Volumetric Modulated Arc Therapy For Cancer Research Articles

Comparison of plan quality and robustness using VMAT and IMRT for breast cancer

Abstract To evaluate the plan quality and robustness of volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) for breast cancer, 50 patients, including 25 patients who received radiotherapy after breast-conserving surgery (BCR) and 25 patients who received postmastectomy radiotherapy (PRT), were selected for this study. Nominal VMAT and IMRT plans were generated for each patient on Eclipse treatment planning system (version 15.6). The dosimetric metrics, dose distribution, gamma passing rate, and delivery time were compared. In addition, 12 uncertainty plans with plan isocenter uncertainty and CT density uncertainty were recalculated based on the nominal plans for each patient. The dose volume histogram (DVH) band width (DVHBW) was adopted to quantify the plan robustness of the nominal plans for the perturbed scenarios in this study. For BCR, the dosimetric metrics except planning target volume (PTV) conformal index (CI) and ipsilateral lung V 5 were not statistically different for IMRT and VMAT plans. PTV CI of VMAT plans was better than that of IMRT plans (VMAT: 0.923 ± 0.024, IMRT: 0.855 ± 0.032, p = 0.003). The ipsilateral lung V 5 of VMAT plan was higher than that of IMRT plan (VMAT: 42.4% ± 2.8%, IMRT: 40.5% ± 4.0%, p = 0.045). The VMAT plans save more than 1.20 min compared to the IMRT plans (VMAT: 0.87 min, IMRT: 2.08 min, p < 0.001). The gamma passing rates of VMAT plans were better than those of IMRT plans (3 mm/3%, VMAT: 99.7% ± 0.2%, IMRT: 99.4% ± 0.4%, p < 0.001; 2 mm/2%, VMAT: 97.2% ± 1.0%, IMRT: 96.9% ± 0.6%, p = 0.108). For PRT, the dosimetric metrics of VMAT plans, including PTV D mean, homogeneity index (HI), CI, and D max of spinal cord, were significantly better than those of IMRT plans. The VMAT plans save more than 45% time compared with IMRT plans (VMAT: 1.54 min, IMRT: 2.81 min, p < 0.001). The difference in gamma passing rates between VMAT plans and IMRT plans was not statistically significant. For the plan robustness, the DVHBW of VMAT plans and IMRT plans for BCR were 2.09% ± 0.23% and 2.98% ± 0.40%, respectively (p < 0.05). For PRT, the DVHBW of VMAT plans was significantly better than those of IMRT plans (VMAT: 3.05% ± 0.26%, IMRT: 3.57% ± 0.27%, p < 0.05). The results show that the dosimetric metrics of VMAT plans were comparable to those of IMRT plans. More importantly, the VMAT plans had excited dose distribution and fast execution efficiency. The plan robustness of VMAT plans were superior.

Multi-center Dose Prediction Using Attention-aware Deep learning Algorithm Based on Transformers for Cervical Cancer Radiotherapy

AimsAccurate dose delivery is crucial for cervical cancer volumetric modulated arc therapy (VMAT). We aimed to develop a robust deep-learning (DL) algorithm for fast and accurate dose prediction of cervical cancer VMAT in multicenter datasets and then explore the feasibility of the DL algorithm to endometrial cancer VMAT with different prescriptions. Materials and methodsWe proposed the AtTranNet algorithm for three-dimensional dose prediction. A total of 367 cervical patients were enrolled in this study. Three hundred twenty-two cervical patients from 3 centers were randomly divided into 70%, 10%, and 20% as training, validation, and testing sets, respectively. Forty-five cervical patients from another center were selected for external testing. Moreover, 70 patients of endometrial cancer with different prescriptions were further selected to test the model. Prediction precision was evaluated by dosimetric difference, dose map, and dose-volume histogram metrics. ResultsThe prediction results were all clinically acceptable. The mean absolute error within the body in internal testing was 0.66 ± 0.63%. The maximum |δD| for planning target volume was observed in D98, which is 1.24 ± 2.73 Gy. The maximum |δD| for organs at risk was observed in Dmean of bladder, which is 4.79 ± 3.14 Gy. The maximum |δV| were observed in V40 of pelvic bones, which is 4.77 ± 4.48%. ConclusionAtTranNet showed the feasibility and reasonable accuracy in the dose prediction for cervical cancer in multiple centers. The model can also be generalized for endometrial cancer with different prescriptions without any transfer learning.

Automatic end-to-end VMAT treatment planning for rectal cancers.

The treatment planning process from segmentation to producing a deliverable plan is time-consuming and labor-intensive. Existing solutions automate the segmentation and planning processes individually. The feasibility of combining auto-segmentation and auto-planning for volumetric modulated arc therapy (VMAT) for rectal cancers in an end-to-end process is not clear. To create and clinically evaluate a complete end-to-end process for auto-segmentation and auto-planning of VMAT for rectal cancer requiring only the gross tumor volume contour and a CT scan as inputs. Patient scans and data were retrospectively selected from our institutional records for patients treated for malignant neoplasm of the rectum. We trained, validated, and tested deep learning auto-segmentation models using nnU-Net architecture for clinical target volume (CTV), bowel bag, large bowel, small bowel, total bowel, femurs, bladder, bone marrow, and female and male genitalia. For the CTV, we identified 174 patients with clinically drawn CTVs. We used data for 18 patients for all structures other than the CTV. The structures were contoured under the guidance of and reviewed by a gastrointestinal (GI) radiation oncologist. The predicted results for CTV in 35 patients and organs at risk (OAR) in six patients were scored by the GI radiation oncologist using a five-point Likert scale. For auto-planning, a RapidPlan knowledge-based planning solution was modeled for VMAT delivery with a prescription of 25Gy in five fractions. The model was trained and tested on 20 and 34 patients, respectively. The resulting plans were scored by two GI radiation oncologists using a five-point Likert scale. Finally, the end-to-end pipeline was evaluated on 16 patients, and the resulting plans were scored by two GI radiation oncologists. In 31 of 35 patients, CTV contours were clinically acceptable without necessary modifications. The CTV achieved a Dice similarity coefficient of 0.85 (±0.05) and 95% Hausdorff distance of 15.25 (±5.59)mm. All OAR contours were clinically acceptable without edits, except for large and small bowel which were challenging to differentiate. However, contours for total, large, and small bowel were clinically acceptable. The two physicians accepted 100% and 91% of the auto-plans. For the end-to-end pipeline, the two physicians accepted 88% and 62% of the auto-plans. This study demonstrated that the VMAT treatment planning technique for rectal cancer can be automated to generate clinically acceptable and safe plans with minimal human interventions.

Feasibility Study of Robust Treatment Planning in VMAT for Head and Neck Cancer

In general, patient positional uncertainty is considered by adding a geometrically expanded margin to clinical target volume (CTV) in photon radiation therapy. However, this method may not be suitable because image-guided radiotherapy is available. In intensity modulated proton beam therapy, robust treatment planning is currently common to take patient positional uncertainty into account in optimization rather than in margins. The purpose of this study is to assess the feasibility of clinical implementation of the method in volumetric modulated arc therapy (VMAT) for head and neck cancer. We quantitatively evaluated whether the plans with the robust optimization (Robust plans) can adequately cover CTV against patients' positional uncertainties and body shape change throughout a treatment course. Ten head and neck cancer patients were chosen, who were treated with PTV-based VMAT plans in our hospital between 2021.5-2022.4. RayStation V10A (RaySearch Laboratories, Stockholm, Sweden) was used for the robust optimization, which was applied to the CTVs with patient positional uncertainty of 5 mm in the 6-axis direction. Dose prescribed to the high- and low-risk CTVs were to 70 and 56 Gy in 35 fractions, respectively. To create the patients' CT images with residual set-up errors and body shape change at the treatment, pseudo simulation-CT images were created by deformable image registration with CBCT and simulation-CT. Dose distribution at the treatment was re-calculated by applying the plan to the pseudo simulation-CT images. The variation of D98 for the high-risk CTV from the time of treatment planning was evaluated on a weekly basis. For comparison, planning target volume (PTV) -based plans (5 mm margin circumference) were created and a similar evaluation was performed. D98 for the high-risk CTV varied between -3∼2% in the robust plan and between -5∼1% in the PTV-based plan during the treatment course. There was no significant difference in the amount of D98 variation between the two plans by t-test, except for one case with hypopharyngeal cancer. In this case, D98 for the high-risk CTV varied within ±1% with the PTV-based plan, whereas the value decreased up to 3% with the robust plan (p < 0.05). This case often had a residual setup error of approximately 5 mm at the sites related to the pitch rotation of head, suggesting that the dose distribution for the robust plan was affected by non-rigid positional errors. Patient weight loss during the treatment period was -3.5±2.4 kg, showing a weak correlation (r = -0.33) with the variation in D98 for the high-risk CTV. The robust treatment planning exhibits comparable CTV coverage to the conventional PTV-based planning against positional uncertainty and body shape change throughout a treatment period. In order to overcome set-up baseline shift by the non-rigid positional errors, re-planning should be recommended. Further planning studies will be conducted to promote clinical implementation of the method.

Effect of topical agents on skin surface dose in volumetric modulated arc therapy for head and neck cancer.

In volumetric modulated arc therapy (VMAT), the effect of an increase in skin surface dose due to topical agents might be negligible. We investigated the bolus effects of three types of topical agents in VMAT for head and neck cancer (HNC). Topical agents of different thicknesses (0.1, 0.5 and 2mm) were prepared. When each topical agent was set, the surface doses were measured for the anterior static field and VMAT, with and without a thermoplastic mask. No significant differences were observed among the three topical agents. For topical agent thicknesses of 0.1, 0.5 and 2mm, the increases in surface dose for the anterior static field without the thermoplastic mask were 7-9, 30-31 and 81-84%, respectively. With the thermoplastic mask, the corresponding increases were 5, 12-15 and 41-43%, respectively. The increases in surface dose for VMAT without the thermoplastic mask were 5-8, 16-19 and 36-39%, respectively, and those with the thermoplastic mask were 4, 7-10 and 15-19%, respectively. The rate of increase in surface dose with the thermoplastic mask was smaller than that without the thermoplastic mask. The increase in surface dose with topical agents of clinical standard thickness (0.02mm) was estimated to be 2% with the thermoplastic mask. The increase in surface dose with topical agents in dosimetric simulation, compared with control situation, is not significant in clinical conditions for HNC patients.

Establishment of a prediction model for severe acute radiation enteritis associated with cervical cancer radiotherapy.

Cervical cancer is one of the most common gynecological malignant tumors. Radiation enteritis (RE) leads to radiotherapy intolerance or termination of radiotherapy, which negatively impacts the therapeutic effect and seriously affects the quality of life of patients. If the incidence of RE in patients can be predicted in advance, and targeted clinical preventive treatment can be carried out, the side effects of radiotherapy in cervical cancer patients can be significantly reduced. Furthermore, accurate prediction of RE is essential for the selection of individualized radiation dose and the optimization of the radiotherapy plan. To analyze the relationships between severe acute RE (SARE) of cervical cancer radiotherapy and clinical factors and dose-volume parameters retrospectively. We included 50 cervical cancer patients who received volumetric modulated arc therapy (VMAT) from September 2017 to June 2018 in the Department of Radiotherapy at The First Affiliated Hospital Soochow University. Clinical and dose-volume histogram factors of patients were collected. Logistic regression analysis was used to evaluate the predictive value of each factor for SARE. A nomogram to predict SARE was developed (SARE scoring system ≥ 3 points) based on the multiple regression coefficients; validity was verified by an internal verification method. Gastrointestinal and hematological toxicity of cervical cancer VMAT gradually increased with radiotherapy and reached the peak at the end of radiotherapy. The main adverse reactions were diarrhea, abdominal pain, colitis, anal swelling, and blood in the stool. There was no significant difference in the incidence of gastrointestinal toxicity between the radical and postoperative adjuvant radiotherapy groups (P > 0.05). There were significant differences in the small intestine V20, V30, V40, and rectal V40 between adjuvant radiotherapy and radical radiotherapy after surgery (P < 0.05). Univariate and multivariate analyses revealed anal bulge rating (OR: 14.779, 95%CI: 1.281-170.547, P = 0.031) and disease activity index (DAI) score (OR: 53.928, 95%CI: 3.822-760.948, P = 0.003) as independent predictors of SARE. Anal bulge rating (> 0.500 grade) and DAI score (> 2.165 points) can predict SARE. The nomogram shows potential value in clinical practice.

Evaluating the effect of high-density measurement mode on patient-specific quality assurance for head and neck cancer with ArcCHECK.

The high-density measurement (HDm) mode of the ArcCHECK device can achieve a twofold resolution enhancement compared to the standard measurement (Sm) mode. The aim of this study was to evaluate the effect of HDm on the gamma passing rate (GPR) for the patient-specific quality assurance (PSQA) in head and neck cancer. We retrospectively evaluated 30 patients who underwent volumetric modulated arc therapy (VMAT) for head and neck cancer. Absolute gamma analysis was performed on Sm and HDm data. We also investigated correlations between the modulation complexity score for VMAT (MCSv) and differences in the GPR between the two measurement modes. The global GPR of Sm and HDm was 81.0% ± 8.4% and 82.6% ± 7.6% for the 2%/2 mm criterion, 94.0% ± 4.1% and 94.9% ± 3.6% for the 3%/2 mm criterion, and 96.6% ± 2.4% and 97.0% ± 2.4% for the 3%/3 mm criterion, respectively. HDm slightly improved GPR (p < 0.01) for the 2%/2 mm criterion. Differences in GPR between Sm and HDm for the 2%/2 mm, 3%/2 mm, and 3%/3 mm criteria were 1.6% ± 3.0%, 0.8% ± 2.0%, and 0.4% ± 1.2%, respectively. No correlation was identified between the MCSv and the difference in GPR between Sm and HDm. Despite an improvement in GPR with HDm, the difference in GPR between Sm and HDm was approximately 2% even when the tighter criteria were used. Moreover, the change in the GPR between Sm and HDm did not depend on plan complexity. Thus, the effect of HDm on GPR is limited for the PSQA in VMAT for head and neck cancer.

Knowledge-Based Treatment Planning Model Improves Organ-at-Risk Sparing and Plan Consistency across Clinics for Prostate Radiation Therapy

<h3>Purpose/Objective(s)</h3> The quality of volumetric modulated arc therapy (VMAT) plans highly depends on the planner's preference and experience. A commercially available knowledge-based planning (KBP) module has been widely implemented to estimate the patient-specific optimal dose-volume histogram and enable semi-automatic treatment planning. The purpose of this study was to investigate whether the KBP clinical implementations have improved organ-at-risk (OAR) sparing and plan quality consistency across clinics within our institution for prostate cancer VMAT treatments. <h3>Materials/Methods</h3> A cohort of 1,484 prostate cancer VMAT treatment plans delivered across three different clinics within our institution from January 2016 to January 2022 were retrospectively identified. The prescription (Rx) schemes of 45 Gy and 70 Gy were selected for statistical investigations since these were the only Rx schemes containing more than 50 VMAT plans created with KBP models. Dosimetric parameters of the bladder, rectum, left/right femoral heads, penile bulb, and volume ratio of 50% isodose line to PTV (R50) were extracted. <h3>Results</h3> Since its first adoption in the last quarter of 2018, KBP planning remained at a low application rate from 0% to 20.0% in each quarter. After publishing KBP models clinically at the beginning of 2021, the application rate of prostate KBP models raised to levels from 53.5% to 71.0% in each quarter. For the 70 Gy Rx scheme, parameters of R50 (w/ KBP: 3.67±4.35 vs w/o KBP: 4.17±6.25, <i>p</i>=0.009), bladder (V_40Gy: 25.49%±13.02% vs 30.50%±16.52%, <i>p</i>=0.002; D_mean: 26.47±9.17 Gy vs 30.51±10.11 Gy, <i>p</i>=0.003) and rectum (V_45Gy: 17.45%±9.25% vs 25.23%±10.40%, <i>p</i><0.001; D_mean: 25.41±5.97 Gy vs 30.59±6.77 Gy, <i>p</i><0.001) were all statistically significantly improved with KBP planning. For the 45 Gy Rx scheme, the results were consistent with the 70 Gy Rx scheme. Across the three different clinics, the investigated parameters became more consistent after the adoption of KBP planning (e.g., bladder D_mean in Gy, w/ KBP: 27.52±10.21, 26.47±9.15 and 31.10±9.83 for clinic 1, 2 and 3, respectively, <i>p</i>₁₂=0.646, <i>p</i>₁₃=0.276, <i>p</i>₂₃=0.453; w/o KBP: 28.03±12.52, 27.02±13.97 and 39.85±23.27 for clinic 1, 2 and 3, respectively, <i>p</i>₁₂=0.425, <i>p</i>₁₃<0.001, <i>p</i>₂₃<0.001). This indicates that, with KBP implementations, we have achieved improved OAR-sparing across the institution as well as increased levels of plan quality standardization. <h3>Conclusion</h3> This study demonstrated that KBP models could improve OAR sparing and plan quality consistency across clinics for prostate VMAT radiation therapy. Clinical adoptions of KBP could potentially reduce inter-planner variations and facilitate the standardization of VMAT treatment planning.

Implementation of TG-218 for patient-specific quality assurance tolerance and action limits determination: Gamma passing rate evaluation using 3DVH software.

To determine the tolerance limit (TL) and action limit (AL) of gamma passing rates (%GP) for volumetric-modulated arc therapy (VMAT) patient-specific quality assurance (PSQA) according to the American Association of Physicists in Medicine (AAPM) Task Group (TG)-218 recommendations, and to comparatively evaluate the clinical relevance of 2D %GP and 3D %GP. PSQA was performed for 100 head and neck (H&N) and 73 prostate cancer VMAT treatment plans. Measurements were acquired using a cylindrical water equivalent phantom, hollow in the center, allowing measurements with homogeneous or heterogeneous inserts. The LINAC-delivered dose distributions were compared to those calculated from the treatment planning system through the gamma index. TL and AL were determined through the computation of two-dimensional (2D) %GP using the recommended acceptance criteria. Dose-volume histograms were reconstructed from the measurements using a commercially available software to detect the dosimetric errors (%DE) between the compared dose distributions. Utilizing the estimated dose on the patient anatomy, structure-specific %GP (3D %GP) were calculated. The 3D %GP were compared to the 2D %GP ones based on their correlation with the %DE. Each metric's sensitivity was determined through receiver operator characteristic analysis. TL and AL were in concordance with the universal ones, regarding the prostate cancer cases, but were lower for the H&N cases. Evaluation of %DE did not deem the plans unacceptable. The 2D %GP and the 3D %GP did not differ significantly regarding their correlation with %DE. For prostate plans, %GP sensitivity was higher than for H&N cases. Determination of institutional-specific TL and AL allows the monitoring of the PSQA procedure, yet for plans close to the limits, clinically relevant metrics should be used before they are deemed unacceptable for the process to be of higher sensitivity and efficiency.

116P Robustness evaluation of VMAT by robust optimization and manual flash approach for breast cancer radiotherapy

The importance of including skin flash in planning strategies for volumetric modulated arc therapy (VMAT) of breast cancer has been proposed by various researchers in the past few years. Recently, the robust planning concept from proton therapy had also incorporated in photon radiotherapy. This may provide a wider scope to deal with uncertainties. This study aimed to compare the conventional manual skin flash (MF) approach with the novel robust optimization (RO) approach in terms of robustness in VMAT for breast cancer.

Planning evaluation of a novel volume-based algorithm for personalized optimization of lung dose in VMAT for esophageal cancer

Radiotherapy treatment planning (RTP) is time-consuming and labor-intensive since medical physicists must devise treatment plans carefully to reduce damage to tissues and organs for patients. Previously, we proposed the volume-based algorithm (VBA) method, providing optimal partial arcs (OPA) angle to achieve the low-dose volume of lungs in dynamic arc radiotherapy. This study aimed to implement the VBA for esophageal cancer (EC) patients and compare the lung dose and delivery time between full arcs (FA) without using VBA and OPA angle using VBA in volumetric modulated arc therapy (VMAT) plans. We retrospectively included 30 patients diagnosed with EC. RTP of each patient was replanned to 4 VMAT plans, including FA plans without (FA-C) and with (FA + C) dose constraints of OARs and OPA plans without (OPA-C) and with (OPA + C) dose constraints of OARs. The prescribed dose was 45 Gy. The OARs included the lungs, heart, and spinal cord. The dose distribution, dose-volume histogram, monitor units (MUs), delivery time, and gamma passing rates were analyzed. The results showed that the lung V5 and V10 in OPA + C plans were significantly lower than in FA + C plans (p < 0.05). No significant differences were noted in planning target volume (PTV) coverage, lung V15, lung V20, mean lung dose, heart V30, heart V40, mean heart dose, and maximal spinal cord dose between FA + C and OPA + C plans. The delivery time was significantly longer in FA + C plans than in OPA + C plans (237 vs. 192 s, p < 0.05). There were no significant differences between FA + C and OPA + C plans in gamma passing rates. We successfully applied the OPA angle based on the VBA to clinical EC patients and simplified the arc angle selection in RTP. The VBA could provide a personalized OPA angle for each patient and effectively reduce lung V5, V10, and delivery time in VMAT.

Dosimetric advantages of volumetric modulated arc therapy (VMAT) with deep inspiration breath hold (DIBH) technique in Halcyon Linac for left breast cancer treatment.

To evaluate the dosimetric advantages of incorporating the deep inspiration breath hold (DIBH) technique into left breast cancer volumetric modulated arc therapy (VMAT) treatment under Halcyon Linac and to investigate the correlation between mean heart dose (MHD) and distance from the heart to target volumes in left breast cancer VMAT treatment. Fifteen Post-lumpectomy, left-sided breast patients treated between January 2017 and October 2020 were selected. Two plans were generated for each patient using Eclipse treatment planning system (TPS) with the prescription of 50.4 Gy to planning target volume (PTV) breast and 58.8 Gy to PTV boost in 28 fractions. For each patient, DIBH and free breathing (FB) VMAT treatment plans under Halcyon Linac were generated. Dosimetric parameters, monitor unit and beam-on time of both DIBH and FB groups were compared. Three-dimensional distances from heart surface to each target volume were measured on computed tomography images using the TPS contouring tool and their correlation with MHD was evaluated by Pearson's correlation coefficient (r). Comparable target coverage was shown in both groups. Mean dose to heart, left anterior descending artery, and left ventricle in Halcyon-DIBH-VMAT group were significantly reduced by 0.49 Gy, 1.19 Gy, and 0.57 Gy, respectively, compared to Halcyon-FB-VMAT (p < 0.001). A significant lung dose reduction was also achieved in Halcyon-DIBH-VMAT group. There was also a strong negative correlation between MHD and distance from heart surface to PTV boost in both FB and DIBH group (r = -0.741, p < 0.001), but not observed for distance from heart surface to PTV breast. Incorporating DIBH into left breast cancer VMAT treatment under Halcyon Linac demonstrated significant cardiac and lung dose reduction. It was also demonstrated that MHD had a strong negative correlation with distance from heart surface to PTV boost but relatively independent of distance from heart surface to PTV breast. Recognizing the distance from the heart surface to PTV boost as the main factor in affecting MHD could potentially facilitate clinical treatment planning workflow and decision.

Accuracy of dose calculation on iterative CBCT for head and neck radiotherapy.

To evaluate the feasibility of the use of iterative cone-beam computed tomography (CBCT) for dose calculation in the head and neck region. This study includes phantom and clinical studies. All acquired CBCT images were reconstructed with Feldkamp-Davis-Kress algorithm-based CBCT (FDK-CBCT) and iterative CBCT (iCBCT) algorithm. The Hounsfield unit (HU) consistency between the head and body phantoms was determined in both reconstruction techniques. Volumetric modulated arc therapy (VMAT) plans were generated for 16 head and neck patients on a planning CT scan, and the doses were recalculated on FDK-CBCT and iCBCT with Anisotropic Analytical Algorithm (AAA) and Acuros XB (AXB). As a comparison of the accuracy of dose calculations, the absolute dosimetric difference and 1%/1mm gamma passing rate analysis were analyzed. The difference in the mean HU values between the head and body phantoms was larger for FDK-CBCT (max value: 449.1HU) than iCBCT (260.0HU). The median dosimetric difference from the planning CT were <1.0% for both FDK-CBCT and iCBCT but smaller differences were found with iCBCT (planning target volume D50%: 0.38% (0.15-0.59%) for FDK-CBCT, 0.28% (0.13-0.49%) for iCBCT, AAA; 0.14% (0.04-0.19%) for FDK-CBCT, 0.07% (0.02-0.20%) for iCBCT). The mean gamma passing rate was significantly better in iCBCT than FDK-CBCT (AAA: 98.7% for FDK-CBCT, 99.4% for iCBCT; AXB: 96.8% for FDK_CBCT, 97.5% for iCBCT). The iCBCT-based dose calculation in VMAT for head and neck cancer was accurate compared to FDK-CBCT.

Dosimetric impact of rotational setup errors in volumetric modulated arc therapy for postoperative cervical cancer.

We aimed to evaluate the impact of rotational setup errors on the doses received during postoperative volumetric-modulated arc therapy (VMAT) for cervical cancer. Overall, 121 cone-beam computed tomography (CBCT) sets from 20 patients were rigidly registered to reference computed tomography (CT) sets based on bony landmarks. The rotational setup errors (pitch, yaw and roll) were calculated. Then, 121 CT sets involving rotational setup errors were created, and the dose distribution in these CT sets were recalculated. The recalculated dosimetric parameters for the clinical target volume (CTV) and organs at risk (OAR) were compared to the reference values, and the correlation coefficients between the dosimetric parameter differences and rotational setup errors were calculated. Only the pitch setup error was moderately correlated with CTV coverage (r ≥ 0.40) and strongly correlated with V45 for the bladder (r ≥ 0.91) and V40 for the rectum, small bowel and bone marrow (r ≥ 0.91). The maximum dosimetric difference in a single fraction and overall fractions was −1.59% and −0.69% in D98 for the CTV, 11.72% and 5.17% in V45 for the bladder and −8.03% and −4.68% in V40 for the rectum, respectively. In conclusion, rotational setup errors only slightly impact dose coverage during postoperative cervical cancer VMAT. However, the pitch setup error occasionally affected the doses received by the bladder or the rectum in the overall fraction when the error was systematic. Thus, rotational setup errors should be corrected by adjusting six-degree-of-freedom (DOF) couches to reduce dosimetric differences in the OARs.

Volumetric Modulated Arc Therapy Improves Outcomes in Definitive Radiochemotherapy for Anal Cancer Whilst Reducing Acute Toxicities and Increasing Treatment Compliance.

Simple SummaryIntensity-modulated radiotherapy (IMRT) is the standard of care in definitive chemoradiotherapy (CRT) for anal cancer. Only a limited number of studies have analyzed the clinical results with VMAT (volumetric modulated arc therapy, the advanced form of IMRT). We conducted a retrospective study on patients treated at our institution. We compared the outcomes of VMAT-treated and 3DCRT (3D conformal radiotherapy)-treated patients. VMAT reduced acute toxicities (i.e., primarily dermatitis and enteritis) to a great extent. Additionally, VMAT relevantly improved treatment compliance (i.e., less CRT interruptions/delays, shorter overall treatment time, and higher absolute 5-fluorouracil dose applied). Finally, we found improved cancer-specific survival and distant control in VMAT-treated patients. The present study underlines the great progress that has been achieved with IMRT/VMAT in the CRT of anal cancer. Our study is the first to demonstrate an improvement in treatment compliance and outcomes with VMAT. Future studies could address whether VMAT is advantageous when compared to conventional IMRT.Background: Intensity-modulated radiotherapy (IMRT) is the standard of care in chemoradiotherapy (CRT) for anal cancer. Until now, only a limited number of studies have analyzed the results with VMAT (volumetric modulated arc therapy). We conducted a retrospective study on patients treated at our institution. Patients and Methods: We included patients who received curative CRT for anal cancer. We compared VMAT-treated and 3DCRT (3D conformal radiotherapy)-treated patients. We analyzed toxicities (acute: CTCAE criteria; late: LENT/SOMA criteria), treatment compliance, overall survival, cancer-specific survival (CSS), distant control (DC), and locoregional control. Results: A total of 149 patients (3DCRT: n = 87, VMAT: n = 62) were included. The median follow-up was longer in 3DCRT-treated patients (3DCRT: 61.3 months; VMAT: 39.1 months; p < 0.05). VMAT-treated patients had more G3 tumors (3DCRT: 12/87 (13.8%); VMAT: 18/62 (29.0%), p < 0.001). VMAT reduced acute toxicities ≥grade 3 (3DCRT: n = 48/87 (55.2%); VMAT: n = 11/62 (17.7%), p < 0.001). VMAT improved treatment compliance (less interruptions/delays) (3DCRT: 37/87, 42.5%; VMAT: 4/62, 6.5%; p < 0.001), provided a shorter median overall treatment time (3DCRT: 41 days; VMAT: 38 days; p = 0.02), and gave a higher median absolute 5-fluorouracil dose (3DCRT: 13,700 mg; VMAT: 14,400 mg; p = 0.001). Finally, we found improved CSS (p = 0.02; 3DCRT: 81.9% at 3 years; VMAT: 94.1% at 3 years) and DC (p = 0.01; 3DCRT: 89.4% at 3 years; VMAT: 100.0% at 3 years) with VMAT. Summary: Our study is the first to demonstrate improved treatment compliance and outcomes with VMAT for anal cancer. Previous studies have indicated that organs at risk sparing might be more improved with the use of VMAT vs. with conventional IMRT. Future studies should address whether these advantages lead to a further reduction in CRT-associated morbidity.

Risk for second bladder and rectal malignancies from cervical cancer irradiation.

The objective of this study was to estimate the risk of developing second malignancies to partially in‐field organs from volumetric modulated arc therapy (VMAT) of cervical cancer and to compare the above risks with those from the conventional three‐dimensional conformal radiotherapy (3D‐CRT). Seventeen consecutive patients with uterine cervix carcinoma were selected. VMAT and 3D‐CRT plans were generated with 6 and 10 MV photons, respectively. The prescribed tumor dose was 45 Gy given in 25 fractions. Differential dose‐volume histogram data from the treatment plans were obtained for the partially in‐field organs such as bladder and rectum. These data were used to estimate the patient‐specific lifetime attributable risk (LAR) for bladder and rectal cancer induction with a non‐linear model based on a mixture of plateau and bell‐shaped dose–response relationships. The estimated risks per 10000 people were compared with the baseline risks for unexposed population. The patient‐specific rectal cancer risk estimates from VMAT were significantly lower than those from 3D‐CRT (P = 0.0144). The LARs for developing bladder malignancies from VMAT were significantly high compared to those from conventional irradiation (P = 0.0003). The mean difference between the patient‐specific LARs for radiation‐induced bladder and rectal malignancies as derived from 3D‐CRT and VMAT plans was 6.6% and 2.0%, respectively. The average LAR for developing bladder and rectal malignant diseases due to VMAT was 9.2 × 10‐4 and 43.7 × 10‐4, respectively. The corresponding risks following 3D‐CRT were 8.6 × 10‐4 and 44.6 × 10‐4. These average risks showed that pelvic irradiation increases the baseline probability for cancer induction by 12.6‐19.1%. The differences in the second cancer risks associated with the VMAT and 3D‐CRT for cervical cancer were found to be small. Both treatment techniques resulted in considerable increased probabilities for developing bladder and rectal malignancies relative to those of unirradiated population.

Evaluation of dose-volume histogram prediction for organ-at risk and planning target volume based on machine learning

The purpose of this work is to evaluate the performance of applying patient dosimetric information induced by individual uniform-intensity radiation fields in organ-at risk (OAR) dose-volume histogram (DVH) prediction, and extend to DVH prediction of planning target volume (PTV). Ninety nasopharyngeal cancer intensity-modulated radiation therapy (IMRT) plans and 60 rectal cancer volumetric modulated arc therapy (VMAT) plans were employed in this study. Of these, 20 nasopharyngeal cancer cases and 15 rectal cancer cases were randomly selected as the testing data. The DVH prediction was performed using two methods. One method applied the individual dose-volume histograms (IDVHs) induced by a series of fields with uniform-intensity irradiation and the other method applied the distance-to-target histogram and the conformal-plan-dose-volume histogram (DTH + CPDVH). The determination coefficient R2 and mean absolute error (MAE) were used to evaluate DVH prediction accuracy. The PTV DVH prediction was performed using the IDVHs. The PTV dose coverage was evaluated using D98, D95, D1 and uniformity index (UI). The OAR dose was compared using the maximum dose, V30 and V40. The significance of the results was examined with the Wilcoxon signed rank test. For PTV DVH prediction using IDVHs, the clinical plan and IDVHs prediction method achieved mean UI values of 1.07 and 1.06 for nasopharyngeal cancer, and 1.04 and 1.05 for rectal cancer, respectively. No significant difference was found between the clinical plan results and predicted results using the IDVHs method in achieving PTV dose coverage (D98,D95,D1 and UI) for both nasopharyngeal cancer and rectal cancer (p-values ≥ 0.052). For OAR DVH prediction, no significant difference was found between the IDVHs and DTH + CPDVH methods for the R2, MAE, the maximum dose, V30 and V40 (p-values ≥ 0.087 for all OARs). This work evaluates the performance of dosimetric information of several individual fields with uniform-intensity radiation for DVH prediction, and extends its application to PTV DVH prediction. The results indicated that the IDVHs method is comparable to the DTH + CPDVH method in accurately predicting the OAR DVH. The IDVHs method quantified the input features of the PTV and showed reliable PTV DVH prediction, which is helpful for plan quality evaluation and plan generation.

Dosimetric Comparison Between Carbon-ion Radiotherapy and Photon Radiotherapy for Stage I Esophageal Cancer.

The present study aimed to compare the radiation dose distribution of carbon-ion radiotherapy (CIRT) for stage I esophageal cancer with three-dimensional conformal radiotherapy (3DCRT) and volumetric modulated arc therapy (VMAT). Fifteen patients with cT1bN0M0 esophageal cancer who received 3DCRT at Kanagawa Cancer Center between January 2014 and April 2019 were enrolled. The dose-volume histogram parameters of the target volume and normal organs planned with CIRT, 3DCRT, and VMAT were evaluated. The homogeneity index for the target volume of CIRT was significantly lower than that of 3DCRT and VMAT. In addition, the radiation dose of CIRT to the heart, lungs, spinal cord, and skin was significantly lower than that of 3DCRT and VMAT. Favorable dose distributions with CIRT were demonstrated compared with 3DCRT and VMAT for esophageal cancer.

Deep learning-based inverse mapping for fluence map prediction

We developed a fluence map prediction method that directly generates fluence maps for a given desired dose distribution without optimization for volumetric modulated arc therapy (VMAT) planning. The prediction consists of two steps. First, projections of the desired dose are calculated and then inversely mapped to fluence maps in the phantom geometry by a deep neural network. Second, a plan scaling technique is applied to scale fluence maps from phantom to patient geometry. We evaluated the performance of the proposed fluence map prediction method for 102 head and neck (H&N) and 14 prostate cancer VMAT plans by comparing the patient doses calculated from the predicted fluence maps with the given desired dose distributions. The mean dose differences were 1.42% ± 0.37%, 1.53% ± 0.44% and 1.25% ± 0.44% for the planning target volume (PTV), the region from the PTV boundary to the 50% isodose line, and the region from the 50% to the 20% isodose line, respectively. The gamma passing rate was 98.06% ± 2.64% with the 3 mm/3% criterion. The prediction time for a single VMAT plan was less than one second. In conclusion, we developed an inverse mapping-based method that predicts fluence maps for desired dose distributions with high accuracy. Our method is effectively an optimization-free inverse planning approach, which was orders of magnitude faster than fluence map optimization. Combining the proposed method with leaf sequencing has the potential to dramatically speed up VMAT treatment planning.

Comparison and evaluation for the dose distribution and physical characteristics between two AAA and AXB algorithms in Eclipse v13.6 software on treatment plans in regions heterogenous densities at 108 Military Central Hospital

The aim of this study is to compare and evaluate the dose distribution and physical characteristics of two algorithms Anisotropic Analytical Algorithm (AAA) and Acuros XB (AXB) inEclipse v13.6 software in regions heterogeneous densities. Computed Tomography Simulation (CT –Sim) data of 48 treated cancer patients (20 head and neck cancer (H&amp;N) patients, 15 esophageal cancer patients, 8 lung cancer patients with 3 Dimensions Conformal Radiation Therapy (3D-CRT)and 5 lung cancer patients treated with Volumetric Modulated Arc Therapy (VMAT)) were used to replan the Eclipse v13.6 software with two algorithm AAA and AXB. For all plans, the Quality of Coverage (Q), the Conformity Index (CI), the Homogeneity Index (HI) and the dose volume histograms (DVH) for the targets and the organs at risk (OARs) were compared and evaluated. Pretreatment quality assurance (QA) was performed using the Electronic Portal Imaging Device(EPID) for all VMAT plans, and the gamma index method was used to qualify the agreement between calculations and measurements. In addition, total Monitor Units (MUs) and the calculation time were investigated. The indicators obtained from the H&amp;N VMAT plans calculated by AAA close to ideal values than AXB. The total MUs obtained from two algorithms are approximately equal. The lung cancer 3D – CRT plans, the indicators for target and OARs are approximately the same. However, the calculation time of the AAA is faster than the AXB from 7.5 to 14 times. The indicator obtained from the lung cancer VMAT plans calculated by two algorithms AAA and AXB are approximately equal. The total MUs and time calculation are approximate the same. However, the V5, V10, V20 and Mean Lung Dose (MLD) obtained from AAA is lower than AXB. For esophageal cancer VMAT plans, the indicators HIRTOG, HIWu, and Q calculated by AAA close to the ideal values than AXB. However, the indicators CIPaddick, CIICRU-62, V5, V10, V20 and MLD calculated by AXB are better than AAA. The dose distribution indicators obtained from AAA algorithm are better than AXB algorithm in H&amp;N cancer and lung cancer plans. For the esophageal cancer plans, AXB algorithm gave the dose distribution indicator are better than AAA.