Multicriteria Optimization Plans Research Articles

Effectiveness of multi-criteria optimization in combination with knowledge-based modeling in radiotherapy of left-sided breast including regional nodes

Multi-criteria optimization (MCO) is a method that was added to treatment planning to create high-quality treatment plans. This study aimed to investigate the effectiveness of MCO in combination with knowledge-based planning (KBP) in radiotherapy for left-sided breasts, including regional nodes. Dose/volume parameters were evaluated for manual plans (MP), KBP, and KBP + MCO. Planning target volume doses of MP had better coverage while KBP + MCO plans demonstrated the lowest organ at risk doses. KBP and KBP + MCO plans had increasing complexity as expressed in the number of monitor units.

Comparative Study of Eclipse and RayStation Multi-Criteria Optimization-Based Prostate Radiotherapy Treatment Planning Quality.

Multi-criteria optimization (MCO) function has been available on commercial radiotherapy (RT) treatment planning systems to improve plan quality; however, no study has compared Eclipse and RayStation MCO functions for prostate RT planning. The purpose of this study was to compare prostate RT MCO plan qualities in terms of discrepancies between Pareto optimal and final deliverable plans, and dosimetric impact of final deliverable plans. In total, 25 computed tomography datasets of prostate cancer patients were used for Eclipse (version 16.1) and RayStation (version 12A) MCO-based plannings with doses received by 98% of planning target volume having 76 Gy prescription (PTV76D98%) and 50% of rectum (rectum D50%) selected as trade-off criteria. Pareto optimal and final deliverable plan discrepancies were determined based on PTV76D98% and rectum D50% percentage differences. Their final deliverable plans were compared in terms of doses received by PTV76 and other structures including rectum, and PTV76 homogeneity index (HI) and conformity index (CI), using a t-test. Both systems showed discrepancies between Pareto optimal and final deliverable plans (Eclipse: -0.89% (PTV76D98%) and -2.49% (Rectum D50%); RayStation: 3.56% (PTV76D98%) and -1.96% (Rectum D50%)). Statistically significantly different average values of PTV76D98%,HI and CI, and mean dose received by rectum (Eclipse: 76.07 Gy, 0.06, 1.05 and 39.36 Gy; RayStation: 70.43 Gy, 0.11, 0.87 and 51.65 Gy) are noted, respectively (p < 0.001). Eclipse MCO-based prostate RT plan quality appears better than that of RayStation.

Feasibility of Mastication-Structure-Sparing Radiotherapy for Head and Neck Cancer

Although radiation-induced side-effects affecting mastication functionality have been studied in head and neck cancer (HNC) radiotherapy (RT), dose constraints for the associated structures are rarely included during treatment plan optimization. Previous research has identified several radiation dose relationships with mean dose thresholds around 30-40 Gy for masseter muscles, 40-50 Gy for pterygoid muscles, and 15-60 Gy for temporomandibular joint (TMJ) relating to a 10% trismus risk post RT. The purpose of this work was to use a multi-criteria optimization (MCO) approach to investigate to what extent doses to these structures can be lowered without violating existing clinical treatment goals in inverse planning of HNC RT.This exploratory treatment planning study used data from 22 HNC patients treated to 68 Gy without mastication-structure-sparing intent in 2017-2019 at one institute in Sweden. Original volumetric-modulated arc therapy (VMAT) plans were re-activated in the treatment planning system and masseter muscles, pterygoid muscles (medial and lateral), and TMJ were consistently delineated according to a previously reported delineation manual4. Re-planning was done using the MCO function of the treatment planning system with the resulting dose distribution normalized to match the clinical target volume (CTV T) mean dose of the clinical treatment plan. Dose differences between MCO and clinical plans were not allowed to exceed 2 Gy for any original clinical treatment goal unless tolerance doses had been substantially exceeded in the clinical treatment plan. To what extent dose to mastication structures could be lowered without violating existing clinical treatment goals were quantified by group and by patient.Altogether, there were 334 clinical treatment goals in the clinical treatment plans (median = 15, range: 7-24 per patient, depending on tumor location), which easily could be met in the corresponding MCO plans. Mean doses to the mastication structures were in most cases below proposed tolerance doses in the clinical plan but could on average be further reduced between 3-5 Gy in the MCO plans (Table). Of the 25/88 patient reductions below 5 Gy (28%), 18/25 (72%) were for the masseter (n = 8) and medial pterygoid (n = 10) muscles.With modern RT, it seems possible to reduce the dose to mastication structures below proposed trismus dose tolerance thresholds for most HNC patients without violating clinical treatment goals. Focusing on masseter and medial pterygoid muscle doses may prove to give the largest benefit in individual cases.

Variations in Head and Neck Treatment Plan Quality Assessment Among Radiation Oncologists and Medical Physicists in a Single Radiotherapy Department.

BackgroundAgreement between planners and treating radiation oncologists (ROs) on plan quality criteria is essential for consistent planning. Differences between ROs and planning medical physicists (MPs) in perceived quality of head and neck cancer plans were assessed.Materials and MethodsFive ROs and four MPs scored 65 plans for in total 15 patients. For each patient, the clinical (CLIN) plan and two or four alternative plans, generated with automated multi-criteria optimization (MCO), were included. There was always one MCO plan aiming at maximally adhering to clinical plan requirements, while the other MCO plans had a lower aimed quality. Scores were given as follows: 1–7 and 1–2, not acceptable; 3–5, acceptable if further planning would not resolve perceived weaknesses; and 6–7, straightway acceptable. One MP and one RO repeated plan scoring for intra-observer variation assessment.ResultsFor the 36 unique observer pairs, the median percentage of plans for which the two observers agreed on a plan score (100% = 65 plans) was 27.7% [6.2, 40.0]. In the repeat scoring, agreements between first and second scoring were 52.3% and 40.0%, respectively. With a binary division between unacceptable (scores 1 and 2) and acceptable (3–7) plans, the median inter-observer agreement percentage was 78.5% [63.1, 86.2], while intra-observer agreements were 96.9% and 86.2%. There were no differences in observed agreements between RO–RO, MP–MP, and RO–MP pairs. Agreements for the highest-quality, automatically generated MCO plans were higher than for the CLIN plans.ConclusionsInter-observer differences in plan quality scores were substantial and could result in inconsistencies in generated treatment plans. Agreements among ROs were not better than between ROs and MPs, despite large differences in training and clinical role. High-quality automatically generated plans showed the best score agreements.

Multi-criteria optimization for planning volumetric-modulated arc therapy for prostate cancer.

We aimed to compare the volumetric-modulated arc therapy (VMAT) plans with or without multi-criteria optimization (MCO) on commercial treatment-planning systems (Eclipse, Varian Medical System, Palo Alto, CA, USA) for patients with prostate cancer. We selected 25 plans of patients with prostate cancer who were previously treated on the basis of a VMAT plan. All plans were imported into the Eclipse Treatment Planning System version 15.6, and re-calculation and re-optimization were performed. The MCO plan was then generated. The dosimetric quality of the plans was evaluated using dosimetric parameters and dose indices that account for target coverage and sparing of the organs at risk (OARs). We defined the rectum, bladder, and bilateral femoral heads. The VMAT-MCO plan offers an improvement of gross treatment volume coverage with increased minimal dose and reduced maximal dose. In the planning treatment volume, the Dmean and better gradient, homogeneity, and conformity indexes improved despite the increasing hot and cold spots. When implemented through the MCO plan, a steeper fall off the adjacent OARs in the overlap area was achieved to obtain lower dose parameters. MCO generated better sparing of the rectum and bladder through a tradeoff of the increasing dose to the bilateral femoral heads within the tolerable dose constraints. Compared with re-optimization and re-calculation, respectively, significant dose reductions were observed in the bladder (241 cGy and 254 cGy; p<0.001) and rectum (474 cGy and 604 cGy, p<0.001) with the MCO. Planning evaluation and dosimetric measurements showed that the VMAT-MCO plan using visualized navigation can provide sparing of OAR doses without compromising the target coverage in the same OAR dose constraints.

Multicriteria optimization: Site-specific class solutions for VMAT plans

Multicriteria optimization (MCO), a novel commercially available optimization method for IMRT and VMAT has the potential to improve treatment planning techniques and workflows. MCO allows planners and physicians to assess in real time the impact and tradeoffs between all clinical goals and organ constraints. We investigate the feasibility of a universal set of objectives and constraints for VMAT plans in different anatomical sites and the impact of involving the Physician in the navigation of the generated Pareto plans. We randomly selected 20 prostate only, 14 whole pelvis, 10 advanced lung, 15 pancreas, and 7 head and neck plans planned with a VMAT technique. Using the clinically delivered isocenter and beam set-up, we retrospectively generated MCO plans with a universal set of constraints and objectives for each anatomical site. The MCO plan scores were compared with clinical plans or an independent plan generated with DMPO. For prostate only plans the TCP values for the clinical and MCO plans were similar and the rectum NTCP values and overall P+ were slightly better for the MCO plans. For whole pelvis, the resulting MCO plans were comparable in all the dosimetric measures to the clinical plans. For lung, the MCO dosimetric comparison also yielded comparable plans but when evaluating individual patients, there were 5 patients for which MCO plans had a clear advantage in reducing dose to lung and/or esophagus while improving/maintaining target coverage, 4 patients with comparable plans and 1 patient where MCO was worse. Allowing the physician to navigate independently produced a different selection of dosimetric trade-offs. Comparable MCO plans were also obtained for pancreas and head and neck. Based on our experience with many anatomical sites and a large number of patient plans, we have found that VMAT MCO plans are comparable to the clinical plans and can be produced with a universal set of objectives and constraints, even for a wide range of geometries and anatomies.

23 First experience of multi-criteria optimization planning of tomotherapy plans

Introduction Following the recent introduction of a Tomotherapy module in the RayStation system (RayTomo), we evaluated the capacities of the new multi-criteria optimizer (MCO), as well as its ability to deliver the plans with phantom measurements. Methods Fifteen patients (including head and neck, pelvis, and breast cases) previously treated with Tomotherapy Planning Station (TomoPS) from Accuray were re-planned with RayTomo. To avoid the variability and user dependence associated with a “classical” inverse optimization algorithm, MCO constraints were generated from a script taking into account the overlap of OARs with the targets [1] . Pareto plans were generated based on these constraints, and after achieving comparable target coverage in the plan navigation, the results were compared in terms of dose to organs-at-risk (OARs). Finally, a plan was exported to the machine and delivered on an Octavius phantom to obtain dose measurements with a 2D chamber array, and results were assessed using local gamma-analysis (3%-3 mm). Results Mean doses to important OARs were substantially reduced in head and neck and pelvic patients (Tables 1 and 2), while maximum doses remained essentially unchanged. Smaller mean dose reductions were also observed for the breast patients, together with a decrease in maximum doses. The Delivery Quality Assurance (DQA) plan showed a passing rate of ⩾ 95% with the 3%(local)-3 mm criterion routinely used in our center, indicating that the calculated MCO plan could reliably be delivered on the machine though the way to use the MLC is different. Download : Download high-res image (167KB) Download : Download full-size image Download : Download high-res image (94KB) Download : Download full-size image Conclusions Results obtained so far suggest that MCO with Tomotherapy might produce better results in OAR sparing than classical inverse optimization, but more importantly, it could greatly reduce the need for user input and interaction, and hence improve the homogeneity of the plans between users and institutions. Further dose measurements are ongoing to ensure the reliability of this new module.

Adaptive method for multicriteria optimization of intensity-modulated proton therapy.

Provide an adaptive multicriteria optimization (MCO) method for intensity-modulated proton therapy (IMPT) utilizing GPU technology. Previously described limitations of MCO such as Pareto approximation and limitation on the number of objectives were addressed. The treatment planning process for IMPT must account for multiple objectives, which requires extensive treatment planning resources. Often a large number of objectives (>10) are required. Hence the need for an MCO algorithm that can handle large number of objectives. The novelty of the MCO method presented here lies on the introduction of the adaptive weighting scheme that can generate a well-distributed and dense representation of the Pareto surface for a large number of objectives in an efficient manner. In our approach the generated Pareto surface is constructed for a set of DVH objectives. The MCO algorithm is based on the augmented weighted Chebychev metric (AWCM) method with an adaptive weighting scheme. This scheme uses the differential evolution (DE) method to generate a set of well-distributed Pareto points. The quality of the Pareto points' distribution in the objective space was assessed quantitatively using the Pareto sampling metric. The MCO algorithm was developed to perform multiple parallel searches to achieve a rapid mapping of the Pareto surface, produce clinically deliverable plans, and was implemented on a GPU cluster. The MCO algorithm was tested on two clinical cases with 10 and 18 objectives. For each case one of the MCO-generated plans was selected for comparison with the clinically generated plan. The MCO plan was randomly selected out of the set of MCO plans that had target coverage similar to the clinically generated plan and the same or better sparing of the organs at risk (OAR). Additionally, a validation study of the AWCM method vs the weighted sum method was performed. The adaptive MCO algorithm generated Pareto points on the Pareto hypersurface in a fast (2-3 hr) and efficient manner for 2 cases with 10 and 18 objectives. The MCO algorithm generated a dense and well-distributed set of Pareto points on the objective space, and was able to achieve minimization of the Pareto sampling metric. The selected MCO plan showed an improvement of the DVH objectives in comparison to the clinically optimized plan in both cases. For case one, the MCO plan showed a 48% reduction of the 50% dose to OARs and a 16% reduction of the 1% dose to OARs. For case 2, the MCO plan showed a 72% reduction of the 50% dose to OARs and a 42% reduction of the 1% dose to OARs. The comparison of AWCM to WS showed that the AWCM method has a dosimetric advantage over WS for both patient cases. We introduced an adaptive MCO algorithm for IMPT accelerated using GPUs. The algorithm is based on an adaptive method for generating Pareto plans in the objective space. We have shown that the algorithm can provide rapid and efficient mapping of the multicriteria Pareto surface with clinically deliverable plans.

A multi-criteria optimization approach for HDR prostate brachytherapy: II. Benchmark against clinical plans

The current iterative approach to inverse planning of high dose rate treatment planning can be time consuming. The purpose of this two-part study is to streamline the planning process while maintaining plan quality. In this second part, a multi-criteria optimization (MCO) planning algorithm is proposed and benchmarked against a standard planning algorithm.With a set of previously established regression models, a patient-specific valid solution space on the Pareto surface was predicted based on the anchor plans results. Alternative plans generated alongside the partial Pareto front were presented to the planner, and one plan was selected as the MCO plan. The dosimetric parameters results as well as the planning time were compared between the MCO plans and the physician-approved standard plans for 236 prostate cases.Results show that the urethra is better spared with MCO planning than with standard planning (a lower mean urethral D10 value of 2.25%). The overall MCO plan quality also outperforms the standard plan quality, since MCO planning is able to increase the frequency of clinically acceptable plans meeting all of RTOG criteria simultaneously without any human intervention (from 83.05% to 97.46%). Finally, the average MCO planning time is without any interventions of treatment planners.The presented MCO planning algorithm constitutes a robust and automated way to improve treatment quality in brachytherapy.

A new strategy for volumetric-modulated arc therapy planning using AutoPlanning based multicriteria optimization for nasopharyngeal carcinoma

BackgroundA new strategy for making the appropriate choice of the representative optimization parameters in planning processes and accurate selection criteria during Pareto surface navigation for general multicriteria optimization (MCO) was recommended in the study. The purpose was to combine both benefits of AutoPlanning optimization and MCO (APMCO) for achieving an individual volumetric-modulated arc therapy (VMAT) plan according to the clinically achieved patient-specific tradeoff among conflicting priorities. The preclinical investigation of this optimization approach for nasopharyngeal carcinoma (NPC) radiotherapy was performed and compared to general MCO VMAT.MethodsA total of 60 NPC patients with various stages were enrolled in this study. General MCO and APMCO plans were generated for each patient on the treatment planning system. The differences between two planning schemes were evaluated and compared.ResultsAll plans were capable of achieving the prescription requirement. The planning target volume coverage and conformation number were remarkably similar between general MCO and APMCO plans. There were no significant differences in most of organs at risk (OARs) sparing. However, in APMCO plans, relatively remarkable decreases were observed in the mean dose (Dmean) to the glottic larynx and pharyngeal constrictor muscles. The reductions of average Dmean to the two OARs were 10.5% (p < 0.0001) and 8.4% (p < 0.0001), respectively. APMCO technique was found to increase the planning time for an average of approximately 5 h and did not lead to a significant increase of monitor units compared to general MCO.ConclusionsThe potential of the APMCO strategy is best realized with a clinical implementation that exploits individual generation of Pareto surface representations without manual interaction. It also assists physicians to ensure navigation in a more efficient and straightforward manner.

Multi-criteria optimization achieves superior normal tissue sparing in intensity-modulated radiation therapy for oropharyngeal cancer patients

ObjectivesTo evaluate the benefit of intensity-modulated radiation therapy (IMRT) with multi-criteria optimization (MCO) in patients with oropharyngeal cancer (OPC) and compare the dose difference between the MCO plans navigated by physicians and dosimetrists. Materials and methodsThe conventional IMRT plans (nonMCO) and MCO IMRT plans navigated by physicians and dosimetrists (MCOp and MCOd) were created for 30patients with OPC. All the plans were reviewed, and the planning time and dose-volume parameters were compared. ResultsThe difference of D95 among three kinds of plans was not significant (p > 0.05). The maximum dose and D2 of spinal cord, brain stem, the mean dose of bilateral parotids, cochlea, oral cavity and glottic larynx were lower in MCO plans than those in nonMCO plans (p < 0.017). Furthermore, MCOp showed better bilateral parotids, oral cavity and glottic larynx sparing compared to MCOd (p < 0.017), in which the magnitude was related to the overlapping volume of the corresponding organ at risk (OAR) and targets. The active planning time was reduced by a median of 94.3 min (MCOd vs. nonMCO) or 91.6 min (MCOp vs. nonMCO). ConclusionMCO IMRT plans significantly reduced the dose of OARs and the active planning time, without compromising the target coverage in OPC patients; navigations by physicians could be beneficial to the dose sparing of the OARs with high complication rate and those overlapping with targets; the constraints could be the predominant factor affecting the results of optimization in the MCO IMRT planning.

Physician Driven Multicriteria Optimization of Advanced Lung Cancer Patients VMAT Plans

Multi-Criteria Optimization (MCO), a novel commercially available optimization method for intensity modulated and volumetric arc therapies (IMRT and VMAT) has the potential to improve treatment planning techniques and workflows. By navigating between Pareto solutions, MCO allows planners and physicians to assess in real time the impact and tradeoffs between all clinical goals and organ constraints. The purpose of our work is to investigate a universal set of objectives and constraints for lung cancer MCO VMAT plans and the impact of involving the Physician in the navigation of the generated Pareto plans. The central hypothesis is that physician-driven MCO VMAT plans will allow choice of optimal dosimetric trade-offs for a given individual patient. We randomly selected ten lung cancer patients (Stage II-IV) planned with a two arcs VMAT technique. Prescription doses ranged from 50.4Gy to 66Gy in 1.8 or 2Gy per fraction, with one case of dose painting. Target volumes were generated per clinical standard of care. The ITVs ranged from 18cc-387cc. Using the clinically delivered isocenter and beam set-up, we retrospectively generated MCO plans with a universal set of constraints and objectives that was developed by trying different combinations in a few patients. Two versions of the MCO plan scores (one navigated by the dosimetrist [MCOd] and one by the physician [MCOp]) were compared with clinical plans generated with Direct Machine Parameter Optimization (DMPO). Dosimetric and biological parameters evaluated were PTV V95%, Conformity Index (CI), PTV Dmax and the un-complicated probability (UP) representing the absence of lung and esophagus complications. The cord dose was not evaluated because almost all plans had Dmax doses of less than 45Gy, with negligible probability of complications. MCOd vs clinical comparison: the values for PTV V95 were MCOd: 99%(95-100) vs clinical plans: 98% (94-100),p-value= 0.2, the CI were similar in both cases (p-value=0.5) but the Dmax was higher for the MCO plans (average 109% vs. 107%, p =0.004), the lung-esophagus UP was similar between MCOd (Mean: 74%, range: 55-87%) and the clinical pla(Mean:75%, range: 60-89%), p= 0.1. Corresponding MCOd versus MCOp comparisons were similar for the parameters tested. However, using real time assessment of dosimetric trade-offs, in each individual plan the physician was able to actively choose a preferred combination of dose to target vs organs. When evaluating individual patients, there were five patients for which MCO plans had a clear advantage in reducing dose to lung and/or esophagus while improving/maintaining target coverage, four patients with comparable plans and one patient where MCO was worse. MCO VMAT lung plans obtained with standardized objectives and constraints generated comparable or better plans than the clinical DMPO plans while allowing physicians to make real time comparisons of dosimetric trade-offs and accept a plan optimal for an individual patient.

WE‐AB‐209‐04: Biological Evaluation of Universal Multi‐Criteria Optimization VMAT Prostate Plans

Purpose:In recent years Multi‐Criteria Optimization (MCO) has become commercially available as a potential optimization method for intensity modulated and volumetric arc therapies (IMRT and VMAT). The purpose of our work is to develop a universal set of objectives and constraints to generate prostate cancer MCO plans with VMAT and evaluate them using biological metrics.Methods:We randomly selected ten prostate plans (two‐arc VMAT) for patients with intermediate risk prostate cancer prescribed 75.6–79.2Gy to the prostate and seminal vesicles. We compared the plan scores to our clinical plans generated with standard IMRT optimization techniques. The planning target volumes (PTV) were 5–10 mm set‐up margin expansion of the gross target volume. Using the same two arcs we generated MCO plans with a standard set of constraints and objectives using Raystation v4.5. The dose‐volume histograms (DVH) for the (PTV), rectum and bladder were exported and used to calculate tumor control probability (TCP) and the complication‐free tumor control probability P+ using biological models from the literature. We classified the plans by their level of difficulty based on the rectum‐PTV overlap and develop MCO plans with similar levels of conformality as the clinical plans.Results:The P+ values of the MCO plans had an average of 86.4%±2.3% and were equivalent to the clinical plans (P+ average of 85.0%±2.1%, p‐value=0.33). The MCO NTCP values for the rectum ranged from 0.7% to 20% and were highly correlated with rectum‐PTV overlap. NTCP values for the bladder were less than 1% for all MCO plans.Conclusion:MCO VMAT prostate plans obtained with standardized objectives and constraints generate biologically equivalent plans to the clinical plans generated with standard optimization techniques.

SU-G-BRC-02: A Novel Multi-Criteria Optimization Approach to Generate Deliverable Intensity-Modulated Radiation Therapy (IMRT) Treatment Plans

Purpose: To present a novel multi-criteria optimization (MCO) solution approach that generates treatment plans with deliverable apertures using column generation. Methods: We demonstrate our method with 10 locally advanced head-and-neck cancer cases retrospectively. In our MCO formulation, we defined an objective function for each structure in the treatment volume. This resulted in 9 objective functions, including 3 distinct objectives for primary target volume, high-risk and low-risk target volumes, 5 objectives for each of the organs-at-risk (OARs) (two parotid glands, spinal cord, brain stem and oral cavity), and one for the non-target non-OAR normal tissue. Conditional value-at-risk (CVaR) constraints were utilized to ensure at least certain fraction of the target volumes receiving the prescription doses. To directly generate deliverable plans, column generation algorithm was embedded within our MCO approach for aperture shape generation. Final dose distributions for all plans were generated using a Monte Carlo kernel-superposition dose calculation. We compared the MCO plans with the clinical plans, which were created by clinicians. Results: At least 95% target coverage was achieved by both MCO plans and clinical plans. However, the average conformity indices of clinical plans and the MCO plans were 1.95 and 1.35, respectively (31% reduction, p<0.01). Compared to the conventional clinical plan, the proposed MCO method achieved average reductions in left parotid mean dose of 5% (p=0.06), right parotid mean dose of 18% (p<0.01), oral cavity mean dose of 21% (p=0.03), spinal cord maximum dose of 20% (p<0.01), brain stem maximum dose of 61% (p<0.01), and normal tissue maximum dose of 5% (p<0.01), respectively. Conclusion: We demonstrated that the proposed MCO method was able to obtain deliverable IMRT treatment plans while achieving significant improvements in dosimetric plan quality.

Multi-criteria optimization achieves superior normal tissue sparing in a planning study of intensity-modulated radiation therapy for RTOG 1308-eligible non-small cell lung cancer patients

PurposeIn this planning study, we studied the benefit of intensity-modulated radiation therapy (IMRT) with multi-criteria optimization (MCO) in locally advanced non-small cell lung carcinoma (NSCLC). MethodsWe selected 10 consecutive patients with gross tumor within 1cm of the esophagus eligible for RTOG 1308, randomized phase II trial of 70Gy protons vs photons. Planning was performed per protocol. In addition, a novel approach for esophagus sparing was applied by making the contralateral esophagus (CE) an avoidance structure. MCO and non-MCO plans underwent double-blinded review. Plan differences in dose–volume histogram parameters were analyzed. ResultsMedian plan differences were mean lung dose=0.8Gy (p=0.01), lung V20=1.1% (p=0.06), heart V30=1.0% (p=0.03), heart V45=0.6% (p=0.03), esophagus V60=1.2% (p=0.04), and CE V45=3.2% (p=0.01), all favoring MCO over non-MCO. PTV coverage with 95% dose was ⩾98.0% for both plans. There were 5 minor protocol deviations with non-MCO plans and 2 with MCO. Median improvement of active planning time with MCO was 88min (p<0.01). Physicians preferred 8 MCO and 2 non-MCO plans (p=0.04). ConclusionsMCO plans yielded significant improvements in organ-at-risk sparing without compromising target coverage, consumed less dosimetrist time, and were preferred by physicians. We suggest incorporating MCO into prospective clinical trials.

MO‐G‐304‐04: Generating Well‐Dispersed Representations of the Pareto Front for Multi‐Criteria Optimization in Radiation Treatment Planning

Purpose:To present a novel multi‐criteria optimization (MCO) solution approach that generates well‐dispersed representation of the Pareto front for radiation treatment planning.Methods:Different algorithms have been proposed and implemented in commercial planning software to generate MCO plans for external‐beam radiation therapy. These algorithms consider convex optimization problems. We propose a grid‐based algorithm to generate well‐dispersed treatment plans over Pareto front. Our method is able to handle nonconvexity in the problem to deal with dose‐volume objectives/constraints, biological objectives, such as equivalent uniform dose (EUD), tumor control probability (TCP), normal tissue complication probability (NTCP), etc. In addition, our algorithm is able to provide single MCO plan when clinicians are targeting narrow bounds of objectives for patients. In this situation, usually none of the generated plans were within the bounds and a solution is difficult to identify via manual navigation. We use the subproblem formulation utilized in the grid‐based algorithm to obtain a plan within the specified bounds. The subproblem aims to generate a solution that maps into the rectangle defined by the bounds. If such a solution does not exist, it generates the solution closest to the rectangle. We tested our method with 10 locally advanced head and neck cancer cases.Results:8 objectives were used including 3 different objectives for primary target volume, high‐risk and low‐risk target volumes, and 5 objectives for each of the organs‐at‐risk (OARs) (two parotids, spinal cord, brain stem and oral cavity). Given tight bounds, uniform dose was achieved for all targets while as much as 26% improvement was achieved in OAR sparing comparing to clinical plans without MCO and previously proposed MCO method.Conclusion:Our method is able to obtain well‐dispersed treatment plans to attain better approximation for convex and nonconvex Pareto fronts. Single treatment plan can be achieved when given bounds on the objectives.

SU‐E‐T‐614: Plan Averaging for Multi‐Criteria Navigation of Step‐And‐Shoot IMRT

Purpose:Step‐and‐shoot IMRT is fundamentally discrete in nature, while multi‐criteria optimization (MCO) is fundamentally continuous: the MCO planning consists of continuous sliding across the Pareto surface (the set of plans which represent the tradeoffs between organ‐at‐risk doses and target doses). In order to achieve close to real‐time dose display during this sliding, it is desired that averaged plans share many of the same apertures as the pre‐computed plans, since dose computation for apertures generated on‐the‐fly would be expensive. We propose a method to ensure that neighboring plans on a Pareto surface share many apertures.Methods:Our baseline step‐and‐shoot sequencing method is that of K. Engel (a method which minimizes the number of segments while guaranteeing the minimum number of monitor units), which we customize to sequence a set of Pareto optimal plans simultaneously. We also add an error tolerance to study the relationship between the number of shared apertures, the total number of apertures needed, and the quality of the fluence map re‐creation.Results:We run tests for a 2D Pareto surface trading off rectum and bladder dose versus target coverage for a clinical prostate case. We find that if we enforce exact fluence map recreation, we are not able to achieve much sharing of apertures across plans. The total number of apertures for all seven beams and 4 plans without sharing is 217. With sharing and a 2% error tolerance, this number is reduced to 158 (73%).Conclusion:With the proposed method, total number of apertures can be decreased by 42% (averaging) with no increment of total MU, when an error tolerance of 5% is allowed. With this large amount of sharing, dose computations for averaged plans which occur during Pareto navigation will be much faster, leading to a real‐time what‐you‐see‐is‐what‐you‐get Pareto navigation experience.Minghao Guo and Hao Gao were partially supported by the NSFC (#11405105), the 973 Program (#2015CB856000) and the Shanghai Pujiang Talent Program (#14PJ1404500).

Advantages and limitations of navigation-based multicriteria optimization (MCO) for localized prostate cancer IMRT planning

Efficacy of inverse planning is becoming increasingly important for advanced radiotherapy techniques. This study’s aims were to validate multicriteria optimization (MCO) in RayStation (v2.4, RaySearch Laboratories, Sweden) against standard intensity-modulated radiation therapy (IMRT) optimization in Oncentra (v4.1, Nucletron BV, the Netherlands) and characterize dose differences due to conversion of navigated MCO plans into deliverable multileaf collimator apertures. Step-and-shoot IMRT plans were created for 10 patients with localized prostate cancer using both standard optimization and MCO. Acceptable standard IMRT plans with minimal average rectal dose were chosen for comparison with deliverable MCO plans. The trade-off was, for the MCO plans, managed through a user interface that permits continuous navigation between fluence-based plans. Navigated MCO plans were made deliverable at incremental steps along a trajectory between maximal target homogeneity and maximal rectal sparing. Dosimetric differences between navigated and deliverable MCO plans were also quantified. MCO plans, chosen as acceptable under navigated and deliverable conditions resulted in similar rectal sparing compared with standard optimization (33.7 ± 1.8Gy vs 35.5 ± 4.2Gy, p = 0.117). The dose differences between navigated and deliverable MCO plans increased as higher priority was placed on rectal avoidance. If the best possible deliverable MCO was chosen, a significant reduction in rectal dose was observed in comparison with standard optimization (30.6 ± 1.4Gy vs 35.5 ± 4.2Gy, p = 0.047). Improvements were, however, to some extent, at the expense of less conformal dose distributions, which resulted in significantly higher doses to the bladder for 2 of the 3 tolerance levels. In conclusion, similar IMRT plans can be created for patients with prostate cancer using MCO compared with standard optimization. Limitations exist within MCO regarding conversion of navigated plans to deliverable apertures, particularly for plans that emphasize avoidance of critical structures. Minimizing these differences would result in better quality treatments for patients with prostate cancer who were treated with radiotherapy using MCO plans.

SU‐E‐T‐648: Multi‐Criteria Optimization for Real‐Time Planning of Lung Cancer Radiotherapy

Purpose: Multi‐criteria optimization (MCO) is implemented for planning lung cancer radiotherapy treatments to clarify patient‐specific tradeoffs and allow real‐time plan decision making. Methods: For four locally advanced lung cancer patients (P1–P4), a basis set of MCO plans are constructed and compared to plans determined from fixed‐objective (FO) optimization for organs at risk (OARs). All optimized plans include constraints on target‐D95&gt;70 Gy and spinal cord Dmax&lt;45 Gy. Five MCO basis plans are designed per patient through weight variation of four non‐zero dose‐volume objectives (DVOs) for ipsilateral lung (iLung), contralateral lung (cLung), heart, and esophagus. The five basis plans are optimized according to: (1) simultaneous minimization of four OAR‐DVOs and (2–5) weight variation for one OAR‐DVO. Results: Patient‐specific tradeoffs between OAR objectives are revealed with MCO which are not evident in FO‐optimization. For P1, MCO basis plans vary iLung‐V20 from 46% to 65% and show that V20&lt;46% is not achievable; the FO iLung‐V20 is 54%. For P2,the FO‐plan trades off a 1% reduction in iLung‐V20 for a 29% increase in esophagus‐V20. An interpolated MCO plan, in this case, takes advantage of this tradeoff to reduce esophagus V20 by from 41% to 8%. P3 shows increasing heart‐V20 by 35% (from 20% to 55%) results in a 7% (34%‐27%) reduction in iLung‐V20. With P4, MCO reveals a tradeoff between the two lungs; varying iLung‐V20 from 23% to 30% corresponds to cLung‐V20 varying from 23% to 17%. The FO plan treats cLung up to the V20 objective (to 29%) without penalty. MCO shows the ability to reduce OAR dose‐volumes, but often led to increased PTV hotspots. Conclusion: Analysis of MCO plans clarifies conflicting objectives and exposes inherent limitations due to patient geometry. Real‐time planning is possible with a small set of MCO plans, and achieves plans which are superior to FO‐optimization. Supported by NIH P01‐CA‐116602 and Philips Medical Systems

Maximizing dosimetric benefits of IMRT in the treatment of localized prostate cancer through multicriteria optimization planning

We examine the quality of plans created using multicriteria optimization (MCO) treatment planning in intensity-modulated radiation therapy (IMRT) in treatment of localized prostate cancer. Nine random cases of patients receiving IMRT to the prostate were selected. Each case was associated with a clinically approved plan created using Corvus. The cases were replanned using MCO-based planning in RayStation. Dose-volume histogram data from both planning systems were presented to 2 radiation oncologists in a blinded evaluation, and were compared at a number of dose-volume points. Both physicians rated all 9 MCO plans as superior to the clinically approved plans (p<10−5). Target coverage was equivalent (p = 0.81). Maximum doses to the prostate and bladder and the V50 and V70 to the anterior rectum were reduced in all MCO plans (p<0.05). Treatment planning time with MCO took approximately 60 minutes per case. MCO-based planning for prostate IMRT is efficient and produces high-quality plans with good target homogeneity and sparing of the anterior rectum, bladder, and femoral heads, without sacrificing target coverage.