IMRT Plans Research Articles

A semi-automatic planning technique for whole breast irradiation with tangential IMRT fields

PurposeTo implement a semi-automatic planning technique for whole breast irradiation with two tangential IMRT fields and to test the produced dose distribution against clinical 3DCRT plans, for introducing the technique in clinical practice. MethodsThe Auto-Planning module of the Pinnacle3 (Philips) treatment planning system was used for generating a Treatment Technique on left-sided breast cancer patients treated in free breathing or in deep inspiration breath hold (DIBH) and to right-sided breast cancer patients. The technique was evaluated against 3DCRT clinical plans in terms of dosimetric plan parameters. Plan robustness toward patient displacements was assessed on a subset of patients by inducing shifts to the isocenter. ResultsA statistically significant improvement in target coverage and dose homogeneity was observed for autoIMRT. No statistically significant differences were observed for ipsilateral organs, except for the ipsilateral lung in left DIBH, where slightly lower Dmean and V18% are registered for autoIMRT. Slightly higher Dmean doses (although far below the constraints) to contralateral organs were observed for autoIMRT plans.AutoIMRT plans were shown to be as robust as 3DCRT plans toward isocenter shifts, with a maximum decrease in CTV coverage of −2.2% and −2.1% for autoIMRT and 3DCRT, respectively. Average planning times were 40 min for 3DCRT and 6 min for IMRT plans. ConclusionsThe developed autoIMRT technique was proven to be advantageous for target coverage and homogeneity and sufficiently robust towards isocenter displacements. The use of automated planning consistently reduces the planning workload with improvements in plan quality.

OC-0938 MLC complexity metrics in clinical online adapted IMRT plans delivered with a double-stacked MLC

OC-0938 MLC complexity metrics in clinical online adapted IMRT plans delivered with a double-stacked MLC

Assessment of developed IMRT and 3D-CRT planning protocols for treating nasopharyngeal cancer patients based on the target and organs at risks common volumes

Assessment of developed IMRT and 3D-CRT planning protocols for treating nasopharyngeal cancer patients based on the target and organs at risks common volumes

Dose to contralateral breast from whole breast irradiation by automated tangential IMRT planning: comparison of flattening-filter and flattening-filter-free modes.

BackgroundThe most common secondary cancer is contralateral breast (CLB) cancer after whole breast irradiation (WBI). The aim of this study was to quantify the reduction of CLB dose in tangential intensity modulated radiotherapy (t-IMRT) for WBI using flattening-filter-free (FFF) beams.Materials and methodsWe generated automated planning of 20 young breast cancer patients with limited user interaction. Dose-volume histograms of the planning target volume (PTV), ipsilateral lung, heart, and CLB were calculated. The dose of PTV, the most medial CLB point, and the CLB point below the nipple was measured using an ionization chamber inserted in a slab phantom. We compared the two t-IMRT plans generated by FFF beams and flattening-filter (FF) beams.ResultsAll plans were clinically acceptable. There was no difference in the conformal index, the homogeneity for FFF was significantly worse. For the ipsilateral lung, the maximum dose (Dmax) was significantly higher; however, V20 showed a tendency to be lower in the FFF plan. No differences were found in the Dmax and V30 to the heart of the left breast cancer. FF planning showed significantly lower Dmax and mean dose to the CLB. In contrast to the calculation results, the measured dose of the most medial CLB point and the CLB point below the nipple were significantly lower in FFF mode than in FF mode, with mean reductions of 21.1% and 20%, respectively.ConclusionsT-IMRT planning using FFF reduced the measured out-of-field dose of the most medial CLB point and the CLB point below the nipple.

Meta-optimization for fully automated radiation therapy treatment planning

Objective. Radiation therapy treatment planning is a time-consuming process involving iterative adjustments of hyperparameters. To automate the treatment planning process, we propose a meta-optimization framework, called MetaPlanner (MP). Approach. Our MP algorithm automates planning by performing meta-optimization of treatment planning hyperparameters. The algorithm uses a derivative-free method (i.e. parallel Nelder–Mead simplex search) to search for weight configurations that minimize a meta-scoring function. Meta-scoring is performed by constructing a tier list of the relevant considerations (e.g. dose homogeneity, conformity, spillage, and OAR sparing) to mimic the clinical decision-making process. Additionally, we have made our source code publicly available via github. Main results. The proposed MP method is evaluated on two datasets (21 prostate cases and 6 head and neck cases) collected as part of clinical workflow. MP is applied to both IMRT and VMAT planning and compared to a baseline of manual VMAT plans. MP in both IMRT and VMAT scenarios has comparable or better performance than manual VMAT planning for all evaluated metrics. Significance. Our proposed MP provides a general framework for fully automated treatment planning that produces high quality treatment plans. Our MP method promises to substantially reduce the workload of treatment planners while maintaining or improving plan quality.

Accuracy Improvement Method Based on Characteristic Database Classification for IMRT Dose Prediction in Cervical Cancer: Scientifically Training Data Selection.

PurposeConsistent training and testing datasets can lead to good performance for deep learning (DL) models. However, a large high-quality training dataset for unusual clinical scenarios is usually not easy to collect. The work aims to find optimal training data collection strategies for DL-based dose prediction models.Materials and MethodsA total of 325 clinically approved cervical IMRT plans were utilized. We designed comparison experiments to investigate the impact of (1) beam angles, (2) the number of beams, and (3) patient position for DL dose prediction models. In addition, a novel geometry-based beam mask generation method was proposed to provide beam setting information in the model training process. What is more, we proposed a new training strategy named “full-database pre-trained strategy”.ResultsThe model trained with a homogeneous dataset with the same beam settings achieved the best performance [mean prediction errors of planning target volume (PTV), bladder, and rectum: 0.29 ± 0.15%, 3.1 ± 2.55%, and 3.15 ± 1.69%] compared with that trained with large mixed beam setting plans (mean errors of PTV, bladder, and rectum: 0.8 ± 0.14%, 5.03 ± 2.2%, and 4.45 ± 1.4%). A homogeneous dataset is more accessible to train an accurate dose prediction model (mean errors of PTV, bladder and rectum: 2.2 ± 0.15%, 5 ± 2.1%, and 3.23 ± 1.53%) than a non-homogeneous one (mean errors of PTV, bladder and rectum: 2.55 ± 0.12%, 6.33 ± 2.46%, and 4.76 ± 2.91%) without other processing approaches. The added beam mask can constantly improve the model performance, especially for datasets with different beam settings (mean errors of PTV, bladder, and rectum improved from 0.8 ± 0.14%, 5.03 ± 2.2%, and 4.45 ± 1.4% to 0.29 ± 0.15%, 3.1 ± 2.55%, and 3.15 ± 1.69%).ConclusionsA consistent dataset is recommended to form a patient-specific IMRT dose prediction model. When a consistent dataset is not accessible to collect, a large dataset with different beam angles and a training model with beam information can also get a relatively good model. The full-database pre-trained strategies can rapidly form an accuracy model from a pre-trained model. The proposed beam mask can effectively improve the model performance. Our study may be helpful for further dose prediction studies in terms of training strategies or database establishment.

Dosimetry impact of gating latency in cine magnetic resonance image guided breath-hold pancreatic cancer radiotherapy

Objective. We investigated dosimetry effect of gating latency in cine magnetic resonance image (cine MRI) guided breath-hold pancreatic cancer radiotherapy. Approach. The gating latency was calculated based on cine MRI obtained from 17 patients who received MRI guided radiotherapy. Because of the cine MRI-related latency, beam overshoot occurs when beam remains on while the tracking target already moves out of the target boundary. The number of beam on/off events was calculated from the cine MRI data. We generated both IMRT and VMAT plans for all 17 patients using 33 Gy prescription, and created motion plans by applying isocenter shift that corresponds to motion-induced tumor displacement. The GTV and PTV coverage and dose to nearby critical structures were compared between the motion and original plan to evaluate the dosimetry change caused by cine MRI latency. Main results. The time ratio of cine MRI imaging latency over the treatment duration is 6.6 ± 3.1%, the mean and median percentage of beam-on events <4 s are 67.0 ± 14.3% and 66.6%. When a gating boundary of 4 mm and a target-out threshold of 5% is used, there is no significant difference for GTV V33Gy between the motion and original plan (p = 0.861 and 0.397 for IMRT and VMAT planning techniques, respectively). However, the PTV V33Gy and stomach Dmax for the motion plans are significantly lower; duodenum V12.5 Gy and V18Gy are significantly higher when compared with the original plans, for both IMRT and VMAT planning techniques. Significance. The cine MRI gating latency can significantly decrease the dose delivered to the PTV, and increase the dose to the nearby critical structures. However, no significant difference is observed for the GTV coverage. The dosimetry impact can be mitigated by implementing additional beam-on control techniques which reduces unnecessary beam on events and/or by using faster cine MRI sequences which reduces the latency period.

Proceedings to the 7th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA)

Proceedings to the 7th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA)

Assessment of efficacy in automated plan generation for Varian Ethos intelligent optimization engine.

Varian Ethos, a new treatment platform, is capable of automatically generating treatment plans for initial planning and for online, adaptive planning, using an intelligent optimization engine (IOE). The primary purpose of this study is to assess the efficacy of Varian Ethos IOE for auto‐planning and intercompare different treatment modalities within the Ethos treatment planning system (TPS). A total of 36 retrospective prostate and proximal seminal vesicles cases were selected for this study. The prescription dose was 50.4 Gy in 28 fractions to the proximal seminal vesicles, with a simultaneous integrated boost of 70 Gy to the prostate gland. Based on RT intent, three treatment plans were auto‐generated in the Ethos TPS and were exported to the Eclipse TPS for intercomparison with the Eclipse treatment plan. When normalized for the same planning target volume (PTV) coverage, Ethos plans D max% were 108.1 ± 1.2%, 108.4 ± 1.6%, and 109.6 ± 2.0%, for the 9‐field IMRT, 12‐field IMRT, and 2‐full arc VMAT plans, respectively. This compared well with Eclipse plan D max% values, which was 108.8 ± 1.4%. OAR indices were also evaluated for Ethos plans using Radiation Therapy Oncology Group report 0415 as a guide and were found to be comparable to each other and the Eclipse plans. While all Ethos plans were comparable, we found that, in general, the Ethos 12‐field IMRT plans met most of the dosimetric goals for treatment. Also, Ethos IOE consistently generated dosimetrically hotter VMAT plans versus IMRT plans. On average, Ethos TPS took 13 min to generate 2‐full arc VMAT plans, compared to 5 min for 12‐field IMRT plans. Varian Ethos TPS can generate multiple treatment plans in an efficient time frame and the quality of the plans could be deemed clinically acceptable when compared to manually generated treatment plans.

English

BACKGROUND The primary objective of this study is a dosimetric comparison for the feasibility of carotid sparing intensity modulated radiation therapy (CS-IMRT) for early glottis cancer. The planning target volume coverage and the spinal cord dose are compared in the 3-dimensional conformal radiotherapy (3DCRT) and IMRT plans. METHODS In this single reconcile study twenty-five patients who had been already treated for early-stage glottis cancer (T1, T2N0M0) from June 2015 to June 2021 with 52.5 Gy/15 fractions were included. All patients were simulated in supine position with an orfit shell and treatment planning computed tomography scans were obtained from the vertex to sternal angle with a 3-mm slice thickness. Treatment was executed with 3-DCRT plan and comparison was made with the newly created IMRT plan. The analysis was made regarding mean dose to the carotid arteries, volume of carotid artery receiving more than 25 Gy (V25), 35 Gy (V35), 50 Gy (V50), planning target coverage and doses to organ at risk. RESULTS The dose to carotids was significantly higher in the 3-DCRT plan compared with the IMRT plan (p=0.004). For target coverage the volume receiving 95% of the dose was significantly higher in IMRT plan (p=.001). The dose to the spinal cord was higher-in the IMRT plan (p=.001) compared to 3-DCRT plan. CONCLUSIONS IMRT maintains target volume coverage with significant reduction in carotid artery dose. This reduces the incidence of cerebrovascular accidents by decreasing the radiation induced carotid artery stenosis, thereby improving the quality of life of patients. KEY WORDS CS-IMRT, 3D-CRT, Mean Carotid Dose

Dose assessment for daily cone-beam CT in lung radiotherapy patients and its combination with treatment planning.

With the increased use of X-ray imaging for patient alignment in external beam radiation therapy, particularly with cone-beam computed tomography (CBCT), the additional dose received by patients has become of greater consideration. In this study, we analysed the radiation dose from CBCT for clinical lung radiotherapy and assessed its relative contribution when combined with radiation treatment planning for a variety of lung radiotherapy techniques. The Monte Carlo simulation program ImpactMC was used to calculate the 3D dose delivered by a Varian TrueBeam linear accelerator to patients undergoing thorax CBCT imaging. The concomitant dose was calculated by simulating the daily CBCT irradiation of ten lung cancer patients. Each case was planned with a total dose of 50-60Gy to the target lesion in 25-30 fractions using the 3DCRT or IMRT plan and retrospectively planned using VMAT. For each clinical case, the calculated CBCT dose was summed with the planned dose, and the dose to lungs, heart, and spinal cord were analysed according to conventional dose conformity metrics. Our results indicate greater variations in dose to the heart, lungs, and spinal cord based on planning technique, (3DCRT, IMRT, VMAT) than from the inclusion of daily cone-beam imaging doses over 25-30 fractions. The average doses from CBCT imaging per fraction to the lungs, heart and spinal cord were 0.52 ± 0.10, 0.49 ± 0.15 and 0.39 ± 0.08cGy, respectively. Lung dose variations were related to the patient's size and body composition. Over a treatment course, this may result in an additional mean absorbed dose of 0.15-0.2Gy. For lung V5, the imaging dose resulted in an average increase of ~ 0.6% of the total volume receiving 5Gy. The increase in V20 was more dependent on the planning technique, with 3DCRT increasing by 0.11 ± 0.09% with imaging and IMRT and VMAT increasing by 0.17 ± 0.05% and 0.2 ± 0.06%, respectively. In this study, we assessed the concomitant dose for daily CBCT lung cancer patients undergoing radiotherapy. The additional radiation dose to the normal lungs from daily CBCT was found to range from 0.15 to 0.2Gy when the patient was treated with 25-30 fractions. Consideration of potential variation in relative biological effectiveness between kilovoltage imaging and megavoltage treatment dose was outside the scope of this study. Regardless of this, our results show that the assessment of imaging dose can be incorporated into the treatment planning process and the relative effect on overall dose distribution was small compared to the difference among planning techniques.

Cost and Toxicity Comparisons of Two IMRT Techniques for Prostate Cancer: A Micro-Costing Study and Weighted Propensity Score Analysis Based on a Prospective Study.

BackgroundIntensity modulated radiation therapy (IMRT) combined with androgen deprivation therapy (ADT) has become the standard treatment for patients with high-risk prostate cancer. Two techniques of rotational IMRT are commonly used in this indication: Volumetric Modulated Arc Therapy (VMAT) and helical tomotherapy (HT). To the best of our knowledge, no study has compared their related costs and clinical effectiveness and/or toxicity in prostate cancer. We aimed to assess differences in costs and toxicity between VMAT and HT in patients with high-risk prostate cancer with pelvic irradiation.Material and MethodsWe used data from the “RCMI pelvis” prospective multicenter study (NCT01325961) including 155 patients. We used a micro-costing methodology to identify cost differences between VMAT and HT. To assess the effects of the two techniques on total actual costs per patient and on toxicity we used stabilized inverse probability of treatment weighting.ResultsThe mean total cost for HT, €2019 3,069 (95% CI, 2,885–3,285) was significantly higher than the mean cost for VMAT €2019 2,544 (95% CI, 2,443–2,651) (p <.0001). The mean ± SD labor and accelerator cost for HT was €2880 (± 583) and €1978 (± 475) for VMAT, with 81 and 76% for accelerator, respectively. Acute GI and GU toxicity were more frequent in VMAT than in HT (p = .021 and p = .042, respectively). Late toxicity no longer differed between the two groups up to 24 months after completion of treatment.ConclusionUse of VMAT was associated with lower costs for IMRT planning and treatment than HT. Similar stabilized long-term toxicity was reported in both groups after higher acute GI and GU toxicity in VMAT. The estimates provided can benefit future modeling work like cost-effectiveness analysis.

Multi-level multi-leaf collimators: Optimization of layer thicknesses and a feasibility study.

The function of multi-leaf collimators (MLC) is to modulate and shape the intensity of a radiotherapy beam by either blocking or unblocking beamlets. A variation on this functionality is tested in this work wherein the MLC is split into layers, with each layer attenuating the beam by a different amount. In this design, full blocking of a beamlet occurs only if all layers are blocked. This work suggests that such a device, a multi-layer MLC (MLMLC), can deliver dose distributions like a single layer MLC can deliver while requiring less time and monitor units (MU) METHODS: Optimal fluences were made for prostate plans using the Eclipse v13.6. An algorithm was developed to create step-and-shoot MLMLC patterns to match these optimal fluences when using up to six layers of MLC. Twelve MLMLC plans were made in total. These patterns were imported back into Eclipse as equivalent tungsten compensators and doses were calculated. Dose-volume histogram (DVH) values, total monitor units (MU), and total time to deliver were compared between arc-style MLMLC plans and nine-field step and shoot IMRT plans created completely in Eclipse using a single layer MLC. When using three or more layers, specified DVH values between the two sets agreed to within 5% while requiring roughly half as much time to deliver and about 20% fewer MU. Demonstrated that having multi-layer MLC can deliver dose distributions like a single layer MLC with less time and monitor units.

Assessment of semi-automated stereotactic treatment planning for online adaptive radiotherapy in ethos.

The Ethos treatment planning system allows for the rapid generation of online adaptive treatment plans while the patient is on the treatment couch. One promising application of online adaptive radiotherapy is its use in stereotactic radiotherapy. The purpose of this study was to ensure the Ethos treatment planning system (TPS) can produce clinically acceptable stereotactic plans, that are non-inferior to those from the Eclipse TPS. Forty patients that received previous stereotactic radiotherapy treatment on a Halcyon, 20 of which were lung cases, and 20 that were brain cases, were replanned using the Ethos TPS. The generated IMRT and VMAT plans were compared to the clinical Eclipse VMAT plan. This study found that the Ethos TPS can produce VMAT plans of equivalent quality (target coverage, conformity and OAR doses) to those from the Eclipse TPS for lung SBRT and brain SRT. The IMRT plans produced by the Ethos planning system were marginally inferior to Eclipse VMAT plans, with the differences likely primarily due to beam geometry rather than the optimization system. Ethos plans were generally more modulated than Eclipse plans. With careful selection of optimization structures and reduction in the body contour, VMAT plan generation time could be reduced by 87%. Ethos can generate stereotactic VMAT plans that are equivalent to those from Eclipse in the timeframe required for online adaptive radiotherapy.

Detection of Suboptimal IMRT Treatment Plan Using Machine Learning on Radiomics Features of Dose Distribution for Lung Cancers

Detection of Suboptimal IMRT Treatment Plan Using Machine Learning on Radiomics Features of Dose Distribution for Lung Cancers

Performance evaluation of a Monte Carlo-based treatment planning system in out-of-field dose estimation during dynamic IMRT with different dose rates

AimThe present study aimed to investigate the effect of dose rate variations in the out-of-field regions on the dose calculation accuracy of an algorithm based on the Monte Carlo (MC) method implemented in Monaco (V.5.11.03) Treatment Planning System (TPS). Materials and methodsNine fields of the IMRT plan for the CShape structure were created in the CIRS IMRT Thorax phantom, and the related doses were calculated using the MC-based algorithm of the Monaco TPS. Afterward, the CIRS IMRT Thorax phantom was irradiated by an Elekta Synergy linear accelerator and the 160-leaf MLC Agility 6 MV photon beams using the Dynamic Intensity Modulated Radiation Therapy (D-IMRT) technique. To this end, 3 ion chambers were inserted in 3 cavities, which were equivalent to water, bone, and lung, and were located in the out-of-field regions within the phantom. Finally, the dose measurements were performed, and the values were compared with the doses calculated by the Monaco TPS. ResultsFindings revealed that the Monaco TPS underestimated the dose by an average of 40% for most of the out-of-field measurement distances. Moreover, at distant positions of the out-of-field edge, out-of-field doses were significantly underestimated for all media and dose rates. Finally, the percentage of the TPS error and out-of-field dose values were different for each dose rate. ConclusionsResults in the present research showed remarkable differences between the measured and calculated doses. Thus, it was concluded that the dose calculation accuracy of the Monaco TPS was not reliable for out-of-field regions at different dose rates, and the application of the current commercial treatment planning systems in these regions could lead to underestimating the risk of secondary cancer development.

Clinical Commissioning and Dosimetric Verification of the Raystation Treatment Planning System

Background: The software used by treatment planning systems (TPS) plays an important role for treatments using radiation. The accuracy of the calculated dose in radiation treatments depends on the assumptions made by the TPS. In this study, we summarize our methods and results regarding clinical commissioning of the basic functions needed for photon therapy. Materials and Method: Measurements were obtained for the 6 and 15 MV photon energies obtained from the Siemens Artiste linear accelerator device. Important data such as percent deep dose, profile and output measurements were taken in the water phantom and transferred to the RayStation Treatment Planning System. Results: When the absolute dose values calculated by the RayStation TPS are compared with the water phantom data, the differences obtained are less than 3%. When the 2-dimensional quality control of asymmetrical areas and patients with IMRT plan was controlled by gamma analysis method, the gamma rate was more than 95%. Conclusion: One of the most important quality control tests is TPS acceptance tests, which must be performed before clinical use. In this study, in which we checked the basic dose measurement and patient planning, it was seen that the RayStation TPS can be used in patient treatment for clinical use. The doses calculated by the RayStation TPS were found to be reliable and within the expected accuracy range. These results are sufficient for the application of 3-dimensional conformal radiotherapy (3D-CRT) and IMRT technique.

Dosimetric comparison between carbon, proton and photon radiation for renal retroperitoneal soft tissue sarcoma recurrence or metastasis after radical nephrectomy

Objective To compare the dosimetric difference between various modalities in the radiation treatment for renal retroperitoneal soft tissue sarcoma recurrence or metastasis (RRSTSRM) after radical nephrectomy, and assess the dosimetric advantage on protecting the organs at risk (OARs) in the carbon and proton radiotherapy for the patients with a single kidney. Methods A total of 12 patients with RRSTSRM who underwent radical nephrectomy were enrolled in this study. Carbon, proton, and photon radiotherapy were implemented for treatment planning. The prescription dose was fulfilled by simultaneously integrated boosting technique, with giving the planning target volume-1 (PTV-1) 51Gy (RBE) and planning target volume-2 (PTV-2) 60 Gy (RBE). Doses in the patient’s spinal cord, stomach, duodenum, bowel, colon, and contralateral kidney were evaluated. The normal tissue complication probability (NTCP) of the duodenum, bowel, colon, and contralateral kidney was derived under Lyman-Kutcher-Burman (LKB) estimation. Results In the carbon plans, the percentage volume of 95% prescription dose (V95%) covering PTV-1 (PTV-2) was 95.93% ± 3.42% (95.61% ± 4.26%). No significant dosimetric difference on the target was obtained between the four radiation modalities (P > .05). The percentage volume of receiving 40 Gy (RBE) [V40Gy (RBE)] in the duodenum could be reduced from 12.94% ± 15.99% in the IMRT plans to 6.36% ± 8.79% (8.44% ± 12.35%) in the carbon (proton) plans (P < .05). The V40Gy (RBE) in the bowel could be reduced from 13.48% ± 13.12% in the IMRT plans to 7.04% ± 9.32% (7.34% ± 9.89%) in the carbon (proton) plans (P < .05). The mean value of NTCP for the duodenum was 0.43 ± 0.47 (0.45 ± 0.48) by using carbon (proton) radiation. The value was 0.05 (0.03) lower than the IMRT plans on average, with a reduction of 0.20 (0.13) for the patients with lesions <5 mm away from the duodenum. The mean doses of the contralateral kidney were 0.28 ± 0.37 Gy (RBE) [0.28 ± 0.40 Gy (RBE)] in the IMCT (IMPT) plans, which was 92.43% (92.43%) lower than the value in the IMRT plans respectively (P < .05). Conclusion Compared to the conventional radiation techniques, particle radiotherapy of carbon and proton could significantly spare more OARs in the treatment for RRSTSRM after radical nephrectomy. Patients, especially those whose residuals are close to the duodenum would potentially benefit from the particle radiation therapy for RRSTSRM on the decrease in radiation-related side-effect.

OD51 - Dosimetric and planning evaluation of IMRT vs VMAT-like plans for magnetic resonance guided radiotherapy treatment

OD51 - Dosimetric and planning evaluation of IMRT vs VMAT-like plans for magnetic resonance guided radiotherapy treatment

Abstract 9609: Pioneering Cardiac Radioablation With the Use of an MRI Linear Accelerator. Can We Use a Gamma Knife ® to the Heart as We Do in the Brain?

Introduction: VT is often refractory to medical therapy and on rare but critical cases, even EP ablation. Despite investigation into endocardial, mesocardial and occasionally even epicardial ablation for these recalcitrant and deadly arrhythmias, there remains an inability to more effectively, non-invasively, treat VT. Hypothesis: We propose that, paralleling a Gamma Knife ® approach, the use of a novel MRI linear accelerator (MR Linac), the Unity ® (Elekta AB, Stockholm, Sweden), a proof of concept could be applied to highly selected pts with obstinate VT. Methods: A multi-center team with EP, Radiation Oncology and CMR (GE 1.5T) in joint development with Pittsburgh, PA and Utrecht, The Netherlands, developed a completely EP-CMR-guided method for non-invasive VT ablation utilizing S tereo T actic A rrhythmia R adioablation (STAR) with 25 Gy in a single fraction via MR Linac. Results: To evaluate deliverability and applicability of MR Linac plans, four IMRT per clinical scan were developed with varying delivery parameters (7A: 7-beams: 52 o in 70 segments (seg), 7B: 7-beams: 52 o in 100 seg, 15A: 15-beams: 24 o in 70 seg, and 15B: 15-beams: 24 o in 100 seg). We used a 0.2 cm dose grid and a 1% uncertainty via Monte Carlo ® dose calculation. Pt specific QA/QC used ArcCHECK ® (Sun Nuclear, FL) to evaluate individual IMRT plans. 3D CMR with LGE scar fusion for lesion integration guided non-invasive MR LinAc ablation. Accordingly, all IMRT plans were clinically acceptable (&gt;97% of 7-beams and ≥98.0% of 15-beams in 3%/3mm gamma) for MR LinAc VT-ablation successfully with pt target effective arrhythmogenic myocardial ROI volume as ascertained via CMR of 63-99cm 3 . All 4 pts tolerated the 25±5min procedure without esophageal, pericardial or pro-arrhythmic complications and were alive at 30d FU with marked attenuation of VT burden. At 30d FU, no SAE's occurred to include pro-arrhythmias, pericardial effusions or esophageal fistulas. Conclusions: Refractory, complex and anatomically endocardially-remote VT has the potential to be curative, incorporating an analogous Gamma Knife ® approach via MR Linac radioablation heralding a migration to the Unity ® platform. This nearly first-in-man p r oof of concept approach may shepherd a new methodologic era into heretofore intractable VT.