and affected the efficiency of treatments Also, determining the optimal gantry spacing to approximate the arcs was a trade-off between optimization time, calculation time and accuracy [2] Since developed, numerous progress has been taken IMAT technique’s advantages and disadvantages have been discovered and analyzed Recently, single-arc forms of IMAT have become officially ratified and VMAT is the symbolic example of single-arc form of IMAT The dose rate and gantry speed of IMAT technique are remained constant Radiation is delivered over multiple gantry arcs, and that how intensity modulation is achieved This means that the quantity of intensity levels is equal to the quantity of gantry arcs Raising dose level resolution requires an increased number of arcs, which significantly raises treatment time Yu found that IMAT treatments took as equal to more time to deliver than fixed-beam IMRT treatments Yu also observed that normal tissue dose is spread around the patient by IMAT treatments, on the other side, fixedbeam IMRT treatments concentrate the normal tissue dose along fixed lines [2] The common between VMAT and IMAT is that radiation is delivered while the gantry rotates around the patient As mentioned above, VMAT is the representative example of IMAT, which is a single-arc form of IMAT that delivers apertures of varying weights with a single-arc rotation that uses dose rate variation of the treatment machine With the development of implementation of VMAT, wide clinical adoption has taken root so quickly However, there is still a lack of general understanding about the planning of arc treatments and what makes delivery limitations and compromises VMAT delivers radiation by rotating the gantry of a linear accelerator through one or more arcs with the radiation continuously on that lead to change of a lot of CHAPTER 3: RESULT AND DISSCUSION The feasibility study showed similar plan quality at reduced delivery times and similar number of MU per fraction for VMAT as compared to IMRT in all cases: 3.1 For the prostate case Single arc VMAT showed better dose homogeneity and target coverage, and similar, mostly even lower dose to the organs at risk Time for optimization and dose calculation increased by a factor of 5.8, treatment time was reduced to 43% Detailed information is given in table Figure shows the dose distribution in transversal CT-slices, figure the respective dose volume histograms (DVH) Figure Dose distributions for prostate cancer Comparison of dose distributions achieved with 7-field IMRT (left) and Single Arc VMAT (right) on representative transversal (top) and sagittal (bottom) CT slices The PTV is drawn in red, the bladder in orange, the rectum in maroon, and the femoral heads in green Isodose lines are shown in percent of the prescription dose, i.e 60 Gy to the average of the PTV [28] 21 Figure Dose volume histograms for prostate cancer Comparison of dose volume histograms achieved with 7-field IMRT (dotted lines) and Single Arc VMAT (solid lines) Plan quality is slightly better for VMAT, with better target coverage and homogeneity and lower OAR doses.[28] 3.2 For the case with cancer of the hypopharynx/larynx Single arc VMAT showed similar target coverage and better sparing of the parotids, but deteriorated homogeneity as compared to IMRT Better overall plan quality including target coverage, homogeneity inside the PTV, as well as OAR sparing could be achieved with dual arc VMAT Even the relative volume of the normal tissue, receiving doses between 20.0 Gy and 50.0 Gy is smaller in case of the dual arc treatment Only the relative volume of the normal tissue receiving between 5.0 Gy and 20.0 Gy is slightly larger Detailed information is given in table Figure shows the dose distribution for dual arc as compared to IMRT in transversal slices, figure the respective DVH Segment shapes for a selected gantry angle are shown in figure 7, illustrating the grouping of the segments into arcs with respect to the leaf positions For dual arc, time for optimization and 22 dose calculation increased by a factor of 6.8, treatment time was reduced to 35%, as compared to IMRT Figure Dose distributions for hypopharynx/larynx cancer Comparison of dose distributions achieved with 7-field IMRT (left) and Dual Arc VMAT (right) on representative transversal (top) and sagittal (bottom) CT slices The PTV is drawn in red, the parotids in blue and purple, the spinal cord in green, and the brain stem in bright blue Isodose lines are shown in percent of the prescription dose, i.e 60 Gy to the average of the PTV.[28] 23 Figure Dose volume histograms for hypopharynx/larynx cancer Comparison of dose volume histograms achieved with 7-field IMRT (dotted lines) and Dual Arc VMAT (solid lines) Plan quality is slightly better for VMAT, with somewhat lower dose to the parotids.[28] Figure Typical MLC positions resulting from Dual Arc optimization In Dual Arc VMAT, segments are grouped into arcs such that leaf travel is minimized during each rotation In the example shown in this figure, arc contains segments with leaves positioned more to the left, arc to the right of the field.[28] 24 3.3 For the patient with metastases in the lumbar vertebra Single arc VMAT showed similar plan quality as compared to IMRT Doses to the GTV were similar, median dose and D95% for the PTV higher, doses to the kidney were also higher but still below the tolerance and fulfilling the DVO used in optimization Time for optimization and dose calculation increased by a factor of 5.0, treatment time was reduced to 41% Since patients with bone metastases suffer from pain and are not able to keep the position for a long time, the VMAT plan was considered superior because of the reduced treatment time Detailed information is given in table Figure shows the dose distribution in transversal, sagittal and coronal slices, figure the respective DVH Figure Dose distributions for metastases in the lumbar vertebra Comparison of dose distributions achieved with 7-field IMRT (left) and Single Arc VMAT (right) on representative transversal (top) and sagittal (bottom) CT slices The PTV is drawn in red, the GTV in orange, the spinal cord in green, and the kidneys in maroon Isodose lines are shown in percent of the prescription dose, i.e 55 Gy to the average of the GTV.[28] 25 Figure Dose volume histograms for metastases in the lumbar vertebra Comparison of dose volume histograms achieved with 7-field IMRT (dotted lines) and Single Arc VMAT (solid lines) Using the same dose volume objectives for optimization, higher doses to the PTV are achieved with VMAT for almost identical GTV coverage and homogeneity and sparing of the spinal cord but somewhat higher dose to the kidneys.[28] Patient and have actually been treated with VMAT after successful completion of commissioning, patient had already finished treatment 3.4 Results For prostate cancer and vertebral metastases single arc VMAT led to similar plan quality as compared to IMRT For treatment of the hypopharynx/larynx cancer, a second arc was necessary to achieve sufficient plan quality As compared to IMRT, treatment time of VMAT was down to 35% to 43% in all three cases However, times required for optimization and dose calculation rose by a factor of 5.0 to 6.8 26 3.5 Discussion The VMAT optimization tool implemented in Oncentra MasterPlan v.3.3 can be delivered in substantially reduced treatment time on an Elekta SynergyS linear accelerator and creates VMAT plans with similar or better plan quality as compared to IMRT For the treatment of prostate cancer and vertebral metastases, with one single arc VMAT the required plan quality could be achieved, which is in agreement with the results published for other types of equipment However, for the treatment of hypopharynx/larynx cancer, single arc VMAT did not achieve sufficient plan quality, reducing target homogeneity as compared to IMRT and violating the DVO for the spinal cord Using the dual arc technique strongly improved plan quality as compared to single arc VMAT but also to IMRT, which also complies with publications to other VMAT solutions The researches of Bertelsen, which had good results for single arc VMAT for head and neck cancer using SmartArc (Philips Healthcare, Andover, MA) could not be confirmed In this case, however, plan comparison was performed for simultaneous treatment of three target levels, which requires certain dose heterogeneity inside the target The applicability of the system to simultaneous integrated boost concepts has been demonstrated for the treatment of vertebral metastases In this case, to achieve the required plan quality, a single arc was sufficient The same concept can be applied for SIB treatments of other target types like prostate or head and neck cancers It might even be possible that single arc treatments are in general suitable for SIB concepts due to the required dose heterogeneity inside the target, which would also explain the results of Bertelsen mentioned above This, still remains to be investigated in a separate study In the VMAT solution implemented in Oncentra MasterPlan v3.3, segment shapes and weights are subject to optimization, which is one of the main differences to the treatment planning system ERGO++: In ERGO++, before 27 optimization, segment shapes have to be defined by the user, and only the segment weights are optimized Therefore, the quality of the VMAT plans resulting from optimization in ERGO++ highly depends on the individual user's experience in creating suitable segment shapes In contrary, the VMAT solution implemented in Oncentra MasterPlan v3.3 is not dependent on individual user because it does not require any user input for the segment shapes The optimization process results segment shapes and weights so that the resulting plan quality is therefore less dependent on the individual user's experience For both VMAT and IMRT, the number of MUs per fraction was equivalent, a noticeable decrease as reported for Varian linacs could not be observed, since the values found for IMRT were already considerably lower than the ones reported for Varian [31] However, as compared to IMRT, treatment times could be substantially reduced to 35% to 43%, whereas calculation times were 5.0 to 6.8 times higher for VMAT The advantage of VMAT over IMRT was demonstrated clearly in the combination of plan quality and treatment time: Treatment time is remarkable reduced, this is an important benefit for patients who suffer from pain or can not keep a certain position for a longer time, as it is the case e.g for patients with bone metastases, or for patients with noticeable internal organ movement, e.g patients with prostate cancer, for which the real delivered dose distribution might be significantly different from the planned dose distribution due to intrafractional movement In these cases using a single arc is enough to achieve the required plan quality, allowing reducing overall treatment time from 11 minutes to well below minutes For the patient with hypopharynx/larynx cancer, plan quality is shown better at 33% of the treatment time by the dual arc VMAT, that decreases patient discomfort in the rigid mask system The delivery time is shorter therefore leading to better patient comfort and possibly also quality of 28 delivery, and simultaneously reduces the workload and increases availability of the linac Increasing calculation time is the only disadvantage that has been found for VMAT as compared to IMRT But this certainly has no influence on patient treatment or on the workload It only impacts availability of the treatment planning station Workload for the planner is virtually the same for VMAT as compared to IMRT, since the steps of the planning procedure, which require user interaction, like definition of structures, beam setup, definition of DVO, are the same in both cases In the future, calculation times can be reduced by using a processor with more than cores or performing the dose calculation on the GPU processor, as it will be implemented in the next version of Oncentra MasterPlan It is clearly that VMAT planning with Oncentra MasterPlan has the potential to create better plan quality while require less delivery time as compared to IMRT However, dedicated planning studies should be performed, varying the user definable parameters e.g maximum treatment time, number of arcs, and gantry angle range, to identify the best parameter set to achieve optimal combination of plan quality and treatment time for each target type Oncentra MasterPlan allows achieving comparable or superior plan quality with VMAT as compared to IMRT Optimization times and dose calculation times are increased, the number of monitor units per fraction is equivalent, and treatment times are significant reduced 29 CONCLUSION As compared to IMRT, VMAT treatments can be delivered significantly faster, that means treatment time is reduced, therefore leading to a better comfort for patient Though calculation times are increased, VMAT’s benefits are still outweigh its drawbacks Furthermore, it could be shown that VMAT can deliver highly conformal dose distributions similar to those created by other forms of intensity-modulated radiation therapy As such, it becomes a valued member of the IMRT-delivery arsenal That unmodulated VMAT fields can deliver the equivalent of modulated beams has recently been explained Though, the universal theory of VMAT is still unclear There is several reasons to explain why VMAT is controversial The first is that there are claims that VMAT can create equivalently conformal dose distributions with fewer monitor units, i.e., in a faster time That improves VMAT is clearly advantageous (shorter treatments; patients feel more comfort; less susceptibility to intrafraction motion; can reduce secondary cancers; faster overall treatment slots…) The other points are base on these following statements: Most of researches focus on comparison between VMAT treatment and fixed-field IMRT treatment These researches which compare a single implementation of each, are valid and reliable but only in specific circumstance The development of the implementation on either side of the balancing scales may lead to another conclusion VMAT showed "does better" than fixed-field IMRT in some situations, but in some other situations, the results are opposite, VMAT "does worse" The question how does the outcome of VMAT depend on the parameters available for variation have not been explained and there is no universal theory about that On the other hand, clear published theories of some of the fixed-field IMRT techniques are already existed [2] 30 VMAT have been debated for a long time and we can not deny the advantages of VMAT Nowadays, VMAT is known as the top radiotherapy of the world, which is better than almost every other therapies existing As time passes, the methodology of VMAT, both in planning and delivery, will evolve and improve There will be more papers comparing VMAT with conventional IMRT The manufacturers will 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74(1), pp 252-259 35 ... IMRT Intensity Modulated Radiation Therapy IMAT Intensity Modulated Arc Therapy IGRT Images guided radiation therapy VMAT Volumetric Modulated Arc Therapy 2D Two-dimensional radiation therapy 3D... radiation therapy (IGRT), Intensity Modulated Arc Therapy (IMAT), heavy particles radiotherapy Each stage has been gone through a long process to create the complete methods for modern radiotherapy... Recently, intensity modulated radiation therapy (IMRT) and images guided radiation therapy (IGRT) are applied to real clinical cases Volumetric modulated arc therapy (VMAT), which is a type of IMRT