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      iCONE‐SRS: Development of inverse treatment planning for cone‐based stereotactic radiosurgery

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          Abstract

          Purpose

          At present, commercially available treatment planning systems (TPS) only offer manual planning functionality for cone‐based stereotactic radiosurgery (SRS) leading to labor intensive treatment planning. Our objective was to reduce treatment planning time through development of a simple inverse TPS for cone‐based SRS.

          Methods

          The iCONE TPS was developed using MATLAB (R2015a, The MathWorks Inc.) and serves as an inverse planning adjunct to a commercially available TPS. Simulated annealing is used to determine optimal table angle, gantry start and stop angles, and cone sizes for a user‐defined number of non‐coplanar arcs relative to user‐defined dose objectives. iCONE and clinically generated plans were compared through a retrospective planning study of 60 patients treated for 1–3 brain metastases (total of 100 lesions).

          Results

          Planning target volume (PTV) coverage was enforced for all plans through normalization. PTV maximum dose was constrained to be within 120%–135% of the prescription dose. The median conformity index for iCONE plans was 1.35, 1.33, and 1.32 for 1, 2, and 3‐target cases respectively corresponding to a median increase of 0.05 (range = −0.1 to 0.5, P < 0.05), 0.06 (range = −0.83 to 0.53, P < 0.05), and 0.03 (range = −1.21 to 0.74, P > 0.05) relative to the clinical plans. No clinically significant differences were found with respect to the dose to organs‐at‐risk. Median iCONE planning times were approximately a factor of five lower than consensus estimates for manual planning provided by local experienced SRS planners.

          Conclusions

          A simple inverse TPS for cone‐based SRS was developed. Plan quality was found to be similar to manually generated plans; however, degradation was observed in some cases highlighting the need for continued oversight and manual adjustment by experienced planners if implemented in the clinic. A factor of five reduction in treatment planning time was estimated.

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          Most cited references4

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          HyperArc VMAT planning for single and multiple brain metastases stereotactic radiosurgery: a new treatment planning approach

          Purpose The HyperArc VMAT (HA-VMAT) planning approach was newly developed to fulfill the demands of dose delivery for brain metastases stereotactic radiosurgery. We compared the dosimetric parameters of the HA-VMAT plan with those of the conventional VMAT (C-VMAT). Material and methods For 23 patients (1–4 brain metastases), C-VMAT and HA-VMAT plans with a prescription dose of 20–24 Gy were retrospectively generated, and dosimetric parameters for PTV (homogeneity index, HI; conformity index, CI; gradient index, GI) and brain tissue (V2Gy-V16Gy) were evaluated. Subsequently, the physical characteristics (modulation complexity score for VMAT, MCSV; Monitor unit, MU) of both treatment approaches were compared. Results HA-VMAT provided higher HI (1.41 ± 0.07 vs. 1.24 ± 0.07, p < 0.01), CI (0.93 ± 0.02 vs. 0.90 ± 0.05, p = 0.01) and lower GI (3.06 ± 0.42 vs. 3.91 ± 0.55, p < 0.01) values. Moderate-to-low dose spreads (V4Gy-V16Gy) were significantly reduced (p < 0.01) in the HA-VMAT plan over that of C-VMAT. HA-VMAT plans resulted in more complex MLC patterns (lower MCSV, p < 0.01) and higher MU (p < 0.01). Conclusions HA-VMAT plans provided significantly higher conformity and rapid dose falloff with respect to the C-VMAT plans.
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            Evaluation of a dedicated brain metastases treatment planning optimization for radiosurgery: a new treatment paradigm?

            Purpose To investigate the feasibility of a novel dedicated treatment planning solution, to automatically target multiple brain metastases with a single isocenter and multiple inversely-optimized dynamic conformal arcs (DCA), and to benchmark it against the well-established multiple isocenter DCA (MIDCA) and volumetric modulated arc therapy (VMAT) approaches. Material and Methods Ten previously treated patients were randomly selected, each representing a variable number of lesions ranging between 1 to 8. The original MIDCA treatments were replanned with both VMAT and the novel brain metastases tool. The plans were compared by means of Paddick conformity (CI) and gradient index (GI), and the volumes receiving 10 Gy (V10) and 12 Gy (V12). Results The brain metastases software tool generated plans with similar CI (0.65 ± 0.08) as both established treatment techniques while improving the gradient (mean GI = 3.9 ± 1.4). The normal tissue exposure in terms of V10 (48.5 ± 35.9 cc) and V12 (36.3 ± 27.1 cc) compared similarly to the MIDCA technique and surpassed VMAT plans. Conclusions The automated brain metastases planning algorithm software is an optimization of DCA radiosurgery by increasing delivery efficiency to the level of VMAT approaches. Improving dose gradients and normal tissue sparing over VMAT, revives DCA as the paradigm for linac-based stereotactic radiosurgery of multiple brain metastases.
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              Dosimetric comparison of different treatment modalities for stereotactic radiotherapy

              Background The modalities for performing stereotactic radiotherapy (SRT) on the brain include the cone-based linear accelerator (linac), the flattening filter-free (FFF) volumetric modulated arc therapy (VMAT) linac, and tomotherapy. In this study, the cone-based linac, FFF-VMAT linac, and tomotherapy modalities were evaluated by measuring the differences in doses delivered during brain SRT and experimentally assessing the accuracy of the output radiation doses through clinical measurements. Methods We employed a homemade acrylic dosimetry phantom representing the head, within which a thermoluminescent dosimeter (TLD) and radiochromic EBT3 film were installed. Using the conformity/gradient index (CGI) and Paddick methods, the quality of the doses delivered by the various SRT modalities was evaluated. The quality indicators included the uniformity, conformity, and gradient indices. TLDs and EBT3 films were used to experimentally assess the accuracy of the SRT dose output. Results The dose homogeneity indices of all the treatment modalities were lower than 1.25. The cone-based linac had the best conformity for all tumors, regardless of the tumor location and size, followed by the FFF-VMAT linac; tomography was the worst-performing treatment modality in this regard. The cone-based linac had the best gradient, regardless of the tumor location and size, whereas the FFF-VMAT linac had a better gradient than tomotherapy for a large tumor diameter (28 mm). The TLD and EBT3 measurements of the dose at the center of tumors indicated that the average difference between the measurements and the calculated dose was generally less than 4%. When the 3% 3-mm gamma passing rate metric was used, the average passing rates of all three treatment modalities exceeded 98%. Conclusions Regarding the dose, the cone-based linac had the best conformity and steepest dose gradient for tumors of different sizes and distances from the brainstem. The results of this study suggest that SRT should be performed using the cone-based linac on tumors that require treatment plans with a steep dose gradient, even as the tumor is slightly irregular, we should also consider using a high dose gradient of the cone base to treat and protect the normal tissue. If normal tissues require special protection exist at positions that are superior or inferior to the tumor, we can consider using tomotherapy or Cone base with couch at 0° for treatment.
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                Author and article information

                Contributors
                Anthony.Lausch@thp.ca
                Journal
                J Appl Clin Med Phys
                J Appl Clin Med Phys
                10.1002/(ISSN)1526-9914
                ACM2
                Journal of Applied Clinical Medical Physics
                John Wiley and Sons Inc. (Hoboken )
                1526-9914
                16 May 2019
                June 2019
                : 20
                : 6 ( doiID: 10.1002/acm2.2019.20.issue-6 )
                : 70-78
                Affiliations
                [ 1 ] Medical Physics Department Carlo Fidani Peel Regional Cancer Centre Trillium Health Partners Mississauga Canada
                Author notes
                [*] [* ] Author to whom correspondence should be addressed. Anthony Lausch

                E‐mail: Anthony.Lausch@ 123456thp.ca

                Telephone: 905-813-1100; Fax: 905-813-4452

                Article
                ACM212609
                10.1002/acm2.12609
                6560236
                31095851
                67766a52-21ee-4a4f-b52d-cc56df1b30a3
                © 2019 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.

                This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 08 January 2019
                : 28 March 2019
                : 18 April 2019
                Page count
                Figures: 5, Tables: 5, Pages: 9, Words: 5991
                Categories
                Radiation Oncology Physics
                Radiation Oncology Physics
                Custom metadata
                2.0
                acm212609
                June 2019
                Converter:WILEY_ML3GV2_TO_NLMPMC version:5.6.4 mode:remove_FC converted:12.06.2019

                cones,inverse planning,simulated annealing,stereotactic radiosurgery

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