Arc Delivery Research Articles

Next Evolutions in Particle Therapy: Spot-Scanning Hadron Arc (SHArc) Therapy

To develop and evaluate spot-scanning hadron arc (SHArc) therapy, the first arc delivery technique for both light and heavy ions, in different clinical scenarios.Robust treatment planning and biological optimization procedures were developed within a GPU-accelerated dose engine and treatment planning system, establishing a dedicated energy/spot/angle selection protocol for robust SHArc delivery. Initial tests were performed for three clinical particle beams (protons, helium, and carbon ions) on water-equivalent cylindrical phantoms for simple targets and clinical-like scenarios with an organ-at-risk (OAR) in proximity of the target to compare SHArc against reference conventional techniques using single and multi-field configurations. SHArc patient treatments were surveyed in various sites (head, H&N, thorax and pelvic region). Dosimetric and biological features were calculated and evaluated applying the modified microdosimetric kinetic model. To determine impact of LET variations within the tumor volume, a model for hypoxia-induced radio-resistance was developed and applied for particle therapy to investigate impact on effective dose.SHArc plans exhibited similar target coverage with unique treatment attributes and distributions compared to conventional planning, with carbon ions demonstrating the greatest potential for tumor control and normal tissue sparing among the arc techniques. All SHArc plans exhibited a low-dose bath outside the target volume with a reduced maximum dose in normal tissues compared to single and multi-field plans. Moreover, favorable LET distributions were possible with the SHArc approach with substantial increases in LETmax and volume containing high-LET components. Moreover, reductions of high-LET regions in normal tissues and OARs were observed compared to static treatment beam delivery.The first arc treatment delivery technique using helium and carbon ion beams is proposed. Evidence suggests that through arc delivery of high-LET particle beams, SHArc therapy may offer uniquely valuable clinical advantages both dosimetrical and biological. Robust SHArc treatments could potentially improve tumor control by overcoming tumor microenvironment resistance factors such as hypoxia induced radio-resistance, and reduce toxicity in critical structures by minimizing high-LET components.

PD-0907 Modeling the first proton arc delivery sequence and investigating its efficiency improvement

PD-0907 Modeling the first proton arc delivery sequence and investigating its efficiency improvement

A Pre-implementation Study of Volumetric Modulated Arc Therapy for Same-day Planning and Treatment of Vertebral Bone Metastases Within a Rapid-access Palliative Radiotherapy Programme

AimsWe aimed to develop a process for same-day contouring, planning, quality assurance and delivery of volumetric modulated arc therapy (VMAT) for vertebral bone metastases within our institution's rapid-access palliative radiotherapy programme. Materials and methodsTwo thoracic (T6–7, T3–7) and two lumbar (L2–3, L1–5) targets were contoured on computed tomography images acquired from an anthropomorphic phantom and five patient scans. Inverse planning aimed to provide coverage of a prescribed dose of 8 Gy with a combined lung V2Gy < 25% and a combined kidney mean dose <2 Gy. Serial plans were created to identify an efficient combination of six main planning variables specific to our treatment planning system: (i) voxel size (3 mm versus 5 mm), (ii) Monte Carlo statistical uncertainty (1% per calculation versus 3% per control point), (iii) fluence smoothing (medium versus high), (iv) number of iterations of segment shape changes during optimisation (1 versus 5), (v) dose calculation algorithm (Monte Carlo versus pencil beam) and (vi) number of arcs (single versus multiple). Contouring, planning, quality assurance and treatment delivery were timed. ResultsThe combination of planning variables deemed efficient and appropriate was: a 3 mm voxel size, statistical uncertainty of 1% per calculation, medium fluence smoothing, five iterations of segment shape changes, Monte Carlo dose calculation and single full arc delivery. Patient scan contouring times ranged from 7 to 9 min (T6–7), 11–13 min (T3–7), 5–7 min (L2–3) and 8–10 min (L1–5) and planning times ranged from 9 to 15 min (T6–7), 13–25 min (T3–7), 18–25 min (L2–3) and 21–31 min (L1–5). Physics quality assurance times ranged from 15 to 21 min and beam-on times ranged from 3 to 6 min. ConclusionsThe combined elements of VMAT for thoracic and lumbar vertebral bone metastases were completed in under 2 h. This new process makes same-day contouring, planning, quality assurance and treatment delivery of VMAT feasible within our rapid-access palliative radiotherapy programme.

Comparison of Treatment Plan Robustness Between Dynamic Trajectory Radiotherapy and VMAT

Dynamic trajectory radiotherapy (DTRT) was recently developed in our institute for a non-coplanar arc delivery technique utilizing additionally to VMAT table and collimator rotations. Recent studies on the dosimetric performance suggest a substantial improvement in organs at risks (OARs) sparing when compared with conventional C-arm VMAT delivery. In this work, the treatment plan robustness for DTRT and VMAT is compared with respect to setup errors. Robustness was assessed by generating DVH bands as well as so-called robustness maps (rMaps) by means of a false/true evaluation of certain dosimetric user-defined limits considered acceptable for selected structures with respect to a range of setup errors considered. The robustness was assessed for a clinically motivated head and neck, a lung and a prostate case. For each case systematic translational (ranging from -6 to 6 mm) and rotational (ranging from -3° to 3°) setup error scenarios were defined and for each scenario Monte Carlo dose calculations for the DTRT and VMAT treatment plans were performed. The resulting dose distributions served as input for the robustness assessment determining DVH bands and rMaps. The acceptance conditions for the OARs were defined such that the mean doses for parallel OARs and near maximum doses for serial OARs do not deteriorate more than 2 Gy. For the CTV V95% a deterioration of 1% was allowed in order to pass the robustness criteria. For the isotropic CTV to PTV margins 4 mm, 5 mm and 10 mm were applied for the head and neck, the prostate and the lung case, respectively, except for the dorsal direction of the prostate case, where 3 mm was used. For the head and neck and the prostate case the percentage of setup error scenarios passing the acceptance criteria were 29% and 63% (VMAT) and 23% and 58% (DTRT) for translations and 60% and 100% (VMAT) and 62% and 100% (DTRT) for rotations, respectively. Depending on the direction of the translation setup error, the VMAT plan is slightly more robust. However, for the lung case the VMAT treatment plan is more robust leading to passing rates of 48% (VMAT) and 20% (DTRT) for translations and 83% (VMAT) and 55% (DTRT) for rotations, respectively. In all cases, the robustness determined by the rMaps is dominated by the acceptance criteria for the OARs and not by the ones for the CTV. The results of this study indicate that DTRT treatment plans using additional dynamic table and collimator rotations leading to complex trajectories result in similar systematic setup error robustness as VMAT treatment plans for the head and neck and the prostate case. For the lung case investigated, the VMAT treatment plans show an improved robustness.

Intrafraction cone beam computed tomography verification of breath hold during liver stereotactic radiation therapy.

IntroductionIntrafraction imaging is an Elekta feature that enables cone beam computed tomography (CBCT) acquisition simultaneously with treatment arc delivery. It has facilitated the introduction of breath‐hold (BH) gated stereotactic body radiation therapy (SBRT) by enabling visualisation of tumour and organs at risk during treatment. The aims of this study were to assess BH reproducibility and use intrafraction CBCT (IF‐CBCT) to quantify any variation in diaphragm position (diaphragmatic feathering) during the multiple BHs performed during each arc.MethodsIF‐CBCTs for consecutive liver SBRT patients where BH was achieved using the Elekta Active Breathing Control (ABC) system were retrospectively evaluated. Average intrafraction couch shifts for deep‐inspiration BH (DIBH) or end‐expiration BH (EEBH) were recorded as an indication of reproducibility. Diaphragmatic feathering was quantified by measuring the difference between the most superior and inferior visible edges of the diaphragm on IF‐CBCTs.ResultsA total of 212 images from 30 patients were reviewed. Twenty‐two (73.3%) patients were treated in EEBH. The mean intrafraction shift was similar between DIBH and EEBH groups with the largest mean shift of 0.22cm occurring in the superior–inferior direction. Mean diaphragmatic feathering was similar between the DIBH and EEBH groups, 0.09cm (0‐0.44cm) and 0.14cm (0–1.89cm) respectively. A higher percentage of EEBH patients demonstrated no diaphragmatic feathering throughout treatment compared with DIBH patients (31.8% vs 25%).ConclusionThe results of this study indicate that BH is reproducible in both DIBH and EEBH for liver SBRT treatment using the ABC system. Appropriate patient selection and BH coaching prior to CT simulation are critical to its success.

Comprehensive investigation into the stability of Varian and Elekta kV imaging systems during arc delivery

In radiotherapy treatments utilizing accelerator gantry rotation, gantry-mounted kilovoltage (kV) imaging systems have become integral to treatment verification. The accuracy of such verification depends on the stability of the imaging components during gantry rotation. In this study, a simple measurement method and accurate algorithm are introduced for investigation of the kV panel and source movement during gantry rotation. The method is based on images of a ball-bearing phantom combined with a Winston-Lutz phantom, and determines the movements of all the mechanical parameters of the kV imaging system relative to the reference at zero gantry angle. Analysis was performed on different linear accelerators and both gantry rotation directions. The precision of the method was tested and was less than 0.04 mm. This method is suitable to be included in the quality assurance testing of linacs to monitor the kV imaging system performance and provides additional mechanical information that previous tests cannot.

Preclinical Model of Stereotactic Ablative Lung Irradiation Using Arc Delivery in the Mouse: Effect of Beam Size Changes and Dose Effect at Constant Collimation

Stereotactic body radiation therapy is a therapeutic option offered to high surgical risk patients with lung cancer. Focal lung irradiation in mice is a new preclinical model to help understand the development of lung damage in this context. Here we developed a mouse model of lung stereotactic therapy using arc delivery and monitored the development of lung damage while varying the beam size and dose delivered. C57BL/6JRj mice were exposed to 90 Gy focal irradiation on the left lung using 1-mm diameter, 3× 3 mm2, 7 × 7 mm2, or 10 × 10 mm2 beam collimation for beam size effect and using 3 × 3 mm2 beam collimation delivering 20 to 120 Gy for dose effect. Long-term lung damage was monitored with micro-computed tomography imaging with anatomopathologic and gene expression measurements in the injured patch and the ipsilateral and contralateral lungs. Both 1-mm diameter and 3 × 3 mm2 beam collimation allow long-term studies, but only 3-mm beam collimation generates lung fibrosis when delivering 90 Gy. Dose-effect studies with constant 3-mm beam collimation revealed a dose of 60 Gy as the minimum to obtain lung fibrosis 6 months postexposure. Lung fibrosis development was associated with club cell depletion and increased type II pneumocyte numbers. Lung injury developed with ipsilateral and contralateral consequences such as parenchymal thickening and gene expression modifications. Arc therapy allows long-term studies and dose escalation without lethality. In our dose-delivery conditions, dose-effect studies revealed that 3 × 3 mm2 beam collimation to a minimum single dose of 60 Gy enables preclinical models for the assessment of lung injury within a 6-month period. This model of lung tissue fibrosis in a time length compatible with mouse life span may offer good prospects for future mechanistic studies.

Dosimetric accuracy of delivering SBRT using dynamic arcs on Cyberknife.

PurposeSeveral studies have demonstrated potential improvements in treatment time through the use of dynamic arcs for delivery of stereotactic body radiation therapy (SBRT) on Cyberknife. However, the delivery system has a finite accuracy, so that potential exists for dosimetric uncertainties. This study estimates the expected dosimetric accuracy of dynamic delivery of SBRT, based on realistic estimates of the uncertainties in delivery parameters.MethodsFive SBRT patient cases (prostate A — conventional, prostate B — brachytherapy‐type, lung, liver, partial left breast) were retrospectively studied. Treatment plans were produced for a fixed arc trajectory using fluence optimization, segmentation, and direct aperture optimization. Dose rate uncertainty was modeled as a smoothly varying random fluctuation of ± 1.0%, ±2.0% or ± 5.0% over a time period of 10, 30 or 60 s. Multileaf collimator uncertainty was modeled as a lag in position of each leaf up to 0.25 or 0.5 mm. Robot pointing error was modeled as a shift of the target location, with the direction of the shift chosen as a random angle with respect to the multileaf collimator and with a random magnitude in the range 0.0–1.0 mm at the delivery nodes and with an additional random magnitude of 0.5–1.0 mm in between the delivery nodes. The impact of the errors was investigated using dose‐volume histograms.ResultsUncertainty in dose rate has the effect of varying the total monitor units delivered, which in turn produces a variation in mean dose to the planning target volume. The random sampling of dose rate error produces a distribution of mean doses with a standard deviation proportional to the magnitude of the dose rate uncertainty. A lag in multileaf collimator position of 0.25 or 0.5 mm produces a small impact on the delivered dose. In general, an increase in the PTV mean dose of around 1% is observed. An error in robot pointing of the order of 1 mm produces a small increase in dose inhomogeneity to the planning target volume, sometimes accompanied by an increase in mean dose by around 1%.ConclusionsBased upon the limited data available on the dose rate stability and geometric accuracy of the Cyberknife system, this study estimates that dynamic arc delivery can be accomplished with sufficient accuracy for clinical application. Dose rate variation produces a change in dose to the planning target volume according to the perturbation of total monitor units delivered, while multileaf collimator lag and robot pointing error typically increase the mean dose to the planning target volume by up to 1%.

Assessment of an Elekta Versa HD linear accelerator for stereotactic radiosurgery with circular cone collimators.

Versa HD linear accelerators (linacs) are used for stereotactic radiosurgery treatment. However, the mechanical accuracy of such systems remains a concern. The purpose of this study was to evaluate the accuracy of an Elekta Versa HD linac. We performed measurements with a ball bearing phantom to calculate the rotational isocenter radii of the linac's gantry, collimator, and table, and determine the relative locations of those isocenters. We evaluated the accuracy of the cone-beam computed tomography (CBCT) guidance with a film-embedding head phantom and circular cone-collimated radiation beams. We also performed dosimetric simulations to study the effects of the linac mechanical uncertainties on non-coplanar cone arc delivery. The mechanical uncertainty of the linac gantry rotation was 0.78 mm in radius, whereas that of the collimator and the table was <0.1 mm and 0.33 mm, respectively. The axes of rotation of the collimator and the table were coinciding with and 0.13 mm away from the gantry isocenter, respectively. Experiments with test plans demonstrated the limited dosimetric consequences on the circular arc delivery given the aforementioned mechanical uncertainties. End-to-end measurements determined that the uncertainty of the CBCT guidance was≤1 mm in each direction with respect to the reference CT image. In arc delivery, the mechanical uncertainties associated with the gantry and the table do not require remarkable increases in geometric margins. If large enough, the residual setup errors following CBCT guidance will dominate the overall dosimetric consequence. Therefore, the Versa HD linac is a valid system for stereotactic radiosurgery using non-coplanar arc delivery.

Balanchine and Kirstein's American Enterprise by James Steichen

Reviewed by: Balanchine and Kirstein's American Enterprise by James Steichen Chantal Frankenbach Balanchine and Kirstein's American Enterprise. James Steichen. New York: Oxford University Press, 2019. Pp. 302. $35.00 (cloth). In 1915, less than twenty years before Russian choreographer George Balanchine arrived in the US, literary critic Van Wyck Brooks observed that antithetical "twin values" of "highbrow" and "lowbrow" still divided every aspect of American life. Between the two brows, Brooks concluded, there was "no genial middle ground."1 For ballet in early twentieth-century America, this seemed particularly true. Russian ballerina Anna Pavlova and the touring offshoots of Sergei Diaghilev's Paris-based Ballets Russes had convinced many Americans that, in contrast to the popular dancing on American stages, classical dance came from afar and on high. Yet a growing number of dance scholars are revealing the crevices in this dichotomy.2 Musicologist and dance historian James Steichen joins them with a richly researched and gracefully written book on the tangled origins of the New York City Ballet (NYCB) and its associated School of American Ballet. Steichen illuminates the collision of aesthetic and economic concerns driving Balanchine and his sponsor–benefactor Lincoln Kirstein in the first seven years (1933–40) of their now-fabled quest to create an American ballet institution. This period of "missteps, overlooked achievements, and unsung heroes," Steichen argues, is no less important to understanding American theater dance than the mature Balanchine ballets it eventually spawned (Balanchine and Kirstein's American Enterprise, 11). Steichen's account of these two remarkably persistent modernists stands to correct the received history that has "papered over" their endeavor's inauspicious origins (8). Scholars and students of American culture will find here a narrative that weaves dance history into theater, music, and film from a remarkable trove of materials, reminding us just how much positivist work still awaits historians of American dance. Titling Balanchine and Kirstein's project an "enterprise" fittingly acknowledges the crossed purposes in their effort to institutionalize ballet in America. An enterprise, after all, suggests something sleek, commercial, market-driven, and risky—something antithetical to any elite aesthetic sensibilities these self-proclaimed modernists might have coveted. Noting the absence of this foundational conflict in the legend and lore of the NYCB's founding, Steichen rejects the temptation of "triumphant teleology" and "retrospective coherence" in exchange for a more warts-and-all look at the initial American Ballet's first staggers and stumbles (11, 7). Drawing extensively from the popular press and numerous archives, Steichen makes good storytelling of Kirstein's colorful diaries and correspondence. A thorough literature review in the introduction; images of rehearsals, programs, and promotional materials; and meticulously sourced notes all add up to a volume of scholarly precision that deliberately avoids any deep dive into cultural analysis.3 The pragmatic year-by-year chapter titles are perhaps a sign of missed opportunities to weave more thematic reflections into the tale. Beginning and ending with thoughts on Serenade's place in the development of the symphonic ballet (unquestionably a signature achievement of Balanchine's), chapter three, for instance, might have developed this topic just enough to warrant a title more pledged to its purpose than "1934–1935." Yet the chronological arc and orderly delivery of Steichen's material has clear merits. Chapter one weaves the early biographies of Balanchine and Kirstein into the network of associates (Romola Nijinsky, Virgil Thomson, Chick Austin, Edward Warburg) who helped to bring Balanchine first to Hartford and then to New York City, where their "exhilarating and haphazard journey" of failures and contradictions began (4). As we see in Kirstein's diaries and correspondence—like the newsy October 1933 letter to his mother reporting that his "ballet people" were about to arrive in New York—his machinations with well-to-do Americans set the stage for the enterprise's [End Page 620] start (18). Chapter two traces the first two performances of the American Ballet: one ill-fated exhibition at the White Plains estate of patron Edward Warburg, and a more successful showing at the Avery Memorial Theater in Hartford. The ballets produced for these debuts (Mozartiana, Errante, Dreams, Transcendence, Serenade, and the football-themed Alma Mater) reveal the...

Treatment planning optimization with beam motion modeling for dynamic arc delivery of SBRT using Cyberknife with multileaf collimation.

PurposeThe use of dynamic arcs for delivery of stereotactic body radiation therapy (SBRT) on Cyberknife is investigated, with a view to improving treatment times. This study investigates the required modeling of robot and multileaf collimator (MLC) motion between control points in the trajectory and then uses this to develop an optimization method for treatment planning of a dynamic arc with Cyberknife. The resulting plans are compared in terms of dose‐volume histograms and estimated treatment times with those produced by a conventional beam arrangement.MethodsFive SBRT patient cases (prostate A — conventional, prostate B — brachytherapy‐type, lung, liver, and partial left breast) were retrospectively studied. A suitable arc trajectory with control points spaced at 5° was proposed and treatment plans were produced for typical clinical protocols. The optimization consisted of a fluence optimization, segmentation, and direct aperture optimization using a gradient descent method. Dose delivered by the moving MLC was either taken to be the dose delivered discretely at the control points or modeled using effective fluence delivered between control points. The accuracy of calculated dose was assessed by recalculating after optimization using five interpolated beams and 100 interpolated apertures between each optimization control point. The resulting plans were compared using dose‐volume histograms and estimated treatment times with those for a conventional Cyberknife beam arrangement.ResultsIf optimization is performed based on discrete doses delivered at the arc control points, large differences of up to 40% of the prescribed dose are seen when recalculating with interpolation. When the effective fluence between control points is taken into account during optimization, dosimetric differences are <2% for most structures when the plans are recalculated using intermediate nodes, but there are differences of up to 15% peripherally. Treatment plan quality is comparable between the arc trajectory and conventional body path. All plans meet the relevant clinical goals, with the exception of specific structures which overlap with the planning target volume. Median estimated treatment time is 355 s (range 235–672 s) for arc delivery and 675 s (range 554–1025 s) for conventional delivery.ConclusionsThe method of using effective fluence to model MLC motion between control points is sufficiently accurate to provide for accurate inverse planning of dynamic arcs with Cyberknife. The proposed arcing method produces treatment plans with comparable quality to the body path, with reduced estimated treatment delivery time.

Kv Intrafraction Verification for SBRT Amplitude-Gated Rapidarc Treatments: An Initial Experience

To report the workflow and the quality assurance program established for the first kV-IGRT intrafraction verification gated RapidArc (RA) treatment successfully delivered in our institution. One patient with stage I NSCLC was treated using the gating technique on a medical linear accelerator. Prescription dose was 48 Gy in four fractions and one fiducial marker was implanted near the tumor. During simulation a gated CT in a Stable Exhale (SE) phase (breath hold pause = 20 sec) was acquired. A 6 MV FFF plan was generated on the gated CT using four partial arcs; the fiducial and its 3 mm PRV were delineated in the planning CT. During each fraction a gating amplitude window of 2.5 mm was set, a gated CBCT on the SE was acquired and positioning was performed according to a tumor fusion. Two orthogonal kV images were then collected to verify the position of the marker. Triggered kV images were acquired immediately before beam-on to verify the intrafraction fiducial position during treatment and to perform an a posteriori evaluation of the marker displacements in the superior-inferior (SI) direction with respect to DRR images. Pretreatment quality assurance was performed using a Delta4 phantom (static delivery) and with EBT3 Gafchromic films coupled with a Quasar moving phantom (gated delivery) using three breathing pattern (BP): 1) FB: free BP of the patient, 2) EX1: SE obtained by modifying the FB pattern and 3) EX2: a random SE. A film irradiated in static delivery was taken as a reference to evaluate the gating deliveries and compared with TPS dose as additional static QA. Beam-on time was 1.8 ± 0.5 min per arc and 7.2 ± 1.4 min per fraction. The duty cycle averaged over all arcs was 42 ± 3.9 % and 56 ± 17 kV triggered images per fraction were acquired. The SI distance between the marker and its expected position was 1.7 ± 0.4 mm on average and 2.9 ± 0.7 mm at 95th percentile (range: 0 - 4.2 mm). During treatment the fiducial was always displayed inside its PRV, except during the delivery of arc 3 in fraction 3. This is in agreement with shifts evaluation, where we found an average displacement of 3.6 ± 0.3 mm. 2%/2mm gamma agreement for the static delivery was 97.8% and 100% for the Delta4 phantom and films, respectively. The gated deliveries were dosimetrically equivalent to the static procedure, with dose differences at isocenter below 1% and gamma pass-rates above 98.2%. Good agreement was also found with TPS (gamma scores > 98.9%). The system capability to superimpose marker PRV on real-time kV images made the clinicians confident during the delivery and the evaluation of the fiducial shifts has proven to be consistent to what was observed during the treatment. A 3 mm margin was required to account for 95% of the gating intrafraction uncertainties. Gated treatments were delivered to a moving phantom and no significant differences were found with respect to a static delivery. The use of a small gate coupled with a SE BP allows delivering acceptable dose distributions with reasonable duty cycles.

Investigation of lung tumour peripheral doses using normoxic polymer gel and film dosimetry techniques

This paper describes the investigation of lung tumour peripheral doses for 6MV, 6MV FFF, 10MV FFF and 15MV conformal arc therapy (CAT) beams calculated in the Monaco® TPS and delivered using a flattening filter free capable Elekta® AgilityTM linac. Two independent high resolution dosimetry techniques were used for investigations. Measurements were performed using the normoxic PAG polymer gel dosimeter and GAFchromicTM EBT3 film and compared against the calculated dose plane from the Monaco treatment planning system. Both measurement methodologies indicate that Monaco is overestimating the lung tumour peripheral dose for the beams investigated in this study. It is shown that when using 10MV FFF in lung for arc deliveries, there is a dosimetric compromise compared with 6MV and 6MV FFF.

The first prototype of spot-scanning proton arc treatment delivery

PurposeWe report the first prototype of spot-scanning arc treatment (SPArc) delivery on a clinical proton beam therapy machine and evaluate its delivery accuracy and efficiency. Methods and materialsA new module called Proton Dynamic Arc Delivery (PDAD) was developed to allow simultaneously delivering spot-scanning proton beam treatments while rotating the gantry on an IBA Proteus®One proton machine. A series of measurements was performed to validate the basic beam characteristics. Subsequently, patient specific quality assurance (QA) of a brain SPArc plan was performed. Total SPArc treatment delivery time was also recorded and compared to the clinically delivered intensity modulated proton therapy (IMPT) treatment time. Finally, the log file of the SPArc plan was analyzed and processed to reconstruct the actual delivered dose. ResultsAll the basic beam characteristics were confirmed in the PDAD mode, similar as those measured using fixed gantry deliveries in clinical mode. The brain SPArc plan with similar or superior plan quality was delivered in 4 mins compared to total 11 mins for the clinical treatment of the three-field IMPT plan. The patient QA result showed a good agreement between the measured and calculated dose distributions with the gamma index of 98.6% (3%/3 mm). The analysis of the log file confirmed the accuracy of the SPArc plan delivery, with the gamma index of 98.3% (1%/1 mm) between reconstructed and the planned doses. ConclusionThe first prototype of dynamic proton arc delivery on a clinical proton therapy system was successfully performed. The measurements and simulations demonstrated the feasibility of SPArc treatment within the clinical requirements.

Dosimetric Advantages of Volumetric Modulated Arc Therapy Based Coronal Arc Delivery Technique in Brain Stereotactic Radiosurgery: A Feasibility Study

The feasibility of a volumetric modulated arc therapy (VMAT) based coronal arc (cARC) technique for treating a single brain metastasis or lesion proximal to the brainstem or optic chiasm was evaluated. Coplanar (CP) and non-coplanar (NCP) treatment plans to an anthropomorphic head/neck phantom scanned head-first supine were compared to a cARC plan with the phantom rotated vertically. A set of planning target volumes (PTVs) were contoured centrally between the brainstem and optic chiasm (“Ant PTVs”) and posterior to brainstem (“Post PTVs”). Dosimetric indices such as conformity index (C.I.), gradient measure (G.M.), and dose volume histograms (DVHs) were compared for CP, NCP and cARC techniques. The TG101 guidelines for organs-at-risk (OARs), and 95% of PTV receiving at least 100% of the prescription dose (D95 = 100%) were used as plan objectives. Reductions in D50 and D30 to the brainstem of 85.1% ± 3.9% and 87.6% ± 3.2%, respectively were seen for “Post PTVs”, and 51.1% ± 17.8% and 85.6% ± 6.0% respectively for “Ant PTVs” using cARC versus CP (p ≤ 0.01). For chiasm, reductions of D50 and D30 were 61.7% ± 3.2% and 44.2% ± 8.9% for “Ant PTVs”, by 69.3% ± 8.0% and 74.3% ± 8.2% for “Post PTVs” (p ≤ 0.01). Comparing cARC to NCP led to similar dosimetric improvements. The conformity index (C.I.) was measured to be 1.101 ± 0.038, 1.088 ± 0.054, and 1.060 ± 0.040 for cARC, CP and NCP respectively (p ≤ 0.01). The overall GM in cm was 0.581 ± 0.097, 0.708 ± 0.064, and 0.476 ± 0.050 for cARC, CP and NCP respectively (p ≤ 0.01). The mean distance gradient fall-off (in cm) was 0.249 ± 0.038 (cARC), 0.749 ± 0.107 (CP), and 0.621 ± 0.068 (NCP) at the center slice in anterior-posterior direction of the target volume (p ≤ 0.01). The objective of this study is to compare the dosimetric indices of cARC with CP and NCP techniques. In conclusion, cARC can provide improved dosimetry as compared to CP and NCP for lesion proximal to the brainstem or optic chiasm.

Extended SSD VMAT treatment for total body irradiation.

In this work, we develop a total body irradiation technique that utilizes arc delivery, a buildup spoiler, and inverse optimized multileaf collimator (MLC) motion to shield organs at risk. The current treatment beam model is verified to confirm its applicability at extended source‐to‐surface distance (SSD). The delivery involves 7–8 volumetric modulated arc therapy arcs delivered to the patient in the supine and prone positions. The patient is positioned at a 90° couch angle on a custom bed with a 1 cm acrylic spoiler to increase surface dose. Single‐step optimization using a patient CT scan provides enhanced dose homogeneity and limits organ at risk dose. Dosimetric data of 109 TBI patients treated with this technique is presented along with the clinical workflow. Treatment planning system (TPS) verification measurements were performed at an extended SSD of 175 cm. Measurements included: a 4‐point absolute depth‐dose curve, profiles at 1.5, 5, and 10 cm depth, absolute point‐dose measurements of an treatment field, 2D Gafchromic® films at four locations, and measurements of surface dose at multiple locations of a Alderson phantom. The results of the patient DVH parameters were: Body‐5 mm D98 95.3 ± 1.5%, Body‐5 mm D2 114.0 ± 3.6%, MLD 102.8 ± 2.1%. Differences between measured and calculated absolute depth‐dose values were all <2%. Profiles at extended SSD had a maximum point difference of 1.3%. Gamma pass rates of 2D films were greater than 90% at 5%/1 mm. Surface dose measurements with film confirmed surface dose values of >90% of the prescription dose. In conclusion, the inverse optimized delivery method presented in the paper has been used to deliver homogenous dose to over 100 patients. The method provides superior patient comfort utilizing a commercial TPS. In addition, the ability to easily shield organs at risk is available through the use of MLCs.

18 SBRT for peripheral lung tumors with linac arctherapy technique: More accurate, fast and safe

Introduction Over the past decade, there have been significant changes in the dosimetric management of peripheral lung tumor treatments with stereotactic radiotherapy. Historically developed on linear accelerators using additional collimators, the treatments are now performed on dedicated accelerators (CyberKnife, Vero, STX TrueBeam, Versa HD for example) with dedicated equipment (positioning imagery, breathing control, contention) and dedicated beam types (Flattening Filter Free). First performed in 3D conformal radiotherapy (3D-CRT), treatments are now indicated in intensity-modulated rotational radiotherapy (VMAT) [1] . Methods This prospective study was conducted on 30 patients with peripheral lung tumor treated by SBRT. The objective was to assess, through metrics (NC, CI, HI, Dmin PTV , and volumes of isodoses 5Gy, 10Gy, D50% and. Dpresc. [2] , the possibility to improve dose distribution and decrease delivery time of SBRT with VMAT and no longer in 3D – CRT. The planning has been conducted with the RayStation v6 TPS. The scheme of radiotherapy was 48Gy in 6 fractions and the average volume of PTV was 18.3 ± 11.8cc. For each patient, the ITV was determined and the PTV achieved by applying margins of 5mm in the cranio-caudal direction and 3mm elsewhere. Two treatment plans were made: one 3D-CRT in 6MV-FFF and the other in VMAT 6MV-FFF with limitation of the movement of the blades. The optimization of the treatment plans was carried out so that 99% of the PTV volume is covered by the prescription isodose with for the 3D-CRT a collimator opening limit of 5 mm and a limit of prescription at Isocenter point of 80%. The metrics of the 30 patients were recorded and compared by a Wilcoxon test. The treatment delivery time was measured for the 3D-CRT technique and the estimate time was provided by the TPS for the VMAT. Results The results are presented in Table 1 and Fig. 1. For almost all of the patients, the coverage of 99% of the PTV was met. Our technique allows to get a better number of conformity (p 0.001) as well as volumes of isodose 10Gy, D50% and Dpresc. smaller (p 0.001). The duration of treatment sessions has been reduced from 150 to 47 sec. Conclusions The limitation of leafs movement, use of partial arcs with only photons flow variation during arc delivery achieve more consistent coverage and lower lung irradiation without interplay effect during irradiation sessions. This technique is now performed in routine.

Design and validation of a MV/kV imaging-based markerless tracking system for assessing real-time lung tumor motion.

Localizing lung tumors during treatment delivery is critical for managing respiratory motion, ensuring tumor coverage, and reducing toxicities. The purpose of this project is to develop a real-time system that performs markerless tracking of lung tumors using simultaneously acquired MV and kV images during radiotherapy of lung cancer with volumetric modulated arc therapy. Continuous MV/kV images were simultaneously acquired during dose delivery. In the subsequent analysis, a gantry angle-specific region of interest was defined according to the treatment aperture. After removing imaging artifacts, processed MV/kV images were directly registered to the corresponding daily setup cone-beam CT (CBCT) projections that served as reference images. The registration objective function consisted of a sum of normalized cross-correlation, weighted by the contrast-to-noise ratio of each MV and kV image. The calculated 3D shifts of the tumor were corrected by the displacements between the CBCT projections and the planning respiratory correlated CT (RCCT) to generate motion traces referred to a specific respiratory phase. The accuracy of the algorithm was evaluated on both anthropomorphic phantom and patient studies. The phantom consisted of localizing a 3D printed tumor, embedded in a thorax phantom, in an arc delivery. In an IRB-approved study, data were obtained from VMAT treatments of two lung cancer patients with three electromagnetic (Calypso) beacon transponders implanted in airways near the lung tumor. In the phantom study, the root mean square error (RMSE) between the registered and actual (programmed couch movement) target position was 1.2mm measured by the MV/kV imaging system, which was smaller compared to the MV or kV alone, of 4.1 and 1.3mm, respectively. In the patient study, the mean and standard deviation discrepancy between electromagnetic-based tumor position and the MV/KV-markerless approach was -0.2±0.6mm, 0.2±1.0mm, and -1.2±1.5mm along the superior-inferior, anterior-posterior, and left-right directions, respectively; resulting in a 3D displacement discrepancy of 2.0±1.1mm. Poor contrast around the tumor was the main contribution to registration uncertainties. The combined MV/kV imaging system can provide real-time 3D localization of lung tumor, with comparable accuracy to the electromagnetic-based system when features of tumors are detectable. Careful design of a registration algorithm and a VMAT plan that maximizes the tumor visibility are key elements for a successful MV/KV localization strategy.

A study of minimum segment width parameter on VMAT plan quality, delivery accuracy, and efficiency for cervical cancer using Monaco TPS

PurposeThe purpose of this study was to study the influence of the minimum segment width (MSW) on volumetric modulated arc therapy (VMAT) plan quality, delivery accuracy, and efficiency for cervical cancer treatment.MethodsNineteen patients with cervical cancer were randomly selected to design VMAT plans. Three VMAT plans were generated for each patient incorporating MSWs of 0.5, 1.0, and 1.5 cm while other planning parameters remained constant using the Monaco treatment planning system (TPS) with 6 MV X rays delivered from an Elekta Synergy linear accelerator. Plan quality and delivery efficiency were evaluated based on dose‐volume histograms (DVHs), control points, monitor units (MUs), dosimetric measurement verification results, and plan delivery time.ResultsExcept for the small difference in target dose coverage and maximum dose, there were no statistically significant differences between the other dosimetric parameters in the planning target volumes. The 1.0 and 1.5 cm MSW plans showed lower maximum doses to the spinal cord than the 0.5 cm plan; doses to other organs at risks were similar regardless of MSWs. The mean reductions of total MUs when compared with the 0.5 cm plan were 14.5 ± 6.1% and 20.9 ± 7.9% for MSWs of 1.0 and 1.5 cm, respectively. The calculated gamma indices using the 3% and 3 mm criteria were 96.2 ± 0.6%, 97.0 ± 0.6%, and 97.6 ± 0.6% for the 0.5, 1.0 and 1.5 cm MSW plans, respectively. The plan delivery times decreased with increasing MSWs (p < 0.05).ConclusionIncreasing the MSW allows for improved plan delivery accuracy and efficiency without significantly affecting the VMAT plan quality. MSWs of 1.0 and 1.5 cm improved the plan quality, delivery accuracy, and efficiency for cervical VMAT radiation therapy.

A continuous arc delivery optimization algorithm for CyberKnife m6.

This study aims to reduce the delivery time of CyberKnife m6 treatments by allowing for noncoplanar continuous arc delivery. To achieve this, a novel noncoplanar continuous arc delivery optimization algorithm was developed for the CyberKnife m6 treatment system (CyberArc-m6). CyberArc-m6 uses a five-step overarching strategy, in which an initial set of beam geometries is determined, the robotic delivery path is calculated, direct aperture optimization is conducted, intermediate MLC configurations are extracted, and the final beam weights are computed for the continuous arc radiation source model. This algorithm was implemented on five prostate and three brain patients, previously planned using a conventional step-and-shoot CyberKnife m6 delivery technique. The dosimetric quality of the CyberArc-m6 plans was assessed using locally confined mutual information (LCMI), conformity index (CI), heterogeneity index (HI), and a variety of common clinical dosimetric objectives. Using conservative optimization tuning parameters, CyberArc-m6 plans were able to achieve an average CI difference of 0.036 ± 0.025, an average HI difference of 0.046 ± 0.038, and an average LCMI of 0.920 ± 0.030 compared with the original CyberKnife m6 plans. Including a 5 s per minute image alignment time and a 5-min setup time, conservative CyberArc-m6 plans achieved an average treatment delivery speed up of 1.545x ± 0.305x compared with step-and-shoot plans. The CyberArc-m6 algorithm was able to achieve dosimetrically similar plans compared to their step-and-shoot CyberKnife m6 counterparts, while simultaneously reducing treatment delivery times.