Conformal Treatment Research Articles

Cochlear sparing in LINAC-based radiosurgery for vestibular schwannoma: a dosimetric comparison of dynamic conformal arc, IMRT and VMAT treatment plans

BackgroundStereotactic radiosurgery (SRS) is the preferred treatment for vestibular schwannoma (VS) in patients with preserved hearing and tumour diameter < 3 cm. Emerging evidence suggests restricting cochlear dose could preserve hearing. This retrospective replanning study aims to compare dynamic conformal arc therapy (DCAT), intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans for superiority of cochlear dose sparing without compromising tumour coverage.MethodsEligibility criteria included sporadic VS, serviceable hearing and availability of CT and MRI for planning. The original gross tumour volume and brainstem OAR volume were retained; the cochlea was newly contoured on the planning CT scan (bone window). Each case was replanned using the three above techniques, prescribing 12 Gy to the 80% isodose line. No dose constraint was applied to the cochlea.ResultsEighteen patients were replanned. Mean tumour volume was 2.25 cc. Tumour coverage and tumour mean dose (DCAT: 14.2, IMRT: 14.6, VMAT: 14.5 Gy) were comparable. Paddick and RTOG conformity indices were better for DCAT (0.66 and 1.6) and VMAT (0.69 and 1.5) compared to IMRT (0.56 and 1.9). DCAT had superior gradient index (3.0) compared to VMAT (3.4) and IMRT (3.4). VMAT delivered the lowest mean brainstem maximum dose (8.3 Gy) and decreased the mean cochlear dose (3.4 Gy) by 2.3 and 2.1 Gy, and the mean cochlear maximum dose (3.6 Gy) by 2.4 and 2.5 Gy relative to DCAT and IMRT, respectively.ConclusionLINAC-based SRS treatment using VMAT can achieve better cochlear dose sparing than DCAT or IMRT while maintaining tumour coverage.

Comparison of the dosimetric benefits of two different three-dimensional conformal radiotherapy treatment approaches for postmastectomy radiotherapy

Comparison of the dosimetric benefits of two different three-dimensional conformal radiotherapy treatment approaches for postmastectomy radiotherapy

Dosimetric comparative study of conformal radiation techniques in patients with glioblastoma multiforme

Purpose: The purpose of the current study is to determine whether patients diagnosed with glioblastoma multiforme (GBM) who underwent radiotherapy (RT) using intensity-modulated RT (IMRT) technique were benefitting from this highly conformal treatment in terms of doses received by planning target volume (PTV) and organs at risk (OARs) in comparison to three-dimensional conventional RT (3DCRT). Materials and Methods: Twelve patients treated with IMRT for GBM were selected for dosimetric comparison with 3DCRT. The prescribed dose was 60 Gy in 30 fractions and seven non-coplanner beams were used in IMRT to cover 95% of target volume. The irradiated patients of GBM were retrieved and replanned with 3DCRT techniques. Dosimetric comparison was done by performing two plans for the same patient; prescription dose and normal tissue constraints were identical for both plans. The dose–volume histograms of target volumes and OAR, dose conformity, and dose homogeneity with 3DCRT and IMRT planning were compared. Statistical analysis was performed to determine the differences. Results: The mean conformity index was 0.99 ± 0.001 for IMRT and 0.97 ± 0.002 for 3DCRT, P = 0.001. The mean homogeneity index was 1.03 ± 0.02 for IMRT and 1.06 ± 0.009 for 3DCRT, P = 0.003, which is statistically significant. The IMRT technique enables dose reduction of normal tissues including brainstem (Dmean by 33.78 ± 5.34 and Dmax 51.84 ± 4.43), optic chiasm (Dmean by 36.92 ± 1.99 and Dmax 44.61 ± 3.72), left optic nerve (Dmean by 28.97 ± 6.51 and Dmax 46.08 ± 10.58), right optic nerve (Dmean by 31.93 ± 11.68 and Dmax 44.63 ± 13.54), left eye (Dmean by 18.66 ± 8.92 and Dmax 37.43 ± 13.47), right eye (Dmean by 14.40 ± 4.87 and Dmax 40.37 ± 11.37), left lens (by Dmax 5.45 ± 1.85), and right lens (Dmax 5.07 ± 0.63). Conclusion: The IMRT provides a real dosimetric advantage, especially for normal brain tissue, and in terms of target coverage. It allows treatment of tumors while respecting OARs' dose constraints. The IMRT technique shows significant advantage in PTV coverage, dose homogeneity, and conformity. In IMRT, the coverage is better where PTV was overlapping with critical OARs.

Importance of conformance control in reinforcing synergy of CO2 EOR and sequestration

Injecting CO 2 into hydrocarbon reservoirs can enhance the recovery of hydrocarbon resources, and simultaneously, CO 2 can be stored in the reservoirs, reducing considerable amount of carbon emissions in the atmosphere. However, injected CO 2 tends to go through fractures, high-permeability channels and streaks present in reservoirs, resulting in inefficient hydrocarbon recovery coupled with low CO 2 storage performance. Conformance treatments with CO 2 -resistant crosslinked polymer gels were performed in this study to mitigate the CO 2 channeling issue and promote the synergy between enhanced oil recovery (EOR) and subsurface sequestration of CO 2 . Based on a typical low-permeability CO 2 -flooding reservoir in China, studies were performed to investigate the EOR and CO 2 storage performance with and without conformance treatment. The effect of permeability contrast between the channels and reservoir matrices, treatment size, and plugging strength on the efficiency of oil recovery and CO 2 storage was systematically investigated. The results indicated that after conformance treatments, the CO 2 channeling problem was mitigated during CO 2 flooding and storage. The injected CO 2 was more effectively utilized to recover the hydrocarbons, and entered wider spectrum of pore spaces. Consequently, more CO 2 was trapped underground. Pronounced factors on the synergy of EOR and CO 2 storage were figured out. Compared with the treatment size, the CO 2 storage efficiency was more sensitive to the plugging strength of the conformance treatment materials. This observation was important for conformance treatment design in CCUS-EOR projects. According to this study, the materials should reduce the channel permeability to make the channel/matrix permeability ratio below 30. The results demonstrate the importance of conformance treatment in maximizing the performance of CCUS-EOR process to achieve both oil recovery improvement and efficient carbon storage. This study provides guidelines for successful field applications of CO 2 transport control in CO 2 geo-utilization and storage.

Experimental Validation of a Real-Time Adaptive 4D-Optimized Particle Radiotherapy Approach to Treat Irregularly Moving Tumors

Treatment of locally advanced lung cancer is limited by toxicity and insufficient local control. Particle therapy could enable more conformal treatment than intensity modulated photon therapy but is challenged by irregular tumor motion, associated range changes, and tumor deformations. We propose a new strategy for robust, online adaptive particle therapy, synergizing 4-dimensional optimization with real-time adaptive beam tracking. The strategy was tested and the required motion monitoring precision was determined. In multiphase 4-dimensional dose delivery (MP4D), a dedicated quasistatic treatment plan is delivered to each motion phase of periodic 4-dimensional computed tomography (4DCT). In the new extension, "MP4D with residual tracking" (MP4DRT), lateral beam tracking compensates for the displacement of the tumor center-of-mass relative to the current phase in the planning 4DCT. We implemented this method in the dose delivery system of a clinical carbon facility and tested it experimentally for a lung cancer plan based on a periodic subset of a virtual lung 4DCT (planned motion amplitude 20mm). Treatments were delivered in a quality assurance-like setting to a moving ionization chamber array. We considered variable motion amplitudes and baseline drifts. The required motion monitoring precision was evaluated by adding noise to the motion signal. Log-file-based dose reconstructions were performed in silico on the entire 4DCT phantom data set capable of simulating nonperiodic motion. MP4DRT was compared with MP4D, rescanned beam tracking, and internal target volume plans. Treatment quality was assessed in terms of target coverage (D95), dose homogeneity (D5-D95), conformity number, and dose to heart and lung. For all considered motion scenarios and metrics, MP4DRT produced the most favorable metrics among the tested motion mitigation strategies and delivered high-quality treatments. The conformity was similar to static treatments. The motion monitoring precision required for D95 >95% was 1.9mm. With clinically feasible motion monitoring, MP4DRT can deliver highly conformal dose distributions to irregularly moving targets.

In silico analysis of optimum photon energy spectra and beam parameters for iodine nanoparticle–aided orthovoltage radiation therapy of brain tumors

In this study, the effect of photon energy spectra on the dose enhancement factor (DEF) and other influencing parameters such as skull–tumor dose ratios were estimated for a confined tumor loaded with iodine nanoparticles (INPs). A mathematical brain phantom with a brain tumor was simulated by the MCNP6 Monte Carlo code. A validated commercial computed tomography model consisting of an X-ray tube, Al–Cu filters, and collimators was used to simulate the rotational conformal treatment of the tumor. INPs with a diameter of 20 nm and concentrations of 10–50 mg/g were introduced inside the tumor as homogenously distributed spherical particles. The dose distribution inside the phantom was scored for several orthovoltage beams with the peak voltages of 140, 200, and 320 kVp as well as two 3.5 and 6 MV megavoltage beams. A significant rise of DEF values with nanoparticle (NP) concentration for orthovoltage beams is revealed; no significant dose enhancement was obtained for megavoltage beams. The highest DEF and skull–tumor dose ratio were obtained for the 140 kVp beam which decreased with the number of directional fields. The clinically optimal plan for a brain tumor, with high DEFs of 2.81–2.24 and acceptable skull–tumor dose ratios of 0.61–0.51, would be feasible for treatment using 200 and 320 kVp beams, an iodine concentration of 20 mg/g, and 8–15 fields. Our calculations show that clinically significant radiation dose enhancements can be obtained for tumors loaded with INPs using orthovoltage beams. Optimal treatment regimens are feasible using a proper selection of photon beam spectrum and sufficient numbers of cross-firing beams. The limiting effect of skull bone could be minimized by increasing the number of radiation fields and the use of higher quality of orthovoltage beams.

PO04: Clinical and Dosimetric Outcomes with Image-Guided High Dose Rate (HDR) Endoluminal Brachytherapy in Endobronchial Tumours: A Single Institute Experience

<h3>Purpose</h3> Endoluminal brachytherapy is an effective treatment modality for endobronchial tumours. With the advent of image-guidance, target coverage has improved and volume-based target delineation has helped in conformal treatment. In this study, we report our experience with high dose rate endobronchial brachytherapy (HDR-EBBT) and to assess its efficacy and tolerability. <h3>Materials and Methods</h3> Between January 2015 to February 2022, a retrospective review of patients with endobronchial tumours treated at our institution with HDR-EBBT was retrospectively assessed. Analysis of disease characteristics and thereafter, the subjective response and treatment related toxicities were extracted from patient records. The follow-up was undertaken as per the institutional protocol. Local control (LC) and overall survival (OS) were analysed. During each procedure of EBBT, a source-centralizing applicator was used which kept the source-dwelling catheter in the centre of bronchial lumen and reference dose point was placed 5 mm from source axis as per the bronchial diameter. <h3>Results</h3> With a median follow up of 18 months, a total of 8 patients with histopathologically proven endobronchial tumours were identified. The median external beam radiation dose was 45Gy in 25 fractions followed by brachytherapy dose of 14Gy in 2 fractions with treatment a week apart. The commonest symptoms to palliate included dyspnea (5/8), cough (3/8), and hemoptysis (4/8). The median disease-free survival and overall survival was 18 months and 21 months respectively. No grade 3-5 acute or late toxicities were reported and only one patient required further palliation measures to control the symptoms. On dosimetric analysis the PTV V95% and V98% were 95.12% and 93.45% respectively. On assessing the D20 and D5 for lungs, the median dose was 1.32Gy and 0.73Gy respectively. Similarly, the D2cc, 1cc and 0.1cc of oesophagus and heart were 1.63, 1.89 and 2.67Gy and 1.15, 1.37 and 1.69Gy respectively. <h3>Conclusion</h3> HDR-EBBT is a promising treatment with minimal complications and improved outcomes and thus provide curative options. If performed properly, desirable dosimetry can be achieved to improve target coverage and reduced normal tissue doses.

AI-Based Auto-Segmentation for Loco-Regional Breast Cancer Radiotherapy: Training, Validation and Clinical Implementation

<h3>Purpose/Objective(s)</h3> To train and validate a comprehensive deep-learning (DL) segmentation model for loco-regional breast cancer with the aim of clinical implementation. <h3>Materials/Methods</h3> 200 left-sided breast cancer cases from two radiotherapy centers in Norway were included in the project. In all cases, 7 clinical target volumes (CTVs) were manually delineated based on the ESTRO guidelines, in addition to 11 organs at risk (OARs). 170 patient cases were used for training, which involved neural networks of 3D CNN U-net type. The remaining 30 cases were used for model validation, which included: 1) evaluation of geometric similarity between DL structures and manually delineated structures using 95-percentile Hausdorff distance (HD95) and Dice similarity coefficient (DSC), benchmarked against inter-observer variation (IOV), 2) qualitative scoring using a 4-step scale according to clinical usability, and 3) dosimetric analysis of conformal treatment plans which were based on uncorrected DL structures. A dedicated team of 3 experienced oncologists (EO) and 3 experienced radiation therapists contributed to the manual delineations for model training and validation, while 5 EOs delineated the same 5 patient cases for evaluation of IOV. To test for difference in model performance and IOV, Mann-Whitney U test was used, while paired sample T-test was used for the dosimetric analysis of OARs. <h3>Results</h3> Geometrically, the model performed better than IOV for all CTVs and most OARs, see Table 1 for main results. Qualitatively, no or only minor corrections were required for 14 % and 71 % of the CTVs and 72 % and 26 % of the OARs, respectively. Major corrections were required for 15 % of the CTVs and 2 % of the OARs, while no structure scored as "not usable". The most frequent corrections were adjustments in the cranial and caudal parts of the structures. Dosimetrically, the CTV coverage, based on D98 > 95 %, was fulfilled for 100 % and 89 % of the breast and lymph node structures, respectively. No differences in OAR dose parameters were considered clinically relevant. The model was implemented in a commercial treatment planning system, which generates the structures in 1.5 minutes. <h3>Conclusion</h3> Convincing results from the validation process led to the decision of clinical implementation. The model is now in clinical use, and will be monitored regarding applicability, standardization and efficiency. Table 1. Geometric performance of the DL model and corresponding IOV for all CTVs and two of the OARs (median values). Bold type indicates the best metric, and underscore indicate statistical significance (p<0.05).

A quantitative and comparative evaluation of stereotactic spine radiosurgery local control: proposing a consistent measurement methodology.

Stereotactic body radiotherapy (SBRT) is a precise and conformal treatment modality used in the management of metastatic spine tumors. Multiple studies have demonstrated its safety and efficacy for pain and tumor control. However, no uniform quantitative imaging methodology exists to evaluate response to treatment in these patients. This study presents radiographic local control rates post-SBRT, systematically compares measurements acquired according to WHO and Response Evaluation Criteria in Solid Tumors (RECIST) criteria, and explores the relationship to patient outcome. The authors performed a retrospective review of prospectively obtained data from a cohort of 59 consecutive patients (81 metastatic isocenters) treated with SBRT and followed with serial MRI scans. Measurements were performed by a neuroradiologist blinded to the patients' clinical course. Local control status was determined according to both WHO and RECIST measurements, and agreement between the measuring methodologies was calculated and reported. Eighty-one isocenters (111 vertebral bodies) were treated with SBRT. The mean treatment dose was 13.96 Gy and the median follow-up duration was 10.8 months, during which 408 MRI scans were evaluated with both WHO and RECIST criteria for each scan point. Imaging demonstrated a mean unidimensional size decrease of 0.2 cm (p = 0.14) and a mean area size decrease of 0.99 cm2 (p = 0.03). Although 88% of the case classifications were concordant and the agreement was significant, WHO criteria were found to be more sensitive to tumor size change. The local control rates according to WHO and RECIST were 95% and 98%, respectively. Although WHO volumetric measurements are admittedly superior for tumor size measurement, RECIST is simpler, reproducible, and for the first time is shown here to be comparable to WHO criteria. Thus, the application of RECIST methodology appears to be a suitable standard for evaluating post-SBRT treatment response. Moreover, using comprehensive and consistent measuring approaches, this study substantiates the efficacy of SBRT in the treatment of spine metastases.

Toward semi-automatic biologically effective dose treatment plan optimisation for Gamma Knife radiosurgery

Objective. Dose-rate effects in Gamma Knife radiosurgery treatments can lead to varying biologically effective dose (BED) levels for the same physical dose. The non-convex BED model depends on the delivery sequence and creates a non-trivial treatment planning problem. We investigate the feasibility of employing inverse planning methods to generate treatment plans exhibiting desirable BED characteristics using the per iso-centre beam-on times and delivery sequence. Approach. We implement two dedicated optimisation algorithms. One approach relies on mixed-integer linear programming (MILP) using a purposely developed convex underestimator for the BED to mitigate local minima issues at the cost of computational complexity. The second approach (local optimisation) is faster and potentially usable in a clinical setting but more prone to local minima issues. It sequentially executes the beam-on time (quasi-Newton method) and sequence optimisation (local search algorithm). We investigate the trade-off between time to convergence and solution quality by evaluating the resulting treatment plans’ objective function values and clinical parameters. We also study the treatment time dependence of the initial and optimised plans using BED95 (BED delivered to 95% of the target volume) values. Main results. When optimising the beam-on times and delivery sequence, the local optimisation approach converges several orders of magnitude faster than the MILP approach (minutes versus hours–days) while typically reaching within 1.2% (0.02–2.08%) of the final objective function value. The quality parameters of the resulting treatment plans show no meaningful difference between the local and MILP optimisation approaches. The presented optimisation approaches remove the treatment time dependence observed in the original treatment plans, and the chosen objectives successfully promote more conformal treatments. Significance. We demonstrate the feasibility of using an inverse planning approach within a reasonable time frame to ensure BED-based objectives are achieved across varying treatment times and highlight the prospect of further improvements in treatment plan quality.

Nanocellulose-regulated robust particle-gel for conformance improvement in fractured tight reservoirs: A mechanistic investigation of transport behavior and EOR performance in fracture models

Owing to the interpenetration of high-modulus nanocellulose into polyacrylamide (HPAM), the mechanical properties of particle gel were substantially improved. Five transport patterns in fractures were demonstrated as defined by particle/aperture ratio. The pressure drop (ΔP) generated by nanocellulose-regulated particle gel (NPG) depended on particle/fracture ratio, followed by NPG content and strength. A numerical model was established to correlate the stable ΔP of NPG with four critical operating parameters. The placement of NPG significantly remedied the conformance of the fractured cores; therefore, the subsequent CO2 and ultralow IFT surfactant injection processes produced additional oil recoveries of 4.7% and 7.1% original oil in place (OOIP), respectively, with the ultimate oil recoveries of 10.8% and 12.2% OOIP. However, the matrix oil was hardly mobilized during brine injection even after conformance treatment due to the adverse wettability and high capillary pressure.

European Society for Radiotherapy and Oncology and European Organisation for Research and Treatment of Cancer consensus on re-irradiation: definition, reporting, and clinical decision making.

Re-irradiation can be considered for local recurrence or new tumours adjacent to a previously irradiated site to achieve durable local control for patients with cancer who have otherwise few therapeutic options. With the use of new radiotherapy techniques, which allow for conformal treatment plans, image guidance, and short fractionation schemes, the use of re-irradiation for different sites is increasing in clinical settings. Yet, prospective evidence on re-irradiation is scarce and our understanding of the underlying radiobiology is poor. Our consensus on re-irradiation aims to assist in re-irradiation decision making, and to standardise the classification of different forms of re-irradiation and reporting. The consensus has been endorsed by the European Society for Radiotherapy and Oncology and the European Organisation for Research and Treatment of Cancer. The use of this classification in daily clinical practice and research will facilitate accurate understanding of the clinical implications of re-irradiation and allow for cross-study comparisons. Data gathered in a uniform manner could be used in the future to make recommendations for re-irradiation on the basis of clinical evidence. The consensus document is based on an adapted Delphi process and a systematic review of the literature was done according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).

Verification of monitoring unit calculations for the 3D conformal radiotherapy treatment planning system

The present work aims to validate an Independent Calculation of Monitoring Units (ICMU) software developed to accurately calculate the number of Monitoring Units (MU) used in radiation treatment. The calculation was performed for the photon beam with a variety of nominal energies (6 MV − 18 MV) and filed size ranging from 3 × 3 cm2 to 40 × 40 cm2. Two set-up conventions of treatment techniques were tested, a constant source to surface distance (SSD) and an isocentric set-up with a constant source to axis distance (SAD). The ICMU software was written in C-sharp (C #), using the equivalent square field size concept to calculate the radiation field quantities and connects to a database containing measurements quantities such as Tissue Phantom ratio (TPR) and Output Factors (OFs). The ICMU was successfully validated by comparing it to the Treatment Planning System (TPS) or CMS Monitor Unit Calculations (CMS_MU). The required standards were satisfactorily met (5.0%).

Statistical breathing curve sampling to quantify interplay effects of moving lung tumors in a 4D Monte Carlo dose calculation framework

PurposeThe interplay between respiratory tumor motion and dose application by intensity modulated radiotherapy (IMRT) techniques can potentially lead to undesirable and non-intuitive deviations from the planned dose distribution. We developed a 4D Monte Carlo (MC) dose recalculation framework featuring statistical breathing curve sampling, to precisely simulate the dose distribution for moving target volumes aiming at a comprehensive assessment of interplay effects. MethodsWe implemented a dose accumulation tool that enables dose recalculations of arbitrary breathing curves including the actual breathing curve of the patient. This MC dose recalculation framework is based on linac log-files, facilitating a high temporal resolution up to 0.1 s. By statistical analysis of 128 different breathing curves, interplay susceptibility of different treatment parameters was evaluated for an exemplary patient case. To facilitate prospective clinical application in the treatment planning stage, in which patient breathing curves or linac log-files are not available, we derived a log-file free version with breathing curves generated by a random walk approach. Interplay was quantified by standard deviations σ in D5%, D50% and D95%. ResultsInterplay induced dose deviations for single fractions were observed and evaluated for IMRT and volumetric arc therapy (σD95% up to 1.3 %) showing a decrease with higher fraction doses and an increase with higher MU rates. Interplay effects for conformal treatment techniques were negligible (σ<0.1%). The log-file free version and the random walk generated breathing curves yielded similar results (deviations in σ< 0.1 %) and can be used as substitutes for interplay assessment. ConclusionIt is feasible to combine statistically sampled breathing curves with MC dose calculations. The universality of the presented framework allows comprehensive assessment of interplay effects in retrospective and prospective clinically relevant scenarios.

Pilot study evaluating the tolerability of a 3Gy × 10 daily fraction 3D-conformal palliative radiation therapy protocol plus toceranib for the treatment of measurable carcinomas in the dog.

The use of radiation therapy in conjunction with small molecule inhibitors is an appealing treatment combination for non-resectable carcinomas, which tend to be locally invasive with variable risk of locoregional metastasis. This prospective, pilot study aimed to evaluate the tolerability and adverse event profile of concurrent toceranib and palliative-intent radiation therapy (PRT) in dogs with measurable carcinoma and to secondarily evaluate short-term measurable tumor response. Fifteen dogs with measurable carcinoma received toceranib and 3D-conformal PRT in 3Gy/fraction for 10 daily fractions. Adverse events were graded using standard schemes and tolerability was followed via quality-of-life questionnaires during the 12-week treatment period. Thirteen dogs (87%) experienced acute radiation toxicity, graded as severe in three dogs. All dogs experienced toceranib toxicity, graded as severe in one dog. Seven dogs (47%) completed the 12-week study protocol; four were withdrawn due to toxicity and/or associated poor quality of life and four developed progressive disease. Based on these preliminary results, this 3D-conformal chemoradiation protocol should be considered with caution and only with proper owner education on potential toxicity. More conformal treatment planning techniques or alternative protocols should be investigated for improved tolerability.

A dosimetric comparison of proton versus photon irradiation for paediatric glomus tumour: a case study

Abstract Background: Intensity-modulated radiation therapy (IMRT) has revolutionised the way head and neck cancers can be treated. It allows for a more conformal treatment plan when compared to 3D conformal radiation therapy. In paediatric patients, however, IMRT continues to deliver higher doses than desirable. Proton beam therapy on the other hand has the potential to further spare organs-at-risk. Methods: A 16-year-old boy with a left-sided paraganglioma of the left base of skull manifested by headaches, neck pain and tongue cramping was simulated, planned and treated with proton therapy with significant contralateral organ-at-risk sparing. Results: For this patient, dosimetric plan comparison between photon and proton plans clearly showed better sparing of contralateral organs-at-risk with protons. The contralateral parotid gland received a mean dose of 386·3 cGy with photons, whereas it received 1·3 cGy (CGE) in the proton plan. Conclusions: The dosimetric advantage of proton beam over photon beam therapy has successfully been demonstrated in this case study for a paediatric patient with a head and neck tumour. Sparing of contralateral structures is especially important in paediatric patients who are at a greater risk of secondary malignancies due to possible long life expectancy.

Application of fuzzy comprehensive evaluation method to assess effect of conformance control treatments on water-injection wells

As an effective method to prolong the life of mature field, conformance control in water-injection well has been used wildly. Naturally, effect evaluation of conformance control has attracted great attention because it is an important guideline for the design of later enhanced oil recovery (EOR) plan. Usually, production responses such as excessive water reduction and oil production increment are widely used as the indicators. However, production responses may be unreliable due to the difficulty in determining an effective injection well which is caused by a large number of treated water-injection wells in a well group. Therefore, with the application of fuzzy comprehension evaluation (FCE), five evaluation indexes (injection pressure, injectivity index, slope of hall curve, variation coefficient and homogenization coefficient of injection profile) describe injection responses were selected to establish a new evaluation method in this paper. Based on fuzzy mathematics, FCE reflects the difference of evaluation units. Meanwhile, weights of evaluation indexes were obtained by analytic hierarchy process (AHP), which made the results more convincing. Taking Bai 239 oilfield as an example, the five injection responses indexes were used to assess treatment effect on five water-injection wells by single index evaluation and FCE. The results showed that among the five evaluation indexes mentioned above, the slope of hall curve was the most important factor affected evaluation result. In single index evaluation, opposite results may be produced easily on account of the one-sidedness of single index or human error. Furthermore, we found that effective treatment was a relative concept actually. The result of FCE was consistent with single index evaluation but FCE was more acceptable. This study suggests that FCE could be applied to another field such as water flooding, acidizing and hydraulic fracturing

Toward Neuro-Oncologic Clinical Trials of High-Dose-Rate Synchrotron Microbeam Radiation Therapy: First Treatment of a Spontaneous Canine Brain Tumor

The high potential of microbeam radiation therapy (MRT) in improving tumor control while reducing side effects has been shown by numerous preclinical studies. MRT offers a widened therapeutic window by using the periodical spatial fractionation of synchrotron generated x-rays into an array of intense parallel microbeams. MRT now enters a clinical transfer phase. As proof of principle and cornerstone for the safe clinical transfer of MRT, we conducted a "first in dog" trial under clinical conditions. In this report, we evaluated whether a 3-dimensional conformal MRT can be safely delivered as exclusive radiosurgical treatment in animal patients METHODS AND MATERIALS: We irradiated a 17.5-kg French bulldog for a spontaneous brain tumor (glioma suspected on magnetic resonance imaging) with conformal high-dose-rate microbeam arrays (50-µm-wide microbeams, replicated with a pitch of 400 μm) of synchrotron-generated x-rays. The dose prescription adjusted a minimal cumulated valley dose of 2.8 Gy to the plnning target volume (PTV) (cinical target volume (CTV)+1 mm). Thus, each beam delivered 20 to 25 Gy to the target as peak doses, and ∼1 Gy as valley doses RESULTS: The treatment was successfully delivered. Clinical follow-up over 3 months showed a significant improvement of the dog's quality of life: the symptoms disappeared. Magnetic resonance imaging, performed 3 months after irradiation, revealed reduction in tumor size (-87.4%) and mass effect with normalization of the left lateral ventricle. To our knowledge, this neuro-oncologic veterinary trial is the first 3-dimensional conformal synchrotron x-ray MRT treatment of a spontaneous intracranial tumor in a large animal. It is an essential last step toward the clinical transfer of MRT in the near future to demonstrate the feasibility and safety of treating deep-seated tumors using synchrotron-generated microbeams.

Robust Direct Aperture Optimization for Radiation Therapy Treatment Planning

Intensity-modulated radiation therapy (IMRT) allows for the design of customized, highly conformal treatments for cancer patients. Creating IMRT treatment plans, however, is a mathematically complex process, which is often tackled in multiple, simpler stages. This sequential approach typically separates radiation dose requirements from mechanical deliverability considerations, which may result in suboptimal treatment quality. For patient health to be considered paramount, holistic models must address these plan elements concurrently, eliminating quality loss between stages. This combined direct aperture optimization (DAO) approach is rarely paired with uncertainty mitigation techniques, such as robust optimization, because of the inherent complexity of both parts. This paper outlines a robust DAO (RDAO) model and discusses novel methodologies for efficiently integrating salient constraints. Because the highly complex RDAO model is difficult to solve, an original candidate plan generation (CPG) heuristic is proposed. The CPG produces rapid, high-quality, feasible plans, which are immediately clinically viable and can also be used to generate a feasible incumbent solution for warm-starting the RDAO model. Computational results obtained using clinical patient data sets with motion uncertainty show the benefit of incorporating the CPG, in terms of both the first incumbent solution and final output plan quality. Summary of Contribution: This paper describes the derivation, implementation, and solution of a large-scale robust direct aperture optimization model for the problem of intensity-modulated radiation therapy planning for cancer treatment. The contribution to operations research lies in the design of a novel mixed-integer programming model that describes all salient mechanical and clinical deliverability requirements for modern delivery equipment. Because of the large-scale nature of the resulting model, a novel tractable heuristic for generating high-quality, feasible treatment plans, as well as warm starts for the full model, is proposed and demonstrated on five clinical patient data sets.

Selective penetration behavior of microgels in superpermeable channels and reservoir matrices

Gel treatment is an effective way to attack excessive water production in many mature oilfields around the world. Selective penetration is desired for successful gel treatments. That is, gel materials should easily penetrate the target zones (i.e., channeling features such as superpermeable channels) without entering/damaging the nontarget zones (i.e., reservoir matrices or oil zones). This study revealed that presence of threshold penetration pressure (ΔPth) was responsible for selective penetration behavior of tested microgels. The concept of ΔPth was utilized to figure out favorable working conditions for effective gel treatments. Microgel dispersions were injected into superpermeable (super-k) sandpacks (mimicking super-k channels in reservoirs, 60–221 darcies), heterogeneous models with super-k channels (79–230 darcies), and sandstone cores (mimicking reservoir matrices, 50–5000 md). The results demonstrated that a minimum differential driving pressure (i.e., threshold penetration pressure, ΔPth) was required to push microgel particles to penetrate channels or matrices. The critical penetration behavior was closely related to the particle/pore size ratio. Low ΔPth at smaller particle/pore ratios was beneficial to allow easy penetration of gel materials into the channeling zones. On the contrary, high ΔPth at larger particle/pore ratios was desirable to prevent gel materials from massively invading and damaging the matrices. Instead, the gel particles accumulated at the inlet surface, and a gel cake was gradually formed. The cake further prevented the invasion of the gels. The cake could be removed by chemical breakers to resume the injectivity/productivity of the matrices. Correlations were developed to describe the relationship between ΔPth and particle/pore ratio. A distinct transition was identified at the particle/pore ratio of about 3. This work could help identify the favorable conditions to achieve successful gel treatments. In an effective conformance treatment, the particle/pore ratio in the channel should be sufficiently low to allow easy penetration of gel materials into the channel (e.g., particle/pore ratio<2 in this study). Meanwhile, the particle/pore ratio in the matrix should be large enough to support a high ΔPth and thus prevent massive gel invasion into the matrix. This study advances the current pore scale studies (a single particle passing through a single channel) to Darcy-scale characterization.