Dynamic Conformal Arc Research Articles

A novel weight optimized dynamic conformal arcs with TrueBeam™ Linac for very small tumors (≤1 cc) with single isocenter of multiple brain metastases (2≤, ≥4) in stereotactic radiosurgery: A comparison with volumetric modulated arc therapy.

We evaluated whether improved increase delivery efficiency of weight optimized dynamic conformal arc (WO-DCA) therapy in comparison to volumetric modulated arc therapy (VMAT) with single isocenter for SRS treatment of very small volume and multiple brain metastases (BMs). 20 patients having a less than 1 cc volume and 2≤, ≥4 of multiple BMs, redesigned for 20 Gy in 1 fraction using WO-DCA and VMAT techniques with double full coplanar and three partial noncoplanar arcs. Plan qualities were compared using tumor coverage, conformity index (CI), gradient index (GI), V4Gy, V10Gy, and V12Gy volumes of brain, monitor units (MUs), and percent of quality assurance pass rate (QA%). Both techniques satisfied clinical requirements in coverage and CI. VMAT had a significantly higher MU and mean GI than WO-DCA (for MUs; 2330 vs. 1991; P < 0.001, and for GI; 4.72 vs. 3.39; P < 0.001). WO-DCA was found significantly lower V4Gy (171.11 vs. 232.80 cm3, P < 0.001), V10Gy (25.82 vs. 29.71 cm3, P < 0.05), and V12Gy (14.35 vs. 17.28 cm3, P < 0.05) volumes than VMAT. WO-DCA was associated with markedly increase QA pass rates for all plans (97.65% vs. 92.64%, P < 0.001). WO-DCA may be the first choice compared to the VMAT in reducing the dose in the brain and minimizing small-field dosimetric errors for very small SRS treatment of brain metastases in the range of ≤ 1 cc and 2≤, ≥4.

The Optimal Choice of Technique for Stereotactic Radiosurgery—A LINAC-Based Dosimetric Study between DCA, DCA-SSO, DCA-SSO-VDR, and VMAT

Abstract Introduction Advanced radiation therapy delivery techniques require greater understanding of various planning sequences and methods. The aim of this study is to determine a class solution that finds the best possible technique to deliver for stereotactic radiosurgery between dynamic conformal arc (DCA) techniques using various options such as DCA, DCA + SSO (segment shape optimization), and DCA + SSO + VDR (variable dose rate) using noncoplanar beam arrangement and volumetric modulated arc therapy (VMAT) using coplanar beams. Materials and Methods In this dosimetric study, 11 brain cases were retrospectively planned for various techniques and analyzed for the Paddick conformity index (CI), Radiation Therapy Oncology Group homogeneity index (HI), Paddick gradient index (GI), treatment time in terms of monitor units (MU) and normal brain dose (V12Gy). The paired t-test was performed to know the statistical significance between the techniques. Results In terms of CI, GI, and control of the normal brain dose, the VMAT plan was superior to other techniques. But, HI was found to be better with DCA. Above all, VMAT delivered higher MU than any other technique. The p-values between DCA + SSO and DCA, DCA + SSO + VDR and DCA + SSO, and VMAT and DCA + SSO + VDR are as follows: CI: 0.0004, 0.015, and 0.03; GI: 0.03, 0.33, and 0.29; HI: 0.008, 0.04, and 0.06; V12 Gy of normal brain: 0.1, 0.01, 0.38. VMAT requires approximately 41 ± 17% more MU than DCA + SSO + VDR. Conclusion VMAT using coplanar beams is preferable among all the techniques, considering the dosimetric parameters studied. If VMAT is not available in the facility, DCA + SSO + VDR technique using non coplanar beams can be used to deliver SRS treatment.

Single-isocenter multiple-target stereotactic radiosurgery for multiple brain metastases: dosimetric evaluation of two automated treatment planning systems

PurposeAutomated treatment planning systems are available for linear accelerator (linac)-based single-isocenter multi-target (SIMT) stereotactic radiosurgery (SRS) of brain metastases. In this study, we compared plan quality between Brainlab Elements Multiple Brain Metastases (Elements MBM) software which utilizes dynamic conformal arc therapy (DCAT) and Varian HyperArc (HA) software using a volumetric modulated arc therapy (VMAT) technique.Patients and methodsBetween July 2018 and April 2021, 36 consecutive patients ≥ 18 years old with 367 metastases who received SIMT SRS at UPMC Hillman Cancer San Pietro Hospital, Rome, were retrospectively evaluated. SRS plans were created using the commercial software Elements MBM SRS (Version 1.5 and 2.0). Median cumulative gross tumor volume (GTV) and planning tumor volume (PTV) were 1.33 cm3 and 3.42 cm3, respectively. All patients were replanned using HA automated software. Extracted dosimetric parameters included mean dose (Dmean) to the healthy brain, volumes of the healthy brain receiving more than 5, 8,10, and 12 Gy (V5Gy, V8Gy, V10Gy and V12Gy), and doses to hippocampi.ResultsBoth techniques resulted in high-quality treatment plans, although Element MBM DCAT plans performed significantly better than HA VMAT plans, especially in cases of more than 10 lesions). Median V12Gy was 13.6 (range, 1.87–45.9) cm3 for DCAT plans and 18.5 (2.2–62,3) cm3 for VMAT plans (p < 0.0001), respectively. Similarly, V10Gy, V8Gy, V5Gy (p < 0.0001) and median dose to the normal brain (p = 0.0001) were favorable for DCAT plans.ConclusionsBoth Elements MBM and HA systems were able to generate high-quality plans in patients with up to 25 brain metastases. DCAT plans performed better in terms of normal brain sparing, especially in patients with more than ten lesions and limited total tumor volume.

Radiosurgery for Five to Fifteen Brain Metastases: A Single Centre Experience and a Review of the Literature.

PurposeStereotactic radiosurgery (SRS) is now mainstream for patients with 1-4 brain metastases however the management of patients with 5 or more brain metastases remains controversial. Our aim was to evaluate the clinical outcomes of patients with 5 or more brain metastases and to compare with published series as a benchmarking exercise.MethodsPatients with 5 or more brain metastases treated with a single isocentre dynamic conformal arc technique on a radiosurgery linac were identified from the institutional database. Endpoints were local control, distant brain failure, leptomeningeal disease and overall survival. Dosimetric data were extracted from the radiosurgery plans. Series reporting outcomes following SRS for multiple brain metastases were identified by a literature search.Results36 patients, of whom 35 could be evaluated, received SRS for 5 or more brain metastases between February 2015 and October 2021. 25 patients had 5-9 brain metastases (group 1) and 10 patients had 10-15 brain metastases (group 2). The mean number of brain metastases in group 1 was 6.3 (5-9) and 12.3 (10-15) in group 2. The median cumulative irradiated volume was 4.6 cm3 (1.25-11.01) in group 1 and 7.2 cm3 (2.6-11.1) in group 2. Median follow-up was 12 months. At last follow-up, local control rates per BM were 100% and 99.8% as compared with a median of 87% at 1 year in published series. Distant brain failure was 36% and 50% at a median interval of 5.2 months and 7.4 months after SRS in groups 1 and 2 respectively and brain metastasis velocity at 1 year was similar in both groups (9.7 and 11). 8/25 patients received further SRS and 7/35 patients received whole brain radiotherapy. Median overall survival was 10 months in group 1 and 15.7 months in group 2, which compares well with the 7.5 months derived from the literature. There was one neurological death in group 2, leptomeningeal disease was rare (2/35) and there were no cases of radionecrosis.ConclusionWith careful patient selection, overall survival following SRS for multiple brain metastases is determined by the course of the extracranial disease. SRS is an efficacious and safe modality that can achieve intracranial disease control and should be offered to patients with 5 or more brain metastases and a constellation of good prognostic factors.

Dosimetric benefits of dynamic conformal arc therapy-combined with active breath-hold in lung stereotactic body radiotherapy.

To test the hypothesis that dynamic conformal arc therapy (DCAT) in Monaco, compared with volumetric modulated arc therapy (VMAT), maintains plan quality with higher delivery efficiency for lung stereotactic body radiotherapy (SBRT) and to investigate dosimetric benefits of DCAT with active breath-hold (DCAT+ABH), compared with free-breathing (DCAT+FB) for varying tumor sizes and motions. Fifty DCAT plans were used for lung SBRT. Randomly selected 17 DCAT plans were evaluated with respect to the retrospectively generated volumetric modulated arc therapy (VMAT) plans. The maximum dose at 2 cm from planning target volume (PTV) in any direction (D2cm/Rx), the ratio of 50% prescription isodose volume to the PTV (R50%), conformity index (CI), the lung volume receiving ≥20 Gy (V20), and monitor unit (MU) were evaluated. A t-test was used to evaluate the difference of plan quality between DCAT and VMAT. Internal target volume (ITV)/integrated-gross target volume (GTV) attributed by intra-fraction motion and lung V20 were stratified for DCAT+ABH and DCAT+FB across varying GTVs. DCAT maintained plan quality (p = 0.154 for D2cm/Rx, p = 0.089 for R50%, p = 0.064 for CI, and p = 0.780 for lung V20) while reducing MUs up to 30% (p <0.001) from 2748 MU (VMAT) to 1868 MU (DCAT). DCAT+ABH, compared to DCAT+FB, reduced tumor motion, resulting in 19% volume reduction of PTV and 60% reduction in lung V20, on average. The difference in lung V20 between DCAT+ABH and DCAT+FB increased as the target size increased. The DCAT is a favorable approach compared with VMAT. These results support the utility of DCAT as a routine planning platform for lung SBRT, especially when utilized with respiratory motion management using the ABH.

Comparison of the dosimetric planning efficiency of dynamic conformal arc (DCA) and volumetric modulated arc therapy (VMAT) techniques for stereotactic body radiotherapy (SBRT) of lung cancer using internal target volume (ITV)

Comparison of the dosimetric planning efficiency of dynamic conformal arc (DCA) and volumetric modulated arc therapy (VMAT) techniques for stereotactic body radiotherapy (SBRT) of lung cancer using internal target volume (ITV)

A Comparison of Robustness of Volumetric Modulated Arc Therapy and Dynamic Conformal Arc Therapy for Lung Stereotactic Body Radiation Therapy

A Comparison of Robustness of Volumetric Modulated Arc Therapy and Dynamic Conformal Arc Therapy for Lung Stereotactic Body Radiation Therapy

A dosimetric comparison of 3D DCAT vs VMAT for palliative and early-stage liver lesions using eclipse TPS.

Volumetric modulated arc therapy (VMAT) and 3D dynamic conformal arc therapy (DCAT) are 2 methods proven useful for the clinical implementation of stereotactic body radiation therapy (SBRT) for lung lesions however, similar comparisons of SBRT liver lesions are lacking. The purpose of this study was to determine if the conformity of dose, irradiated volume, and dose to organs at risk (OAR) are equivalent or improved with the use of DCAT as an alternative treatment method when compared to standard VMAT for SBRT delivery of palliative and early-stage liver lesions. Twenty patients with liver lesions sized 2.0 to 5.0 cm were selected for this study. Plans were created with both DCAT and VMAT techniques for each patient. Metrics evaluated included the mean heart, kidney, large bowel, small bowel, esophagus, and stomach doses, the lung volume receiving 20 Gy (V20), the volume of the normal liver receiving 15 Gy (V15), conformity index (CI), heterogeneity index (HI), and the irradiated volume or volume receiving 25 Gy (V25). The p-values for the mean dose to kidneys, small bowel, esophagus, and the lung V20 were greater than 0.05, and no statistical difference could be determined between DCAT and VMAT. The p-values for the mean heart, large bowel, stomach, and liver V15 were less than 0.05, indicating statistical significance and superiority of VMAT for minimizing dose to these organs, especially V15 of the liver. The DCAT technique produced CI greater than 1.0 for all patients proving superior coverage, while standard VMAT produced significantly improved V25 with p-values less than 0.0001, and consequently higher HI.

Modern Linear Accelerator–Based Radiotherapy Is Safe and Effective in the Treatment of Secretory and Nonsecretory Pituitary Adenomas

Adjuvant radiotherapy (RT) can help achieve local control (LC) and reduce hormonal overexpression for pituitary adenomas (PAs). Prior reports involved Gamma Knife or older linear accelerator (LINAC) techniques. The aim of this study was to report long-term outcomes for modern LINAC RT. Institutional retrospective review of LINAC RT for PAs with minimum 3 years of magnetic resonance imaging follow-up was performed. Hormonal control was defined as biochemical remission in absence of medications targeting hormone excess. LC defined using Response Evaluation Criteria in Solid Tumors on surveillance magnetic resonance imaging. Progression-free survival defined as time alive with LC without return of or worsening hormonal excess from secretory PA. Kaplan-Meier and Cox proportional hazard models used. From 2003 to 2017, 140 patients with PAs (94 nonsecretory, 46 secretory) were treated with LINAC RT (105 fractionated RT, 35 radiosurgery) with median follow-up of 5.35 years. Techniques included fixed gantry intensity-modulated radiotherapy (51.4%), dynamic conformal arcs (9.3%), and volumetric modulated arc therapy (39.3%). Progression-free survival at 5 years was 95.3% for secretory tumors and 94.8% for nonsecretory tumors. Worse progression-free survival was associated with larger planning target volume on multivariable analysis (hazard ratio 2.87, 95% confidence interval 1.01-8.21, P= 0.049). Hormonal control at 5 years was 50.0% and associated with higher dose to tumor (hazard ratio 1.05, 95% confidence interval 1.02-1.09, P= 0.005) and number of surgeries (hazard ratio 1.74, 95% confidence interval 1.05-2.89, P= 0.032). Patients requiring any pituitary hormone replacement increased from 57.9% to 70.0% after RT. Modern LINAC RT for patients with PAs was safe and effective for hormonal control and LC. No difference in LC was noted for functional versus nonfunctional tumors, possibly owing to higher total dose and daily image guidance.

New dosimetric guidelines for linear Boltzmann transport equations through comparative evaluation of stereotactic body radiation therapy for lung treatment planning.

PurposeTo propose guidelines for lung stereotactic body radiation therapy (SBRT) when using Acuros XB (AXB) equivalent to the existing ones developed for convolution algorithms such as analytic anisotropic algorithm (AAA), considering the difference between the algorithms.MethodsA retrospective analysis was performed on 30 lung patients previously treated with SBRT. The original AAA plans, which were developed using dynamic conformal arcs, were recalculated and then renormalized for planning target volume (PTV) coverage using AXB. The recalculated and renormalized plans were compared to the original plans based on V100% and V90% PTV coverage, as well as V105%, conformality index, D2cm, Rx/Dmax, R50, and Dmin. These metrics were analyzed nominally and on variations according to RTOG and NRG guidelines. Based on the relative difference between each metric in the AAA and AXB plans, new guidelines were developed. The relative differences in our cohort were compared to previously documented AAA to AXB comparisons found in the literature.ResultsAAA plans recalculated in AXB had a significant reduction in most dosimetric metrics. The most notable changes were in V100% (4%) and the conformality index (7.5%). To achieve equal PTV coverage, AXB required an average of 1.8% more monitor units (MU). This fits well with previously published data. Applying the new guidelines to the AXB plans significantly increased the number of minor violations with no change in major violations, making them comparable to those of the original AAA plans.ConclusionThe relative difference found between AAA and AXB for SBRT lung plans has been shown to be consistent with previous works. Based on these findings, new guidelines for lung SBRT are recommended when planning with AXB.

Survival Outcomes following LINAC based Stereotactic Radiosurgery/Stereotactic Radiotherapy (SRST) treatment of brain metastases: The Wessex Experience

Abstract Aims Since 2016, the University Hospital Southampton NHS Foundation Trust (UHSFT) has been commissioned by NHS England to deliver SRST to brain metastases. At UHSFT, all referrals are discussed at the Wessex Neurosciences multidisciplinary team meeting. Referrals that satisfy the criteria set by NHS England (estimated prognosis greater than 6 months, absence or controlled extracranial disease or potentially controllable extracranial disease with a Karnofsky Performance Status &amp;gt;70%) will be offered SRST. This retrospective study was performed to assess overall survival rates of patients with brain metastases treated with SRST with further tumour subtype analysis. We also benchmarked our results with other SRST centres. Method Retrospective data collection was performed for all the patients who have been treated with SRST. Patients who received SRST to a single metastasis, multiple metastases and/or to the resection cavity between 01/01/2017 to 30/09/2019 were included in this study. All treatment was delivered using a LINAC based SRST platform. Prescription doses ranged from 13.5 Gy to 21 Gy in a single fraction, 21 to 24 Gy in 3 fractions and 25 Gy in 5 fractions. Patients are treated using a stereotactic thermoplastic immobilisation shell and dynamic conformal arc therapy with ExacTrac TM and Cone Beam CT imaging. Dates of death were obtained from the NHS Digital Spine and survival analysis using median overall survival was performed using the Kaplan Meier Method. Results 277 patients were treated between 01/01/17 and 30/9/2019. The median overall survival from the Kaplan Meier Method was shown to be 14.7 months and the 6-month overall survival was 71% for all patients. Sub-group analysis of individual tumour sites showed: lung (n=110) median OS 12.1 months, melanoma (n=58) median OS 26.4 months, breast (n=46) median OS not reached (67% still alive) but 18 months survival was 70%, renal (n=22) median OS 15.4 months and colorectal (n=19) median OS 6 months. “Other” tumour sites (n=22) included patients with ovarian, neuroendocrine, sarcoma, testis, oesophagus, unknown primary and gallbladder which were grouped together due to small patient numbers. 41% of patients treated were alive at the time of analysis. Conclusion Patients with brain metastases treated with SRST at UHFST have similar outcomes compared to other SRST centres. These patients have a median overall survival of 14.7 months. However, 29% of patients analysed did not survive more than 6 months. Further collection and analysis of the data might improve patient selection and their outcomes.

Dosimetric comparison among dynamic conformal arc therapy, coplanar and non-coplanar volumetric modulated arc therapy for single brain metastasis.

In the delivery of stereotactic radiosurgery (SRS) by linear accelerator (LINAC), dynamic conformal arc therapy (DCAT) with non-coplanar beams is conventionally used. However, volumetric modulated arc therapy (VMAT) can improve target conformity, thereby decreasing the dose to organs at risk by inversed planning methods, but few studies have directly compared DCAT and VMAT with and without non-coplanar beams in patients with single brain metastasis. We therefore conducted a planning study to compare the dose distribution in DCAT, VMAT using only a coplanar arc (CoVMAT) and VMAT with non-coplanar arcs (NcVMAT) in the treatment of single brain metastasis. DCAT, CoVMAT and NcVMAT plans were created for 15 patients. The three modalities were compared in terms of target conformity, target coverage, the dose to normal brain tissue, monitor units (MUs) and beam-on time. Both conformity indices (RTOG-CI and IP-CI) as well as the D98% of the gross target volume (GTV) were significantly better in the NcVMAT plans than in the DCAT plans. Comparisons of the doses to normal brain tissue revealed that the V20Gy, V15Gy, V12Gy, V10Gy and V5Gy were significantly smaller in the NcVMAT plans than in the plans based on the other two modalities. The MUs of the DCAT and NcVMAT plans were larger than those of the CoVMAT plans, and the beam-on time was longer in the NcVMAT and CoVMAT plans than in the DCAT plans. Compared to the CoVMAT and DCAT plans, NcVMAT plans significantly improved target conformity and reduced the doses to normal brain tissue at V20Gy, V15Gy, V12Gy, V10Gy and V5Gy.

Novel Clinically Weight-Optimized Dynamic Conformal Arcs (WO-DCA) for Liver SBRT: A Comparison with Volumetric Modulated Arc Therapy (VMAT).

PurposeTo evaluate the feasibility of shortening the duration of liver stereotactic radiotherapy (SBRT) without jeopardizing dosimetry or conformity by utilizing weight-optimized dynamic conformal arcs (WO-DCA) as opposed to volumetric modulated arc therapy (VMAT) for tumors away from critical structures.MethodsNineteen patients with liver metastasis were included, previously treated with 50 Gy in 4 fractions with VMAT technique using two partial coplanar arcs of 6 MV beams delivered in high-definition multi-leaf collimator (HD-MLC). Two coplanar partial WO-DCA were generated on Pinnacle treatment planning system (TPS) for each patient; and MLC aperture around the planning target volume (PTV) was automatically generated at different margins for both arcs and maintained dynamically around the target during arc rotation. Weight of the two arcs using optimization method was adjusted between the arcs to maximize tumor coverage and protect organs at risk (OAR) based on the RTOG‐0438 protocol.ResultsThe WO-DCA plans successfully “agreed” with the standard VMAT for OAR (liver, spinal cord, stomach, duodenum, small bowel, and heart) and PTV (Dmean, D98%, D2%, CI, and GI), with superior mean quality assurance (QA) pass rate (97.06 vs 93.00 for VMAT; P < 0.001 and t = 8.87). Similarly, the WO-DCA technique additionally reduced the beam‐on time (3.26 vs 4.43; P < 0.001) and monitor unit (1860 vs 2705 for VMAT; P < 0.001) values significantly.ConclusionThe WO‐DCA plans might minimize small‐field dosimetry errors and defeat patient‐specific VMAT QA requirements due to the omission of MLC beam modulation through the target volume. The WO‐DCA plans may additionally enable faster treatment delivery times and lower OAR without sacrificing target doses in SBRT of liver tumors away from critical structures.

Absolute dose measurements for lung gated delivery stereotactic body radiation therapy

PurposeTo evaluate absolute dose between phase- and amplitude-gated modes for lung stereotactic body radiation therapy (SBRT), using the moving targets developed in-house. MethodsThe moving targets were developed in-house, allowing measurements of absolute dose using Semiflex ion chamber, Pinpoint ion chamber and microDiamond detector. 24 plans were generated in the Pinnacle 16.2 treatment planning system (TPS). 720 partial dynamic conformal arcs (DCA), 120 for phase- and 120 for amplitude-gated mode per detector, were performed to compare dose discrepancy (planned vs measured doses), for all detectors. Single fraction of 15 Gy was delivered with TrueBeam Novalis STx, triggered on the stable phases (phase-gated mode) or near the end-exhalation (amplitude-gated mode), for a breathing period ranging from 2 s to 7 s, using flattened filter free beams (FFF). ResultsThe lowest discrepancy between measured and planned dose was obtained using the microDiamond detector in the phase-gated −0.1 (−0.2 to 0) % and −0.3 (−0.4 to −0.1) % in amplitude-gated mode (p < 0.001). Using PinPoint ion chamber, greater discrepancy was obtained in phase-gated −0.5 (−0.7 to −0.3) %, comparing to the amplitude-gated mode −0.1 (−0.2 to 0) % (p < 0.001). The greatest discrepancy was observed using the Semiflex ion chamber, with lesser differences between the phase-gated 1.5 (1.2–1.7) % and amplitude-gated mode 1.4 (1.2–1.5) (p = 0.134). ConclusionDetectors with low discrepancy, PinPoint ion chamber and microDiamond detectors, can be used in routine quality assurance for lung gated delivery in SBRT treatment, for commercial phantom as for phantom developed in-house.

Interfractional target changes in brain metastases during 13-fraction stereotactic radiotherapy

BackgroundThe risk for radiation necrosis is lower in fractionated stereotactic radiotherapy (SRT) than in conventional radiotherapy, and 13-fraction SRT is our method of choice for the treatment of brain metastases ≥ around 2 cm or patients who are expected to have a good prognosis. As 13-fraction SRT lasts for at least 17 days, adaptive radiotherapy based on contrast-enhanced mid-treatment magnetic resonance imaging (MRI) is often necessary for patients undergoing 13-fraction SRT. In this study, we retrospectively analyzed interfractional target changes in patients with brain metastases treated with 13-fraction SRT.MethodsOur analyses included data from 23 patients and 27 metastatic brain lesions treated with 13-fraction SRT with dynamic conformal arc therapy. The peripheral dose prescribed to the planning target volume (PTV) was 39–44.2 Gy in 13-fractions. The gross tumor volume (GTV) of the initial SRT plan (initial GTV), initial PTV, and modified GTV based on the mid-treatment MRI scan (mid-treatment GTV) were assessed.ResultsThe median initial GTV was 3.8 cm3 and the median time from SRT initiation to the mid-treatment MRI scan was 6 days. Compared to the initial GTV, the mid-treatment GTV increased by more than 20% in five lesions and decreased by more than 20% in five lesions. Interfractional GTV volume changes of more than 20% were not significantly associated with primary disease or the presence of cystic components/necrosis. The mid-treatment GTV did not overlap perfectly with the initial PTV in more than half of the lesions.ConclusionsCompared to the initial GTV, the mid-treatment GTV changed by more than 20% in almost one-third of lesions treated with 13-fraction SRT. As SRT usually generates a steep dose gradient as well as increasing the maximum dose of PTV compared to conventional radiotherapy, assessment of the volume and locational target changes and adaptive radiotherapy should be considered as the number of fractions increases.

Technical Note: Collimator angle optimization for multiple brain metastases in dynamic conformal arc treatment planning

To reduce the exposed area by the multileaf collimator between lesions for single-isocenter dynamic conformal arc (DCA) therapy for stereotactic radiosurgery treatment of multiple brain metastases by optimizing the collimator angle orientation. In particular, this is achieved by the avoidance of collimator angles where multiple lesions are exposed by the same leaf pairs. An algorithm that estimates the quality of an arc by considering the target projections onto the plane perpendicular to the central axis of the arc beam. A penalty proportional to the exposure of healthy tissue between metastases is assigned to each control point and each feasible collimator angle from a discretized set of angles. The algorithm can generate two outputs: the fixed optimal collimator angle over all the control points, or the optimal collimator angle trajectory through all the control points considering the rotation speed of the collimator. The first output is based on explicit enumeration of all collimator angles, and the second one generates the optimal trajectory using dynamic programming to find the globally optimal solution with respect to the objective function cost. The algorithm was validated on eight clinical cases having a different number of cranial metastases: two metastases (n=1), three metastases (n=5), four metastases (n=1), and five metastases (n=1). Plans with optimized fixed collimator angles and plans with optimized dynamic collimator trajectories were compared between each other. When comparing optimal dynamic trajectories to fixed optimal collimator trajectories, the resulting plans demonstrated a total reduction of the exposed area between lesions over the entire beam configuration from 21.7% up to 71.3%; similarly, beam-wise reductions ranging from 5.83% to over 90% have been registered. Collimator angle optimization has the potential to reduce the magnitude of the exposed area between lesions in an efficient way for non-isocentric treatments where multiple lesions are treated simultaneously. Dynamic trajectories are capable of limiting the island blocking problem more than optimal fixed trajectories by exploiting the extra degree of freedom of rotating the multileaf collimator. The algorithm can also lead to time saving during the treatment planning process.

Quality of Automated Stereotactic Radiosurgery Plans in Patients with 4 to 10 Brain Metastases.

Simple SummaryStereotactic radiosurgery (SRS) and hypofractionated stereotactic radiotherapy (SRT) are promising treatment options for patients with multiple brain metastases in the current era of personalized medicine. Recent international guidelines propose SRS also in patients with more than three brain metastases with low-volume disease. Optimal treatment quality with sparing of healthy brain tissue is essential to avoid SRS/SRT complications such as brain necrosis. The aim of this study was to compare linac (linear accelerator)-based SRS/SRT plan quality of automated planning, intensity modulated radiotherapy (IMRT), volumetric modulated arc radiotherapy (VMAT) and manually planned dynamic conformal arc (DCA) plans as well as single- and multiple-isocenter techniques. We found that automated planning with DCA or IMRT can make linac-based SRS/SRT plan quality with single isocenter comparable with a manually planned DCA plan with a separate isocenter for each metastasis.The purpose was to compare linac-based stereotactic radiosurgery and hypofractionated radiotherapy plan quality of automated planning, intensity modulated radiotherapy (IMRT) and manual dynamic conformal arc (DCA) plans as well as single- and multiple-isocenter techniques for multiple brain metastases (BM). For twelve patients with four to ten BM, seven non-coplanar linac-based plans were created: a manually planned DCA plan with a separate isocenter for each metastasis, a single-isocenter dynamic IMRT plan, an automatically generated single-isocenter volumetric modulated arc radiotherapy (VMAT) plan, four automatically generated single-isocenter DCA plans with three or five couch angles, with high or low sparing of normal tissue. Paddick conformity index, gradient index (GI), mean dose, total V12Gy and V5Gy of uninvolved brain, number of monitor units (MUs), irradiation time and pass rate were compared. The GI was significantly higher for VMAT than for separate-isocenter, IMRT, and all automatically generated plans. The number of MUs was lowest for VMAT, followed by automatically generated DCA and IMRT plans and highest for manual DCA plans. Irradiation time was the shortest for automatically planned DCA plans. Automatically generated linac-based single-isocenter plans for multiple BM reduce the number of MUs and irradiation time with at least comparable GI and V5Gy relative to the reference separate-isocenter DCA plans.

Technical Note: A 3D-printed phantom for radiochromic film evaluation of moving lung tumor SBRT without dose convolution.

A common dosimetric quality assurance (QA) method in stereotactic body radiation therapy (SBRT) of lung tumors is to use lung phantoms with radiochromic film. However, in most phantoms, the film moves with the tumor, leading to the blurring effect. This technical note presents the QA performance of a novel phantom in which the film is fixed; this phantom can be used for both patient-specific QA and end-to-end testing. Lung tumor motion was simulated with the CIRS Model 008A phantom. A lung-equivalent insert that consisted of a fixed radiochromic film around which a 2-cm tumor moved in the inferior/superior direction (i.e., mimicking respiration-induced tumor motion) was generated by 3D printing. Two common SBRT plans [dynamic conformal arc (DCA) and volumetric-modulated arc therapy (VMAT)] were calculated on the average intensity projection (AIP) image set in Varian Eclipse using the dose calculation algorithm Acuros XB. The plans were delivered by a Varian TrueBeam STx accelerator using 6-MV flattening filter-free energy. EBT3 films were used for treatment-dose verification. The measured and planned dose distributions were compared by using the local gamma index at 3% and 2 mm. Mean gamma pass rates of film and planned dose distributions were all ≥95%. DCA and VMAT plans did not differ in gamma pass rates. Planned and measured dose distributions agreed well, as did planned and measured gamma maps. With this new insert, measured and planned dose distributions were very similar, which supports the current view in the field that dose calculations on AIP image sets account sufficiently for tumor motion during treatment. The phantom also performed well despite challenging breathing parameters (large tumor amplitude and slow breathing rate) and the application of a complex treatment technique (VMAT). This phantom could facilitate clinical and end-to-end film-based dosimetric QA for lung SBRT. Twenty-seven TH- Radiation dose measurement devices. Eleven Phantoms for dosimetric measurement.

Comparison of 2 dynamic conformal arc plans based on high-dose rate flattening filter free beams for peripheral lung cancer.

To compare 2 dynamic conformal arc plans based on the high dose rate flattening filter free (FFF) beams, and to evaluate the dosimetric differences. A total of 20 patients with early peripheral non-small cell lung cancer were selected, and 2 dynamic conformal arc plans were designed in the Eclipse 10.0 treatment planning system (TPS). One of them was based on tumor-center (T-DCA), and the other was based on iso-center (Iso-DCA). Both plans were created by using the Truebeam linear accelerator, based on 6 MV FFF photons with a dose rate at 1 400 monitor unit (MU)/min. All patients received the prescribed dose of 4 800 cGy in 4 fractions (1 200 cGy/fraction). Target coverage and organ at risk limits were planned and designed according to the Radiation Therapy Oncology Group (RTOG) Criteria, and were compared between the T-DCA and the Iso-DCA plans. There was no significant difference in the target coverage between the T-DCA and Iso-DCA plans (P>0.05). Conformal index and homogeneity index had no significant differences (both P>0.05), but the percentage of the maximum dose in any direction 2 cm away from the planned target area (D2 cm) and the ratio of the volume wrapped by the isodose line of 50% prescription dose to the volume of the planned target area (R50%) showed significant differences (both P<0.05). The MU of the Iso-DCA plan was increased by 21% compared with that of the T-DCA plan. Except the maximum dose of spinal cord and esophagus, there was no significant difference in the other dosimetric parameters of the organs at risk between the T-DCA and the Iso-DCA plans (all P>0.05). The dose fall-off of Iso-DCA plan is better than T-DCA plan, but the T-DCA plan is consistently superior in sparing dose to spinal cord and esophagus, and the T-DCA plan has fewer MU.

A Study of the Impact of TRS-483 Recommended Correction Factors for Dosimetry of Small Fields in Flattening Filter Free Beams used in TrueBeam Linear Accelerators

Introduction: To study the effect of the International Atomic Energy Agency (IAEA) TRS-483 recommended beam quality correction factor in reference dosimetry and to examine the recommended field output correction factor for relative dosimetry of 6-MV flattening filter free (FFF) small fields, used in a Varian TrueBeam linear accelerator (LINAC). Material and Methods: The beam quality and field output correction for 6-MV FFF beams were adopted from the TRS-483 protocol. Monte Carlo (MC) simulation of the output factor was performed using the PENELOPE-based PRIMO software and compared with the TRS-483 corrected output factors. Two analytical anisotropic algorithm (AAA) models in the EclipseTM treatment planning system (TPS) were created; one with an output factor taken as the ratio of meter readings and one with an output factor obtained by multiplying the TRS-483 correction factor by the ratio of meter readings. Besides, box field and dynamic conformal arc (DCA) plans were created for both AAA models for verification and validation. The patient-specific quality assurances (QA) for ten different targets were performed, and deviations between the measured and TPS-calculated point doses in both models were examined. Results: Separate beam quality correction factors for FFF beams in the TRS-483 protocol only resulted in an improvement of 0.1% in reference dosimetry. The TRS-483 corrected output factor was in a better agreement with the MC-calculated output factor. For a patient-specific QA of DCA plans, the output factor-corrected AAA dose calculation algorithm showed a better agreement between the measured and simulated doses. Also, there was a smaller deviation (1.2%) for the smallest target of 0.23 cc (8 mm equivalent sphere diameter) used in this study. Conclusion:The field output factors for the LINAC small beams can be improved by incorporating the TRS-483 correction factors. However, the extent of improvement that can be expected depends on the source model of the calculation algorithm and how these well-generalized corrections are suitable for user beams and detectors.