Intensity-modulated Radiation Therapy Treatment Plans Research Articles

Effects of bladder status on cervical cancer treatment with intensity‐modulated radiation therapy plans

AbstractObjectiveThe present study aimed to compare the effects of different bladder statuses on cervical cancer treatment with intensity‐modulated radiation therapy (IMRT) plans.MethodsA total of 21 cervical cancer patients who were willing to be treated with IMRT in the prone position at the Third Affiliated Hospital of Kunming Medical University from December 1, 2014 to October 31, 2015 were selected for this study. IMRT treatment plans were carried out using computed tomography images of the full and empty bladder. Data were collected to compare the differences between clinical target volume, planning target volume, and the percentage of irradiated volume of the bladder, small bowel, rectum, and caput femoris in patients with full and empty bladders.ResultsClinical target volume, planning target volume, and the volume of organs at risk did not show obvious differences (P > 0.05 in all respects) in patients with different bladder statuses. The average radiation dose of the small bowel of a patient with a full bladder (2056.7 ± 364.7 cGy) was significantly lower than that of a patient with an empty bladder (2319.5 ± 451.58 cGy), P < 0.001. The average radiation dose of the rectum of a patient with a full bladder (4663.7 ± 68.94 cGy) was higher than that of a patient with an empty bladder (4621.6 ± 54.86 cGy), P = 0.039. The percentages of irradiated volume covered by the 5–45 Gy isodose curve (V5–V45) of the small bowel were lower in the full bladder patients than in the empty bladder patients (P < 0.001 in all respects), whereas the percentages of irradiated volume covered by the 45 Gy isodose curve (V45) of the rectum were higher in the full bladder patients (P < 0.05). If a patient had lymphatic metastasis, the V45 irradiated volume ratio (IVR) of the small bowel of a patient with a full bladder was lower than that of a patient with an empty bladder, P < 0.001, whereas the V45 IVR of the rectum increased (P = 0.04). For patients without lymphatic metastasis, the V45 IVR of the small bowel and bladder both decreased with a full bladder compared with an empty bladder (P = 0.002 and 0.01, respectively), and there was no difference in the V45 IVR of the rectum (P = 0.275).ConclusionsIMRT plans delivered to patients with a full bladder in the prone position can reduce the percentage of irradiated volume in the small bowel. For patients with lymphatic metastasis, although keeping a full bladder reduces the percentage of irradiated volume in the intestine, it also increases the percentage of irradiated volume in the rectum

Assessment of a knowledge‐based RapidPlan model for patients with postoperative cervical cancer

AbstractObjectiveTo show the feasibility of using a knowledge‐based RapidPlan model to generate new cervical intensity modulated radiation therapy (IMRT) plans.MethodsA database of 20 cervical IMRT treatment plans was assembled to create a knowledge‐based IMRT RapidPlan model. Another 19 clinical cases were selected to test the model. A comparison analysis of the difference in dose–volume histograms between the semiautomated treatment plans and the original treatment plans was carried out.ResultsOn average, the new knowledge‐based RapidPlans can achieve planning target volume coverage that is highly comparable with the original plan, within 1%, as evaluated for D98, D95, and D1. For the rectum, the mean and standard deviation of the dose percentage differences for D20, D30, and D50 were 3.79 ± 8.31%, 4.00 ± 9.87%, and 1.52 ± 10.89%, respectively. For the bladder, the mean and standard deviation of the dose percentage differences for D20, D30, and D50 were –2.43 ± 9.40%, –2.03 ± 10.17%, and –2.94 ± 12.30%, respectively. For the femoral heads, the mean and standard deviation of the dose percentage differences for the left and right were 3.15 ± 18.29% and –3.18 ± 13.79%, respectively.ConclusionWe showed a knowledge‐based IMRT plan model for cervical cancer that can generate clinically acceptable treatment plans of high quality. This semiautomated approach can improve the efficiency of the treatment planning process while ensuring that high‐quality plans are developed.

T2 Star-weighted Angiography (SWAN) Allows to Concomitantly Assess the Prostate Contour While Detecting Fiducials Before MR-based Intensity-modulated Radiation Therapy in Prostate Carcinoma

To evaluate the performance of T2 star-weighted angiography (SWAN) to concomitantly assess the prostate contour while detecting fiducials before magnetic resonance (MR)-based intensity-modulated radiation therapy (IMRT) in prostate carcinoma. Forty patients (mean age: 73.1 ± 7.5 years; average Gleason score: 7 ± 1; average prostate-specific antigen: 14.7 ± 11.6 ng/mL) underwent MR and computed tomography imaging before fiducial-based IMRT. MR protocol included SWAN, T2-weighted (T2w) and diffusion-weighted imaging in a first group (n = 20) and SWAN, T2w and T2-star weighted imaging in a second group (n = 20). In group 1, the depiction of fiducials, image sharpness and visibility of prostate boundaries were independently evaluated by 2 readers on SWAN, T2w or diffusion-weighted images. In group 2, a similar evaluation was performed by 2 other readers on SWAN and T2-star images only. Depiction of fiducials was compared to computed tomography findings. The median scores of visibility of prostate boundaries, image sharpness and depiction of fiducials by SWAN were above average to excellent for all readers. In group 1, readers correctly located 56 of 57 (98.2%) and 47 of 57 (82.5%) fiducials, respectively; and 50 of 51 (98%), and 48 of 51 (88.2%) fiducials in group 2, respectively. By allowing adequate visualization of the prostate boundaries and high depiction of fiducial markers concomitantly, SWAN might be used for treatment planning of IMRT. The use of this sequence might simplify the registration process and limit any errors associated with image fusion.

Retrospective analysis of portal dosimetry pre-treatment quality assurance of prostate volumetric-modulated arc therapy (VMAT) plans

AbstractBackgroundElectronic portal imaging device (EPID) offers high-resolution digital image that can be compared with a predicted portal dose image. A very common method to quantitatively compare a measured and calculated dose distribution that is routinely used for quality assurance (QA) of volumetric-modulated arc therapy (VMAT) and intensity-modulated radiation therapy treatment plans is the evaluation of the gamma index. The purpose of this work was to evaluate the gamma passing rate (%GP), maximum gamma (γmax), average gamma (γave), maximum dose difference (DDmax) and the average dose difference (DDave) for various regions of interest using Varian’s implementation of three absolute dose gamma calculation techniques of improved, local, and combined improved and local.Methods and materialsWe analyzed 232 portal dose images from 100 prostate cancer patients’ VMAT plans obtained using the Varian EPID on TrueBeam Linacs.ResultsOur data show that the %GP, γmax and γave depend on the gamma calculation method and the acceptance criteria. Higher %GP values were obtained compared with both our current institutional action level and the American Association of Physicists in Medicine Task Group 119 recommendations.ConclusionsThe results of this study can be used to establish stricter action levels for pre-treatment QA of prostate VMAT plans. A stricter 3%/3 mm improved gamma criterion with a passing rate of 97% or the 2%/2 mm improved gamma criterion with a passing rate of 95% can be achieved without additional measurements or configurations.

L 1-l 2 regularization of split feasibility problems

Numerous problems in signal processing and imaging, statistical learning and data mining, or computer vision can be formulated as optimization problems which consist in minimizing a sum of convex functions, not necessarily differentiable, possibly composed with linear operators and that in turn can be transformed to split feasibility problems (SFP), see for example \cite{ce94}. Each function is typically either a data fidelity term or a regularization term enforcing some properties on the solution, see for example \cite{cpp09} and references therein. In this paper we are interested in Split Feasibility Problems which can be seen as a general form of $Q$-Lasso introduced in \cite{aasnx13} that extended the well-known Lasso of Tibshirani \cite{Tibshirani96}. $Q$ is a closed convex subset of a Euclidean $m$-space, for some integer $m\geq1$, that can be interpreted as the set of errors within given tolerance level when linear measurements are taken to recover a signal/image via the Lasso. Inspired by recent works by Lou et al \cite{ly, xcxz12}, we are interested in a nonconvex regularization of SFP and propose three split algorithms for solving this general case. The first one is based on the DC (difference of convex) algorithm (DCA) introduced by Pham Dinh Tao, the second one in nothing else than the celebrate forward-backward algorithm and the third one uses a method introduced by Mine and Fukushima. It is worth mentioning that the SFP model a number of applied problems arising from signal/image processing and specially optimization problems for intensity-modulated radiation therapy (IMRT) treatment planning, see for example \cite{cbmt06}.

Correlation between delivered radiation doses to the brainstem or vestibular organ and nausea & vomiting toxicity in patients with head and neck cancers \u2013 an observational clinical trial

ObjectiveToday intensity modulated radiation therapy (IMRT) can be considered the standard of care in patients with head and neck tumors. IMRT treatment plans are proven to reduce acute treatment related side effects by optimal sparing of organs at risk (OAR). At the same time, areas that were out of the former 3D fields now receive low radiation doses. Amongst those areas the brainstem (BS) and the vestibular system (VS) are known to be physiologically connected to nausea and vomiting (NV). In our study we tried to find out, if doses to these areas are linked to NV.Material & MethodsNV were assessed at different time points during treatment in 26 patients leading to 98 documented toxicity scores that were later correlated to dose deposition in the described areas. Patients were either treated with normo-fractionated or simultaneously integrated boost IMRT plans in a curative approach. Subareas of the BS as well as the VS were delineated. Toxicity was rated based on the common toxicity criteria (CTCAE Version 4.0). Other factors such as age, gender, chemotherapy, location of the tumor, irradiated volume and unilateral dose to the VS were taken into account and analyzed also.ResultsThe majority (65.4%) of our patients experienced an episode of NV at least once during treatment. NV was more frequent when treating the oropharyngeal region compared to the hypopharyngeal region, as well as when patients were female and/ or of a younger age. Nevertheless, upon statistical analysis (ROC analysis, ‘within/ between analysis’) no significant association between delivered doses to subareas and toxicity could be demonstrated.ConclusionIn our analysis, no significant correlation between radiation dose to the BS or the VS and the occurrence of NV could be found. Therefore, until conclusive data are available, we recommend to rely on the published data regarding OAR tolerance within the BS and not to compromise on dose coverage.

Investigating multi-objective fluence and beam orientation IMRT optimization

Radiation Oncology treatment planning requires compromises to be made between clinical objectives that are invariably in conflict. It would be beneficial to have a ‘bird’s-eye-view’ perspective of the full spectrum of treatment plans that represent the possible trade-offs between delivering the intended dose to the planning target volume (PTV) while optimally sparing the organs-at-risk (OARs). In this work, the authors demonstrate Pareto-aware radiotherapy evolutionary treatment optimization (PARETO), a multi-objective tool featuring such bird’s-eye-view functionality, which optimizes fluence patterns and beam angles for intensity-modulated radiation therapy (IMRT) treatment planning.The problem of IMRT treatment plan optimization is managed as a combined monolithic problem, where all beam fluence and angle parameters are treated equally during the optimization. To achieve this, PARETO is built around a powerful multi-objective evolutionary algorithm, called Ferret, which simultaneously optimizes multiple fitness functions that encode the attributes of the desired dose distribution for the PTV and OARs. The graphical interfaces within PARETO provide useful information such as: the convergence behavior during optimization, trade-off plots between the competing objectives, and a graphical representation of the optimal solution database allowing for the rapid exploration of treatment plan quality through the evaluation of dose-volume histograms and isodose distributions.PARETO was evaluated for two relatively complex clinical cases, a paranasal sinus and a pancreas case. The end result of each PARETO run was a database of optimal (non-dominated) treatment plans that demonstrated trade-offs between the OAR and PTV fitness functions, which were all equally good in the Pareto-optimal sense (where no one objective can be improved without worsening at least one other). Ferret was able to produce high quality solutions even though a large number of parameters, such as beam fluence and beam angles, were included in the optimization.

Note on the modified relaxation CQ algorithm for the split feasibility problem

In this paper we are concerned with the Split Feasibility Problem (SFP) in which there are given two Hilbert spaces $$H_1$$ and $$H_2$$ , nonempty, closed and convex sets $$C\subseteq H_1$$ and $$Q\subseteq H_2$$ , and a bounded and linear operator $$A:H_1 \rightarrow H_2$$ . The SFP is then to find a point $$x^*\in C$$ such that its image under A belongs to Q, meaning that $$Ax^*\in Q$$ . This reformulation was employed successfully for solving many inverse problems: for example, in intensity-modulated radiation therapy treatment planning. One of the typical classes of methods that have been used to solve the SFP is the class of projection method. This note focuses on the modified relaxation CQ algorithm with the Armijo-line search rule for solving the SFP. Under common and standard assumptions, we show that the proposed method weakly converges to a solution of the SFP. Numerical examples illustrating our method’s efficiency are presented for solving the LASSO problem in which the goal is to recover a sparse signal from a limited number of observations.

Reduction in stray radiation dose using a body-shielding device during external radiation therapy.

With the purpose of reducing stray radiation dose (SRD) in out‐of‐field region (OFR) during radiotherapy with 6 MV intensity‐modulated radiation therapy (IMRT), a body‐shielding device (BSD) was prepared according to the measurements obtained in experimental testing. In experimental testing, optimal shielding conditions, such as 1 mm lead, 2 mm lead, and 1 mm lead plus 10 mm bolus, were investigated along the medial axis of a phantom using thermoluminescent dosimeters (TLDs). The SRDs at distances from field edge were then measured and analyzed for a clinical IMRT treatment plan for nasopharyngeal carcinoma before and after shielding using the BSD. In addition, SRDs in anterior, posterior, left and right directions of phantom were investigated with and without shielding, respectively. Also, the SRD at the bottom of treatment couch was measured. SRD decreased exponentially to a constant value with increasing distance from field edge. The shielding rate was 50%–80%; however, there were no significant differences in SRDs when shielded by 1 mm lead, 2 mm lead, or 1 mm lead plus 10 mm bolus (P>0.05). Importantly, the 10 mm bolus absorbed back‐scattering radiation due to the interaction between photons and lead. As a result, 1 mm lead plus 10 mm bolus was selected to prepare the BSD. After shielding with BSD, total SRDs in the OFR decreased to almost 50% of those without shielding when irradiated with IMRT beams. Due to the effects of treatment couch and gantry angle, SRDs at distances were not identical in anterior, posterior, left and right direction of phantom without BSD. As higher dose in anterior and lower dose in posterior, SRDs were substantial similarities after shielding. There was no significant difference in SRDs for left and right directions with or without shielding. Interestingly, SRDs in the four directions were similar after shielding. From these results, the BSD developed in this study may significantly reduce SRD in the OFR during radiotherapy, thus decreasing the risk of secondary cancers.

Development and verification of a time delivery model for prostate intensity modulated radiotherapy using a Siemens® Artiste™ 160 Multi-leaf Collimator Linac.

Time delivery models thus far proposed for prediction of radiotherapy delivery times are not applicable to all makes of Linac. Our purpose was to develop a time delivery model, which would also be applicable for a Siemens® ARTISTE™ 160 Multi-leaf Collimator (MLC) linear accelerator (Linac) and validate the model using prostate Intensity Modulated Radiation Therapy (IMRT) treatment plans. To our knowledge, a time delivery model has not yet been proposed for a Siemens® ARTISTE™ 160 MLC Linac. We used the principles of the time delivery model created for a Varian® Linac and added the radio frequency (RF) wave component, and the MLC delay time to the MLC travel time component. Machine input parameters were confirmed using a WIN® stopwatch. We tested our derived model by selecting ten random 15 MV prostate IMRT treatment plans from our clinic. The delivery time was measured three times, once per day on three different days. The calculated and measured times were compared by means of correlation. The time delivery ranged between 314 and 480s. The largest percentage difference was 3.3% (16s) and the smallest 0.2% (1s); the mean percentage difference was 1.9%. MLC delay and MLC speed, representing segment delivery, had the greatest uncertainties. From the successfully verified time delivery model created, it is concluded that the inter-segmental component of the process is most time-consuming. In order to decrease delivery time it is proposed that the total segments of a treatment plan be decreased.

Three-dimensional quality assurance of IMRT prostate plans using gel dosimetry

Intensity modulated radiotherapy (IMRT) is one of the most modern radiation therapy treatment techniques. Although IMRT can deliver high and complex conformational doses to the tumor volume, its implementation requires rigorous quality assurance (QA) procedures that include a dosimetric pre-treatment verification of individual patient planning. This verification usually involves measuring a small volume of absolute dose with an ionization chamber and checking bi-dimensional fluency with an array of detectors. The planning technique has tri-dimensional characteristics, but no tridimensional dosimetry has been established in the clinical routine. One strategy to perform three-dimensional dosimetry is to use polymeric gels associated with magnetic resonance imaging to evaluate dose distribution. Here, we have compared the results of conventional QA procedures involving one- and two-dimensional dosimetry to the results of three-dimensional dosimetry conducted with MAGIC-f gel in 10 cases of prostate cancer IMRT planning. More specifically, we used the gamma index (3%/3mm) to compare the results of three-dimensional dosimetry to the expected dose distributions obtained with the treatment planning system. Except for one IMRT treatment plan, the gel dosimetry results agreed with the conventional quality control and provided an overview of dose distribution in the target volume.

Impact of Multileaf Collimator Configuration Parameters on the Dosimetric Accuracy of 6-MV Intensity-Modulated Radiation Therapy Treatment Plans.

The purpose of this study was to evaluate the impact of selected configuration parameters that govern multileaf collimator (MLC) transmission and rounded leaf offset in a commercial treatment planning system (TPS) (Pinnacle3, Philips Medical Systems, Andover, MA, USA) on the accuracy of intensity-modulated radiation therapy (IMRT) dose calculation. The MLC leaf transmission factor was modified based on measurements made with ionization chambers. The table of parameters containing rounded-leaf-end offset values was modified by measuring the radiation field edge as a function of leaf bank position with an ionization chamber in a scanning water-tank dosimetry system and comparing the locations to those predicted by the TPS. The modified parameter values were validated by performing IMRT quality assurance (QA) measurements on 19 gantry-static IMRT plans. Planar dose measurements were performed with radiographic film and a diode array (MapCHECK2) and compared to TPS calculated dose distributions using default and modified configuration parameters. Based on measurements, the leaf transmission factor was changed from a default value of 0.001 to 0.005. Surprisingly, this modification resulted in a small but statistically significant worsening of IMRT QA gamma-index passing rate, which revealed that the overall dosimetric accuracy of the TPS depends on multiple configuration parameters in a manner that is coupled and not intuitive because of the commissioning protocol used in our clinic. The rounded leaf offset table had little room for improvement, with the average difference between the default and modified offset values being −0.2 ± 0.7 mm. While our results depend on the current clinical protocols, treatment unit and TPS used, the methodology used in this study is generally applicable. Different clinics could potentially obtain different results and improve their dosimetric accuracy using our approach.

An Efficient Method for Improving the Dose-Volume-Based Optimization Plan Quality

Dose-volume (DV)-based objectives are widely used in most intensity-modulated radiation therapy treatment planning, because numerous DV endpoints have been utilized. In clinical practice, DV-based optimization (DVO) with uniform or random initial intensity distributions is utilized, but without considering the non-convexity of the DV objectives. To improve the quality of DVO radiotherapy plan and reduce the local minimum error generated by non-convexity of the DV objective, we proposed an efficient method (an organ-model-based optimization guiding DVO) to determine the initial intensity distributions for DVO. The new approach includes two steps. First, fluence map optimization, based on the organ model that adopts our proposed increasing objective function, to assure organ evaluation criteria Pareto surface, was performed. Second, DVO procedure was performed by using the initial intensity distributions determined in the first step. We demonstrated this technique in two kinds of clinical cases. DV histogram metrics were adopted as the criterion to evaluate the treatment plans. Compared with the conventional DVO plan with uniform initial intensity distributions, the improved DVO plan provided better protection of organ at risk (OAR); the planning target volume coverage was similar. Moreover, the improved DVO plan was better than the plan generated in the first step. The proposed method, with advantages in determining the initial intensity distributions, was highly efficient to improve DVO plans.

Particle swarm optimizer for weighting factor selection in intensity-modulated radiation therapy optimization algorithms

In inverse treatment planning of intensity-modulated radiation therapy (IMRT), the objective function is typically the sum of the weighted sub-scores, where the weights indicate the importance of the sub-scores. To obtain a high-quality treatment plan, the planner manually adjusts the objective weights using a trial-and-error procedure until an acceptable plan is reached. In this work, a new particle swarm optimization (PSO) method which can adjust the weighting factors automatically was investigated to overcome the requirement of manual adjustment, thereby reducing the workload of the human planner and contributing to the development of a fully automated planning process. The proposed optimization method consists of three steps. (i) First, a swarm of weighting factors (i.e., particles) is initialized randomly in the search space, where each particle corresponds to a global objective function. (ii) Then, a plan optimization solver is employed to obtain the optimal solution for each particle, and the values of the evaluation functions used to determine the particle’s location and the population global location for the PSO are calculated based on these results. (iii) Next, the weighting factors are updated based on the particle’s location and the population global location. Step (ii) is performed alternately with step (iii) until the termination condition is reached. In this method, the evaluation function is a combination of several key points on the dose volume histograms. Furthermore, a perturbation strategy – the crossover and mutation operator hybrid approach – is employed to enhance the population diversity, and two arguments are applied to the evaluation function to improve the flexibility of the algorithm. In this study, the proposed method was used to develop IMRT treatment plans involving five unequally spaced 6MV photon beams for 10 prostate cancer cases. The proposed optimization algorithm yielded high-quality plans for all of the cases, without human planner intervention. A comparison of the results with the optimized solution obtained using a similar optimization model but with human planner intervention revealed that the proposed algorithm produced optimized plans superior to that developed using the manual plan. The proposed algorithm can generate admissible solutions within reasonable computational times and can be used to develop fully automated IMRT treatment planning methods, thus reducing human planners’ workloads during iterative processes.

The Effect of Beams' Orientations on the Intensity-Modulated Radiation Therapy Plan Quality

Purpose: The work aims at studying forty Intensity-modulated radiation therapy (IMRT) plans designed using KonRad system and evaluating each of them under different conditions to study the effect of beams' orientations on the plan quality. Methods: Clinical step-and-shoot IMRT treatment plans were designed for twenty patients, suffering from different types of non-CNS solid tumors, to be delivery on a Siemens Oncor accelerator with multi-leaf collimators MLCs (82 leaf). To ensure that the similarity or difference between the plans was due to effect of beams' orientations, the same optimization constraints were applied for each plan and all other parameters were kept constant. Results: The analysis of performance was based on isodose distributions, Dose Volume Histograms (DVHs) for Planning Target Volume (PTV), the relevant Organs at Risk (OARs) as well as several physical indices like mean dose (Dmean), maximum dose (Dmax), 95% dose (D95), integral dose, volume of tumor receiving 2 Gy and 5 Gy, total number of segments and monitor units (MUs). Homogeneity index and conformation number were two other evaluation parameters that were considered in this study. Conclusion: All coplanar CP and non-coplanar NC techniques result in clinically acceptable plans, with comparable target doses and dose to critical organs within prescribed dose constraints. For different organs at risk, the coplanar IMRT, the greatest advantage of non-coplanar IMRT was the marked reduction of general trend was that non-coplanar plans achieved the lowest values, while coplanar plans showed the highest. Significant differences (P<0.05) exist only between the homogeneity index HI (1.092 and 1.088) and Monitor Unit MU (357.79 and 341.80) of CP and NC plans respectively. Compared with the integral dose (p=0.007).

Consideration of Dose Error in Dynamic MLC IMRT Using MLC Speed Control with Dose Rate Change.

In dynamic multi-leaf collimator (MLC) intensity-modulated radiotherapy (IMRT), the accuracy of delivered dose is influenced by the positional accuracy of the moving MLC. In order to assess the accuracy of the delivered dose during dynamic MLC IMRT, the delivered dose error in dynamic MLC IMRT using the MLC speed control with dose rate change was investigated. Sweeping gap sequence irradiation was performed with constant MLC leaf speed at 0.6 to 5 cm/s or changed MLC speed (4 steps). The positional accuracy of the moving MLC was evaluated from the trajectory log file. Absorbed dose measurements with sweeping field (Field size: 10 cm×10 cm, MLC leaf speed: 0.6 to 2.7 cm/s, MLC leaf gap width: 0.2 to 2.0 cm) were performed. The delivered dose error at each gap width was evaluated according to MLC leaf speed change. MLC positional errors and changes in delivered dose according to MLC leaf speed were within 0.07 mm and 0.6%, respectively, for all measurements. Beam hold-off did not occur under any conditions. We confirmed that TrueBeam can regulate MLC leaf speed below the maximum limit (2.5 cm/s) by changing the dose rate in real-time during irradiation in dynamic MLC IMRT. MLC gap error during irradiation was estimated within 0.2 mm at the maximum dose rate from the results of absolute dose measurements using dynamic MLC irradiation. In conclusion, TrueBeam can use the maximum dose rate for the treatment planning of dynamic MLC IMRT, which has an advantage of shorter treatment time.

Quick, efficient and effective patient-specific intensity-modulated radiation therapy quality assurance using log file and electronic portal imaging device.

The aim of work is to explore a quick, efficient, and effective patient-specific intensity-modulated radiation therapy (IMRT) quality assurance (QA). Software tools were developed to extract and analyze the multi-leaf collimator (MLC) leaf positions (LPs) from electronic portal imaging device (EPID) images for Varian C-series machine and TrueBeam, to extract useful data from MLC log file of C-series linear accelerator (LINAC), to extract useful information from the trajectory log binary file of TrueBeam LINAC, to compare LPs derived from EPID images with log file/trajectory log data, and to analyze IMRT treatment files using the MATLAB programming language. The difference in LP determined from the trajectory log and EPID images was proposed for patient-specific QA. It was found that the differences in LP for regular radiation fields generated using stationary leaves are <0.5 mm for all the field sizes while for regular radiation fields generated using the moving leaves are more but <2 mm. The differences in LPs for IMRT field were also determined and found to be <2 mm. The methodology demonstrated can be used for establishing the accuracy of trajectory log data and for independent routine IMRT QA by generating single number like gamma index to indicate pass or fail of an IMRT treatment plan. The QA indices such as numbers of occurrences of ≥2 mm error in LPS are found more than 5% of total number of occurrences; the dosimetric review of planned treatment is advisable.

The risk of secondary cancer in nasopharyngeal carcinoma paediatric patients due to intensity modulated radiotherapy and mega-voltage cone beam computed tomography.

There is a growing interest in the study of radiation-induced secondary cancer. The aim of this work is (i) to estimate the peripheral doses attributable to intensity modulated radiotherapy (IMRT) and mega-voltage cone beam computed tomography (MV-CBCT) for some organs at risk (OARs) which surround the target being treated (Nasopharynx) in paediatric patients. (ii) To estimate the risk of radiation-induced secondary cancers attributable to patient setup verification imaging dose using MV-CBCT for Nasopharyngeal Carcinoma (NPC) in paediatric patients and comparing it with that attributable to the therapeutic dose using IMRT. Intensity modulated radiotherapy treatment planning of 10 NPC paediatric patients was carried out on KonRad release 2.2.23. The additional radiation doses to the patients attributable to MV-CBCT were calculated also using Xio Version 4.4. A paediatric phantom and thermoluminescent dosimeters (TLDs) were used to measure the patient doses attributable to IMRT. These doses were then compared with the calculated doses. The risk of induced secondary cancers attributable to IMRT and MV-CBCT was calculated and compared to each other. The absorbed doses (mean dose) for the OARs (Brain, Brain stem, spinal cord, thyroid, oesophagus, mandible, heart, optic nerve, lung and eye) were higher for the therapeutic dose than for the imaging dose used in the verification of patient position before and during the treatment. The risk of induced secondary cancers in thyroid, oesophagus and lung (the only organs from the OARs which have tabulated values for risk calculations) was higher for therapeutic dose (7.29±0.73%, 2.62±0.17% and 6.76±0.87%, respectively) than for verification imaging dose (0.14±0.00%, 0.06±0.00%, 0.10±0.03% respectively). The risk of secondary cancers attributable to verification imaging dose using MV-CBCT is very small compared to therapeutic dose using IMRT. Therefore, it is important to focus on the risk of secondary cancers attributable to therapeutic dose especially when using IMRT, where the produced leakage radiation is considerably high compared to some other techniques (such as conformal radiotherapy).

Fully Automated Multicriteria Optimization (MCO) Treatment Plan Generation for Radiation Treatment Planning

To develop a novel multi-criteria optimization (MCO) solution approach to generate treatment plans without Pareto front navigation (any user-computer interaction). Current MCO algorithms consider convex optimization problems and create an approximation of the Pareto front and then navigate over the approximation to obtain the final treatment plan. Our proposed method is able to handle nonconvex optimization optimization problems which includes dose-volume objectives/constraints, tumor control probability (TCP), normal tissue complication probability (NTCP), etc. In addition, instead of creating an approximation and navigation, our method targets the solution without any time-consuming human-computer interaction steps. This is achieved by a solution approach that utilizes given dose bounds on the structures by clinicians. We tested our method with 10 locally advanced head-and-neck cancer patients retrospectively using the concept of segment weight optimization. Monitor units were reoptimized using the segments extracted from the conventional intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT). We compared the results with conventional clinical plans and current MCO approach. Our MCO formulation had total 9 objective functions, which included 3 distinct objectives for primary target volume, high-risk and low-risk target volumes, 5 objectives for each of the organs-at-risk (OAR) (two parotid glands, spinal cord, brain stem, and oral cavity), and one for the non-target non-OAR normal tissue. Compared to the conventional clinical plan and current MCO method, the proposed MCO method achieved average reductions in left parotid mean dose of 8% (P < 0.01) and 7% (P < 0.01), right parotid mean dose of 12% (P < 0.01), and 8% (P = 0.02), oral cavity mean dose of 1% (P = 0.63) and 5% (P = 0.28) and spinal cord maximum dose of 28% (P < 0.01) and 10% (P = 0.02), brain stem maximum dose of 41% (P < 0.01) and 18% (P = 0.01), and normal tissue maximum dose of 9% (P < 0.01) and 8% (P < 0.01), respectively. We proposed a novel MCO solution approach that generated superior high quality IMRT and VMAT treatment plans without any human-computer interactions.

A derivative‐free multistart framework for an automated noncoplanar beam angle optimization in IMRT

The inverse planning of an intensity-modulated radiation therapy (IMRT) treatment requires decisions regarding the angles used for radiation incidence, even when arcs are used. The possibility of improving the quality of treatment plans by an optimized selection of the beam angle incidences-beam angle optimization (BAO)-is seldom done in clinical practice. The inclusion of noncoplanar beam incidences in an automated optimization routine is even more unusual. However, for some tumor sites, the advantage of considering noncoplanar beam incidences is well known. This paper presents the benefits of using a derivative-free multistart framework for the optimization of the noncoplanar BAO problem. Multistart methods combine a global strategy for sampling the search space with a local strategy for improving the sampled solutions. The proposed global strategy allows a thorough exploration of the continuous search space of the highly nonconvex BAO problem. To avoid local entrapment, a derivative-free method is used as local procedure. Additional advantages of the derivative-free method include the reduced number of function evaluations required to converge and the ability to use multithreaded computing. Twenty nasopharyngeal clinical cases were selected to test the proposed multistart framework. The planning target volumes included the primary tumor, the high and low risk lymph nodes. Organs-at-risk included the spinal cord, brainstem, optical nerves, chiasm, parotids, oral cavity, brain, thyroid, among others. For each case, a setup with seven equispaced beams was chosen and the resulting treatment plan, using a multicriteria optimization framework, was then compared against the coplanar and noncoplanar plans using the optimal beam setups obtained by the derivative-free multistart framework. The optimal noncoplanar beam setup obtained by the derivative-free multistart framework leads to high quality treatment plans with better target coverage and with improved organ sparing compared to treatment plans using equispaced or optimal coplanar beam angle setups. The noncoplanar treatment plans achieved, e.g., an average reduction in the mean dose of the oral cavity of 6.1 Gy and an average reduction in the maximum-dose of the brainstem of 7 Gy when compared to the equispaced treatment plans. The noncoplanar BAO problem is an extremely challenging multimodal optimization problem that can be successfully addressed through a thoughtful exploration of the continuous highly nonconvex BAO search space. The proposed framework is capable of calculating high quality treatment plans and thus can be an interesting alternative toward automated noncoplanar beam selection in IMRT treatment planning which is nowadays the natural trend in treatment planning.