Hybrid Planning Research Articles

Technical Note: Development of 3D‐printed breast phantoms for end‐to‐end testing of whole breast volumetric arc radiotherapy

End‐to‐end testing of a new breast radiotherapy technique preferably requires realistic phantom geometries, which is challenging to achieve using currently commercially available solutions. We have developed a series of three‐dimensional (3D)‐printed breast phantoms, with ionization chamber and radiochromic film inserts, which can be attached to a commercial anthropomorphic thorax phantom. A contoured left breast from a patient’s planning CT was mapped onto a CT of the CIRS E2E thorax phantom (CIRS Inc.) and cropped to fit the surface. Four versions of the breast were 3D printed, containing a cavity for an ionization chamber and slits for radiochromic film insertion in the three cardinal planes, respectively. The phantoms were fully compatible with surface scanning technology used for setup. The phantoms were validated using a whole‐breast volumetric modulated arc therapy protocol with a simultaneous integrated boost to the tumor bed (VMAT‐SIB). Six patient plans and one original plan on the breast phantom were verified with planar portal imaging, point dose, and film measurements in the MultiCube phantom and planar γ‐analysis using ArcCHECK diode array. Six patient plans were recalculated on the breast phantom (hybrid plans) and delivered with point dose and film measurements with 3% (local)/2 mm γ‐analysis. One complete end‐to‐end test on the breast phantom was performed. All plan quality verifications had point dose differences below 2.4% from the calculated dose and γ‐agreement scores (γAS) > 87.3% for film measurements in the MultiCube, portal dosimetry, and ArcCHECK. Point dose differences in the 3D‐printed phantoms were below 2.6% (median −1.4%, range −2.6%; 0.3%). Median γAS was 96.4% (range 80.1%–99.7%) for all film inserts. The proposed 3D‐printed attachable breast dosimetry phantoms have been shown to be a valuable tool for end‐to‐end testing of a new radiotherapy protocol. The workflow described in this report can aid users to create their own phantom‐specific breast 3D‐printed phantoms.

An AI-Based Planning Framework for HAPS in a Time-Varying Environment

A High-Altitude Pseudo-Satellite (HAPS) is a fixed-wing, solar-powered Unmanned Aerial Vehicle (UAV) developed to become a flexible alternative to satellites with fixed-orbits for monitoring ground activities over long periods of time. However, given its lightweight build and weak electro-motors, the platform is rather sensitive to weather and cannot fly around hazardous weather zones swiftly. In this work, we formulate the problem of planning missions for multiple HAPS as a hybrid planning problem expressed in PDDL+. The formulation also considers the problem of modeling the platform dynamics, the time-varying environment, and the heterogeneous tasks that need to be carried out. Additionally, we propose a framework that combines a PDDL+ automated planner with an Adaptive Large Neighborhood Search (ALNS) approach, developed to couple the automated planner with a meta-heuristic that is specific for the problem. The task and motion planning are done in an intertwined way within the framework, preserving hence a common decision/search space. We validate our approach with a third-party realistic simulator for HAPS, as well as with a set of benchmark tests, showing that our integrated approach produces executable mission plans.

Refining Process Descriptions from Execution Data in Hybrid Planning Domain Models

The creation and maintenance of a domain model is a well recognised bottleneck in the use of automated planning; indeed, ensuring a planning engine is fed with an accurate model of an application is essential in order that generated plans are effective. Engineering domain models using a hybrid representation is particularly challenging as it requires accurately describing continuous processes, which can have complex numeric effects. In this work we consider the problem of the refinement of an engineered hybrid domain model, to more accurately capture the effect of the underlying processes. Our approach exploits the information content of the original model, utilising machine learning techniques to identify important situation and temporal features that indicate a variation in the original effect. We use the problem of modelling traffic flows in an Urban Traffic Management setting as a case study and demonstrate in our evaluation that the refined domain models provide more accurate simulation, which can lead to higher quality plans. The contribution of this work is a general approach to the automated refinement of hybrid planning domain models that reduces the knowledge engineering effort in producing a detailed process model. The approach can be used for refining the domain model during the initial stages of development, or for re-configuring the domain model when used in the same problem area but with a different scenario. We test out the approach within a real world case study.

Dosimetric comparison of helical tomotherapy and hybrid (3DCRT-VMAT) technique for locally advanced non-small cell lung cancer

AbstractAim:The purpose of the present study is to compare hybrid [three-dimensional conformal radiation therapy-volumetric-modulated arc therapy (3DCRT-VMAT)] and helical tomotherapy (HT) techniques in terms of both planning target volume (PTV) and organs at risk (OARs) in the plans we made in locally advanced non-small cell lung cancer (NSCLC) patientsMaterial and methods:Radiotherapy was planned for 15 locally advanced NSCLC patients with 2 different techniques. Large tumours with positive mediastinal lymph nodes were preferred. The prescription dose was determined as 60 Gy at 30 fractions.Results:Mean PTV volume was 602·5 cc (range: 265–1461). Mean total lung volume was 4264 cc (range: 1885–6803). Homogeneity index, Dmean, Dmax, D2 and V105 were found to be lower in HT, V100, total monitor units (MU) and total beam on time were found to be lower in the hybrid plan. Total lung Dmean was found to be 17 Gy in both techniques. V10 value was 42·85 in the hybrid plan and 48·67 in HT (p = 0·037). Heart Dmean was 14·5 Gy in the hybrid plan and 18·7 in HT (p < 0·001), and V30 values were 18·1 and 22·9, respectively (p = 0·009).Conclusion:Suitable dose coverage and OAR doses can be provided with both techniques. Especially the opposite lung, heart and oesophagus doses can be kept lower with the hybrid plan, and lower MU and shorter beam on time can be provided.

A sizing-validation approach to hybrid power system design and planning

Renewable energy (RE) is an important emissions reduction technology for climate change mitigation. Hybrid power systems (HPSs) are designed to facilitate the deployment of RE. This paper addresses HPS design under RE resource uncertainties and presents a two-step mathematical approach. The method involves the use of an optimisation model for HPS sizing and Monte Carlo simulation for results validation. The superstructure-based model considers all feasible power allocation options in an HPS and allows the selection of energy storage technologies. To account for resource uncertainty, chance-constrained programming is applied in the optimisation model and the effective power output of renewable sources can be computed according to the specified system reliability. The optimised HPS configuration is then simulated and its reliability estimated to ensure that the specified system reliability level is achieved. Two case studies of isolated and on-grid HPSs are used to demonstrate the proposed approach. The results show that for higher system reliability, the isolated system requires larger generator and energy storage capacities, whilst the on-grid system requires more grid electricity instead of intermittent RE. Further analyses are performed to explore the trade-off between cost and carbon emissions as well as to assess the effects of electricity price and emission factors on HPS design.

Breast boost vector: a new metric proposed to optimise isocentre location in an fIMRT–VMAT hybrid technique for a simultaneous integrated boost in breast radiotherapy

AbstractPurpose:Evaluating the improvements of placing the treatment isocentre at the boost centre of mass (CoM) in a hybrid treatment for breast cancer radiotherapy.Material and methods:Twenty-two patients were planned in two isocentre locations with two forward intensity-modulated radiation therapy (fIMRT) tangentials to the breast and a volumetric-modulated arc therapy (VMAT) to the boost. A simultaneous integrated boost technique was used. Breast Boost (BB) Vector was investigated as a criterion for selecting an appropriate isocentre placement. Various metrics for boost, breast and hybrid plans were analysed using analysis of variance statistics.Results:Comparing hybrid plans at the boost CoM vs. hybrid plans at the breast CoM, no significant differences were found. Analysis of relative variations of planning target volume (PTV) boost coverage vs. BB Vector indicated an upgrade in boost CoM isocentre strategy. Dose to organs at risk was comparable: V5Gy (26·24 vs. 25·69%, p = 0·8), V20Gy (14·66 vs. 14·58%, p = 0·959) and the mean dose (7·37 Gy vs. 7·26 Gy, p = 0·879) to ipsilateral lung; V5Gy (15·60 vs. 15·22%, p = 0·903), and the mean dose (4·91 Gy vs. 4·86 Gy, p = 0·950) to heart and dose to free breast of boost (46·71 Gy vs. 46·62 Gy, p = 0·408).Findings:The hybrid fIMRT–VMAT technique centred at the boost CoM resulted equivalent to plans centred at the breast CoM, while benefiting from an enhancement in PTV boost coverage for patients with BB Vector superior to 5.

Enable faster and smoother spatio-temporal trajectory planning for autonomous vehicles in constrained dynamic environment

Trajectory planning is of vital importance to decision-making for autonomous vehicles. Currently, there are three popular classes of cost-based trajectory planning methods: sampling-based, graph-search-based, and optimization-based. However, each of them has its own shortcomings, for example, high computational expense for sampling-based methods, low resolution for graph-search-based methods, and lack of global awareness for optimization-based methods. It leads to one of the challenges for trajectory planning for autonomous vehicles, which is improving planning efficiency while guaranteeing model feasibility. Therefore, this paper proposes a hybrid planning framework composed of two modules, which preserves the strength of both graph-search-based methods and optimization-based methods, thus enabling faster and smoother spatio-temporal trajectory planning in constrained dynamic environment. The proposed method first constructs spatio-temporal driving space based on directed acyclic graph and efficiently searches a spatio-temporal trajectory using the improved A* algorithm. Then taking the search result as reference, locally convex feasible driving area is designed and model predictive control is applied to further optimize the trajectory with a comprehensive consideration of vehicle kinematics and moving obstacles. Results simulated in four different scenarios all demonstrated feasible trajectories without emergency stop or abrupt steering change, which is kinematic-smooth to follow. Moreover, the average planning time was 31 ms, which only took 59.05%, 18.87%, and 0.69%, respectively, of that consumed by other state-of-the-art trajectory planning methods, namely, maximum interaction defensive policy, sampling-based method with iterative optimizations, and Graph-search-based method with Dynamic Programming.

A study on prostate movement and dosimetric variation because of bladder and rectum volumes changes during the course of image-guided radiotherapy in prostate cancer.

AimTo study the impact of bladder and rectum volume changes on prostate positioning and the dosimetric parameters.BackgroundProstate is a moving organ, and its position is also affected by bladder and rectum volumes. Image-guided radiotherapy (IGRT) is being practiced widely for the treatment of prostate carcinoma (Ca). So, it is important to accurately study the effect of bladder and rectum volume changes in treatment.Materials and methodsThirty patients with Ca prostate were included in this study, and all were treated with 50 Gray (Gy) in 25 fractions for the first phase of treatment. A total of 750 cone-beam computed tomography (CBCT) sessions were performed. Prostate position w.r.t. its day one position was noted, and the bladder and rectum volumes were compared with their volumes on day one. Also, repeat CT was done for five patients after 10 fractions. The initial plan was imported as it was on the repeat CT images, and a hybrid plan was prepared by putting the plan isocenter at the relative anatomical reference point in repeat CT images as it was in primary CT images. The multileaf collimators (MLC) fluence was put as it is, and the dose was calculated using the monitoring units (MU), which were in the initial plan. Doses to bladder, rectum, and the target were analyzed.ResultsThe mean prostate motion in lateral and anterior-posterior direction was found to be 0.71 (±0.69) centimeter cm) and 0.77 (±0.57) cm, respectively. The mean change in bladder and rectum volumes as compared to that in day one CT images was found to be 110.51 (±84.25) cubic centimeters (cc) and 10.89 (±10.17) cc, respectively. No significant variation was observed in the doses to bladder, rectum, and the target volume in a hybrid plan, as compared to that in actual initial plan.ConclusionsBladder and rectum volume affects the position of prostate, rather the dosimetric parameters, and therefore, it can be concluded that daily CBCT should be done for accurate IGRT delivery to the prostate cancer.

Hybrid planning techniques for hypofractionated whole-breast irradiation using flattening filter-free beams.

The aim of this study was to assess the feasibility of flattening filter-free (FFF) photon beams in hybrid intensity-modulated radiation therapy (H-IMRT) and hybrid volumetric modulated arc therapy (H-VMAT) for left-sided whole-breast radiation therapy with aboost volume (RT) using ahypofractionated dose regimen. RT plans of 25patients with left-sided early-stage breast cancer were created with H‑IMRT and H‑VMAT techniques under breath-hold conditions using 6‑MV FFF beams. In hybrid techniques, three-dimensional conformal radiotherapy (3DCRT) plans were kept as base-dose plans for the VMAT and IMRT plans. In addition, H‑IMRT in step-and-shoot mode was also calculated to assess its achievability with FFF beams. All hybrid plans achieved the expected target coverage. H‑VMAT showed better coverage and homogeneity index results for the boost target (p < 0.002), while H‑IMRT presented better results for the whole-breast target (p < 0.001). Mean doses to normal tissues were comparable between both plans, while H‑IMRT reduced the low-dose levels to heart and ipsilateral lung (p < 0.05). H‑VMAT revealed significantly better results with regard to monitor units (MU) and treatment time (p < 0.001). The 6‑MV FFF beam technique is feasible for large-field 3DCRT-based hybrid planning in whole-breast and boost planning target volume irradiation. For breath-hold patients, the H‑VMAT plan is superior to H‑IMRT for hypofractionated dose regimens, with reduced MU and treatment delivery time.

Planning for Flexible Surgical Robots via Bézier Spline Translation

In a minimally invasive surgery, new flexible instruments enable safer and easier access to difficult-to-reach anatomical regions. However, their introduction into the clinical workflow requires robust replanning because navigation errors during surgery render initially planned trajectories infeasible. Such replanning requires to regularly solve an expensive two-point boundary value problem (BVP) that connects the target pose of the instrument with the currently measured one. We propose a hybrid planning scheme that features both robust and safe replanning. This two-step approach first solves the BVP and then transforms the result to circular arcs that fit the motion of our instruments’ models. We exploit implicitly defined Bezier splines as a robust method for interpolation in the first step. A novel geometric translation of these splines, then, provides a convenient solution for movement along circular arcs. We consider two example applications: 1) planning for a drilling unit in temporal bone surgery; and 2) guidewires in catheter insertion. Evaluation on real patient data of both temporal bone and aorta show that our proposed hybrid two-step approach achieves, on average, ${\text{55}\%}$ higher replanning rates and provides ${\text{31}\%}$ larger clearance to risk structures, thus improving trajectory quality with regard to clinical safety.

Dosimetric comparison between volumetric-modulated arc therapy and a hybrid volumetric-modulated arc therapy and segmented field-in-field technique for postmastectomy chest wall and regional lymph node irradiation

Decreasing radiotoxicity to the heart, lungs, and contralateral breast has proven to lower the risk of secondary malignancy and improve overall outcomes when treating chest wall (CW) and regional lymph nodes in postmastectomy breast cancer patients. In this retrospective study, 11 postmastectomy patients were selected and planned with a novel hybrid treatment method and a traditional volumetric arc therapy (VMAT) approach for comparison. This hybrid technique was able to optimize tangential beams to minimize heart dose and the VMAT contribution to improve dose conformity around the planning target volume (PTV). Overall, this hybrid technique produced more homogenous target dose coverage and demonstrated a decrease of integral dose to organs at risk (OAR), while the VMAT technique demonstrated a higher affinity for maintaining dose conformity. Further observation of dose distributions also revealed that the hybrid plans were more effective in sparing low-dose spread to healthy tissue in both right- and left-sided cases. This observation was made evident by the reduction in heart V5 and Dmean, decreases in all parameters regarding the contralateral lung, as well as all values other than the V20 of the ipsilateral lung. This unique hybrid planning technique could present an alternative to standard intensity-modulated radiation therapy (IMRT) planning when treating postmastectomy CW and regional lymph nodes, as it has shown the capacity to decrease cardiac, lung, and contralateral breast toxicity while maintaining quality PTV coverage.

Spatial challenges in contemporary African New Towns and potentials for alternative planning strategies

ABSTRACTNew Towns in development across Africa are overwhelmingly designed according to twentieth-century planning models ranging from functionalist Chinese grids to American gated communities. Contemporary African New Towns based on these models are often unable to adapt to stimuli and, as a result, exacerbate both spatial and ecological challenges. The objective of this paper is to argue that African New Towns require a substantial shift from current practice and that planners must imagine new, hybrid planning strategies. This paper takes an exploratory approach and identifies the spatial challenges specific to contemporary African New Towns. Building on the argument that planning benefits from linkages between critical social theory and environmental science, this paper asserts that an adaptive urban planning approach that effectively engages citizens can be a more sustainable alternative to current practice. The paper concludes with implications for future research on the translation of challenges into potentials for African New Towns.

SBRT combined with concurrent chemoradiation in stage III NSCLC: Feasibility study of the phase I Hybrid trial

PurposeTo assess the technical and clinical feasibility of the phase I Hybrid trial (NCT01933568), combining SBRT of the primary tumor (PT) and fractionated radiotherapy (FRT) to the lymph nodes (LN). Materials and methodsTen patients with stage III NSCLC with a peripheral PT < 5 cm were prospectively selected. The EQD2 corrected normal tissue dose parameters of the FRT plan of 24×2.75 Gy to PT and 24×2.42 Gy to LN (IMRT) was compared with 3×18 Gy on the PT and 24×2.42 Gy on the LN (VMAT) using a Wilcoxon signed-rank test. To anticipate differential motion between PT and LN, worst-case scenarios for OAR were calculated. Electronic portal imaging device (EPID) dosimetry analysis was performed to rule out dosimetric errors during delivery. ResultsThe Hybrid plans revealed a significant decrease of esophagus EUD n = 0.13, lung V5 and V20 and a significant increase in Dmax of the PRV of the mediastinal envelope. Plans were robust against differential motion of 5 mm between PT and LN in 8 patients and failed in 2 patients due to spinal cord constraints. Average pass rates were ≥87% for EPID dosimetry. ConclusionsSBRT and FRT could be combined within the given OAR constraints. Safety will be assessed in the Hybrid trial.

Hard work with soft spaces (and vice versa): problematizing the transforming planning spaces

ABSTRACTThis article studies spaces and spatial imageries in planning from two viewpoints. First, it discusses how contemporary planning paradigms contribute to a process that can be labelled the ‘softening of hard spaces’. This means that typically old, well-established (planning) spaces with relatively hard administrative borders become redefined and treated in planning practice as soft entities with fuzzier or more porous borders. Second, it discusses how new soft spaces – such as gateways, new cross-border supranational spaces and ad hoc regional spaces – tend to simultaneously harden through intensifying institutional practices and discourses, as well as because of the need to define what is included and excluded in such new spatial structures/networks. These two processes, the softening of hard spaces and the hardening of soft spaces, are then scrutinized in tandem, and a conceptualization of intermediary hybrid planning spaces is proposed. This conceptual opening, labelled ‘penumbral’ space/border, is then examined. The explanatory value of these arguments is demonstrated by comparing the transformation of Northern Ostrobothnia, an old, well-established region in Finland, and the mobilization of Bothnian Arc, a new soft space stretching across the Swedish-Finnish border.

Hybrid planning and distributed iterative repair for multi-robot missions with communication losses

This paper presents a planning and execution architecture suited for the initial planning, the execution and the on-board repair of a plan for a multi-robot mission. The team as a whole must accomplish its mission while dealing with online events such as robots breaking down, new objectives for the team, late actions and intermittent communications. We have chosen a “plan then repair” approach where an initial plan is computed offline and updated online whenever disruptive events happen. We have defined an hybrid planner that mixes Partial Order Planning (POP) with a Hierarchical Task Network (HTN)-based modelling of actions. This planner, called HiPOP for Hierarchical Partial-Order Planner, computes plans with temporal flexibility (thus easing its execution) and abstract actions (thus easing the repair process). It uses a symbolic representation of the world and has been extended with geometrical reasoning to adapt to multi-robots missions. Plans are executed in a distributed way: each robot is responsible of executing its own actions, and to propagate delays in its local plan, taking benefit from the temporal flexibility of the plan. When an inconsistency or a failure arises, a distributed repair algorithm based on HiPOP is used to repair the plan, by iteratively removing actions in the plan in order to amend the global plan. This repair is done onboard one of the robot of the team, and takes care of partial communication. The whole architecture has been evaluated through several benchmarks, statistical simulations, and field experiments involving 8 robots.

Integration of biological factors in the treatment plan evaluation in breast cancer radiotherapy.

Tumor biology and patient smoking status have clear effects on the benefit of breast radiotherapy. This study developed treatment evaluation strategies that integrated dosimetry, tumor aggressiveness and smoking status for patients undergoing hypo-fractionated whole breast irradiation with simultaneous integrated boost. The evaluation method Plan Quality Metrics (PQM) was adapted for breast cancer. Radiotherapy (RT) benefit was assessed for three levels of tumor aggressiveness; RT risk was estimated using mean dose to organs at risk and published Excess Relative Risk per Gy data for lung cancer and cardiac mortality for smokers and non-smokers. Risk for contralateral breast cancer was also evaluated. PQM and benefit/risk was applied to four patient groups (n = 10 each). Plans using 3D conformal radiotherapy (3DCRT), 3DCRT plus intensity-modulated radiation therapy (IMRT), 3DCRT plus volumetric modulated arc therapy (VMAT) and VMAT were evaluated for each patient. 3DCRT-IMRT hybrid planning resulted in higher PQM score (median 87.0 vs. 3DCRT 82.4, p < 0.01), better dose conformity, lower doses to the heart, lungs and contralateral breast. Survival benefit was most predominant for patients with high-risk breast cancer (>7% and >4.5% gain for non-smokers and smokers). For smokers with intermediate- or low-risk breast cancer, RT induced mortality risk dominated for all techniques. When considering the risk of local recurrence, RT benefitted also smokers (>5% and >2% for intermediate- and low-risk cancer). PQM methodology was suggested for breast cancer radiotherapy evaluation. Further validation is needed. RT was beneficial for all patients with high risk of recurrence. A survival benefit for smokers with low or intermediate risk of recurrence could not be confirmed.

Cultivating Pension Plans

Federal law both cultivates and regulates employer-sponsored pension plans in the United States. Some believe that because employers have been migrating away from traditional defined benefit pension plans in the United States, the plan cultivation provisions of federal law have failed to encourage U.S. employers to offer pension benefits to their employees. However, Congress has allowed each employer to decide for itself whether to provide pension benefits to its employees and, if so, what kind of pension benefits to provide. Employers appear to have migrated away from traditional defined benefit plans primarily because employers have concluded that defined contribution plans and some hybrid plans are more compatible with their own interests and the interests of their employees than are traditional defined benefit plans.

United States Pension Benefit Plan Design Innovation: Labor Unions as Agents of Change

Labor unions played an historic role creating the occupational pension system in the private and public sectors in the post-World War II era. That system, which was dominated by defined benefit pension plans, is in decline. The transition to a new system is economically and socially painful, and has been accelerated by two financial crises in the past decade. This paper uses a case study of a private sector union to demonstrate how labor unions can influence the renegotiation of the pension contract for American workers. The case study describes how one union evaluated the pension crisis from a sustainability viewpoint, and responded pro-actively by developing a hybrid pension plan that attempted to align the interest of all the stakeholders through equitable risk sharing. The hybrid plan developed by this union eventually had a broader influence on the pension community at large and the public policy debate around the pension crisis.

Evaluation of optimal treatment planning for radiotherapy of synchronous bilateral breast cancer including regional lymph node irradiation

BackgroundWe evaluated the optimal radiotherapy (RT) plan for synchronous bilateral breast cancer (SBBC), especially treatment plans including the regional lymph node (LN) area.MethodsThis study was conducted using 15 patients with SBBC (5 with small breasts, 5 with large breasts, and 5 who underwent a left total mastectomy). The clinical target volume (CTV) was defined as the volume enveloping the bilateral whole breasts/chest wall and left regional LN area. We established the following plans: 1) volumetric-modulated arc therapy (VMAT)-the only plan using two pairs of partial arcs for the whole target volume, 2) VMAT using one partial arc for the left CTV followed by a 3D tangential technique for the right breast (primary hybrid plan), and 3) VMAT for the left CTV followed by a tangential technique using an automatically calculated prescription dose for the right breast, considering the background dose from the left breast VMAT plan (modified hybrid plan). The Tukey test and one-way analysis of variance were used to compare the target coverage and doses to organs at risk (OARs) of the three techniques.ResultsFor target coverage, the VMAT-only and modified hybrid plans showed comparable target coverage in terms of Dmean (50.33 Gy vs. 50.53 Gy, p = 0.106). The primary hybrid plan showed the largest distribution of the high-dose volume, with V105% of 25.69% and V110% of 6.37% for the planning target volume (PTV) (p < 0.001). For OARs including the lungs, heart, and left anterior descending artery, the percentages of volume at various doses (V5Gy, V10Gy, V20Gy, V30Gy) and Dmean were significantly lower in both the primary and modified hybrid plans compared to those of the VMAT-only plan. These results were consistent in subgroup analyses of breast size and morphological variation.ConclusionsThe modified hybrid plan, using an automatically calculated prescription dose for the right breast and taking into consideration the background dose from the left breast VMAT plan, showed comparable target coverage to that of the VMAT-only plan, and was superior for saving OARs. However, considering that VMAT can be adjusted according to the physician’s intention, further evaluation is needed for developing a better plan.

Adaptive intensity-modulated radiotherapy in head-and-neck cancer: A volumetric and dosimetric study.

Anatomic and volumetric changes occur in head-and-neck cancer during fractionated radiotherapy (RT), and the actual dose received by patient is considerably different from the original plan. The purpose of this study is to evaluate volumetric and dosimetric changes occurring during radiation therapy. Ten patients of locally advanced head-and-neck cancer, 6 oropharynx, 3 larynx, and 1 hypopharynx underwent computed tomography (CT) simulation before treatment and after 4 weeks during RT treatment. Original plan (OPLAN) was generated based on initial CT scan for the entire course of treatment. The initial plan is implemented on the second planning CT scan, and the dose distribution is recalculated. Beam configuration of OPLAN was applied onto the second CT scan and then hybrid plan (HPLAN30) was generated. RPLAN30 is the intensity-modulated RT replan generated on the second CT scan for the remaining 30 Gy. Dose and volume parameters between OPLAN30 (based on the first CT scan for the remaining 30 Gy), HPLAN30, and RPLAN30 were compared. The volume reduction of planning target volume (PTV), ipsilateral and contralateral parotid after 4 weeks of RT, was statistically significant (P < 0.05). D2% and V > 107% of PTV were higher in HPLAN than that of RPLAN (P < 0.05). Hybrid plans showed increase in delivered dose to spinal cord. Mid treatment replanning reduced doses to spinal cord (Dmax and D1%), which is statistically significant (P < 0.05). Mean doses to ipsilateral and contralateral parotid of RPLAN (21.4 Gy and 16.74 Gy, respectively) were reduced when compared to that of HPLAN (22.99 Gy and 22 Gy, respectively). Interim CT scanning and replanning (adaptive) improves target volume coverage and normal tissue sparing.