On Quality in Radiotherapy Treatment Plan Optimisation

Radiotherapy is one of the essential treatments used in the fight against cancer. The goal of radiotherapy is to deliver a high dose of ionising radiation to the tumour volume and at the same time minimise the effect on healthy tissue by reducing the radiation to critical organs. This contradiction is challenging and has been driving the research and development of the treatments.Over the last two decades, there has been tremendous technical development inradiotherapy. The rapid increase in computational power introduced treatment plan optimisation and intensity-modulated radiotherapy (IMRT). IMRT made it possible to shape the radiation dose distribution closely around the target volume avoiding critical organs to a greater extent. Rotational implementation of IMRT, e.g. Volumetric Modulated Arc Therapy (VMAT) further improved this “dose shaping” ability. With these techniques increasing the ability to produce better treatment plans, there was a need for evaluation tools to compare the treatment plan quality. A plan can be judged by how well it fulfils the prescription and dose-volume constraints, ideally based on treatment outcome. In this work, this is denoted Required Plan Quality, the minimum quality to accept a plan for clinical treatment. If a plan does not fulfil all the dose-volume constraints, there should be a clear priority of which constraints are crucial to achieve. On the other hand, if the constraints are easily fulfilled, there might be a plan of better quality only limited by the treatment systems ability to find and deliver it. This is denoted Attainable Plan Quality in this work– the quality possible to achieve with a given treatment system for a specific patient group.In work described in this thesis, the so-called Pareto front method was used to search for the attainable plan quality to compare different treatment planning systems and optimisation strategies. More specifically, a fall-back planning system for backup planning and an optimiser to find the best possible beam angles. The Pareto method utilises a set of plans to explore the trade-off between target and nearby risk organs.The Pareto plan generation is time-consuming if done manually. The Pareto method was then used in a software that automated the plan generation allowing for a more accurate representation of the trade-off. The software was used to investigate the attainable plan quality for prostate cancer treatments. In the last two publications in this thesis, machine learning approaches were developed to predict a treatment plancloser to the attainable plan quality compared to a manually generated plan.In the thesis, tools have been developed to help move the treatment plan qualityfrom Required Plan Quality towards the Attainable Plan Quality, i.e. the best quality we can achieve with our current system

Conversion of helical tomotherapy plans to step-and-shoot IMRT plans-Pareto front evaluation of plans from a new treatment planning system

Purpose: The resulting plans from a new type of treatment planning system called SharePlan (TM) have been studied. This software allows for the conversion of treatment plans generated in a TomoTherapy system for helical delivery, into plans deliverable on C-arm linear accelerators (linacs), which is of particular interest for clinics with a single TomoTherapy unit. The purpose of this work was to evaluate and compare the plans generated in the SharePlan system with the original TomoTherapy plans and with plans produced in our clinical treatment planning system for intensity-modulated radiation therapy (IMRT) on C-arm linacs. In addition, we have analyzed how the agreement between SharePlan and TomoTherapy plans depends on the number of beams and the total number of segments used in the optimization. Methods: Optimized plans were generated for three prostate and three head-and-neck (H&N) cases in the TomoTherapy system, and in our clinical treatment planning systems (TPS) used for IMRT planning with step-and-shoot delivery. The TomoTherapy plans were converted into step-and-shoot IMRT plans in SharePlan. For each case, a large number of Pareto optimal plans were created to compare plans generated in SharePlan with plans generated in the Tomotherapy system and in the clinical TPS. In addition, plans were generated in SharePlan for the three head-and-neck cases to evaluate how the plan quality varied with the number of beams used. Plans were also generated with different number of beams and segments for other patient cases. This allowed for an evaluation of how to minimize the number of required segments in the converted IMRT plans without compromising the agreement between them and the original TomoTherapy plans. Results: The plans made in SharePlan were as good as or better than plans from our clinical system, but they were not as good as the original TomoTherapy plans. This was true for both the head-and-neck and the prostate cases, although the differences between the plans for the latter were small. The evaluation of the head-and-neck cases also showed that the plans generated in SharePlan were improved when more beams were used. The SharePlan Pareto front came close to the front for the TomoTherapy system when a sufficient number of beams were added. The results for plans generated with varied number of beams and segments demonstrated that the number of segments could be minimized with maintained agreement between SharePlan and TomoTherapy plans when 10-19 beams were used. Conclusions: This study showed (using Pareto front evaluation) that the plans generated in SharePlan are comparable to plans generated in other TPSs. The evaluation also showed that the plans generated in SharePlan could be improved with the use of more beams. To minimize the number of segments needed in a plan with maintained agreement between the converted IMRT plans and the original TomoTherapy plans, 10-19 beams should be used, depending on target complexity. SharePlan has proved to be useful and should thereby be a time-saving complement as a backup system for clinics with a single TomoTherapy system installed alongside conventional C-arm linacs. (C) 2011 American Association of Physicists in Medicine. [DOI: 10.1118/1.3592934

Comparison of IMRT delivery techniques and helical Tomo Therapy using Pareto front evaluation

Purpose: The purpose of this work was to explore the possibility to compare treatment-planning- and treatment-delivery systems for intensity modulated radiation therapy (IMRT) using an objective approach. The approach investigated was the Pareto front concept. An additional aim was to adequately compare three different IMRT treatment planning and delivery systemsMaterials and methods: In IMRT treatment planning the goal is to find an optimal compromise between organ at risk (OAR) sparing and target coverage. During the optimization process objectives are chosen for each OAR and for the planning target volume (PTV). For a Pareto optimal plan one objective cannot be improved without worsening another objective. This makes IMRT optimization suitable for Pareto front evaluation. A set of Pareto optimal plans form a Pareto front. By using Pareto front evaluation the influence of individual plans is suppressed and the whole range of plans with the chosen objectives can be evaluated at the same time. Pareto fronts from different treatment planning systems (TPSs) are expected to differ from each other. In this study, different head and neck cases were used. Several plans with varying importance concerning the sparing of a specific OAR were created for each case using different TPSs. The importance of the PTV coverage was held constant for all plans. The TPSs used in the study were Oncentra Masterplan (OMP) (Nucletron B.V.), Eclipse (Varian Medical Systems) and TomoTherapy (Tomotherapy inc.) planning system. A Pareto front was obtained for each TPS by plotting the average OAR dose as a function of underdosed volume of the PTV. The underdosed volume was defined as the relative volume that receives less than 95% of the prescribed dose. Each plan fulfilled the dose restrictions for OARs according to the clinical protocol used apart from the OAR chosen for the trade-off.Results: The TomoTherapy Pareto front is situated below both the OMP front and the Eclipse front indicating that for the same target coverage, the sparing of the parotid is always favourable for this technology. For low priority OAR sparing, however, the Eclipse and the TomoTherapy fronts exhibit almost equal target coverage. As the importance of the OAR increases the target coverage decreases faster for the Eclipse front compared to the TomoTherapy front and is approaching the same coverage as OMP.Conclusion: The results clearly indicate that the approach of using Pareto fronts for different systems is a feasible way to compare different methods and technologies for advanced radiotherapy. For the particular cases studied, TomoTherapy seems to be superior to OMP and Eclipse regarding target coverage and sparing of the parotid gland

Recent Regionalization Discourses and Projects in Romania with Special Focus on the Székelyland

The paper discusses the post-communist development and evolution of the regionalization process in Romania. In the frst part, we distin-guish between two periods of regionalization: the preparation period for the EU accession, and the post-accession period. It turns out that the process of regionalization was oriented to EU criteria and expectations, which are in turn low in what it concerns the establishment of regional development institutions and of different territori-al levels of the NUTS system. A radical change into this question was introduced very recently, at the beginning of 2013, when different region-alization projects have been launched by politi-cal parties and academics as well. Therefore, in the second part of the paper our main aim is to analyze the latest regionalization projects and scenarios, emphasizing one of the most contro-versial questions of this process related to the ethno-cultural diversity of the country and to the question of Székelyland

The effect of prostate motion during hypofractionated radiotherapy can be reduced by using flattening filter free beams

Background and purpose: Hypofractionated radiotherapy of prostate cancer reduces the overall treatment time but increases the per-fraction beam-on time due to the higher fraction doses. This increased fraction treatment time results in a larger uncertainty of the prostate position. The purpose of this study was to investigate the effect of prostate motion during flattening filter free (FFF) Volumetric Modulated Arc Therapy (VMAT) in ultrahypofractionation of prostate cancer radiotherapy with preserved plan quality compared to conventional flattened beams. Materials and methods: Nine prostate patients from the Scandinavian HYPO-RT-PC trial were re-planned using VMAT technique with both conventional and flattening filter free beams. Two fractionation schedules were used, one hypofractionated (42.7 Gy in 7 fractions), and one conventional (78.0 Gy in 39 fractions). Pre-treatment verification measurements were performed on all plans and the treatment time was recorded. Measurements with simulated prostate motion were performed for the plans with the longest treatment times. Results: All the 10FFF plans fulfilled the clinical gamma pass rate, 90% (3%, 2 mm), during all simulated prostate motion trajectories. The 10MV plans only fulfilled the clinical pass rate for three of the trajectories. The mean beam-on-time for the hypofractionated plans were reduced from 2.3 min to 1.0 min when using 10FFF compared to 10MV. No clinically relevant differences in dose distribution were identified when comparing the plans with different beam qualities. Conclusion: Flattening-filter free VMAT reduces treatment times, limiting the dosimetric effect of organ motion for ultrahypofractionated prostate cancer with preserved plan quality. Keywords: Hypofractionation, Prostate motion, FFF, Prostate cancer, VMA

Strategies for quality assurance of intensity modulated radiation therapy

In late 2011 The Swedish Society of Radiation Physics formed a working group to concentrate on the Quality Assurance of modern radiation therapy techniques. The given task was to identify and summarise the different QA strategies in Sweden and also the international recommendations. This was used to formulate recommendations for practical guidelines within Sweden. In this paper a brief summery of the group's work is presented. All the Swedish radiation therapy centres do a pre treatment verification measurement as QA for every new IMRT and VMAT plan. Physicists do it and they believe it to be time consuming. A general standpoint from all the centres was that new guidelines and legislation is needed to allow QA that does not require a measurement. Based on various international publications and recommendations the working group has presented two strategies, one where all new plans are checked through measurement and one where no measurement is needed. The measurement-based strategy is basically the same as the one used today with an extended machine QA part. The other presented strategy is process oriented where all the different parts of the treatment chain are checked separately. The final report can be found in Swedish on http://www.radiofysik.org

Strategies for quality assurance of intensity modulated radiation therapy

In late 2011 The Swedish Society of Radiation Physics formed a working group to concentrate on the Quality Assurance of modern radiation therapy techniques. The given task was to identify and summarise the different QA strategies in Sweden and also the international recommendations. This was used to formulate recommendations for practical guidelines within Sweden. In this paper a brief summery of the group's work is presented. All the Swedish radiation therapy centres do a pre treatment verification measurement as QA for every new IMRT and VMAT plan. Physicists do it and they believe it to be time consuming. A general standpoint from all the centres was that new guidelines and legislation is needed to allow QA that does not require a measurement. Based on various international publications and recommendations the working group has presented two strategies, one where all new plans are checked through measurement and one where no measurement is needed. The measurement-based strategy is basically the same as the one used today with an extended machine QA part. The other presented strategy is process oriented where all the different parts of the treatment chain are checked separately. The final report can be found in Swedish on http://www.radiofysik.org

Strategies for quality assurance of intensity modulated radiation therapy

In late 2011 The Swedish Society of Radiation Physics formed a working group to concentrate on the Quality Assurance of modern radiation therapy techniques. The given task was to identify and summarise the different QA strategies in Sweden and also the international recommendations. This was used to formulate recommendations for practical guidelines within Sweden. In this paper a brief summery of the group's work is presented. All the Swedish radiation therapy centres do a pre treatment verification measurement as QA for every new IMRT and VMAT plan. Physicists do it and they believe it to be time consuming. A general standpoint from all the centres was that new guidelines and legislation is needed to allow QA that does not require a measurement. Based on various international publications and recommendations the working group has presented two strategies, one where all new plans are checked through measurement and one where no measurement is needed. The measurement-based strategy is basically the same as the one used today with an extended machine QA part. The other presented strategy is process oriented where all the different parts of the treatment chain are checked separately. The final report can be found in Swedish on http://www.radiofysik.org

Strategies for quality assurance of intensity modulated radiation therapy

In late 2011 The Swedish Society of Radiation Physics formed a working group to concentrate on the Quality Assurance of modern radiation therapy techniques. The given task was to identify and summarise the different QA strategies in Sweden and also the international recommendations. This was used to formulate recommendations for practical guidelines within Sweden. In this paper a brief summery of the group's work is presented. All the Swedish radiation therapy centres do a pre treatment verification measurement as QA for every new IMRT and VMAT plan. Physicists do it and they believe it to be time consuming. A general standpoint from all the centres was that new guidelines and legislation is needed to allow QA that does not require a measurement. Based on various international publications and recommendations the working group has presented two strategies, one where all new plans are checked through measurement and one where no measurement is needed. The measurement-based strategy is basically the same as the one used today with an extended machine QA part. The other presented strategy is process oriented where all the different parts of the treatment chain are checked separately. The final report can be found in Swedish on http://www.radiofysik.org

Introducing multiple treatment plan-based comparison to investigate the performance of gantry angle optimisation (GAO) in IMRT for head and neck cancer

Background and purpose. The purpose of this study was to evaluate the performance of gantry angle optimisation (GAO) compared to equidistant beam geometry for two inverse treatment planning systems (TPSs) by utilising the information obtained from a range of treatment plans. Material and methods. The comparison was based on treatment plans generated for four different head and neck (H&N) cancer cases using two inverse treatment planning systems (TPSs); Varian Eclipse (TM) representing dynamic MLC intensity modulated radiotherapy (IMRT) and Oncentra (R) Masterplan representing segmented MLC-based IMRT. The patient cases were selected on the criterion of representing different degrees of overlap between the planning target volume (PTV) and the investigated organ at risk, the ipsilateral parotid gland. For each case, a number of 'Pareto optimal' plans were generated in order to investigate the trade-off between the under-dosage to the PTV (V-PTV,V-D ((parotid gland)). Results. For the Eclipse system, GAO had a clear advantage for the cases with smallest overlap (Cases 1 and 2). The set of data points, representing the underlying trade-offs, generated with and without using GAO were, however, not as clearly separated for the cases with larger overlap (Cases 3 and 4). With the OMP system, the difference was less pronounced for all cases. The Eclipse GAO displays the most favourable trade-off for all H&N cases. Conclusions. We have found differences in the effectiveness of GAO as compared to equidistant beam geometry, in terms of handling conflicting trade-offs for two commercial inverse TPSs. A comparison, based on a range of treatment plans, as developed in this study, is likely to improve the understanding of conflicting trade-offs and might apply to other thorough comparison techniques