Dual-arc VMAT Research Articles

860: A comparative study of single-arc vs dual-arc VMAT techniques in Linac-based prostate cancer SBRT

860: A comparative study of single-arc vs dual-arc VMAT techniques in Linac-based prostate cancer SBRT

Treatment Optimization in Linac-Based SBRT for Localized Prostate Cancer: A Single-Arc versus Dual-Arc Plan Comparison.

This study aimed to comprehensively present data on treatment optimization in linac-based SBRT for localized prostate cancer at a single institution. Moreover, the dosimetric quality and treatment efficiency of single-arc (SA) versus dual-arc (DA) VMAT planning and delivery approaches were compared. Re-optimization was performed on twenty low-to-intermediate-risk- (36.25 Gy in 5 fractions) and twenty high-risk (42.7 Gy in 7 fractions) prostate plans initially administered with the DA FFF-VMAT technique in 2021. An SA approach was adopted, incorporating new optimization parameters based on increased planning and clinical experience. Analysis included target coverage, organ-at-risk (OAR) sparing, treatment delivery time, and the pre-treatment verification's gamma analysis-passing ratio. The SA optimization technique has consistently produced superior plans. Rectum and bladder mean doses were significantly reduced, and comparable target coverage and homogeneity were achieved in order to maintain a urethra protection strategy. The mean SA treatment delivery time was reduced by 22%; the mean monitor units increased due to higher plan complexity; and dose measurements demonstrated optimal agreement with calculations. The substantial reduction in treatment delivery time decreased the probability of prostate motion beyond the applied margins, suggesting potential decrease in treatment-related toxicity and improved target coverage in prostate SBRT. Further investigations are warranted to assess the long-term clinical outcomes.

PO-2323 Comparison between single and dual arc VMAT for online adaptive prostate SBRT

PO-2323 Comparison between single and dual arc VMAT for online adaptive prostate SBRT

Application of piecewise VMAT technique to whole-brain radiotherapy with simultaneous integrated boost for multiple metastases

PurposeThis study implemented a piecewise volumetric modulated arc therapy (P-VMAT) for realizing whole-brain radiation therapy (WBRT) with simultaneous integrated boost (SIB) for multiple brain metastases (> 40 metastases) with a conventional C-arm linear accelerator.Materials and methodsThis study retrospectively analyzed 10 patients with multiple brain metastases (40–120 metastases, median 76), who underwent WBRT and SIB using helical tomotherapy (HT). The prescribed doses were 40 Gy/20 f and 60 Gy/20 f for WBRT and SIB, respectively. Corresponding new HT plans were designed with P-VMAT using 7 arcs. For each arc, the collimator was rotated to 45°, and the field width was limited to 2.5 cm with 0.5 cm overlap with adjacent arcs. Thus, each arc covered only one section of the brain target volume. A conventional dual arc VMAT (DA-VMAT) plan was also designed. HT, P-VMAT, and DA-VMAT plans were compared using dose distribution reviews and dosimetric parameters. ArcCHECK phantom measurements were performed for verification of P-VMAT plans.ResultsNo significant differences in the mean coverage of the whole-brain target and metastases were observed between HT and P-VMAT (p > 0.05). The conformity index for the whole-brain target improved with P-VMAT compared with HT (p < 0.05). Furthermore, the volume of 44 Gy V44 (110% of prescribed dose for WBRT) received for whole-brain significantly reduced with P-VMAT from 38.2 ± 12.9% to 23.3 ± 9.4% (p < 0.05), and the maximum dose for organs at risks such as the hippocampus, optical nerve, optical chiasm, and spinal cord declined with P-VMAT (p < 0.05). Unlike HT and P-VMAT, DA-VMAT was clinically unacceptable because V44 in the whole-brain was too high (54.7 ± 8.2%). The mean absolute dose gamma passing rate for P-VMAT plans was 97.6 ± 1.1% (3%/3 mm criterion, 10%).ConclusionsP-VMAT is favorable for WBRT and SIB for multiple brain metastases. It provides comparable coverage of whole-brain target and SIB, with better conformity, lower V44, and better dose sparing of organs at risk compared with HT. Furthermore, results show that DA-VMAT fails clinical practice even for a relatively large number of brain metastases with a high degree of plan complexity. The patient specific verification demonstrates the feasibility of P-VMAT for clinical application.

Automated treatment planning of prostate stereotactic body radiotherapy with focal boosting on a fast-rotating O-ring linac: Plan quality comparison with C-arm linacs.

PurposeThe integration of auto‐segmentation and automated treatment planning methods on a fast‐rotating O‐ring linac may improve the time efficiency of online adaptive radiotherapy workflows. This study investigates whether automated treatment planning of prostate SBRT with focal boosting on the O‐ring linac could generate plans that are of similar quality as those obtained through manual planning on clinical C‐arm linacs.MethodsFor 20 men with prostate cancer, reference treatment plans were generated on a TrueBeam STx C‐arm linac with HD120 MLC and a TrueBeam C‐arm linac with Millennium 120 MLC using 6 MV flattened dual arc VMAT. Manual planning on the Halcyon fast‐rotating O‐ring linac was performed using 6 MV FFF dual arc VMAT (HA2‐DL10) and triple arc VMAT (HA3‐DL10) to investigate the performance of the dual‐layer MLC system. Automated planning was performed for triple arc VMAT on the Halcyon linac (ET3‐DL10) using the automated planning algorithms of Ethos Treatment Planning. The prescribed dose was 35 Gy to the prostate and 30 Gy to the seminal vesicles in five fractions. The iso‐toxic focal boost to the intraprostatic tumor nodule(s) was aimed to receive up to 50 Gy. Plan deliverability was verified using portal image dosimetry measurements.ResultsCompared to the C‐arm linacs, ET3‐DL10 shows increased seminal vesicles PTV coverage (D99%) and reduced high‐dose spillage to the bladder (V37Gy) and urethra (D0.035cc) but this came at the cost of increased high‐dose spillage to the rectum (V38Gy) and a higher intermediate dose spillage (D2cm). No statistically significant differences were found when benchmarking HA2‐DL10 and HA3‐DL10 with the C‐arm linacs. All plans passed the patient‐specific QA tolerance limit.ConclusionsAutomated planning of prostate SBRT with focal boosting on the fast‐rotating O‐ring linac is feasible and achieves similar plan quality as those obtained on clinical C‐arm linacs using manual planning.

Complementing Prostate SBRT VMAT With a Two-Beam Non-Coplanar IMRT Class Solution to Enhance Rectum and Bladder Sparing With Minimum Increase in Treatment Time.

PurposeEnhance rectum and bladder sparing in prostate SBRT with minimum increase in treatment time by complementing dual-arc coplanar VMAT with a two-beam non-coplanar IMRT class solution (CS).MethodsFor twenty patients, an optimizer for automated multi-criterial planning with integrated beam angle optimization (BAO) was used to generate dual-arc VMAT plans, supplemented with five non-coplanar IMRT beams with individually optimized orientations (VMAT+5). In all plan generations, reduction of high rectum dose had the highest priority after obtaining adequate PTV coverage. A CS with two most preferred directions in VMAT+5 and largest rectum dose reductions compared to dual-arc VMAT was then selected to define VMAT+CS. VMAT+CS was compared with automatically generated i) dual-arc coplanar VMAT plans (VMAT), ii) VMAT+5 plans, and iii) IMRT plans with 30 patient-specific non-coplanar beam orientations (30-NCP). Plans were generated for a 4 x 9.5 Gy fractionation scheme. Differences in PTV doses, healthy tissue sparing, and computation and treatment delivery times were quantified.ResultsFor equal PTV coverage, VMAT+CS, consisting of dual-arc VMAT supplemented with two fixed, non-coplanar IMRT beams with fixed Gantry/Couch angles of 65°/30° and 295°/-30°, significantly reduced OAR doses and the dose bath, compared to dual-arc VMAT. Mean relative differences in rectum Dmean, D1cc, V40GyEq and V60GyEq were 19.4 ± 10.6%, 4.2 ± 2.7%, 34.9 ± 20.3%, and 39.7 ± 23.2%, respectively (all p<0.001). There was no difference in bladder D1cc, while bladder Dmean reduced by 17.9 ± 11.0% (p<0.001). Also, the clinically evaluated urethra D5%, D10%, and D50% showed small, but statistically significant improvements. All patient VX with X = 2, 5, 10, 20, and 30 Gy were reduced with VMAT+CS, with a maximum relative reduction for V10Gy of 19.0 ± 7.3% (p<0.001). Total delivery times with VMAT+CS only increased by 1.9 ± 0.7 min compared to VMAT (9.1 ± 0.7 min). The dosimetric quality of VMAT+CS plans was equivalent to VMAT+5, while optimization times were reduced by a factor of 25 due to avoidance of individualized BAO. Compared to VMAT+CS, the 30-NCP plans were only favorable in terms of dose bath, at the cost of much enhanced optimization and delivery times.ConclusionsThe proposed two-beam non-coplanar class solution to complement coplanar dual-arc VMAT resulted in substantial plan quality improvements for OARs (especially rectum) and reduced irradiated patient volumes with minor increases in treatment delivery times.

Six degrees of freedom dynamic motion-including dose reconstruction in a commercial treatment planning system.

Intrafractional motion during radiotherapy delivery can deteriorate the delivered dose. Dynamic rotational motion of up to 38 degrees has been reported during prostate cancer radiotherapy, but methods to determine the dosimetric consequences of such rotations are lacking. Here, we create and experimentally validate a dose reconstruction method that accounts for dynamic rotations and translations in a commercial treatment planning system (TPS). Interplay effects are quantified by comparing dose reconstructions with dynamic and constant rotations. The dose reconstruction accumulates the dose in points of interest while the points are moved in six degrees of freedom (6DoF) in a precalculated time-resolved four-dimensional (4D) dose matrix to emulate dynamic motion in a patient. The required 4D dose matrix was generated by splitting the original treatment plan into multiple sub-beams, each representing 0.4s dose delivery, and recalculating the dose of the split plan in the TPS (Eclipse). The dose accumulation was performed via TPS scripting by querying the dose of each sub-beam in dynamically moving points, allowing dose reconstruction with any dynamic motion. The dose reconstruction was validated with film dosimetry for two prostate dual arc VMAT plans with intra-prostatic lesion boosts. The plans were delivered to a pelvis phantom with internal dynamic rotational motion of a film stack (21 films with 2.5mm separation). Each plan was delivered without motion and with three prostate motion traces. Motion-including dose reconstruction was performed for each motion experiment using the actual dynamic rotation as well as a constant rotation equal to the mean rotation during the experiment. For each experiment, the 3%/2mm γ failure rate of the TPS dose reconstruction was calculated with the film measurement being the reference. For each motion experiment, the motion-induced 3%/2mm γ failure rate was calculated using the static delivery as the reference and compared between film measurements and TPS dose reconstruction. DVH metrics for RT structures fully contained in the film volume were also compared between film and TPS. The mean γ failure rate of the TPS dose reconstructions when compared to film doses was 0.8% (two static experiments) and 1.7% (six dynamic experiments). The mean (range) of the motion-induced γ failure rate in film measurements was 35.4% (21.3-59.2%). The TPS dose reconstruction agreed with these experimental γ failure rates with root-mean-square errors of 2.1% (dynamic rotation dose reconstruction) and 17.1% (dose reconstruction assuming constant rotation). By DVH metrics, the mean (range) difference between dose reconstructions with dynamic and constant rotation was 4.3% (-0.3-10.6%) (urethra ), -0.6% (-5.6%-2.5%) (urethra ), 1.1% (-7.1-7.7%) (GTV ), -1.4% (-17.4-7.1%) (GTV ), -1.2% (-17.1-5.7%) (GTV ), and -0.1% (-3.2-7.6%) (GTV mean dose). Dose reconstructions with dynamic motion revealed large interplay effects (cold and hot spots). A method to perform dose reconstructions for dynamic 6DoF motion in a TPS was developed and experimentally validated. It revealed large differences in dose distribution between dynamic and constant rotations not identifiable through dose reconstructions with constant rotation.

Online adaptive radiotherapy compared to plan selection for rectal cancer: quantifying the benefit

BackgroundTo compare online adaptive radiation therapy (ART) to a clinically implemented plan selection strategy (PS) with respect to dose to the organs at risk (OAR) for rectal cancer.MethodsThe first 20 patients treated with PS between May–September 2016 were included. This resulted in 10 short (SCRT) and 10 long (LCRT) course radiotherapy treatment schedules with a total of 300 Conebeam CT scans (CBCT). New dual arc VMAT plans were generated using auto-planning for both the online ART and PS strategy.For each fraction bowel bag, bladder and mesorectum were delineated on daily Conebeam CTs. The dose distribution planned was used to calculate daily DVHs. Coverage of the CTV was calculated, as defined by the dose received by 99% of the CTV volume (D99%). The volume of normal tissue irradiated with 95% of the prescribed fraction dose was calculated by calculating the volume receiving 95% of the prescribed fraction or more dose minus the volume of the CTV. For each fraction the difference between the plan selection and online adaptive strategy of each DVH parameter was calculated, as well as the average difference per patient.ResultsTarget coverage remained the same for online ART. The median volume of the normal tissue irradiated with 95% of the prescribed dose dropped from 642 cm3 (PS) to 237 cm3 (online-ART)(p < 0.001). Online ART reduced dose to the OARs for all tested dose levels for SCRT and LCRT (p < 0.001). For V15Gy of the bowel bag the median difference over all fractions of all patients was − 126 cm3 in LCRT, while the average difference per patient ranged from − 206 cm3 to − 40 cm3. For SCRT the median difference was − 62 cm3, while the range of the average difference per patient was − 105 cm3 to − 51 cm3.For V15Gy of the bladder the median difference over all fractions of all patients was 26% in LCRT, while the average difference per patient ranged from − 34 to 12%. For SCRT the median difference of V95% was − 8%, while the range of the average difference per patient was − 29 to 0%.ConclusionsOnline ART for rectal cancer reduces dose the OARs significantly compared to a clinically implemented plan selection strategy, without compromising target coverage.Trial registrationMedical Research Involving Human Subjects Act (WMO) does not apply to this study and was retrospectively approved by the Medical Ethics review Committee of the Academic Medical Center (W19_357 # 19.420; Amsterdam University Medical Centers, Location Academic Medical Center, Amsterdam, The Netherlands).

Comprehensive Comparison of Progressive Optimization Algorithm Based Automatic Plan and Manually Planned Treatment Technique for Cervical-Thoracic Esophageal Cancers.

Purpose:The purpose of the present study was first to apply the progressive optimization algorithm based automatic volumetric modulated arc therapy (POA-VMAT) technology to accelerate and improve the radiotherapy of cervicothoracic esophageal cancer (CTEC). We comprehensive analyze the feasibility, normal tissue complication probability (NTCP) and dosimetric results of POA-VMAT, manual based VMAT and step-shoot intensity-modulated radiation therapy (IMRT) plans in the treatment of CTEC.Methods:Sixty patients with CTEC with or without concomitant chemotherapy at our institution between 2017 and 2019 were retrospectively identified. The manual 7field-IMRT (7f-IMRT), Single-arc-VMAT and Double-arc-VMAT (Single-Arc/Double-Arc) plans were generated in all cases. The POA-VMAT was designed using the automatic dual-arc VMAT technology of Pinnacle3 9.10 planning system based on progressive optimization algorithm. Specially, it includes the selection of treatment techniques, the running of automated planning scripts, and the evaluation of the final radiotherapy regimen. Subsequently, quantitative evaluation of plans was performed by means of standard dose–volume histograms, homogeneity index (HI) and conformity index (CI).Results:Target dose conformity of the 7f-IMRT plan was inferior to all plans, whereas the Double-Arc plan was slightly inferior to the POA-VMAT but superior to the Single-Arc and 7f-IMRT plan. The HI for 7f-IMRT, Single-Arc, Double-Arc and POA-VMAT were 0.17 ± 0.08, 0.28 ± 0.06, 0.29 ± 0.06 and 0.28 ± 0.03, respectively. For the NTCP results, there was significant statistical difference among POA-VMAT, IMRT and VMAT plans. The total MU was reduced by 48.3% and 42.1% in Single-Arc and POA-VMAT plans compare to IMRT plans.Conclusions:By comprehensive consideration, POA-VMAT efficiently generate acceptable treatment plans for CTEC without dose escalation to OARs and overall superior to manual planning which is a good option for treating CTEC.

39. In-silico dosimetric evaluation of a new Linac MRI guided for pancreatic cancer SBRT treatment

Purpose MR-guided adaptive Radiotherapy (MRgART) is considered a promising resource for pancreatic cancer, as it allows to online modify the dose distribution according to daily anatomy. This in silico study aims to compare the dosimetric performance of a 6 MV MR-Linac (MRIdian Linac, ViewRay) with those obtained using a standard 6 MV SBRT-Linac (Edge, Varian). Methods Ten patients affected by locally advanced pancreatic cancer were considered. GTV, stomach, duodenum, liver, bowel bag, spinal cord and kidneys were contoured on the simulation CT scan and CTV was considered equal to GTV. PTV was generated from CTV adding an isotropic 3 mm margin and excluding areas of overlap with organ at risks (OARs). IMRT plans with 20 equidistant beams were performed for the MR-Linac, while dual arc VMAT plans were optimised for the SBRT-Linac. Prescription dose was 40 Gy in 5 fractions. All plans had to respect the following OARs constraints: V33Gy [1] . The dosimetric comparison was performed on target coverage (D98CTV and V95PTV), dose homogeneity (HI), conformity index (CI) and dose diffusion (V10Gy,V20Gy). Statistical significance was estimated using the Wilcoxon-Mann-Whitney test for paired samples. Results All results are summarised in Table 1 and Fig. 1: nine plans were considered clinically acceptable (V95PTV > 95%). Plans calculated with standard Linac show less low dose diffusion and higher CTV homogeneity, probably due to the different optimisation software, that is more sophisticated but also slower in processing (optimisation mean time 25 min) in comparison to the MR-Linac one (∼2 min). Conclusions Dosimetric performance between MR and standard Linac is comparable in SBRT pancreatic treatment. Considering the MRgART need to optimise the treatment plan while the patient is on the couch, MR Linac allows to elaborate clinically and dosimetrically satisfying SBRT plans for pancreatic cancer.

EP-1883: Class-solution for Pinnacle Autoplan using dual arc VMAT for head and neck cancer

EP-1883: Class-solution for Pinnacle Autoplan using dual arc VMAT for head and neck cancer

VMAT plus a few computer-optimized non-coplanar IMRT beams (VMAT+) tested for liver SBRT

PurposeTo propose a novel treatment approach, designated VMAT+, involving addition of <5 IMRT beams with computer-optimized non-coplanar orientations to VMAT, and evaluate it for liver Stereotactic Body Radiation Therapy (SBRT). VMAT+ is investigated as an alternative for (1) coplanar VMAT and (2) multi-beam non-coplanar treatment. Methods/materialsFor fifteen patients with liver metastases, VMAT+ plans were compared with (1) dual-arc VMAT and (2) 25-beam, non-coplanar treatment with computer-optimized beam orientations (25-NCP). All plans were generated fully automatically for delivery of the highest feasible tumor Biologically Effective Dose (BED). OAR doses, intermediate-dose-spillage, dose-compactness, and measured delivery times were evaluated. ResultsWith VMAT+ the maximum achievable tumor BED was equal to that of 25-NCP. Conversely, VMAT resulted in a lower tumor BED in 5 patients. Compared to VMAT, VMAT+ yielded significant dose reductions in OARs. Intermediate-dose-spillage and dose-compactness were significantly improved by 9.8% and 17.3% (p≤0.002), respectively. Treatment times with VMAT+ were only enhanced by 4.1min on average, compared to VMAT (8.4min). Improvements in OAR sparing with 25-NCP, compared to VMAT+, were generally modest and/or statistically insignificant, while delivery times were on average 20.5min longer. ConclusionsFor liver SBRT, VMAT+ is equivalent to time-consuming treatment with 25 non-coplanar beams in terms of achievable tumor BED. Compared to VMAT, OAR sparing and intermediate-dose-spillage are significantly improved, with minor increase in delivery time.

Validation of Fully Automated VMAT Plan Generation for Library-Based Plan-of-the-Day Cervical Cancer Radiotherapy.

PurposeTo develop and validate fully automated generation of VMAT plan-libraries for plan-of-the-day adaptive radiotherapy in locally-advanced cervical cancer.Material and MethodsOur framework for fully automated treatment plan generation (Erasmus-iCycle) was adapted to create dual-arc VMAT treatment plan libraries for cervical cancer patients. For each of 34 patients, automatically generated VMAT plans (autoVMAT) were compared to manually generated, clinically delivered 9-beam IMRT plans (CLINICAL), and to dual-arc VMAT plans generated manually by an expert planner (manVMAT). Furthermore, all plans were benchmarked against 20-beam equi-angular IMRT plans (autoIMRT). For all plans, a PTV coverage of 99.5% by at least 95% of the prescribed dose (46 Gy) had the highest planning priority, followed by minimization of V45Gy for small bowel (SB). Other OARs considered were bladder, rectum, and sigmoid.ResultsAll plans had a highly similar PTV coverage, within the clinical constraints (above). After plan normalizations for exactly equal median PTV doses in corresponding plans, all evaluated OAR parameters in autoVMAT plans were on average lower than in the CLINICAL plans with an average reduction in SB V45Gy of 34.6% (p<0.001). For 41/44 autoVMAT plans, SB V45Gy was lower than for manVMAT (p<0.001, average reduction 30.3%), while SB V15Gy increased by 2.3% (p = 0.011). AutoIMRT reduced SB V45Gy by another 2.7% compared to autoVMAT, while also resulting in a 9.0% reduction in SB V15Gy (p<0.001), but with a prolonged delivery time. Differences between manVMAT and autoVMAT in bladder, rectal and sigmoid doses were ≤ 1%. Improvements in SB dose delivery with autoVMAT instead of manVMAT were higher for empty bladder PTVs compared to full bladder PTVs, due to differences in concavity of the PTVs.ConclusionsQuality of automatically generated VMAT plans was superior to manually generated plans. Automatic VMAT plan generation for cervical cancer has been implemented in our clinical routine. Due to the achieved workload reduction, extension of plan libraries has become feasible.

Volumetric modulated arc therapy with dynamic collimator rotation for improved multileaf collimator tracking of the prostate

PurposeTo improve MLC tracking of prostate VMAT plans by dynamic rotation of the collimator to align the MLC leaves with the dominant prostate motion direction. MethodsFor 22 prostate cancer patients, two dual arc VMAT plans were made with (1) fixed collimators (45° and 315°) and (2) a rotating collimator that aligned the MLC leaves with the dominant prostate motion direction (population-based first principal component). The fixed and rotating collimator plan quality was compared using selected dose–volume indices. Next, MLC tracking treatments were simulated with 695 patient-measured prostate traces. The MLC exposure error (under- and overexposed MLC area in beam’s eye view) was calculated as a surrogate for the MLC tracking error. Finally, motion including dose reconstruction was performed for 35 motion traces for one patient, and the root-mean-square dose error was compared with the MLC exposure error. ResultsRotating collimator VMAT plans were of similar quality as the fixed collimator plans, but significantly improved MLC tracking with 33% lower MLC exposure errors (p≪0.0001). The reductions in MLC exposure error correlated significantly with dose error reductions. ConclusionProstate VMAT plans with rotating collimator were of similar quality as fixed collimator plans, but more suitable for MLC tracking with significantly better agreement between planned and delivered dose distributions. MLC tracking for prostate cancer patients can therefore be improved without the requirement of additional efforts or hardware changes.

Comparison of planning parameter selection for volumetric modulated arc therapy of nasopharyngeal carcinoma in two different treatment planning systems

Objective To investigate the impact of planning parameter settings on plan quality and delivery efficiency of VMAT for nasopharyngeal carcinoma with two treatment planning systems (TPS), as references for clinic plan optimization. Methods 25 patients with nasopharyngeal carcinoma were selected and planned for SIB-VMAT treatment. The same planning aims were used in the two kinds of TPS (TPS-1 and TPS-2). Multiple planning parameters were set for plan optimization. Dose distribution to the target volumes and organs at risk, monitor unit (MU) and delivery time were compared. Paired t-test or one-way ANOVA was used for the data which was in accordance to normal distribution; otherwise, nonparametric Wilcoxon signed rank test or nonparametric Friedman test was used. Results More segments lead to better plan quality and less MU but longer delivery time (Minor impact was observed when segment number was larger than 120) in TPS-1, while it had little impact on both plan quality and delivery efficiency in TPS-2.Comparing to single-arc plans, dual-arc VMAT achieved no significant benefit in plan quality but had more MU and longer delivery time in TPS-1(P=0.000). However, dual-arc VMAT plans had better dose distribution in TPS-2, decreased the maximum and mean dose for spinal cord in 3.9% and 13.7% respectively (P=0.000, 0.000). Changing the settings of maximum or minimum dose rate did not affect the plan quality in both of the tested TPSs. Increasing the maximum or minimum dose rate reduced the delivery time but the latter increased the number of MU (P=0.000, 0.000). Conclusions VMAT plan quality and delivery efficiency is affected significantly and differently by planning parameter settings for two TPSs. Trial test should be conducted for different TPS to determine the optimal parameter settings. Key words: Nasopharyngeal neoplasms/volumetric modulated arc therapy; Operation parameter; Plan quality; Delivery efficiency

Comparison of VMAT and IMRT strategies for cervical cancer patients using automated planning

Background and purposeIn a published study on cervical cancer, 5-beam IMRT was inferior to single arc VMAT. Here we compare 9, 12, and 20 beam IMRT with single and dual arc VMAT. Material and methodsFor each of 10 patients, automated plan generation with the in-house Erasmus-iCycle optimizer was used to assist an expert planner in generating the five plans with the clinical TPS. ResultsFor each patient, all plans were clinically acceptable with a high and similar PTV coverage. OAR sparing increased when going from 9 to 12 to 20 IMRT beams, and from single to dual arc VMAT. For all patients, 12 and 20 beam IMRT were superior to single and dual arc VMAT, with substantial variations in gain among the study patients. As expected, delivery of VMAT plans was significantly faster than delivery of IMRT plans. ConclusionsOften reported increased plan quality for VMAT compared to IMRT has not been observed for cervical cancer. Twenty and 12 beam IMRT plans had a higher quality than single and dual arc VMAT. For individual patients, the optimal delivery technique depends on a complex trade-off between plan quality and treatment time that may change with introduction of faster delivery systems.

Patients with breast cancer in post-mastectomy radiotherapy employed with heart faced radiation beam : dosimetric risk and benefits analysis

Objective To evaluate the dosimetry for the patients with breast cancer in post-mastectomy radiotherapy. Methods Thirty one patients from Nov 2012 to May 2013 with breast cancer were treated with mastectomy surgery followed by radiotherapy. They were planned using: 1) improved tangential wedge-based fields IMRT(P1) ; 2) 4 beam rotary inverse IMRT(P2) ; 3) 5 beam-field IMRT(P3) ; and 4) Dual arc VMAT(P4) .The PTV and OAR including the cardiac, left anterior descending artery(LAD) , the right coronary artery(RCA) , ipsilateral lung. The CI and HI of PTV and volumetric dose PRV-OAR were analyzed by single factor variance analysis or χ2 test methods. Results The CI and HI for P1-P4 with both sides were L: P=0.009, R: P=0.000. The NTCP_Heart with tumor in right side was: 0.19%, 4.76×10-3%, 0, 0 (P=0.568) , with tumor in the other side was: 2.7%, 1.1%, 1.3%, 0.86% (P=0.390). The NTCP_Lung_Sick for P1-P4 were left side: 9.73%, 7.52%, 8.86%, 10.73% (P=0.953) ; Right side: 11.73%, 8.65%, 7.02%, 11.25% (P=0.437) .The TCP for P1-P4 with both sides were L: P=0.000, R: P=0.000) . Conclusions There had no statistically difference of NTCP_Heart and NTCP_Lung_Sick in plans employed with heart faced(involved)beams or arc within our research group, while had statistically benefit to improve the CI of PTV and the dose homogeneity of target, 5 beam-field IMRT or VMAT plan could be choose as cardiac safe and efficient techniques for patients with breast cancer in post-mastectomy surgery. Key words: Breast neoplasms/postoperative radiotherapy; Routine intensity-modulated panning; Volumetric modulated planning; Dosimetry

The first clinical treatment with kilovoltage intrafraction monitoring (KIM): a real-time image guidance method.

Kilovoltage intrafraction monitoring (KIM) is a real-time image guidance method that uses widely available radiotherapy technology, i.e., a gantry-mounted x-ray imager. The authors report on the geometric and dosimetric results of the first patient treatment using KIM which occurred on September 16, 2014. KIM uses current and prior 2D x-ray images to estimate the 3D target position during cancer radiotherapy treatment delivery. KIM software was written to process kilovoltage (kV) images streamed from a standard C-arm linear accelerator with a gantry-mounted kV x-ray imaging system. A 120° pretreatment kV imaging arc was acquired to build the patient-specific 2D to 3D motion correlation. The kV imager was activated during the megavoltage (MV) treatment, a dual arc VMAT prostate treatment, to estimate the 3D prostate position in real-time. All necessary ethics, legal, and regulatory requirements were met for this clinical study. The quality assurance processes were completed and peer reviewed. During treatment, a prostate position offset of nearly 3 mm in the posterior direction was observed with KIM. This position offset did not trigger a gating event. After the treatment, the prostate motion was independently measured using kV/MV triangulation, resulting in a mean difference of less than 0.6 mm and standard deviation of less than 0.6 mm in each direction. The accuracy of the marker segmentation was visually assessed during and after treatment and found to be performing well. During treatment, there were no interruptions due to performance of the KIM software. For the first time, KIM has been used for real-time image guidance during cancer radiotherapy. The measured accuracy and precision were both submillimeter for the first treatment fraction. This clinical translational research milestone paves the way for the broad implementation of real-time image guidance to facilitate the detection and correction of geometric and dosimetric errors, and resultant improved clinical outcomes, in cancer radiotherapy.

The first clinical implementation of electromagnetic transponder-guided MLC tracking.

We report on the clinical process, quality assurance, and geometric and dosimetric results of the first clinical implementation of electromagnetic transponder-guided MLC tracking which occurred on 28 November 2013 at the Northern Sydney Cancer Centre. An electromagnetic transponder-based positioning system (Calypso) was modified to send the target position output to in-house-developed MLC tracking code, which adjusts the leaf positions to optimally align the treatment beam with the real-time target position. Clinical process and quality assurance procedures were developed and performed. The first clinical implementation of electromagnetic transponder-guided MLC tracking was for a prostate cancer patient being treated with dual-arc VMAT (RapidArc). For the first fraction of the first patient treatment of electromagnetic transponder-guided MLC tracking we recorded the in-room time and transponder positions, and performed dose reconstruction to estimate the delivered dose and also the dose received had MLC tracking not been used. The total in-room time was 21 min with 2 min of beam delivery. No additional time was needed for MLC tracking and there were no beam holds. The average prostate position from the initial setup was 1.2 mm, mostly an anterior shift. Dose reconstruction analysis of the delivered dose with MLC tracking showed similar isodose and target dose volume histograms to the planned treatment and a 4.6% increase in the fractional rectal V60. Dose reconstruction without motion compensation showed a 30% increase in the fractional rectal V60 from that planned, even for the small motion. The real-time beam-target correction method, electromagnetic transponder-guided MLC tracking, has been translated to the clinic. This achievement represents a milestone in improving geometric and dosimetric accuracy, and by inference treatment outcomes, in cancer radiotherapy.

Fully automated treatment plan generation in daily routine

Background: Currently, treatment plans are generated by dosimetrists using a trial-and-error procedure. The process may take several hours and plan quality is dependent on the skills and experience of the dosimetrist, and on allotted time. We have developed and clinically introduced a system for fully automatic plan generation, using lexicographic multi-criterial optimization to replace the labour-intensive and operator-dependent trialand-error approach. Materials and Methods: For each patient, the treatment plan is fully automatically generated by the clinical treatment planning system (Monaco, Elekta AB), based on a patient-specific template that is automatically pre-generated with our in-house lexicographic multi-criterial optimizer (“Erasmus-iCycle”, Med Phys. 2012; 39(2): 951). Automatic plan generation in Erasmus-iCycle is based on a ‘wishlist’ with hard constraints and treatment objectives with assigned priorities. For each treatment site (e.g. HN 85(3): 866-72). For a group of 44 cervical cancer patients, dual-arc VMAT AUTO-plans were superior to MANUAL-plans generated by an expert cervical cancer planner, spending many hours; reduced small bowel V 15Gy ,V 45Gy ,a nd Dmean, bladder Dmean, and rectum Dmean ,p <0.001. For 30 prostate cancer patients, differences between VMAT AUTO- and MANUAL-plans, the latter generated by an expert planner with up to 4 hours planning hands-on time, were statis