Dual-arc Volumetric Modulated Arc Therapy Research Articles

DOSIMETRIC COMPARISON OF INTENSITY-MODULATED RADIATION THERAPY (IMRT) AND VOLUMETRIC-MODULATED ARC THERAPY (VMAT) IN RECTAL CANCER PATIENTS: A COMPREHENSIVE ANALYSIS

This study aimed to conduct a thorough dosimetric comparison between two advanced radiotherapy techniques, Intensity-Modulated Radiation Therapy (IMRT) and Volumetric-Modulated Arc Therapy (VMAT), to ascertain the superior modality in terms of dose distribution and organ-at-risk sparing for rectal cancer patients. Thirty-three patients with ECOG performance status 1, aged between 18 to 60 years, diagnosed with Stage II to III rectal cancer, were included in this prospective study. Each patient underwent treatment planning with IMRT and VMAT techniques using Varian system simulation computed tomography scans. The dosimetric analysis encompassed the evaluation of target volume dose homogeneity, conformity, and doses to at-risk organs. The dosimetric comparison was conducted utilizing seven-field IMRT and dual arc VMAT plans. Statistical analysis was performed using paired t-tests and SPSS 20 software. Treatment plan constraints adhered to the RTOG 9406 guidelines, ensuring adequate planning target volume (PTV) coverage, homogeneity index, conformity index, and dose limits for organs at risk, including small bowel V20 (<200cc), bladder V45 (<21Gy), and femoral head V50 (≤30 Gy). Volumetric arc therapy plans demonstrated superior dose homogeneity to fixed-field intensity-modulated plans (p-value = 0.04), particularly in femoral head dose-limiting toxicity (p-value = 0.00). However, intensity-modulated therapy exhibited equivalent or superior performance in other evaluated parameters. Our findings suggest that while VMAT offers advantages in PTV coverage homogeneity and femoral head dose-limiting toxicity, IMRT remains competitive and potentially preferable in certain dosimetric aspects. The choice between IMRT and VMAT should be carefully considered based on individual patient characteristics and treatment goals. This comprehensive dosimetric comparison contributes valuable insights into optimizing radiotherapy planning for rectal cancer patients, potentially guiding clinical decision-making and improving treatment outcomes.

Comparison of photon energies and field techniques for ovarian dose reduction in volumetric modulated arc therapy

For fertility preservation in young female patients undergoing pelvic radiotherapy for cervical cancer, lateral ovarian transposition (LOT) is a procedure that moves the ovaries away from the radiation field. However, it is still challenging to fully protect the ovaries from radiation damage in volumetric modulated arc therapy (VMAT). In this study, we optimized VMAT techniques and simulated the effect of the LOT position on the ovarian dose. Ten cervical cancer patients who received pelvic radiotherapy after LOT were retrospectively analyzed. A restricted arc plus split field technique, which incorporated beam avoidance sectors, split field, fixed jaw, and orthogonal collimator orientation with 10 MV energy (rasf-10MV-VMAT), was designed to minimize the dose to the ovaries. This technique was compared with dual-arc conventional VMAT (dac-6MV-VMAT) and restricted arc and field VMAT (raf-6MV-VMAT) techniques with 6 MV energy. Ovarian dose, target coverage, and organs at risk (OAR) sparing were compared. The location of the ovaries in the anterior-posterior and superior-inferior directions was changed to simulate the effect of the LOT position on the ovarian dose. Compared to dac-6MV-VMAT and raf-6MV-VMAT, rasf-10MV-VMAT decreased the ovarian dose significantly more, especially for a low-dose volume. Both ovaries, received a 44.0–52.1 % lower volume of >3 Gy dose, and (0.5–1.9 Gy) lower maximum and mean doses with rasf-10MV-VMAT (p < 0.05). Rasf-10MV-VMAT also improved target conformity and coverage more than raf-6MV-VMAT (p < 0.05) and reduced the bladder mean dose more than dac-6MV-VMAT (p < 0.05). The ovarian dose decreased with the distance from the target contour, and placing the ovaries near the mid-frontal plane or as high as possible after the LOT lowered ovarian exposure. This technique, using 10 MV photon energy combined with field technique optimization, reduced the ovarian dose, particularly by decreasing the low-dose exposure of ovarian tissue and improving the target conformity simultaneously. The ovarian dose could be minimized by a proper LOT position. This optimized technique could enhance ovarian protection and fertility preservation for young female survivors of cervical cancer.

Dosimetric comparison of dual arc- volumetric modulated arc therapy (DA-VMAT) and seven-field inverse intensity modulated radiotherapy (IMRT) applied in the curative treatment of cervical cancer

Dosimetric comparison of dual arc- volumetric modulated arc therapy (DA-VMAT) and seven-field inverse intensity modulated radiotherapy (IMRT) applied in the curative treatment of cervical cancer

Analytical setup margin for spinal stereotactic body radiotherapy based on measured errors

BackgroundNo consensus currently exists about the correct margin size to use for spinal SBRT. Margins have been proposed to account for various errors individually, but not with all errors combined to result in a single margin value. The purpose of this work was to determine a setup margin for five-fraction spinal SBRT based on known errors during radiotherapy to achieve at least 90% coverage of the clinical target volume with the prescription dose for at least 90% of patients and not exceed a 30 Gy point dose or 23 Gy to 10% of the spinal cord subvolume.MethodsThe random and systematic error components of intrafraction motion, residual setup error, and end-to-end system accuracy were measured. The patient’s surface displacement was measured to quantify intrafraction motion, the residual setup error was quantified by re-registering accepted daily cone beam computed tomography setup images, and the displacement between measured and planned dose profiles in a phantom quantified the end-to-end system accuracy. These errors and parameters were used to identify the minimum acceptable margin size. The margin recommendation was validated by assessing dose delivery across 140 simulated patient plans suffering from various random shifts representative of the measured errors.ResultsThe errors were quantified in three dimensions and the analytical margin generated was 2.4 mm. With this margin applied in the superior/inferior direction only, at least 90% of the CTV was covered with the prescription dose for 96% of the 140 patients simulated with minimal negative effect on the spinal cord dose levels.ConclusionsThe findings of this work support that a 2.4 mm margin applied in the superior/inferior direction can achieve at least 90% coverage of the CTV for at least 90% of dual-arc volumetric modulated arc therapy spinal SBRT patients in the presence of errors when immobilized with vacuum bags.

Optimization of collimator angles in dual-arc volumetric modulated arc therapy planning for whole-brain radiotherapy with hippocampus and inner ear sparing

To optimize the collimator angles in dual-arc volumetric modulated arc therapy (VMAT) plans for whole-brain radiotherapy with hippocampus and inner ear sparing (HIS-WBRT). Two sets of dual-arc VMAT plans were generated for 13 small-cell lung cancer patients: (1) The collimator angles of arcs 1 and 2 (θ1/θ2) were 350°/10°, 350°/30°, 350°/45°, 350°/60°, and 350°/80°, i.e., the intersection angle of θ1 and θ2 (Δθ) increased. (2) θ1/θ2 were 280°/10°, 300°/30°, 315°/45°, 330°/60°, and 350°/80°, i.e., Δθ = 90°. The conformity index (CI), homogeneity index (HI), monitor units (MUs), and dosimetric parameters of organs-at-risk were analyzed. Quality assurance for Δθ = 90° plans was performed. With Δθ increasing towards 90°, a significant improvement was observed for most parameters. In 350°/80° plans compared with 350°/10° ones, CI and HI were improved by 1.1% and 25.2%, respectively; MUs were reduced by 16.2%; minimum, maximum, and mean doses (D100%, Dmax, and Dmean, respectively) to the hippocampus were reduced by 5.5%, 6.3%, and 5.4%, respectively; Dmean to the inner ear and eye were reduced by 0.7% and 5.1%, respectively. With Δθ kept at 90°, the plan quality was not significantly affected by θ1/θ2 combinations. The gamma-index passing rates in 280°/10° and 350°/80° plans were relatively lower compared with the other Δθ = 90° plans. Δθ showed a significant effect on dual-arc VMAT plans for HIS-WBRT. With Δθ approaching 90°, the plan quality exhibited a nearly continuous improvement, whereas with Δθ = 90°, the effect of θ1/θ2 combination was insignificant.

Significant Reduction in Vertebral Artery Dose by Intensity Modulated Proton Therapy: A Pilot Study for Nasopharyngeal Carcinoma.

Intensity modulated proton therapy (IMPT) with the vertebral artery (VA)-sparing technique has been initially proposed in our institution. This pilot study was conducted to compare the dose to VAs between IMPT and volumetric-modulated arc therapy (VMAT) for patients with nasopharyngeal carcinoma (NPC). A total of six patients with NPC treated by IMPT were enrolled in the study. Target volumes and organs at risk (OARs) were delineated, including 12 samples of right and left VAs, respectively, for each patient. Treatment planning by IMPT and dual-arc VMAT was carried out for comparison. The IMPT plan significantly reduced VA mean dose, V10, V20, V30, V40, and V50, compared to the VMAT plan in all 12 samples (p < 0.001). The average mean dose to VAs for IMPT was 35.2% (23.4–46.9%), which was less compared to VMAT (p < 0.001). Adequate dose coverage was achieved with both IMPT and VMAT plans for three different dose levels of target volumes for all patients. IMPT significantly reduces VA dose while maintaining adequate dose coverage of all target volumes. For patients with head and neck cancer who seek to preserve their blood flow to the brain in order to decrease late vascular and neurologic sequelae, IMPT should be considered. A prospective study with longer follow-up is ongoing to confirm our preliminary results.

Optimal VMAT Delivery for Elekta MLC Beam Modulator: A Study of Collimator Rotation for Head and Neck Planning

BackgroundWell-optimized treatment planning parameters are vital for optimum beam delivery in advanced radiotherapy techniques. The Elekta “Beam-Modulator” (BM) is a high-resolution multileaf collimation system where each individual leaf is 4 mm wide at the isocentre, without backup diaphragms and jaws. Its maximum aperture is 21 × 16 cm2, which results in a limited clinical use for the target geometry of maximum 20 cm in length. The collimator rotation provides an opportunity to treat slightly extended treatment length with optimal target coverage. The study aims to observe the collimator rotation influence on volumetric modulated arc therapy (VMAT) plan quality for different head and neck target geometries using limited field collimator of BM. MethodsTen patients with head and neck cancer were planned by means of simultaneous integrated boost to deliver VMAT for five patients with three dose levels (70/60/56) and five patients with two dose levels (60/54). The single arc, dual arc, and combined two independent single arcs of 356° each were well optimized for four collimator angles (C) 15°,30°, 45°, and 90°. The plans were prepared for BM with SmartArc module of Pinnacle³ treatment planning system. Statistical significance (P ≤ .05) among collimator angles for planning target volume dose-volume indices was calculated with Student's t-test. Organ-at-risk doses were compared and monitor units were also evaluated as a parameter for dose-delivery efficiency and out-of-field dose index. ResultsThe dual arc and combined two independent single arcs achieved planning objectives for C15°, C30°, and C45°. Single arc for all collimator angles and C90° for all VMAT schemes failed to achieve planning objectives. The spread of low dose bath 20, 35, and 40 Gy and deterioration of doses were higher towards periphery at C90° and statistically significant. ConclusionThe small and medium collimator angles for dual-arc VMAT scheme(s) are suitable, whereas single arc and C90° are not suitable in VMAT implementation for Elekta Beam-Modulator collimation system.

Dose distribution of the brain tissue associated with cognitive functions in high-grade glioma patients

PurposeThe purpose of this prospective dosimetric study was to assess the dose distribution regarding the brain areas implied in cognitive functions using two approaches: volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT). Patients and methodsThirty-seven patients were treated using a dual-arc VMAT approach for supratentorial glioblastoma between 2016 and 2018. The total dose of 60Gy in 30 daily fractions was administered to the planning target volume (PTV). The brain structures that play an important role in cognitive physiology, such as the hippocampi, corpus callosum, cerebellum, subventricular zones (SVZ), were delineated. For each patient, a new treatment plan in HT was determined by a second medical physicist in a blindly fashion according to the same dose constraints and priorities. Statistical analyses were performed using the Wilcoxon-signed rank test. ResultsConformity indexes remained similar with both techniques. The mean values were 0.96 (0.19–1.00) for VMAT and 0.98 (range, 0.84–1.00) for HT, respectively (P=0.73). Significant D50% reductions were observed with VMAT compared to HT: 14.6Gy (3.8–28.0) versus 17.4Gy (12.1–25.0) for the normal brain (P=0.014); 32.5Gy (10.3–60.0) versus 35.6Gy (17.1–58.0) for the corpus callosum (P=0.038); 8.1Gy (0.4–34.0) versus 12.8Gy (0.8–27.0) for the cerebellum (P<0.001), respectively. ConclusionThe VMAT approach seemed to improve the sparing of the key brain areas implied in cognitive functions without jeopardizing PTV coverage.

Investigating the impact of patient arm position in an MR-linac on liver SBRT treatment plans.

The superior soft-tissue contrast offered by the integrated magnetic resonance imaging (MRI) of the Unity MR-linac compared to the x-ray-based image guidance on conventional linacs potentially allows for liver stereotactic body radiation therapy (SBRT) without the need for implanted markers or other surrogates. On conventional linacs, liver SBRT patients are typically positioned with their arms above their heads (arms-up) to minimize exposure to healthy tissue. However, the spatial confinement of the MRI-bore and increased treatment delivery times can make the arms-up position straining. Therefore, we assessed the plan quality for MR-linac treatment plans with the patient in the arms-up and in the arms-down position. Additionally, we compared the MR-linac plans with clinically used arms-up treatment plans made for a conventional linac. Fifteen consecutively treated patients with oligometastatic liver disease were included in this retrospective study. For each patient, a planning computed tomography (CT) with delineations, a diagnostic MRI, and a 3×20Gy dual-arc volumetric modulated arc therapy (VMAT) plan, which was used to treat the patient in an arms-up position on the conventional linac, were available. For the MR-linac, 15-beam step-and-shoot intensity-modulated radiation therapy (IMRT) plans were created for four patient positioning scenarios: arms-up, mimicking current clinical practice; arms-down, with treatment beams avoiding the arms on the entrance side; arms-through, arms are down but not avoided, and right-arm-up; only the right arm is up and the left arm is avoided on the entrance side. Resulting treatment plans were compared. Bonferroni-corrected two-sided Wilcoxon signed-ranks tests were used to assess statistical significance (P<0.05). No significant differences were found in gross tumour volume (GTV) coverage (D , D , and D ) or liver sparing (liver-GTV V ) between the clinical plans and any of the MR-linac plans. The median target conformity [exterior V /planning target volume (PTV)] was significantly better in the clinical plans (5.8) than in the MR-linac scenarios (arms-down: 6.6, arms-up/right-arm-up: 6.2, arms-through: 6.3). No MR-linac plan violated any additional organ-at-risk (OAR) constraint that was not already violated in the clinical plans. In the arms-down scenario a significantly increased median spinal cord D (14.5Gy) was detected compared to the clinical setup (7.2Gy). For the arms-down (arms-through) scenario, the median left arm D was 1.5 (2.7)Gy, the median right arm D was 5.8 (22.7)Gy, and the median right arm V was 0.0 (14.7) cc. These differences were statistically significant. For the right-arm-up scenario, the median left arm D (2.3Gy) and V (0.0) were not significantly different compared to the arms-down scenario. Mimicking the current clinical practice by treating patients in the arms-up/right-arm-up position on the MR-linac leads to plans which are dosimetrically very similar to the conventional linac plans. Treating in the arms-down position is expected to increase patient comfort at the cost of a small reduction in OAR sparing for individual patients. Treating through the arms is not encouraged due to substantial dose deposition in the arms.

Evaluation of different volumetric-modulated arc therapy for the large planning target volume in T3 lung cancer

Objective To investigate the feasibility and dosimetric characteristics of using dual-arc volumetric modulated arc therapy and multiple partial-arc VMAT for T3 lung cancer. Methods From June 2016 to May 2018, thirteen lung cancer patients with large planning target volume were replanned with dual full arcs VMAT(F-VMAT) and six partial-arc s VMAT(P-VMAT)on RayStation v4.5 RayArc function.PTV volume median was 550.9cm3(ranged 402.2-834.8cm3) and to a prescribed dose of 60 Gy in 30 fractions.Equivalent target coverage was required for all plans, and clinical goals were evaluated using various dose-volume metrics.These included PTV dose conformity, mean lung/heart dose, lung V5, V10, V20, V30, heart V30 and V40, and Dmax of spinal canal.The total monitor units (MUs) were also examined. Results All VMAT plans satisfied the treatment criteria.F-VMAT achieved better homogeneity index(HI) and MUs than P-VMRT(t=-3.904, P=0.002), and the conformal number(CN) of tumor volumes was likely clinically indistinguishable.However, F-VMAT significantly reduced lung V5, V10 and mean lung dose[V5: (51.31±5.36)% vs.(43.44±5.28)%, t=6.908, P=0.00; V10: (38.34±3.26)% vs.(34.05±3.74)%, t=4.632, P=0.001; Dmean: (1 449±117.19)cGy vs.(1 375.38±148.98)cGy, t=4.93, P=0.00], and heart dosimetric parameters were also observed in favor of P-VMRT[V30: (20.6±10.4)% vs.(16.4±8.9)%, t=3.822, P=0.02; V40: (14.6±7.5)% vs.(11.88±7.1)%, t=3.096, P=0.009; Dmean: (1 442.9±651.2)cGy vs.(1 263.5±605.6)cGy, t=3.986, P=0.02], and there were no statistically significant differences in lung V20, V30 and spinal cord Dmax between the two groups(all P>0.05). Conclusion VMAT is an effective treatment for stage T3 lung cancer patients.The primary advantage of P-VMAT was the reduction in low dose area and decreased risk of symptomatic radioactive lung injury.It may be a priority for pulmonary malignancy patients with the large planning target volume. Key words: Lung neoplasms; Radiotherapy; Radiotherapy, intensity-modulated; Radiometry; Radiotherapy dosage; Radiation injuries; Organs at risk; Comparative study

Dosimetric comparison between intensity-modulated radiotherapy and volumetric-modulated arc therapy in hippocampus sparing in brain metastasis treated by whole-brain irradiation and simultaneous integrated boost

AbstractBackground:While treating brain metastasis with whole-brain radiotherapy incorporating a simultaneous integrated boost (WBRT-SIB), the risk of hippocampus injury is high. The aim of this study is to compare dosimetrically between intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) in sparing of hippocampus and organs at risk (OARs) and planning target volume (PTV) coverage.Methods:In total, 16 patients presenting with more than one brain metastases were previously treated and then retrospectively planned using VMAT and IMRT techniques. For each patient, a dual-arc VMAT and another IMRT (five beams) plans were created. For both techniques, 30 Gy in 10 fractions was prescribed to the whole brain (WB) minus the hippocampi and 45 Gy in 10 fractions to the tumour with 0·5 cm margin. Dose–volume histogram (DVH), conformity index (CI) and homogeneity index (HI) of PTV, hippocampus mean and maximum dose and other OARs for both techniques were calculated and compared.Results:A statistically significant advantage was found in WB-PTV CI and HI with VMAT, compared to IMRT. There were lower hippocampus mean and maximum doses in VMAT than IMRT. The maximum hippocampus dose ranged between 15·5 and 19·2 Gy and between 18·4 and 20·6 Gy in VMAT and IMRT, respectively. The mean dose of the hippocampus ranged between 11·5 and 17·7 Gy and between 13·2 and 18·3 Gy in VMAT and IMRT, respectively.Conclusion:Using WBRT-SIB technique, VMAT showed better PTV coverage with less mean and maximum doses to the hippocampus than IMRT. Clinical randomised studies are needed to confirm safety and clinical benefit of WBRT-SIB.

Dosimetric Comparison of Pelvic Bone Marrow Preservation between Volumetric-Modulated Arc Therapy and Intensity-Modulated Radiotherapy in Radical Radiotherapy of High-Risk Prostate Cancer

Background: Pelvic bone marrow (PBM) preservation is one of the factors that should be taken into consideration while choosing a technique for radiotherapy of pelvic malignancies. Aim: To dosimetrically compare between volumetric-modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) in PBM preservation in radical treatment of high-risk prostate cancer. Methods: In 26 patients with high-risk prostatic carcinoma, dual arc VMAT and 7 fields IMRT plans were generated. In every patient, two targets were defined, clinical target volume (CTV) including the prostate and seminal vesicles (CTV-PSV) and CTV including pelvic lymph nodes (CTV-LN). The organs at risk delineated were the rectum, urinary bladder, small intestine, bulb of the penis, femoral heads bilaterally and PBM. The dose prescribed to the CTV-PSV was 76 Gy in 38 fractions given over 7.5 weeks and the dose to CTV-LN was 54 Gy in 38 fractions given over 7.5 weeks. Planning target volume (PTV) was created from the CTV with a margin of 5 mm in all direction. For assessment of PBM dose, V10, V20, V30, V40, V50 and mean dose were calculated. The dose volume histogram of PTV and PBM for both techniques was compared. Results: The mean dose of PTV 54 Gy was achieved in both techniques adequately with better sparing of organs at risk with the VAMT technique. The mean dose for PBM in the VMAT technique was significantly less than that in the IMRT (21.7 Gy vs. 25.8 Gy, respectively; p < 0.001). The significant differences in PBM doses were in the range of 20 Gy to 40 Gy. Conclusion: In radical treatment of prostate cancer, VMAT technique can offer comparable conformality to IMRT with better PBM preservation. Awareness of PBM delineation and reduction of its doses using VMAT can help to decrease the hematological toxicity.

Study of the optimal thresholds of gamma passing rate in VMAT plan verification for cervical cancer

Objective To investigate the optimal thresholds of the passing rate with different gamma measurement criteria (percent dose difference/DTA) based on the Delta 4 three-dimensional dosimetric verification system in the verification of volumetric modulated arc-therapy (VMAT) plan for cervical cancer. Methods Thirty clinically-approved dual-arc VMAT plans using the RapidArcTM (Varian Medical Systems Inc.) for cervical cancer were randomly selected. The gamma analysis and dose-volume histogram (DVH) evaluation were performed using Delta 4. All the plans were classified according to the following two criteria: 1. If the absolute percentage dose errors of all specific dosimetry indices on the DVH were less than 5%, the plan was regarded as clinically acceptable. 2. If the gamma passing rate was 90% or 95% under the criteria of 2%/2 mm and 3%/3 mm, the plan was regarded as acceptable. The sensitivity and specificity analyses were conducted based on the classification results and the receiver operating characteristic (ROC) curve was plotted. By calculating the Youden Index, the optimal thresholds under different Gamma criteria (global and local 2%/2 mm and 3%/3 mm) were investigated. Finally, the ability of distinguishing the plan was clinically acceptable or not between the conventional and optimal thresholds was quantitatively compared according to the sensitivity and specificity analyses. Results The optimal thresholds under the global 3%/3 mm and 2%/2 mm criteria were 98.3% and 87.05%; and 97.55%、86.05% for the local gamma analysis. Compared with the conventional thresholds, the sensitivity of the optimal thresholds was 0.93 by using the global and local gamma analyses under the 3%/3 mm criterion. Under the 2%/2 mm criterion, the sensitivity of the optimal thresholds was 0.65 and the specificity was 0.49 by using the global gamma analysis. The sensitivity was 0.7 and the specificity was 0.46 by using the local gamma analysis, suggesting that the sensitivity and the specificity were more balanced under the 2%/2 mm criterion. Conclusions Application of the optimal thresholds in the verification of VMAT plans can maintain the balance between the sensitivity and specificity, prevent the harm of clinically unacceptable plans to patients to certain extent and reduce the probability of increasing the daily work load for physicists due to the misjudgement of clinically acceptable plans. Key words: Volumetric modulated arc-therapy; Plan verification; Receiver operating characteristic curve; Optimal threshold

A Collimator Setting Optimization Algorithm for Dual-Arc Volumetric Modulated Arc Therapy in Pancreas Stereotactic Body Radiation Therapy.

Purpose:To optimize collimator setting to improve dosimetric quality of pancreas volumetric modulated arc therapy plan for stereotactic body radiation therapy.Materials and Methods:Fifty-five volumetric modulated arc therapy cases in stereotactic body radiation therapy of pancreas were retrospectively included in this study with internal review board approval. Different from the routine practice of initializing collimator settings with a template, the proposed algorithm simultaneously optimizes the collimator angles and jaw positions that are customized to the patient geometry. Specifically, this algorithm includes 2 key steps: (1) an iterative optimization algorithm via simulated annealing that generates a set of potential collimator settings from 39 cases with pancreas stereotactic body radiation therapy, and (2) a multi-leaf collimator modulation scoring system that makes the final decision of the optimal collimator settings (collimator angles and jaw positions) based on organs at risk sparing criteria. For validation, the other 16 cases with pancreas stereotactic body radiation therapy were analyzed. Two plans were generated for each validation case, with one plan optimized using the proposed algorithm (Planopt) and the other plan with the template setting (Planconv). Each plan was optimized with 2 full arcs and the same set of constraints for the same case. Dosimetric results were analyzed and compared, including target dose coverage, conformity, organs at risk maximum dose, and modulation complexity score. All results were tested by Wilcoxon signed rank tests, and the statistical significance level was set to .05.Results:Both plan groups had comparable target dose coverage and mean doses of all organs at risk. However, organs at risk (stomach, duodenum, large/small bowel) maximum dose sparing (D0.1 cc and D0.03 cc) was improved in Planopt compared to Planconv. Planopt also showed lower modulation complexity score, which suggests better capability of handling complex shape and sparing organs at risk .Conclusions:The proposed collimator settings optimization algorithm successfully improved dosimetric performance for dual-arc pancreas volumetric modulated arc therapy plans in stereotactic body radiation therapy of pancreas. This algorithm has the capability of immediate clinical application.

Adaptive Imaging Versus Periodic Surveillance for Intrafraction Motion Management During Prostate Cancer Radiotherapy.

Objective:To evaluate the benefits of adaptive imaging with automatic correction compared to periodic surveillance strategies with either manual or automatic correction.Methods:Using Calypso trajectories from 54 patients with prostate cancer at 2 institutions, we simulated 5-field intensity-modulated radiation therapy and dual-arc volumetric-modulated arc therapy with periodic imaging at various frequencies and with continuous adaptive imaging, respectively. With manual/automatic correction, we assumed there was a 30/1 second delay after imaging to determine and apply couch shift. For adaptive imaging, real-time “dose-free” cine-MV images during beam delivery are used in conjunction with online-updated motion pattern information to estimate 3D displacement. Simultaneous MV-kV imaging is only used to confirm the estimated overthreshold motion and calculate couch shift, hence very low additional patient dose from kV imaging.Results:Without intrafraction intervention, the prostates could on average have moved out of a 3-mm margin for ∼20% of the beam-on time after setup imaging in current clinical situation. If the time interval from the setup imaging to beam-on can be reduced to only 30 seconds, the mean over-3 mm percentage can be reduced to ∼7%. For intensity-modulated radiation therapy simulation, with manual correction, 110 and 70 seconds imaging periods both reduced the mean over-3 mm time to ∼4%. Automatic correction could give another 1% to 2% improvement. However, with either manual or automatic correction, the maximum patient-specific over-3 mm time was still relatively high (from 6.4% to 12.6%) and those patients are actually clinically most important. In contrast, adaptive imaging with automatic intervention significantly reduced the mean percentage to 0.6% and the maximum to 2.7% and averagely only ∼1 kV image and ∼1 couch shift were needed per fraction. The results of volumetric-modulated arc therapy simulation show a similar trend to that of intensity-modulated radiation therapy.Conclusions:Adaptive continuous monitoring with automatic motion compensation is more beneficial than periodic imaging surveillance at similar or even less imaging dose.

Evaluation of optimization workflow using design of experiment (DoE) for various field configurations in volumetric-modulated arc therapy

PurposeIn volumetric-modulated arc therapy (VMAT), field configurations such as couch or arc angles are defined manually or using a template. A field configuration is reselected through trial-and-error in the case of undesirable resultant planning. To efficiently plan for desirable quality, configurations should be assessed before dose calculation. Design of experiments (DoE) is an optimization technique that efficiently reveals the influence of inputs on outputs. We developed an original tool using DoE to determine the field configuration selection and evaluated the efficacy of this workflow for clinical practice. MethodsComputed-tomography scans of 17 patients and target structures were acquired retrospectively from a brain tumor treated using a dual-arc VMAT plan. The configurations of the couch, arc, collimator angles, field sizes, and beam energy were determined using DoE. The resultant dose distributions obtained using the DoE-selected configuration were compared with the clinical plan. ResultsThe averaged differences between the DoE and clinical plan for 17 patients of doses to 50% of the planning target volume (PTV-D50%), Brain-D60%, Brain-D30%, Brain stem-D1%, Left eye-D1%, Right eye-D1%, Optic nerve-D1%, and Chiasm-D1% were 0.2 ± 0.5%, −1.0 ± 4.6%, 1.7 ± 3.5%, −2.5 ± 6.7%, −0.2 ± 4.9%, −1.2 ± 3.6%, −2.8 ± 7.3%, and −2.1 ± 5.7%, respectively. ConclusionsOur optimization workflow obtained using DoE for various field configurations provided the same or slightly superior plan quality compared with that created by experts. This process is feasible for clinical practice and will efficiently improve treatment quality while removing the influence of the planner’s experience.

Quality assurance of volumetric-modulated arc therapy head and neck cancer treatment using PRESAGE® dosimeter

AbstractBackgroundAccurate three-dimensional dosimetry is essential in modern radiotherapy techniques such as volumetric-modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT). In this research work, the PRESAGE® dosimeter was used as quality assurance (QA) tool for VMAT planning for head and neck (H&amp;N) cancer.Material and methodComputer tomography (CT) scans of an Image Radiation Oncology Core (IROC) H&amp;N anthropomorphic phantom with both IROC standard insert and PRESAGE® insert were acquired separately. Both CT scans were imported into the Pinnacle (9.4 version) TPS for treatment planning, where the structures [planning target volume (PTV), organs at risk) and thermoluminescent detectors (TLDs) were manually contoured and used to optimise a VMAT plan. Treatment planning was done using VMAT (dual arc: 182°–178°, 178°–182°). Beam profile comparisons and gamma analysis were used to quantify agreement with film, PRESAGE® measurement and treatment planning system (TPS) calculated dose distribution.ResultsThe average ratio of TLD measured to calculated doses at the four PTV locations in the H&amp;N phantom were between 0·95 to 0·99 for all three VMAT deliveries. Dose profiles were taken along the left–right, the anterior–posterior and superior–inferior axes, and good agreement was found between the PRESAGE® and Pinnacle profile. The mean value of gamma results for three VMAT deliveries in axial and sagittal planes were found to be 94·24 and 93·16% when compared with film and Pinnacle, respectively. The average values comparing the PRESAGE® results and dose values calculated on Pinnacle were observed to be 95·29 and 94·38% in the said planes, respectively, using a 5%/3 mm gamma criteria.ConclusionThe PRESAGE® dose measurements and calculated dose of pinnacle show reasonable agreement in both axial and sagittal planes for complex dual arc VMAT treatment plans. In general, the PRESAGE® dosimeter is found to be a feasible QA tool of VMAT plan for H&amp;N cancer treatment.

Volumetric modulated arc therapy of head-and-neck cancer on a fast-rotating O-ring linac: Plan quality and delivery time comparison with a C-arm linac

Background and purposeLinac improvements in gantry speed, leaf speed and dose rate may increase the time-efficiency of volumetric modulated arc therapy (VMAT) delivery. The plan quality achievable with faster VMAT however remains to be investigated. In this study, a fast-rotating O-ring linac with fast-moving leaves is compared with a C-arm linac in terms of plan quality and delivery time for VMAT of head-and-neck cancer (HNC). Material and methodsFor 30 patients with HNC, treatment planning was performed using dual-arc (HA2) and triple-arc (HA3) VMAT on a Halcyon fast-rotating O-ring linac and using dual-arc VMAT on a TrueBeam C-arm linac (TB2). Target coverage metrics and complication probabilities were compared. Plan delivery was verified using 3%/3 mm gamma-index analysis of helical diode array measurements. Volumetric image acquisition and plan delivery times were compared. ResultsAll studied VMAT-techniques fulfilled the target coverage objectives. D2% to the boost volume was higher for HA2 (median 103.7%, 1st–3rd quartile [103.5%;104.0%]) and HA3 (103.2% [103.0%;103.7%)] than for TB2 (102.6% [102.3%;103.0%)], resulting in an increased boost target dose heterogeneity for HA2 and HA3. Complication probabilities were comparable between HA2 and TB2, while HA3 showed a xerostomia probability reduction (0.8% [0.2%;1.8%]) and dysphagia probability reduction (1.0% [0.2%;1.8%]) compared with TB2. Gamma-index agreement scores were never below 93.0% for HA2, HA3 and TB2. Volumetric imaging and plan delivery time was shorter for HA2 (1 m 24 s ± 1 s) and HA3 (1 m 54 s ± 1 s) than for TB2 (2 m 47 s ± 1 s). ConclusionFor VMAT of HNC, the fast-rotating O-ring linac at least maintains the plan quality of two arcs on a C-arm linac while reducing the image acquisition and plan delivery time.

Automated VMAT planning for postoperative adjuvant treatment of advanced gastric cancer

BackgroundPostoperative/adjuvant radiotherapy of advanced gastric cancer involves a large planning target volume (PTV) with multi-concave shapes which presents a challenge for volumetric modulated arc therapy (VMAT) planning. This study investigates the advantages of automated VMAT planning for this site compared to manual VMAT planning by expert planners.MethodsFor 20 gastric cancer patients in the postoperative/adjuvant setting, dual-arc VMAT plans were generated using fully automated multi-criterial treatment planning (autoVMAT), and compared to manually generated VMAT plans (manVMAT). Both automated and manual plans were created to deliver a median dose of 45 Gy to the PTV using identical planning and segmentation parameters. Plans were evaluated by two expert radiation oncologists for clinical acceptability. AutoVMAT and manVMAT plans were also compared based on dose-volume histogram (DVH) and predicted normal tissue complication probability (NTCP) analysis.ResultsBoth manVMAT and autoVMAT plans were considered clinically acceptable. Target coverage was similar (manVMAT: 96.6 ± 1.6%, autoVMAT: 97.4 ± 1.0%, p = 0.085). With autoVMAT, median kidney dose was reduced on average by > 25%; (for left kidney from 11.3 ± 2.1 Gy to 8.9 ± 3.5 Gy (p = 0.002); for right kidney from 9.2 ± 2.2 Gy to 6.1 ± 1.3 Gy (p < 0.001)). Median dose to the liver was lower as well (18.8 ± 2.3 Gy vs. 17.1 ± 3.6 Gy, p = 0.048). In addition, Dmax of the spinal cord was significantly reduced (38.3 ± 3.7 Gy vs. 31.6 ± 2.6 Gy, p < 0.001). Substantial improvements in dose conformity and integral dose were achieved with autoVMAT plans (4.2% and 9.1%, respectively; p < 0.001). Due to the better OAR sparing in the autoVMAT plans compared to manVMAT plans, the predicted NTCPs for the left and right kidney and the liver-PTV were significantly reduced by 11.3%, 12.8%, 7%, respectively (p ≤ 0.001). Delivery time and total number of monitor units were increased in autoVMAT plans (from 168 ± 19 s to 207 ± 26 s, p = 0.006) and (from 781 ± 168 MU to 1001 ± 134 MU, p = 0.003), respectively.ConclusionsFor postoperative/adjuvant radiotherapy of advanced gastric cancer, involving a complex target shape, automated VMAT planning is feasible and can substantially reduce the dose to the kidneys and the liver, without compromising the target dose delivery.

Comparison of planning quality and delivery efficiency between volumetric modulated arc therapy and dynamic intensity modulated radiation therapy for nasopharyngeal carcinoma with more than 4 prescribed dose levels

The aim of this study is to compare the planning quality and delivery efficiency between dynamic intensity modulated radiation therapy (d-IMRT) and dual arc volumetric modulated arc therapy (VMAT) systematically for nasopharyngeal carcinoma (NPC) patients with multi-prescribed dose levels, and to analyze the correlations between target volumes and plan qualities. A total of 20 patients of NPC with 4-5 prescribed dose levels to achieve simultaneous integrated boost (SIB) treated by sliding window d-IMRT in our department from 2014 to 2015 were re-planned with dual arc VMAT. All optimization objectives for each VMAT plan were as the same as the corresponding d-IMRT plan. The dose parameters for targets and organ at risk (OAR), the delivery time and monitor units (MU) in two sets of plans were compared respectively. The treatment accuracy was tested by three dimensional dose validation system. Finally, the correlations between the difference of planning quality and the volume of targets were discussed. The conform indexes (CIs) of planning target volumes (PTVs) in VMAT plans were obviously high than those in d-IMRT plans ( P < 0.05), but no significant correlations between the difference of CIs and the volume of targets were discovered ( P > 0.05). The target coverage and heterogeneity indexes (HIs) of PTV 1 and PGTV nd and PTV 3 in two sets of plans were consistent. The doses of PTV 2 decreased and HIs were worse in VMAT plans. VMAT could provide better spinal cord and brainstem sparing, but increase mean dose of parotids. The average number of MUs and delivery time for d-IMRT were 3.32 and 2.19 times of that for VMAT. The γ-index (3 mm, 3%) analysis for each plans was more than 97% in COMPASS ® measurement for quality assurance (QA). The results show that target dose coverages in d-IMRT and VMAT plans are similar for NPC with multi-prescribed dose levels. VMAT could improve the the CIs of targets, but reduce the dose to the target volume in neck except for PGTV nd. The biggest advantages of VMAT over d-IMRT are delivery efficiency and QA.