Intensity-modulated Arc Therapy Plans Research Articles

A Dosimetric Comparative Study of Carbon-Ion Radiotherapy Versus X-ray Volumetric Modulated Arc Therapy for Stage III Non-Small-Cell Lung Cancer.

Compared to photon beam, carbon-ion radiotherapy (CIRT) has both physical and biological advantages. To examine whether two-dimensional (2D) CIRT is dosimetrically superior to photon beam volume-modulated arc therapy (VMAT) in protecting the normal tissues for stage III non-small-cell lung cancer (NSCLC). A retrospective study was conducted. Thirteen patients with stage III NSCLC treated in our center with curative CIRT and a sham photon beam VMAT treatment planning with the same normal tissue dose constraints were included for analysis. Target dose distributions and the homogeneity index (HI) within the planning target volumes were compared. Both CIRT and VMAT plans have good tumor coverage with no significant differences in D98, D95, and D50 of Planning target volume 1 (PTV1) between the two plans. The HIs between the two plans are similar. The HI of PTV2 is superior in the CIRT plan (CIRT vs. VMAT: 0.08 vs. 0.16, P < 0.05). In general, CIRT results in a lower dose of the organ-at-risk (OAR) than the photon plans. The V5, V10, V20, V30, V40, and Dmean of the contralateral lung in the CIRT plan are significantly lower than that of the photon VMAT. For the ipsilateral lung, the V5 of CIRT is significantly lower. The CIRT also had significantly lower spinal cord Dmax, esophageal Dmean and V50, V10 and V30 of bone, and V50 of the trachea and bronchial tree. Compared with photon VMAT, 2D-CIRT using the passive beam scanning technique significantly reduces the radiation dose to the OARs in curative radiotherapy of stage III NSCLC, suggesting a better protection of the normal tissues.

Validation of a 2D dose verification systemfor intensity-modulated arc therapy

ObjectiveThe measured dose was shown to be dependent on the angle of beam incidence and influenced by couch absorption when a 2D detector was used in a stationary phantom. The use of a 2D array (MatriXX) in combination with a solid water phantom (RW3) dose verification system was explored, which could take into account the couch absorption influences, generate correction factors (CFs) for each detector element, and also calibrate the measured dose for accurate validation of intensity-modulated arc therapy (IMAT) treatment plans. MethodsBased on the introduction of a homogeneous treatment bed model in the Monaco treatment planning system, CFs(θ) were constructed for all incidence angles using 6 MV photon lines in a 28 cm × 28 cm field for MatriXX at different field incidence angles (0°–360°) as a relative ratio of simulated and measured values. The accuracy of the 2D array in combination with the solid water phantom (MatriXX/RW3) was systematically investigated by verifying 12 IMAT plans with and without CFs. In addition, the resulting assessments were evaluated by 40 additional IMAT plans of different tumor sites, using the COMPASS three-dimensional (3D) dose validation device measurements as a benchmark. ResultsAfter correction based on CFs(θ), the effect of the mean pass rates (3%/3 mm) of the MatriXX 2D array for 12 IMAT plan QA can be seenan explicit improvement of 6.1% was observed with the CFs(θ). The average pass rate increased from 92.0% to 98.1%, and the additional 40 IMAT plans QA γ(3mm/3%) matched well between COMPASS and the measurements for MatriXX/RW3, with CFs(θ)'s of 98.4 ± 1.5 vs. 99.1 ± 0.9 for the phantom plans. For different tumor sites, the cervical, thoracic, and abdominal cases for the 3D COMPASS validation devices were 97.9 ± 1.5 vs. 99.4 ± 0.3, 99.1 ± 0.9 vs. 98.6 ± 1.6, and 98.7 ± 0.9 vs. 99.3 ± 0.7, respectively, with P = 0.051, 0.420, and 0.175. For head tumors, the 2D MatriXX validation pass rate was slightly lower than 3D COMPASS (97.7 ± 2.0 vs. 99.2 ± 0.5, P = 0.048). ConclusionsThe combination of MatriXX with the solid water RW3 phantom and CFs(θ)'s incorporation of the main couch model (iBEAM evo Couchtop EP) proved to be a fast and reliable method for pre-treatment verification of arc therapy with sufficient accuracy. Slight deviations were found for patients with head tumors treated with the treatment bed extension plate assembly iBEAM® evo Extension 415. These could be minimized by constructing the extension plate couch model and then reconstructing the MatriXX/RW3 calibration factor.

Comparative dosimetric and radiobiological assessment of left-sided whole breast and regional nodes with advanced radiotherapy techniques.

The aim of this study was to analyze the dosimetric and radiobiologic differences of the left-sided whole breast and regional nodes in intensity-modulated radiotherapy (IMRT), volume-modulated arc therapy (VMAT), and helical tomotherapy (HT). The IMRT, VMAT, and HT plans in this study were generated for thirty-five left-sided breast cancer patients after breast-conserving surgery (BCS). The planning target volume (PTV) included the whole breast and supraclavicular nodes. PTV coverage, homogeneity index (HI), conformity index (CI), dose to organs at risk (OARs), secondary cancer complication probability (SCCP), and excess absolute risk (EAR) were used to evaluate the plans. Compared to IMRT, the VMAT and HT plans resulted in higher PTV coverage and homogeneity. The VMAT and HT plans also delivered a lower mean dose to the ipsilateral lung (9.19±1.36 Gy, 9.48±1.17 Gy vs. 11.31±1.42 Gy) and heart (3.99±0.86 Gy, 4.48±0.62 Gy vs. 5.53±1.02 Gy) and reduced the V5Gy, V10Gy, V20Gy, V30Gy, and V40Gy of the ipsilateral lung and heart. The SCCP and EAR for the ipsilateral lung were reduced by 3.67%, 3.09% in VMAT, and 22.18%, 19.21% in HT, respectively. While were increased for the contralateral lung and breast. This study showed that VMAT plans provide a more homogeneous dose distribution to the PTV, minimizing exposure to ipsilateral structures and significantly reducing SCCP and EAR, and slightly increasing dose to contralateral structures. Overall, the VMAT plan can be considered a beneficial technique for BCS patients whose PTV includes the whole breast and regional nodes.

Stereotactic Arrhythmia Radioablation in Europe—Treatment Planning Benchmark Results of the STOPSTORM.eu Consortium

<h3>Purpose/Objective(s)</h3> In patients with refractory ventricular tachycardia (VT), Stereotactic Arrhythmia Radioablation (STAR) showed promising results for otherwise untreatable patients. The STOPSTORM.eu project coordinates European efforts to clinically validate STAR and to refine protocols and guidelines. The aim of this work is to present the current clinical STAR practice in Europe based on three examples as baseline for further optimization. <h3>Materials/Methods</h3> Target Volumes (TV) and Organs-at-Risk (OAR) were generated from previous consortium benchmarks and consensus definitions for three well-selected STAR cases. Planning Target Volumes (PTV) were generated based on three different compensation strategies for cardiac and respiratory motion and overlapped/close OARs like coronary arteries or stomach. The STOPSTORM.eu members were asked to generate single fraction treatment plans with 25 Gy dose prescription based on ICRU report 91 for each case based on their STAR clinical practice through multi-disciplinary discussion. Resulting dose distributions were analyzed independently using a customized platform for multi-center treatment planning studies. <h3>Results</h3> By November 2021, 20 centers submitted 22, 23 and 22 treatment plans for case 1, 2 and 3, respectively, mostly (75% of plans) using Intensity Modulated Arc Therapy (IMAT) with 6 MeV FFF beams (73% of the IMAT plans) among other commonly used techniques for stereotactic radiotherapy. Presently, used guidelines for STAR treatment planning and OAR dose limits vary greatly and are mostly based on the AAPM TG-101 report and RAVENTA trial publication. As a major finding, 73% of the submitted plans showed close OAR sparing overachieving high PTV coverage (Figure 1 and Table 1) arguing that lower doses may also result in clinical efficiency. Cases 1 and 3 dose distributions (referenced as A. and C. in Figure 2) highlighted how OARs sparing also resulted in heavy PTV under dosing for some participants. <h3>Conclusion</h3> From this first STOPSTORM.eu multi-center/multi-platform treatment planning benchmark study we obtained important information concerning current clinical practice from major European centers performing Stereotactic Arrhythmia Radioablation for VT. With the strongly varying approaches of the centers as basis, the key task for the STOPSTORM.eu project is to find consensus, aiming to harmonize and optimize STAR practice in Europe.

Treatment Planning Comparison of Intensity Modulated Arc Therapy and CyberKnife Techniques in Early Stage Glottic Larynx Radiotherapy

We aimed to compare two radiotherapy techniques (the robotic-based linear accelerator Stereotactic Body Radiotherapy (SBRT) and linear accelerator-based Intensity Modulated Arc Therapy (IMAT)) dosimetrically on Early Glottic Larynx Cancerx (EGL) treatment plans in the terms of target volume and critical organ doses. The computerized tomography (CT) images of 15 patients treated with EGL diagnosis were used retrospectively. The Planning Target Volumes (PTV) was generated with a margin of 0.5 cm from the laryngeal volume. The PTV dose was defined as 45 Gy delivered in 10 fractions within each of treatment plans. At least 95% of PTV treatment volumes (D95%) were to receive the treatment dose. The average PTV volume was 95.56 cm3 (range: 68.8 cm3 - 142.6 cm3). The average D98%, D2% and Dmean values of PTV were lower in IMAT plan than in CK plan. In CK plans, the mean of the spinal cord maximum dose (Dmax) for all patients was statistically significantly lower than in IMAT plans. Dmax and Dmean values for the right and left carotid arteries was significantly lower in IMAT plans. Also, the Dmean value of thyroid gland was significantly lower in IMAT plans. Our dosimetric comparison study made using images of 15 EGL cancer patients shows that the desired critria for the critical organ doses can not reached with CK plans, especially when the treatment volume is large.

Stereotactic arrhythmia radioablation in europe: treatment planning benchmark results of the STOPSTORM consortium

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): EU Background In patients with refractory ventricular tachycardia (VT), STereotactic Arrhythmia Radioablation (STAR) showed promising results for otherwise untreatable patients [1]. The STOPSTORM.eu project coordinates European efforts to clinically validate STAR and to refine protocols and guidelines to ensure treatment harmonization. Purpose The aim of this work is to present the current clinical STAR practise in Europe based on three examples as baseline for further optimization. Methods Target Volumes (TV) and Organs-at-Risk (OAR) were generated from previous consortium benchmarks and consensus definitions for three well-selected STAR cases [1]. Planning Target Volumes (PTV) were generated based on three different compensation strategies for cardiac and respiratory motion [2] and overlapped close OAR like coronary arteries or stomach in some areas. The STOPSTORM.eu members were asked to generate single fraction treatment plans with 25 Gy dose prescription based on ICRU report 91 for each case based on their clinical practise and preferences for STAR including multi-disciplinary discussion and plan approval. Resulting dose distributions were analysed independently using a customized platform for multi-center treatment planning studies [3]. Results Twenty centers submitted 22, 23 and 22 treatment plans for case 1, 2 and 3, respectively, mostly (75% of all plans) using Intensity Modulated Arc Therapy (IMAT) with 6 MeV FFF beams (73% of the IMAT plans) among other commonly used techniques for stereotactic radiotherapy. At this current stage, used guidelines for STAR treatment planning and OAR dose limits vary greatly and are mostly based on the AAPM TG-101 report or the RAVENTA trial publication [4]. As a major finding, 73% of all plans submitted preferred close OAR sparing over achieving high PTV coverage arguing that lower doses down to 20 Gy may also result in clinical efficiency as recently suggested [5]. As a minor finding, 80% of the centers chose to override strong artifact regions originating from e.g. left ventricular assist devices. Conclusion From this first STOPSTORM.eu multi-center multi-platform treatment planning benchmark study we obtained important information concerning current clinical preference and practise from major European centers performing STereotactic Arrhythmia Radioablation for VT. Using the individual and strongly varying approaches of the centers, the key task for the STOPSTORM.eu project is now to find consensus in order to harmonize and optimize STAR practise in Europe.

Dosimetric Comparison of Helical Tomotherapy, Volume-Modulated Arc Therapy, and Fixed-Field Intensity-Modulated Radiation Therapy in Locally Advanced Nasopharyngeal Carcinoma.

ObjectiveTo compare the dosimetric parameters of different radiotherapy plans [helical tomotherapy (HT), volume-modulated arc therapy (VMAT), and fixed-field intensity-modulated radiation therapy (FF-IMRT)] for locally advanced nasopharyngeal carcinoma (NPC).MethodsA total of 15 patients with locally advanced NPC were chosen for this retrospective analysis and replanned for HT, VMAT, and FF-IMRT. The prescribed planning target volume (PTV) dose for the primary tumor and metastatic lymph nodes was 70 Gy (2.12 Gy/fraction, delivered over 33 fractions). The prescribed PTV dose for the high-risk subclinical region was 59.4 Gy (1.8 Gy/fraction, delivered over 33 fractions). The dosimetric parameters of the PTV and organs at risk (OARs) and the efficiency of radiation delivery were assessed and compared using the paired-samples t-test.ResultsCompared with VMAT and FF-IMRT plans, HT plans significantly improved the mean conformity index (CI) and homogeneity index (HI). The HT plans reduced the maximum doses delivered to OARs, such as the brainstem, spinal cord, and optic nerves, and significantly reduced the volume delivered to the high-dose region, especially when examining the V 30 value of the parotid glands. However, VMAT reduced the treatment time and improved the efficiency of radiation delivery compared with HT.ConclusionsFor locally advanced NPC, the results showed that HT and VMAT possessed better target homogeneity and conformity, reducing the dose delivered to OARs compared with conventional FF-IMRT, with HT achieving the best effect. Among the techniques studied, VMAT had the shortest radiation delivery time. The results of this study can provide guidance for the selection of appropriate radiation technologies used to treat patients with locally advanced NPC who are undergoing concurrent chemoradiotherapy.

Investigation of Predictors to Achieve Acceptable Lung Dose in T-Shaped Upper and Middle Esophageal Cancer With IMRT and VMAT.

PurposeThe purpose of this study is to investigate whether there are predictors and cutoff points that can predict the acceptable lung dose using intensity-modulated radiation therapy (IMRT) and volume-modulated arc therapy (VMAT) in radiotherapy for upper ang middle esophageal cancer.Material and MethodsEighty-two patients with T-shaped upper-middle esophageal cancer (UMEC) were enrolled in this retrospective study. Jaw-tracking IMRT plan (JT-IMRT), full-arc VMAT plan (F-VMAT), and pactial-arc VMAT plan (P-VMAT) were generated for each patient. Dosimetric parameters such as MLD and V20 of total lung were compared among the three plannings. Ten factors such as PCTVinferior length and PCTVinferior length/total lung length were calculated to find the predictors and cutoff points of the predictors. All patients were divided into two groups according to the cutoff points, and the dosimetric differences between the two groups of the three plans were compared. ANOVA, receiver operating characteristic (ROC) analysis, and Mann–Whitney U-test were performed for comparisons between datasets. A p <0.05 was considered statistically significant.ResultThe quality of the targets of the three plannings was comparable. The total lung dose in P-VMAT was significantly lower than that in JT IMRT and F-VMAT. Monitor unit (MU) of F-VMAT and P-VMAT was significantly lower than that of JT IMRT. ROC analysis showed that among JT IMRT, F-VMAT, and P-VMAT, PCTVi-L, and PCTVi-L/TLL had diagnostic power to predict the suitability of RT plans according to lung dose constraints of our department. For JT IMRT, the cutoff points of PCTVi-L and PCTVi-L/TLL were 16.6 and 0.59. For F-VMAT, the cutoff points of PCTVi-L and PCTVi-L/TLL were 16.75 and 0.62. For P-VMAT, the cutoff points of PCTVi-L and PCTVi-L/TLL were 15.15 and 0.59. After Mann–Whitney U-test analysis, it was found that among the three plannings, the group with lower PCTVi-L and PCTVi-L/TLL could significantly reduce the dose of total lung and heart (p <0.05).ConclusionPCTVi-L <16.6 and PCTVi-L/TLL <0.59 for JT IMRT, PCTVi-L <16.75 and PCTVi-L/TLL <0.62 for F-VMAT and PCTVi-L <15.15, and PCTVi-L/TLL <0.59 for P-VMAT can predict whether patients with T-shaped UMEC can meet the lung dose limits of our department.

Effect of isocenter deviation on volume modulated arc therapy plan results and gamma passing rate in the treatment of cervical cancer.

BackgroundIsocenter deviation, often induced by small displacements of both the device and the patient, is a common error seen in radiotherapy. In this study, we investigated the impact of isocenter deviation on the results of the volumetric modulated arc therapy (VMAT) plan and dosimetric verification gamma passing rate in the treatment of cervical cancer.MethodsThe clinical data of 15 patients with cervical cancer who were treated with VMAT were retrospectively collected and analyzed. In this study, the isocenter site modification method was adopted. The VMAT plan with isocenter deviation adjustment was set as the experimental group, while the original plan was set as the control group. The impact of isocenter deviation on the results of the VMAT plan and dosimetric verification gamma passing rate was analyzed. Applying gamma analysis with different test criterions, the impact of isocenter deviation on the gamma passing rates was evaluated, and the sensitivity of different test criterions in identifying isocenter deviation was also analyzed.ResultsThere was a significant difference in the average dose in the target area between experimental group and control group (P<0.05). In organs at risk (OAR) terms, isocenter deviations also caused significant differences in dose parameters between the two groups. Except that there was no significant difference in the rectal V40 between two groups when the isocenter deviation was greater than 3 mm in the y axis direction. With the increase in the isocenter deviation, there was a trend towards decreased gamma passing rates with different analysis criterions in the experimental group. The 2 mm/2% standard had the highest sensitivity for identifying isocenter deviation.ConclusionsIsocenter deviation has significant effects on the results of the volume rotation intensity modulation plan and dosimetric verification gamma passing rates in the treatment of cervical cancer. When the isocenter deviation was less than 3 mm, a higher gamma passing rate (>90%) could also be obtained under the condition of the 3 mm/3% test criterions. It is recommended that the 2 mm/2% test standard should be utilized in clinical practice.

Comparative dosimetrical analysis of intensity-modulated arc therapy, CyberKnife therapy and image-guided interstitial HDR and LDR brachytherapy of low risk prostate cancer.

The objective of the study was to dosimetrically compare the intensity-modulated-arc-therapy (IMAT), Cyber-Knife therapy (CK), single fraction interstitial high-dose-rate (HDR) and low-dose-rate (LDR) brachytherapy (BT) in low-risk prostate cancer. Treatment plans of ten patients treated with CK were selected and additional plans using IMAT, HDR and LDR BT were created on the same CT images. The prescribed dose was 2.5/70 Gy in IMAT, 8/40 Gy in CK, 21 Gy in HDR and 145 Gy in LDR BT to the prostate gland. EQD2 dose-volume parameters were calculated for each technique and compared. EQD2 total dose of the prostate was significantly lower with IMAT and CK than with HDR and LDR BT, D90 was 79.5 Gy, 116.4 Gy, 169.2 Gy and 157.9 Gy (p < 0.001). However, teletherapy plans were more conformal than BT, COIN was 0.84, 0.82, 0.76 and 0.76 (p < 0.001), respectively. The D2 to the rectum and bladder were lower with HDR BT than with IMAT, CK and LDR BT, it was 66.7 Gy, 68.1 Gy, 36.0 Gy and 68.0 Gy (p = 0.0427), and 68.4 Gy, 78.9 Gy, 51.4 Gy and 70.3 Gy (p = 0.0091) in IMAT, CK, HDR and LDR BT plans, while D0.1 to the urethra was lower with both IMAT and CK than with BTs: 79.9 Gy, 88.0 Gy, 132.7 Gy and 170.6 Gy (p < 0.001). D2 to the hips was higher with IMAT and CK, than with BTs: 13.4 Gy, 20.7 Gy, 0.4 Gy and 1.5 Gy (p < 0.001), while D2 to the sigmoid, bowel bag, testicles and penile bulb was higher with CK than with the other techniques. HDR monotherapy yields the most advantageous dosimetrical plans, except for the dose to the urethra, where IMAT seems to be the optimal modality in the radiotherapy of low-risk prostate cancer.

Dosimetric evaluation of synthetic CT image generated using a neural network for MR-only brain radiotherapy.

Purpose and backgroundThe magnetic resonance (MR)‐only radiotherapy workflow is urged by the increasing use of MR image for the identification and delineation of tumors, while a fast generation of synthetic computer tomography (sCT) image from MR image for dose calculation remains one of the key challenges to the workflow. This study aimed to develop a neural network to generate the sCT in brain site and evaluate the dosimetry accuracy.Materials and methodsA generative adversarial network (GAN) was developed to translate T1‐weighted MRI to sCT. First, the "U‐net" shaped encoder‐decoder network with some image translation‐specific modifications was trained to generate sCT, then the discriminator network was adversarially trained to distinguish between synthetic and real CT images. We enrolled 37 brain cancer patients acquiring both CT and MRI for treatment position simulation. Twenty‐seven pairs of 2D T1‐weighted MR images and rigidly registered CT image were used to train the GAN model, and the remaining 10 pairs were used to evaluate the model performance through the metric of mean absolute error. Furthermore, the clinical Volume Modulated Arc Therapy plan was calculated on both sCT and real CT, followed by gamma analysis and comparison of dose‐volume histogram.ResultsOn average, only 15 s were needed to generate one sCT from one T1‐weighted MRI. The mean absolute error between synthetic and real CT was 60.52 ± 13.32 Housefield Unit over 5‐fold cross validation. For dose distribution on sCT and CT, the average pass rates of gamma analysis using the 3%/3 mm and 2%/2 mm criteria were 99.76% and 97.25% over testing patients, respectively. For parameters of dose‐volume histogram for both target and organs at risk, no significant differences were found between both plans.ConclusionThe GAN model can generate synthetic CT from one single MRI sequence within seconds, and a state‐of‐art accuracy of CT number and dosimetry was achieved.

Pencil Beam Scanning Proton Therapy Case Selection for Paediatric Abdominal Neuroblastoma: Effects of Tumour Location and Bowel Gas

AimsPencil beam scanning (PBS) proton therapy is an increasingly used radiation modality for childhood malignancies due to its ability to minimise dose to surrounding organs. However, the dosimetry is extremely sensitive to anatomical and density changes. The aims of this study were to investigate if there is a dosimetric benefit or detriment with PBS for paediatric abdominal neuroblastoma, assess gastrointestinal air variability and its dosimetric consequences, plus identify if there are factors that could assist case selection for PBS referral. Materials and methodsTwenty neuroblastoma cases were double-planned with PBS and intensity-modulated arc therapy (IMAT). Cases were divided into unilateral, midline unilateral and midline bilateral locations in relation to the kidneys. Plans were recalculated after the gastrointestinal volume was simulated as air (Hounsfield Units –700) and water (Hounsfield Units 0), then compared with nominal plans (recalculated – nominal, ΔD). Forty-three weekly cone beam computed tomography scans were analysed to quantify gastrointestinal air variability during treatment. ResultsPBS reduced the mean dose to normal tissues at all tumour locations, particularly unilateral tumours. However, 15% had better dosimetry with IMAT, all of which were midline tumours. Increased gastrointestinal air caused significant compromises to PBS versus IMAT plans for midline tumours [median/maximum ΔD95% clinical target volume (CTV) –2.4%/–15.7% PBS versus 1.4%/0% IMAT, P = 0.003], whereas minimal impact was observed for unilateral tumours (ΔD95% CTV –0.5%/–1.9% PBS versus 0.5%/–0.5% IMAT, P = 0.008). D95% CTV was significantly decreased in PBS plans if planning target volume (PTV) ≥400 cm3 (median –4.1%, P = 0.001) or PTV extension ≥60% anterior to vertebral body (–2.1%, P = 0.002). A larger variation in gastrointestinal air was observed in patients treated under general anaesthesia (median 38.4%) versus awake (11.5%); P = 0.004. ConclusionIn this planning study, tumours at the unilateral location consistently showed improved dose reductions to normal tissue with minimal dose degradation from increased gastrointestinal air with PBS plans. Tumour location, PTV volume and anterior extension of PTV are useful characteristics in facilitating patient selection for PBS.

Effect of the rotation errors on the γ pass rate of volume-modulated arc therapy plan in rectal cancer.

To study the effect of rotation errors on the γ pass rate of volume-modulated arc therapy (VMAT) plan in rectal cancer based on the ArcCheck phantom. CT data from 20 rectal cancer patients underwent VMRT were selected randomly for this study. Targeting areas were selected, and clinical radiotherapy and validation plans were formulated. ArcCheck model was selected to validate the radiotherapy plans. The effect of the rotation errors on the dosimetric verification for VMAT in rectal cancer was simulated and analyzed with ArcCheck model software. When there was no rotation errors, the γ pass rate of VMRT plans was more than 95%. When the absolute rotation angle was less than or equal to 1°, the γ pass rate of VMAT plans was more than 90%, meeting the clinical requirements. When the absolute rotation angle was greater than 1°, the γ pass rate was less than 90%, which did not meet clinical requirements. The rotation errors affect the γ pass rate of VMAT plans. The larger the rotation angle, the lower the γ pass rate. It meets clinical requirements when the rotation error is less than or equal to 1°.

Comparison of nodal irradiation dose using radiotherapy for patients with thoracic esophageal cancer.

The present study aimed to compare incidental nodal irradiation (INI) doses using volume-modulated arc therapy (VMAT), 5-field intensity-modulated radiotherapy (5F-IMRT) and 3D-conformal radiotherapy (3D-CRT) treatment plans for patients with thoracic esophageal cancer (EC). A total of 15 patients with thoracic EC were selected for participation between October 2016 and July 2017 at the Hangzhou Cancer Hospital. Regional lymph nodal stations were contoured according to 3D CT-based images of the Japan Esophageal Society Guidelines. All patients were treated with 60 Gy using VMAT, 5F-IMRT and 3D-CRT plans. Dose-volume histograms of planning target volume (PTV), lung, heart, spinal cord and incidental nodal irradiation were compared between the three plans. 5F-IMRT was superior in PTV_V95% (the volume of the PTV receiving 95% of the prescription dose, P=0.003) and the VMAT plan was best in terms of conformal index (P=0.005). V20 and V30 were reduced by 10.7-22.6% (P=0.002) and 12.8-21% (P=0.026), respectively, in normal lung tissue using the VMAT plan. 5F-IMRT demonstrated the lowest maximum dose (Dmax) for the spinal cord (P=0.037). For the INI, 3D-CRT exhibited the highest equivalent uniform dose (EUD) values for 106pre (P=0.014) and 106tb-L (P=0.03) in upper-thoracic EC. The mean EUD of all lymph nodal regions in middle-thoracic EC were >40 Gy in VMAT and 5F-IMRT plans; the VMAT plan had higher EUD values in lower-thoracic EC compared with 5F-IMRT, 3D-CRT plans for INI. VMAT were comparable to the 5F-IMRT plan with respect to dosimetric characteristics for planning and INI doses to thoracic nodal levels NO 105-112 are considerable for thoracic EC.

Knowledge-based planning for oesophageal cancers using a model trained with plans from a different treatment planning system

Background: This study aimed to evaluate knowledge-based volume modulated arc therapy (VMAT) plans for oesophageal cancers using a model trained with plans optimised with a different treatment planning system (TPS) and to compare lung dose sparing in two TPSs, Eclipse and RayStation.Materials and methods: A total of 64 patients with stage I–III oesophageal cancers were treated using hybrid VMAT (H-VMAT) plans optimised using RayStation. Among them, 40 plans were used for training the model for knowledge-based planning (KBP) in RapidPlan. The remaining 24 plans were recalculated using RapidPlan to validate the KBP model. H-VMAT plans calculated using RapidPlan were compared with H-VMAT plans optimised using RayStation with respect to planning target volume doses, lung doses, and modulation complexity.Results: In the lung, there were significant differences between the volume ratios receiving doses in excess of 5, 10, and 20 Gy (V5, V10, and V20). The V5 for the lung with H-VMAT plans optimised using RapidPlan was significantly higher than that of H-VMAT plans optimised using RayStation (p < .01), with a mean difference of 10%. Compared to H-VMAT plans optimised using RayStation, the V10 and V20 for the lung were significantly lower with H-VMAT plans optimised using RapidPlan (p = .04 and p = .02), with differences exceeding 1.0%. In terms of modulation complexity, the change in beam output at each control point was more constant with H-VMAT plans optimised using RapidPlan than with H-VMAT plans optimised using RayStation. The range of the change with H-VMAT plans optimised using RapidPlan was one third that of H-VMAT plans optimised using RayStation.Conclusion: Two optimisers in Eclipse and RayStation had different dosimetric performance in lung sparing and modulation complexity. RapidPlan could not improve low lung doses, however, it provided an appreciate intermediated doses compared to plans optimised with RayStation.

Gamma Evaluation with Octavius 4D Phantom for PreTreatment of Modern Radiotherapy Treatment Techniques

Purpose: In modern radiotherapy techniques such as intensity-modulated radiation therapy (IMRT) and volume modulated arc therapy (VMAT), the quality assurance (QA) process is vital. The goal of the study was to verify the treatment planning dose delivered during delivery of complex treatment plans. The QA standard is to perform patient-specific comparisons between planned doses and doses measured in a phantom. Materials and Methods: Ninety-five complex IMRT and VMAT plans for different pathologies planned using Eclipse treatment planning system (TPS). The Octavius 4D phantom has been used to verify patient specific quality assurance of all VMAT plans calculating with different algorithms. Conclusion: Overall, good agreement was observed between measured and calculated doses in most cases with gamma values above 1 in >95% of measured points in volumetric 3D analysis and 1 in >90% in 2D analysis. The Octavius 4D phantom is an effective and efficient method for patient specific QA.

Comparative analysis of image-guided adaptive interstitial brachytherapy and intensity-modulated arc therapy versus conventional treatment techniques in cervical cancer using biological dose summation.

PurposeTo compare image-guided adaptive interstitial brachytherapy (BT) and intensity-modulated arc therapy (IMAT) with conventional treatment techniques in cervical cancer using an alternative biological dose summation method.Material and methodsInitially, 21 interstitial BT and IMAT plans of patients with cervical cancer were included and additional plans were created (inverse optimized interstitial, optimized intracavitary, non-optimized intracavitary BT plans, and conformal external beam radiotherapy [EBRT]). The most exposed volume of critical organs in BT were identified manually on EBRT CT images. Biological total doses (EQD2) were calculated and compared between each combination of BT and EBRT plans. This method was compared with uniform dose conception (UDC) in IMAT and conformal EBRT plans.ResultsThe D90 of high-risk CTV and D2 of bladder and sigmoid were different in BT techniques only: p = 0.0149, < 0.001, < 0.001, respectively. The most advantageous values were obtained in the interstitial treatment plans and inverse optimized interstitial plans did not differ dosimetrically from these, while optimized intracavitary plans resulted in worse dose-volume parameters, and the worst of all were intracavitary plans without optimization. The D2 of rectum was significantly lower with IMAT than with conformal EBRT plans (p = 0.037) and showed the same trend in BT plans as the other parameters (p < 0.001). The UDC dose summation method overestimated D2 of bladder, rectum, and sigmoid (p < 0.001 for all).ConclusionsAlthough optimization improves the quality of conventional BT plans, interstitial plans produce significantly higher dose coverage of high-risk clinical target volume (HR-CTV) and lower doses to organs at risk (OARs). IMAT plans decrease the dose to the rectum. UDC overestimates OARs doses.

A preliminary study of template library-based auto-planning of volume modulated arc therapy

Objective To explore the feasibility of the volume modulated arc therapy (VMAT) auto-planning based on template library (TL). Methods VMAT plans of 68 patients diagnosed with postoperative rectal cancer in Eclipse system were retrospectively selected. The prescription dose was 50 Gy/25F. In 19 patients, the feature values of target and organs at risk were extracted as the vectors. The final optimized restricted conditions were saved as the TL. Then, the plans of 15 rectal cancer patients (10 cases from TL and 5 outside TL) were automatically optimized. According to the multi-dimensional vector similarity principle, the similarity parameter αwas defined. The designed program automatically selected the optimal-object template in an in-house software developed with Matlab. The dosimetric parameters of the auto-optimized plans with the optimal-object template (ATP) and the clinical plan (CP) were compared by the paired t-test. The changes in the dosimetric parameters and similarity parameter α were statistically compared by Pearson′s correlation analysis. The linear fitting of the dosimetric parameters with α was used by least squares method to explore the tendency of the ATP dosimetric parameters relative to CP. Results The dosimetric parameters of ATP for 13 cases were slightly worse than those of CP. The conformal index (P=0.004), heterogeneous index (P=0.015), V40(P=0.003) and mean dose (P=0.022) of the intestine significantly differed. The α values of these 13 cases were 2.67, 2.60, 2.60, 2.49, 2.67, 2.74, 2.72, 2.48, 2.53, 2.86, 2.68, 2.56 and 2.63. The α value was significantly correlated with the V40 or mean dose of the bladder (r=0.649 and 0.603, P=0.016 and 0.029). Along with the increase of α value, V40 and mean dose of the intestine for ATP were gradually deteriorated than those of CP. The remaining dosimetric para-meters of ATP were close to or superior to those of CP. Conclusions The results of ATP are slightly worse than those of CP, whereas can satisfy the clinical requirements. The TL, the quality of TL and ATP remain to be further optimized. Key words: Radiotherapy; Template library; Auto-optimize; Volume modulated arc therapy plan

A retrospective comparison of intensity-modulated arc therapy and 3-dimensional conformal approaches in the planning of grade 3 gliomas

AbstractPurposeTo evaluate the extent to which intensity-modulated arc therapy (IMAT) for high-grade gliomas is comparable with three-dimensional conformal radiotherapy (3DCRT) in relation to the dose delivered to normal brain tissue (NBT), planning target volume (PTV) conformity and the dose delivered to brainstem and optic chiasma.MethodA total of 16 randomly selected 3DCRT treatment plans of grade 3 gliomas were re-planned using an IMAT planning technique and dose–volume histograms were compared. Primary outcomes were maximum, mean, 1/3 and 2/3 doses to NBT outside the PTV. Also the maximum, mean, D50 and D20 doses to PTV. Secondary outcomes were maximum and mean doses to the brainstem and optic chiasm. Wilcoxon signed rank test was used to compare data.ResultsIMAT led to a statistically significant increase in mean dose to NBT (34·4 versus 33·3 Gy, (p=0·047) but a statistically significant reduction in maximum dose to NBT (62·7 versus 63·8 Gy, p=0·004) compared with 3DCRT. IMAT led to statistically significant reductions in maximum, D50 and D20 doses to the PTV (63·3 versus 64·7 Gy, p=0·001; 60·0 versus 60·7 Gy, p=0·001 and 60·5 versus 61·8 Gy, p=0·002, respectively). No statistically significant differences were seen in doses to brainstem and optic chiasm.ConclusionIMAT is at least comparable with 3DCRT in relation to minimising dose to NBT and ensuring good PTV conformity. Doses delivered to organs at risk using IMAT were also comparable with 3DCRT. This study supports the continued use of IMAT for the treatment of high-grade gliomas.

Radiation Planning Assistant - A Streamlined, Fully Automated Radiotherapy Treatment Planning System.

The Radiation Planning Assistant (RPA) is a system developed for the fully automated creation of radiotherapy treatment plans, including volume-modulated arc therapy (VMAT) plans for patients with head/neck cancer and 4-field box plans for patients with cervical cancer. It is a combination of specially developed in-house software that uses an application programming interface to communicate with a commercial radiotherapy treatment planning system. It also interfaces with a commercial secondary dose verification software. The necessary inputs to the system are a Treatment Plan Order, approved by the radiation oncologist, and a simulation computed tomography (CT) image, approved by the radiographer. The RPA then generates a complete radiotherapy treatment plan. For the cervical cancer treatment plans, no additional user intervention is necessary until the plan is complete. For head/neck treatment plans, after the normal tissue and some of the target structures are automatically delineated on the CT image, the radiation oncologist must review the contours, making edits if necessary. They also delineate the gross tumor volume. The RPA then completes the treatment planning process, creating a VMAT plan. Finally, the completed plan must be reviewed by qualified clinical staff.