Radiosurgery For Multiple Brain Metastases Research Articles

Interinstitutional Plan Quality Assessment of 2 Linac-Based, Single-Isocenter, Multiple Metastasis Radiosurgery Techniques

PurposeInterest and application of stereotactic radiosurgery for multiple brain metastases continue to increase. Various planning systems are available for linear accelerator (linac)–based single-isocenter multiple metastasis radiosurgery. Two of the most advanced systems are BrainLAB Multiple Metastases Elements (MME), a dynamic conformal arc (DCA) approach, and Varian RapidArc (RA), a volumetric modulated arc therapy (VMAT) approach. In this work, we systematically compared plan quality between the 2 techniques. Methods and MaterialsThirty patients with 4 to 10 metastases (217 total; median 7.5; Vmin = 0.014 cm3; Vmax = 17.73 cm3) were planned with both Varian RA and MME at 2 different institutions with extensive experience in each respective technique. All plans had a single isocenter and used Varian linac equipped with high-definition multileaf collimator. RA plans used 2 to 4 noncoplanar VMAT arcs with 10 MV flattening filter-free beam. MME plans used 4 to 9 noncoplanar DCAs and 6 MV flattening filter-free beam, (minimum planning target volume [PTVmin] = 0.49 cm3; PTVmax = 27.32 cm3; PTVmedian = 7.05 cm3). Prescriptions were 14 to 24 Gy in a single fraction. Target coverage goal was 99% of volume receiving prescription dose (D99% ≥ 100%). Plans were evaluated by Radiation Therapy Oncology Group/Paddick conformity index (CI) score, 12 Gy volume (V12Gy), V8Gy, V5Gy, mean brain dose (Dmean), and beam-on time. ResultsConformity was favorable among RA plans (median: MME CIRTOG = 1.38; RA CIRTOG = 1.21; P < .0001). V12Gy and V8Gy were lower for RA plans (median: MME V12 = 23.7 cm3; RA V12 = 19.2 cm3; P = .0001; median: MME V8Gy = 53.6 cm3; RA V8Gy = 44.1 cm3; P = .024). V5Gy was lower for MME plans (median: MME V5Gy = 141.4 cm3; RA V5Gy = 142.8 cm3; P = .009). Mean brain was lower for MME plans (median: MME Dmean = 2.57 Gy; RA Dmean = 2.76 Gy; P < .0001). ConclusionsFor linac-based multiple metastasis stereotactic radiosurgery, RapidArc VMAT facilitates favorable conformity and V12Gy/V8Gy volume compared with the MME DCA plan. MME planning facilitates reduced dose spill at levels ≤V5Gy.

Single isocenter stereotactic radiosurgery for patients with multiple brain metastases: dosimetric comparison of VMAT and a dedicated DCAT planning tool

BackgroundIn this dosimetric study, a dedicated planning tool for single isocenter stereotactic radiosurgery for multiple brain metastases using dynamic conformal arc therapy (DCAT) was compared to standard volumetric modulated arc therapy (VMAT).MethodsTwenty patients with a total of 66 lesions who were treated with the DCAT tool were included in this study. Single fraction doses of 15–20 Gy were prescribed to each lesion. Patients were re-planned using non-coplanar VMAT. Number of monitor units as well as V4Gy, V5Gy and V8Gy were extracted for every plan. Using a density-based clustering algorithm, V10Gy and V12Gy and the volume receiving half of the prescribed dose were extracted for every lesion. Gradient indices and conformity indices were calculated. The correlation of the target sphericity, a measure of how closely the shape of the target PTV resembles a sphere, to the difference in V10Gy and V12Gy between the two techniques was assessed using Spearman’s correlation coefficient.ResultsThe automated DCAT planning tool performed significantly better in terms of all investigated metrics (p < 0.05), in particular healthy brain sparing (V10Gy: median 3.2 cm3 vs. 4.9 cm3), gradient indices (median 5.99 vs. 7.17) and number of monitor units (median 4569 vs. 5840 MU). Differences in conformity indices were minimal (median 0.75 vs. 0.73) but still significant (p < 0.05). A moderate correlation between PTV sphericity and the difference of V10Gy and V12Gy between the two techniques was found (Spearman’s rho = 0.27 and 0.30 for V10Gy and V12Gy, respectively, p < 0.05).ConclusionsThe dedicated DCAT planning tool performed better than VMAT in terms of healthy brain sparing and treatment efficiency, in particular for nearly spherical lesions. In contrast, VMAT can be superior in cases with irregularly shaped lesions.

Stereotactic Radiosurgery for Multiple Brain Metastases.

To give an overview on the current evidence for stereotactic radiosurgery of brain metastases with a special focus on multiple brain metastases. While the use of stereotactic radiosurgery in patients with limited brain metastases has been clearly defined, its role in patients with multiple lesions (> 4) is still a matter of controversy. Whole-brain radiation therapy (WBRT) has been the standard treatment approach for patients with multiple brain lesions and is still the most commonly used treatment approach worldwide. Although distant brain failure is improved by WBRT, the overall survival is not readily impacted. As WBRT is associated with significant neurocognitive decline compared to stereotactic radiosurgery (SRS), SRS has been explored and increasingly utilized for selected patients with multiple brain metastases. Recent clinical data indicated the feasibility of stereotactic radiosurgery to multiple brain metastases with a similar survival in patients with more than 4 brain metastases versus patients with a maximum of 4 brain metastases. Also, neurocognitive function and quality of life was maintained after stereotactic radiosurgery which is essential in a palliative setting. The application of stereotactic radiosurgery with Gamma Knife, Cyberknife, or LINAC-based equipment has emerged as an effective and widely available treatment option for patients with limited brain metastases. Although not formally proven in prospective studies, SRS may also be considered as a safe and effective treatment option in selected patients with multiple brain metastases. Especially in patients with a favorable prognosis, survival over several years is observed also in the setting of multiple BM. For these patients, avoidance of the neurocognitive damage of WBRT is desirable, and SRS is often a more appropriate treatment in the current multimodality treatment of BM in which systemic treatment is often the cornerstone of the treatment. For patients with an intermediate (3-12months) and poor prognosis (< 3months), the application of WBRT becomes more and more controversial, because of its acute side effects, such as hair loss and fatigue and, thereby, detrimental effect on quality of life. For these patients, best supportive care, primary systemic treatment, and even SRS may be preferred over WBRT on an individualized patient basis.

End-to-end testing of automatic plan optimization using RayStation scripting for hypofractionated multimetastatic brain stereotactic radiosurgery

For external beam stereotactic radiosurgery of multiple brain metastatic lesions, it is difficult to select optimal treatment isocenters because the orientation and volume of each planning target volume (PTV) and its proximity to critical structures are unique for each patient. The RayStation treatment planning system offers Python-based scripting to optimize the placement of the treatment isocenter by comparing scenario-based plans. This can improve the plan quality by reducing the dose to the normal brain and increasing planning efficiency. The purpose of the current study was to compare the isocenter-optimized plans generated by RayStation with clinical plans created by the Pinnacle treatment planning system and to validate the RayStation treatment planning and delivery with end-to-end testing. Ten patient plans were automatically regenerated using the script in RayStation. For each patient, 4 plans with 4 different types of isocenters were generated: (1) 2 separate isocenters at the PTV centroids, (2) a single isocenter at the mid-point of 2 centroids, (3) a single isocenter at PTV1, and (4) a single isocenter at PTV2. The best plans were compared with paired Pinnacle plans using plan quality parameters, including normal brain volume excluding PTVs receiving 4 Gy (V4Gy), normal brain volume excluding PTVs receiving 12 Gy (V12Gy), maximum dose to the brainstem, homogeneity index, conformity indices, gradient index of each PTV, and monitor units per fraction. All plans were verified with a cylindrical quality assurance phantom, and end-to-end testing was performed with an anthropomorphic head phantom with a radiochromic film. The script was executed within 5-6 minutes to generate 4 scenario-based automatic plans. The homogeneity index and conformity indices showed small but statistically significant improvement with the RayStation plans. The gradient index (3.9 ± 0.9 for Pinnacle and 3.5 ± 0.6 for RayStation, p = 0.04) was also more favorable in the RayStation plans. V12Gy was significantly reduced by 13% and V4Gy was reduced by 5%. The total monitor units per fraction was significantly reduced by 20% for the RayStation plans. Plan optimization time using RayStation was reduced by 64%. The measured doses at each PTV centroid agreed within 3%, and all RayStation plans passed quality assurance verification tests. Scenario-based automatic plan generation using Python scripting helps identify an optimal treatment isocenter to reduce the dose to the normal brain and improve planning efficiency. RayStation plans provided better plan quality, especially lower doses to the normal brain, than Pinnacle plans. Thus, RayStation is a suitable planning modality for hypofractionated stereotactic radiosurgery for multiple brain metastases.

Linac-based radiosurgery for multiple brain metastases: Comparison between two mono-isocenter techniques with multiple non-coplanar arcs

Background and purposeThree mono-isocenter techniques with multiple non-coplanar arcs are nowadays clinically available for linac-based stereotactic radiosurgery (SRS) of multiple brain metastases (BM): HyperArc (HA), Multiple Brain Mets (MBM), and Monaco-HDRS. Two of them, HA and MBM, are here compared in terms of plan-quality, and dosimetric consistency between planning and delivering. Materials and methodsFor 20 patients with multiple BM (2–10), treated by mono-isocenter volumetric modulated arc therapy (VMAT) HA plans, mono-isocenter MBM dynamic conformal arc plans were generated. Prescription dose (Dp) was 18–25 Gy, for single-fraction, and 21–27 Gy, for three-fractions. Mean overall Planning Target Volume (PTV), expanded by 2 mm from each lesion, was 9.6 cm3 (0.5–27.9 cm3). Dose normalization of 100%Dp at 98%PTV was adopted. Plan-quality was compared by the Paddick conformity (CI) and gradient (GI) index, for the target, mean dose and V12 volume, for the healthy brain, and number of monitor units (MU). Further, verification dosimetry by radiochromic films was performed for each plan, thus comparing also, by γ-analysis, the consistency between in-phantom computed and measured dose distributions. ResultsCI significantly improved for HA plans, changing on average from 0.75 (MBM) to 0.94 (HA) (p < .001). No significant differences between HA and MBM plans were computed for GI (p = .216), and for mean dose (p = .436) and V12 (p = .062) to the healthy brain; although V12 increased on average from 23.7 cm3 (HA) to 37.3 cm3 (MBM). No significant difference resulted for MU (p = .107), whereas γ (1 mm, 3%) and γ (2 mm, 2%) passing-rates significantly improved for HA plans (p = .006; p = .023). ConclusionsHA plans assured a higher CI, while no significant difference resulted for any of the other planning metrics. Although on average slightly higher for HA plans, the dosimetric consistency between planned and delivered was satisfactory from both techniques. Hence, our judgement of near equal plan-quality from HA and MBM SRS-techniques.

4 Clinical implementation of a dedicated brain treatment planning optimizer for stereotactic treatments: A new treatment paradigm

Introduction Clinical implementation of a novel dedicated and automated treatment-planning solution for cranial indications, Elements. Single lesions can be targeted with an inversely optimized VMAT approach using automated arc trajectory optimization (Cranial SRS Element) while up to fifteen metastatic brain tumors can be automatically targeted with a single isocenter and multiple inversely-optimized dynamic conformal arcs (Multiple Brain Mets SRS Element). Material and Methods The very first 15 treated patients were analyzed, each representing a variable number of lesions (1–12). Depending on the number and location of the lesions a dedicated Element was selected and used in order to achieve the specific planning constraints. The plans were evaluated by means of Paddick conformity (CI) and gradient index (GI). Patient specific quality assurance (QA) was performed with gafchromic EBT3 film and portal imager. Results The Elements software tools generated plans with CI of 0.71 ± 0.09 and a gradient index of 3.9 ± 1.4. All plans achieved the organ at risk constraints. A gamma of 3%/3 mm was used for the QA. A 98 % and 98,2 % passing rate was found for the EBT3 film and portal imager, respectively. This shows also the good concordance between film and EPID, suggesting that patient specific QA can be perform with the portal imager rather than the time consuming films. Conclusions The automated dose planning Elements revive dynamic conformal arcs as the paradigm for linac-based stereotactic radiosurgery of multiple brain metastases and at the same time implements an improved VMAT approach for single lesions with the use of automated arc trajectory optimization. This study shows the implementation of this technique in the routine clinical environment with an improved planning and treatment efficiency.

Single-Isocenter, Volumetric Modulated Arc Radiosurgery for Multiple Brain Metastases in a Single Session

Single-Isocenter, Volumetric Modulated Arc Radiosurgery for Multiple Brain Metastases in a Single Session

P2.01-98 Single-Isocenter Volumetric-Modulated Arc Radiosurgery for Non-Small-Cell Lung Cancer Patients with Multiple Brain Metastases

Radiosurgery for multiple brain metastases (BMs) in patients with non-small-cell-lung cancer (NSCLC) is a well-established treatment option. However, only 1–4 BMs can be treated by conventional linear-accelerator-based radiosurgery because the treatment time becomes longer as the number of BMs increases. Advanced volumetric modulated arc therapy combined with image-guided radiotherapy enables the realization of single-isocenter volumetric-modulated arc radiosurgery (VMAR), a novel irradiation technique. VMAR irradiates multiple BMs simultaneously using only one isocenter and within a short treatment time. Here we report our initial experience with VMAR. The clinical records of 19 patients with 115 BMs from NSCLC were retrospectively analyzed. All patients were treated by VMAR for multiple BMs from October 2015 to September 2017 at our institution and received follow-up magnetic resonance imaging at least once after VMAR. The median patient age was 69 years. The median Karnofsky Performance Scale score was 90; five patients had been previously treated with whole-brain radiotherapy. The histology of the primary tumor was squamous-cell carcinoma in one patient and adenocarcinoma in 18 patients; 12 patients had either an EGFR or ALK alteration. A planning target volume (PTV) was created by expanding the contrast-enhanced lesion with a 1- or 2-mm margin. The median peripheral prescribed dose was 28 Gy, delivered in five fractions. All lesions were set to be covered by ≥99.5 % of the prescribed dose. The median follow-up period was 8.5 (range, 1.7–29.9) months. The median number of PTVs was four (range, 2–18). The median PTV was 0.49 (range, 0.13–13.49) cm3, and the median total PTV 8.3 (range, 1.52–18.87) cm3. The median PTV was significantly smaller in patients with than without genetic alterations to their tumor. The probabilities of local control, overall survival, and developing new BMs at 12 months were 100%, 68.4%, and 51.1%, respectively. Acute adverse events included grade 2 alopecia in four patients and seizure in one patient. The number of PTVs in patients with grade 2 alopecia was more than six. Two patients developed grade 2 central nervous system necrosis as a late adverse event. No grade 3 or higher toxicities were noted. While VMAR achieves good local control, the development of temporary alopecia remains to be addressed. More cases and a longer- follow-up period are required to verify the efficacy of VMAR.

Radiosurgery for multiple brain metastases: two cases reports

Radiosurgery for multiple brain metastases: two cases reports

In silico assessment of the dosimetric quality of a novel, automated radiation treatment planning strategy for linac-based radiosurgery of multiple brain metastases and a comparison with robotic methods

BackgroundTo appraise the dosimetric features and the quality of the treatment plan for radiosurgery of multiple brain metastases optimized with a novel automated engine and to compare with plans optimized for robotic-based delivery.MethodsA set of 15 patients with multiple brain metastases was selected for this in silico study. The technique under investigation is the recently introduced HyperArc. For all patients, three treatment plans were computed and compared: i: a HyperArc; ii: a standard VMAT; iii) a CyberKnife. Dosimetric features were computed for the clinical target volumes as well as for the healthy brain tissue and the organs at risk.ResultsThe data showed that the best dose homogeneity was achieved with the VMAT technique. HyperArc allowed to minimize the volume of brain receiving 4Gy (as well as for the mean dose and the volume receiving 12Gy, although not statistically significant). The smallest dose on 1 cm3 volume for all organs at risk is for CK techniques, and the biggest for VMAT (p < 0.05). The Radiation Planning Index coefficient indicates that, there are no significant differences among the techniques investigated, suggesting an equivalence among these.ConclusionAt treatment planning level, the study demonstrates that the use of HyperArc technique can significantly improve the sparing of the healthy brain while maintaining a full coverage of the target volumes.

Stereotactic radiosurgery for multiple brain metastases: Results of multicenter benchmark planning studies

PurposeStereotactic radiosurgery is indicated for treatment of multiple brain metastases. Various treatment platforms are available, but most comparisons are limited to single-center studies. As part of a national commissioning program, benchmark planning cases were completed by 21 clinical centers, providing a unique dataset of current practice across a large number of providers and equipment platforms. Methods and materialsTwo brain metastases cases were provided, with images and structures predrawn, involving 3 and 7 lesions. Centers produced plans according to their local practice, which were reviewed centrally using metrics for target coverage, selectivity, gradient fall-off, and normal tissue sparing. ResultsFifty plans were submitted, using 24 treatment platforms. Eleven plans were revised following feedback, including 2 centers that acquired a new platform; 1 other center accepted a restriction of service. All centers prioritized coverage, with the prescription isodose covering ≥95% of 233 of 235 target volumes. Selectivity was much more variable, especially for smaller lesions, and when combined with poor gradient indices resulted in large volumes of normal tissue being irradiated. Tomotherapy submissions were outliers for either selectivity or gradient index, but other platforms could produce plans with relatively low gradient indices for larger lesion volumes. There was more variation among Varian and Elekta LINAC plans than for Gamma Knife and CyberKnife, and larger differences for smaller targets, both inter- and intratreatment platform. Doses to normal brain and brainstem were highest when margins were applied, but improvements were possible by replanning alone. ConclusionsMulticenter benchmarking exercises have highlighted some variation in clinical practice and priorities, with a few outliers. Most platforms are able to achieve comparable plans, except for the smallest volumes and when larger planning margins are used. The data will be used to advance standardization and quality improvement of national services and can provide useful guidance for centers worldwide.

Excellent Outcomes with Radiosurgery for MultipleBrain Metastases in ALK and EGFR DrivenNon-Small Cell Lung Cancer.

Patients with brain metastases (BMs) arising from EGFR-mutated and anaplastic lymphoma kinase gene (ALK)-rearranged NSCLC have a favorable prognosis compared with patients with non-oncogene-addicted NSCLC, emphasizing the importance of minimizing toxicities such as the cognitive sequelae of whole brain radiation therapy (WBRT). Although radiosurgery without WBRT is the preferred strategy for one to three BMs, this paradigm remains controversial for patients with multiple BMs. We reviewed the cases of patients with EGFR-mutated and ALK-rearranged NSCLC presenting to our cancer center between 2008 and 2017 and included only patients receiving treatment to four or more BMs in a single radiosurgery session. We identified 35 patients with a median follow-up of 4.1 years. The maximum number of BMs treated in a single radiosurgery session ranged from four to 26 (median number of BM treated per radiosurgery course: 6), and in total over all courses the number ranged from four to 47 (median: 10). The median survival was 3.0 years (4.2 for ALK-rearranged NSCLC; 2.4 for EGFR-mutated NSCLC) from the diagnosis of BM, and survival was comparable regardless of number of radiosurgery courses, number of BMs treated in total, or number of BMs treated in a single radiosurgery session. The mean hippocampal and whole-brain doses were exceedingly low even for patients receiving treatment to more than 10 BMs (1.2 and 0.8 Gy, respectively). Radiosurgery was well tolerated overall and the 5-year rate of freedom from neurologic death was 84%. The 5-year rate of freedom from WBRT was 97%. Radiosurgery for multiple BMs is controversial, yet patients with EGFR-mutated and ALK-rearranged NSCLC may be uniquely suited to benefit from this approach. These results support single and multiple courses of radiosurgery without WBRT for patients with oncogene-addicted NSCLC with four or more BMs.

15. Evaluation of a dedicated brain metastases treatment planning optimization for radiosurgery: A new treatment paradigm?

Introduction 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. 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.

Low Risk of Symptomatic Radionecrosis Following Stereotactic Radiosurgery for Multiple Brain Metastases

Low Risk of Symptomatic Radionecrosis Following Stereotactic Radiosurgery for Multiple Brain Metastases

Technical Note: Using k-means clustering to determine the number and position of isocenters in MLC-based multiple target intracranial radiosurgery.

PurposeTo present the k‐means clustering algorithm as a tool to address treatment planning considerations characteristic of stereotactic radiosurgery using a single isocenter for multiple targets.MethodsFor 30 patients treated with stereotactic radiosurgery for multiple brain metastases, the geometric centroids and radii of each met were determined from the treatment planning system. In‐house software used this as well as weighted and unweighted versions of the k‐means clustering algorithm to group the targets to be treated with a single isocenter, and to position each isocenter. The algorithm results were evaluated using within‐cluster sum of squares as well as a minimum target coverage metric that considered the effect of target size. Both versions of the algorithm were applied to an example patient to demonstrate the prospective determination of the appropriate number and location of isocenters.ResultsBoth weighted and unweighted versions of the k‐means algorithm were applied successfully to determine the number and position of isocenters. Comparing the two, both the within‐cluster sum of squares metric and the minimum target coverage metric resulting from the unweighted version were less than those from the weighted version. The average magnitudes of the differences were small (−0.2 cm2 and 0.1% for the within cluster sum of squares and minimum target coverage, respectively) but statistically significant (Wilcoxon signed‐rank test, P < 0.01).ConclusionsThe differences between the versions of the k‐means clustering algorithm represented an advantage of the unweighted version for the within‐cluster sum of squares metric, and an advantage of the weighted version for the minimum target coverage metric. While additional treatment planning considerations have a large influence on the final treatment plan quality, both versions of the k‐means algorithm provide automatic, consistent, quantitative, and objective solutions to the tasks associated with SRS treatment planning using a single isocenter for multiple targets.

Linac-based radiosurgery for multiple brain metastases: A quality assurance and feasibility study.

2077 Background: The classical treatment for multiple brain metastases is whole brain radiotherapy (WBRT). For patients with 1-3 brain metastases stereotactic radiosurgery (SRS) results in better response, similar survival and less short and long term toxicity such as neurocognitive dysfunction than WBRT. For patients with &gt; 3 metastases there is little prospective data of SRS partly due to the technical and logistic difficulties of delivering SRS to multiple metastases. We present a new SRS planning program (MMM) that allows the planning and delivery of linac-based SRS to up to 10 brain metastases simultaneously in less overall time than for WBRT. Methods: Between August 2014 and August 2016, patients referred for RT with 2 or more brain metastases were offered treatment with MMM. System QA included ArcCheck diode array and film dosimetry and gel dosimetry based on a patient derived phantom. Individual QA included replanting treatment arcs on an independent system. Results: 94 patients with 2-10 (median 5) metastases and a combined volume of 0.01-8.64 cc were treated. Planning time including image fusion, target delineation and RT plan generation required on average 20 minutes minutes. SRS was delivered using 4-5 (is more 7-10 since return arcs do not address the same targets) non-coplanar arcs and a single isocenter at the center of mass of the metastases. Treatment time to deliver 18-24 Gy to all metastases was 25 mins (beam on time ~6 minutes) for a total time of 45 minutes. This is the same as the time for each individual metastasis on earlier planning systems and compares to 20 minutes planning time and 12 mins delivery time for each of 10 fractions for a conventional 2 field WBRT plan WBRT (total 140 minutes). At 6 months follow up, 88% of treated metastases had decreased in size, 10% were stable and 2% grew. Acute toxicity was mild except for one patient with intractable seizures. Conclusions: Linac based SRS for multiple brain metastases is efficient, requiring the same resources as for treatment of a single metastasis and less resources than for WBRT, with a high rate of local control. Appropriate equipment is available in most radiotherapy departments which will allow more prospective studies of SRS for multiple metastases.

Dosimetric Study of Automatic Brain Metastases Planning in Comparison with Conventional Multi-Isocenter Dynamic Conformal Arc Therapy and Gamma Knife Radiosurgery for Multiple Brain Metastases.

ObjectiveThe efficacy of stereotactic radiosurgery (SRS) using Gamma Knife (GK) (Elekta, Tokyo) is well known. Recently, Automatic Brain Metastases Planning (ABMP) Element (BrainLAB, Tokyo) for a LINAC-based radiation system was commercially released. It covers multiple off-isocenter targets simultaneously inside a multi-leaf collimator field and enables SRS / stereotactic radiotherapy (SRT) with a single group of LINAC-based dynamic conformal multi-arcs (DCA) for multiple brain metastases. In this study, dose planning of ABMP (ABMP-single isocenter DCA (ABMP-SIDCA)) for SRS of small multiple brain metastases was evaluated in comparison with those of conventional multi-isocenter DCA (MIDCA-SRS) (iPlan, BrainLAB, Tokyo) and GK-SRS (GKRS).MethodsSimulation planning was performed with ABMP-SIDCA and GKRS in the two cases of multiple small brain metastases (nine tumors in both), which had been originally treated with iPlan-MIDCA. First, a dosimetric comparison was done between ABMP-SIDCA and iPlan-MIDCA in the same setting of planning target volume (PTV) margin and D95 (dose covering 95% of PTV volume). Second, dosimetry of GKRS with a margin dose of 20 Gy was compared with that of ABMP-SIDCA in the setting of PTV margin of 0, 1 mm, and 2 mm, and D95=100% dose (20 Gy).ResultsFirst, the maximum dose of PTV and minimum dose of gross tumor volume (GTV) were significantly greater in ABMP-SIDCA than in iPlan-MIDCA. Conformity index (CI, 1/Paddick’s CI) and gradient index (GI, V (half of prescription dose) / V (prescription dose)) in ABMP-SIDCA were comparable with those of iPlan-MIDCA. Second, PIV (prescription isodose volume) of GKRS was consistent with that of 1 mm margin - ABMP-SIDCA plan in Case 1 and that of no-margin ABMP-SIDCA plan in Case 2. Considering the dose gradient, the mean of V (half of prescription dose) of ABMP-SIDCA was not broad, comparable to GKRS, in either Case 1 or 2.ConclusionsThe conformity and dose gradient with ABMP-SIDCA were as good as those of conventional MIDCA for each lesion. If the conditions of the LINAC system permit a minimal PTV margin (1 mm or less), ABMP-SIDCA might provide excellent dose fall-off comparable with that of GKRS thereby enabling a short treatment time.

The Projection Summing Optimization Algorithm Can Effectively Reduce Normal Brain Dose in Stereotactic Radiosurgery of Multiple Brain Metastases With Single Isocenter

The Projection Summing Optimization Algorithm Can Effectively Reduce Normal Brain Dose in Stereotactic Radiosurgery of Multiple Brain Metastases With Single Isocenter

Challenges in Quality Assurance for Volumetric Radiosurgery of Multiple Brain Metastases

Challenges in Quality Assurance for Volumetric Radiosurgery of Multiple Brain Metastases

Optimization of Treatment Geometry to Reduce Normal Brain Dose in Radiosurgery of Multiple Brain Metastases with Single-Isocenter Volumetric Modulated Arc Therapy.

Treatment of patients with multiple brain metastases using a single-isocenter volumetric modulated arc therapy (VMAT) has been shown to decrease treatment time with the tradeoff of larger low dose to the normal brain tissue. We have developed an efficient Projection Summing Optimization Algorithm to optimize the treatment geometry in order to reduce dose to normal brain tissue for radiosurgery of multiple metastases with single-isocenter VMAT. The algorithm: (a) measures coordinates of outer boundary points of each lesion to be treated using the Eclipse Scripting Application Programming Interface, (b) determines the rotations of couch, collimator, and gantry using three matrices about the cardinal axes, (c) projects the outer boundary points of the lesion on to Beam Eye View projection plane, (d) optimizes couch and collimator angles by selecting the least total unblocked area for each specific treatment arc, and (e) generates a treatment plan with the optimized angles. The results showed significant reduction in the mean dose and low dose volume to normal brain, while maintaining the similar treatment plan qualities on the thirteen patients treated previously. The algorithm has the flexibility with regard to the beam arrangements and can be integrated in the treatment planning system for clinical application directly.