Volumetric Modulated Radiotherapy Research Articles

Automated target placement for VMAT lattice radiation therapy: enhancing efficiency and consistency

Objective. An algorithm was developed for automated positioning of lattice points within volumetric modulated arc lattice radiation therapy (VMAT LRT) planning. These points are strategically placed within the gross tumor volume (GTV) to receive high doses, adhering to specific separation rules from adjacent organs at risk (OARs). The study goals included enhancing planning safety, consistency, and efficiency while emulating human performance. Approach. A Monte Carlo-based algorithm was designed to optimize the number and arrangement of lattice points within the GTV while considering placement constraints and objectives. These constraints encompassed minimum spacing between points, distance from OARs, and longitudinal separation along the z-axis. Additionally, the algorithm included an objective to permit, at the user’s discretion, solutions with more centrally placed lattice points within the GTV. To validate its effectiveness, the automated approach was compared with manually planned treatments for 24 previous patients. Prior to clinical implementation, a failure mode and effects analysis (FMEA) was conducted to identify potential shortcomings. Main results. The automated program successfully met all placement constraints with an average execution time (over 24 plans) of 0.29 ±0.07 min per lattice point. The average lattice point density (# points per 100 c.c. of GTV) was similar for automated (0.725) compared to manual placement (0.704). The dosimetric differences between the automated and manual plans were minimal, with statistically significant differences in certain metrics like minimum dose (1.9% versus 1.4%), D5% (52.8% versus 49.4%), D95% (7.1% versus 6.2%), and Body-GTV V30% (20.7 c.c. versus 19.7 c.c.). Significance. This study underscores the feasibility of employing a straightforward Monte Carlo-based algorithm to automate the creation of spherical target structures for VMAT LRT planning. The automated method yields similar dose metrics, enhances inter-planner consistency for larger targets, and requires fewer resources and less time compared to manual placement. This approach holds promise for standardizing treatment planning in prospective patient trials and facilitating its adoption across centers seeking to implement VMAT LRT techniques.

P07.03.A COMPLETE LONG-LASTING RESPONSE TO MULTIMODAL THIRD LINE TREATMENT WITH NEUROSURGICAL RESECTION, CARMUSTINE WAFER IMPLANTATION AND DABRAFENIB PLUS TRAMETINIB IN A BRAFV600E MUTATED HIGH-GRADE GLIOMA

Abstract BACKGROUND BRAF mutations are drivers of oncogenesis in a variety of tumors and they can be successfully targeted with small molecule inhibitors. In primary central nervous system tumors, BRAFV600E mutations are most frequently found in pleomorphic xanthoastrocytoma, ganglioglioma, pilocytic astrocytoma and epithelioid glioblastoma. Dabrafenib is a potent and selective inhibitor of BRAF-mutant kinase that was approved, as monotherapy or in combination with trametinib (mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor), for unresectable or metastatic BRAF-mutated melanoma, advanced non-small cell lung cancer and anaplastic thyroid cancer harboring BRAFV600E mutation. MATERIAL AND METHODS In February 2016, a 21-year-old female was admitted to our Unit for seizures. A brain magnetic resonance imaging (MRI) revealed a frontal contrast enhanced lesion. Neurosurgical resection was performed. The histological analysis diagnosed anaplastic pleomorphic xanthoastrocytoma (PXA) WHO grade III. A volumetric modulated radiotherapy course was delivered for a total dose of 59,4 Gy in 33 fractions with concomitant and adjuvant temozolomide therapy (Stupp protocol). In October 2017, a brain MRI showed relapsing disease. Six courses of chemotherapy with procarbazine, lomustine and vincristine (PCV) were administered, and then neurosurgical partial removal and carmustine wafer implantation were performed. The histological analysis confirmed BRAF V600E mutated anaplastic PXA. RESULTS In April 2019 the 24-year-old female patient with BRAF mutated anaplastic PXA started her third-line therapy with dabrafenib. The well-known tumor residue was less evident on the subsequent MRIs performed every three/four months. Given the literature data of the most effectiveness and the best control of the side effects, in August 2020 the patient was put on combined treatment with dabrafenib plus trametinib. Since December 2021 the residual tumor has not been longer visible. Last MRI evaluation, performed on January 26th 2023, showed no recurrence of the disease, four years after BRAF inhibitor treatment beginning. CONCLUSION Dabrafenib plus trametinib is a promising new therapy for patients affected by BRAFV600E-mutant glioma, with high overall response and manageable toxicity. Due to very poor prognosis, there are a few described cases of high-grade glioma (HGG) patients in third-line therapy, showing complete response and for such a long time. The emergence of optimized sequencing strategies and targeted agents, including multimodal treatment and systemic therapy with dabrafenib plus trametinib, will continue to broaden personalized therapy in HGG and to improve patient outcomes.

Deep learning-based detection and classification of multi-leaf collimator modeling errors in volumetric modulated radiation therapy.

The purpose of this study was to create and evaluate deep learning-based models to detect and classify errors of multi-leaf collimator (MLC) modeling parameters in volumetric modulated radiation therapy (VMAT), namely the transmission factor (TF) and the dosimetric leaf gap (DLG). A total of 33 clinical VMAT plans for prostate and head-and-neck cancer were used, assuming a cylindrical and homogeneous phantom, and error plans were created by altering the original value of the TF and the DLG by±10, 20, and 30% in the treatment planning system (TPS). The Gaussian filters of and 1.0 were applied to the planar dose maps of the error-free plan to mimic the measurement dose map, and thus dose difference maps between the error-free and error plans were obtained. We evaluated 3 deep learning-based models, created to perform the following detections/classifications: (1) error-free versus TF error, (2) error-free versus DLG error, and (3) TF versus DLG error. Models to classify the sign of the errors were also created and evaluated. A gamma analysis was performed for comparison. The detection and classification of TF and DLG error were feasible for ; however, a considerable reduction of accuracy was observed for depending on the magnitude of error and treatment site. The sign of errors was detectable by the specifically trained models for and 1.0. The gamma analysis could not detect errors. We demonstrated that the deep learning-based models could feasibly detect and classify TF and DLG errors in VMAT dose distributions, depending on the magnitude of the error, treatment site, and the degree of mimicked measurement doses.

Development of programs to predict the occurrence of mucositis from digital imaging and communications in medicine data by machine learning in head and neck volumetric modulated radiotherapy.

Volumetric modulated arc therapy (VMAT) with cisplatin for head and neck cancer is often accompanied by symptoms of pharyngeal and oral mucositis. However, no standard medical program exists for the prevention and treatment of mucositis, and the mechanisms of mucositis have not yet been fully proven. Therefore, adaptive radiotherapy (ART), which is a re-planning process, is administered when severe mucositis develops during the treatment period. We extracted the treatment plans of patients who developed severe mucositis from DICOM data and used machine learning to determine its quantitative features. This study aimed to develop a machine learning program that can predict the development of mucositis requiring ART. This study included 61 patients who received concurrent chemotherapy and radiotherapy (RT). For each patient, the equivalent square field size of each segmental irradiation field used for VMAT, dose per segment (Gy), clinical target volume high, and mean dose of the oral cavity (Gy) were calculated. Furthermore, 671 five-dimensional lists were generated from the acquired data. Support vector machine (SVM) and K-nearest neighbor (KNN) were used for machine learning. For the accuracy score, the test size was varied from 10% to 90%, and the random number of data extracted in each test size was further varied from 1 to 100 to calculate a mean accuracy score. The mean accuracy scores of SVM and KNN were 0.981±0.020 and 0.972±0.033, respectively. The presence or absence of ART for mucositis was classified with high accuracy. The classification of the five-dimensional list was implemented with high accuracy, and a program was constructed to predict the onset of mucositis requiring ART before treatment began. This study suggests that it may support preventive measures against mucositis and the completion of RT without having to re-plan.

Dosimetric effects of the custom dose iteration times on stereotactic radiotherapy for lung cancer

PurposeTo evaluate the dosimetric effects of the custom dose iteration function in the Monaco 6.0 planning system on stereotactic radiotherapy for lung cancer. MethodsUsing the custom dose iterative function segment shape optimization (SSO) times in the Monaco 6.0 treatment planning system, the iterative times were set as 3, 5, 8, 10, and 12, respectively. Five volumetric modulated arc stereotactic body radiation therapy (SBRT) plans were made for each patient, and other optimization parameters and optimization functions were kept consistent. The dose volume histogram (DVH) statistical table was used to evaluate the dose of the target area and organs at risk (OAR). Statistical analysis was performed using SPSS 25 software, and the results were statistically different when p < 0.05. ResultsFor the target area dose analysis, SSO8, SSO10, and SSO12 groups showed similar results, significantly better than both SSO3 and SSO5 groups (p < 0.05). With the increase in the times of SSO, the protection of the heart was better, except for SSO3, the maximum dose of the esophagus and V47Gy of great vessels were significantly lower than SSO5 in all groups. The mean dose of heart was significantly lower in SSO10 and SSO12 than SSO5 (p < 0.05). There was no significant difference in other OAR among the groups. The optimization time (OT) of each group was statistically different, the maximum OT exceeded 1000s, the maximum deviation between groups exceeded 600s, and the OT increased significantly with the times of SSO (p < 0.05). There was no statistically significant difference between the 5 groups of monitor unit (MU), and segment was not significantly different between the groups except SSO3 which was significantly higher than SSO5 (p < 0.05). The delivery time (DT) was statistically different between the groups except for SSO3. ConclusionsIn the treatment of left-sided lung cancer patients with volumetric modulated arc SBRT, considering both calculation accuracy and clinical treatment efficiency, SSO times of 8 is recommended for designing SBRT for lung cancer with the Monaco treatment planning system.

Clinical Practice Evolvement for Post-Operative Prostate Cancer Radiotherapy—Part 2: Feasibility of Margin Reduction for Fractionated Radiation Treatment with Advanced Image Guidance

Purpose: Planning target volume (PTV) expansion for post-prostatectomy radiotherapy is typically ≥5 mm. Recent clinical trials have proved the feasibility of a reduced margin of 2−3 mm for treatments on MRI-linac. We aim to study the minimum PTV margin needed using iterative cone-beam CT (iCBCT) as image guidance on conventional linacs. Materials/Methods: Fourteen patients who received post-prostatectomy irradiation (8 with an endorectal balloon and 6 without a balloon) were included in this study. Treatment was delivered with volumetric modulated radiation therapy (VMAT). Fractional dose delivery was evaluated in 165 treatment fractions. The bladder, rectal wall, femoral heads, and prostate bed clinical tumor volume (CTV) were contoured and verified on daily iCBCT. PTV margins (0 mm, 2 mm, and 4 mm) were evaluated on daily iCBCT. CTV coverage and OAR dose parameters were assessed with each PTV margin. Results: CTV D100% was underdosed with a 0 mm margin in 32% of fractions in comparison with 2 mm (6%) and 4 mm (6%) PTV margin (p ≤ 0.001). CTV D95% > 95% was met in 93−94% fractions for all PTV expansions. CTV D95% > 95% was achieved in more patients with an endorectal balloon than those without: 0 mm—90/91 (99%) vs. 63/74 (85%); 2 mm—90/91 (99%) vs. 65/75 (87%); 4 mm—90/90 (100%) vs. 63/73 (86%). There was no difference in absolute median change in CTV D95% (0.32%) for 0-, 2-, and 4 mm margins. The maximum dose remained under 108% for 100% (0 mm), 97% (2 mm), and 98% (4 mm) of images. Rectal wall maximum dose remained under 108% for 100% (0 mm), 100% (2 mm), and 98% (4 mm) of images. Conclusions: With high-quality iCBCT image guidance, PTV margin accounting for inter-fractional uncertainties can be safely reduced for post-prostatectomy radiotherapy. For fractionated radiotherapy, an isotropic expansion of 2 mm and 4 mm may be considered for margin expansion with and without the endorectal balloon. Future application for margin reduction needs to be further evaluated and considered with the advent of shorter post-prostatectomy radiation courses.

Clinical Practice Evolvement for Post-Operative Prostate Cancer Radiotherapy-Part 1: Consistent Organs at Risk Management with Advanced Image Guidance.

Purpose: Post-operative prostate cancer patients are treated with full bladder instruction and the use of an endorectal balloon (ERB). We reassessed the efficacy of this practice based on daily image guidance and dose delivery using high-quality iterative reconstructed cone-beam CT (iCBCT). Methods: Fractional dose delivery was calculated on daily iCBCT for 314 fractions from 14 post-operative prostate patients (8 with and 6 without ERB) treated with volumetric modulated radiotherapy (VMAT). All patients were positioned using novel iCBCT during image guidance. The bladder, rectal wall, femoral heads, and prostate bed clinical tumor volume (CTV) were contoured and verified on daily iCBCT. The dose-volume parameters of the contoured organs at risk (OAR) and CTV coverage were assessed for the clinical impact of daily bladder volume variations and the use of ERB. Minimum bladder volume was studied, and a straightforward bladder instruction was explored for easy clinical adoption. Results: A “minimum bladder” contour, the overlap between the original bladder contour and a 15 mm anterior and superior expansion from prostate bed PTV, was confirmed to be effective in identifying cases that might fail a bladder constraint of V65% <60%. The average difference between the maximum and minimum bladder volumes for each patient was 277.1 mL. The daily bladder volumes varied from 62.4 to 590.7 mL and ranged from 29 to 286% of the corresponding planning bladder volume. The bladder constraint of V65% <60% was met in almost all fractions (98%). CTVs (D90%, D95%, and D98%) remained well-covered regardless of the absolute bladder volume daily variation or the presence of the endorectal balloon. Patients with an endorectal balloon showed smaller variation but a higher average maximum rectal wall dose (D0.03mL: 104.3% of the prescription) compared to patients without (103.3%). Conclusions: A “minimum bladder” contour was determined that can be easily generated and followed to ensure sufficient bladder sparing. Further analysis and validation are needed to confirm the utility of the minimal bladder contour. Accurate dose delivery can be achieved for prostate bed target coverage and OAR sparing with or without the use of ERB.

Efficacy of Scalp-Sparing VMAT Approach in Reducing Scalp Radiation Dose for Patients with Glioblastoma

<h3>Purpose/Objective(s)</h3> Radiation therapy is integral to the treatment of glioblastomas. Radiation induced scalp toxicity, however, is common and can negatively impact patients' quality of life. Volumetric modulated radiation therapy (VMAT) can optimize dose to organs at risk. We hypothesize that scalp-sparing VMAT (SSV) can significantly reduce undesirable dose to the scalp without compromising target dose. In this study, we evaluate the dosimetric feasibility and benefit of SSV for patients with newly diagnosed glioblastomas (GBM). <h3>Materials/Methods</h3> This is a retrospective study of GBM patients who received radiation treatment at our institution with conventional VMAT without scalp-sparing optimization. We contoured the scalp for these patients, which was defined as a 5 mm ring structure beneath the skin, above the foramen magnum. We replanned these patients using non-coplanar SSV techniques. Dosimetric data for scalp, target, and critical normal structure were collected and compared. <h3>Results</h3> 20 patients with newly diagnosed GBM were selected for this study. All patients received a total radiation dose of 60 Gy in 30 fractions. 10 patients received 60 Gy in 30 fractions in a single-course. The rest received radiation in a split-course, with 46 Gy in 23 fractions to an initial volume followed by 14 Gy in 7 fractions to a cone-down volume, for a combined dose of 60 Gy in 30 fractions. New VMAT plans were generated after adding scalp as an organ at risk. Median scalp volume was 410 cc (range: 377-443 cc). With SSV, there was no significant reduction in maximum scalp dose. However, SSV significantly reduced mean scalp dose, doses received by 20cc and 30 cc of the scalp, and volumes of the scalp receiving 30 Gy, 40 Gy and 50 Gy. Median reduction in mean scalp dose was 21.4% (range: 5.0–39.9%), from 14.6 Gy to 10.9 Gy. Median reduction in 20 cc scalp dose was 33.9% (range: 2.7–36.9%), from 43.9 Gy to 33.9 Gy, and 30 cc scalp dose was 24.2% (range: 5.3-39.5%), from 36.6 Gy to 28.1 Gy. There were significant reductions in the volumes of scalp receiving 30 Gy, 40 Gy, and 50 Gy as well. There were no significant differences in the doses of target, brainstem, and optic nerves between non-SSV and SSV plans. <h3>Conclusion</h3> Scalp-sparing VMAT is a feasible technique and can significantly reduce scalp radiation dose without compromising target coverage or critical normal structure constraints. This may lead to reduced acute and late radiation toxicity to the scalp. A prospective trial evaluating the clinical benefit of this technique is ongoing (NCT03251027).

Injection of hydrogel spacer increased maximal intrafractional prostate motion in anterior and superior directions during volumetric modulated arc therapy-stereotactic body radiation therapy for prostate cancer

BackgroundThe aim of this study was to clarify the association between intrafractional prostate shift and hydrogel spacer.MethodsThirty-eight patients who received definitive volumetric modulated arc therapy (VMAT)-stereotactic body radiation therapy (SBRT) for prostate cancer with prostate motion monitoring in our institution in 2018–2019 were retrospectively evaluated. In order to move the rectum away from the prostate, hydrogel spacer (SpaceOAR system, Boston Scientific, Marlborough, the United States) injection was proposed to the patients as an option in case of meeting the indication of use. We monitored intrafractional prostate motion by using a 4-dimensional (4D) transperineal ultrasound device: the Clarity 4D ultrasound system (Elekta AB). The deviation of the prostate was monitored in each direction: superior-inferior, left–right, and anterior–posterior. We also calculated the vector length. The maximum intrafractional displacement (MID) per fraction for each direction was detected and mean of MIDs was calculated per patient. The MIDs in the non-spacer group and the spacer group were compared using the unpaired t-test.ResultsWe reviewed 33 fractions in eight patients as the spacer group and 148 fractions in 30 patients as the non-spacer group. The superior MID was 0.47 ± 0.07 (mean ± SE) mm versus 0.97 ± 0.24 mm (P = 0.014), the inferior MID was 1.07 ± 0.11 mm versus 1.03 ± 0.25 mm (P = 0.88), the left MID was 0.74 ± 0.08 mm versus 0.87 ± 0.27 mm (P = 0.55), the right MID was 0.67 ± 0.08 mm versus 0.92 ± 0.21 mm (P = 0.17), the anterior MID was 0.45 ± 0.06 mm versus 1.16 ± 0.35 mm (P = 0.0023), and the posterior MID was 1.57 ± 0.17 mm versus 1.37 ± 0.22 mm (P = 0.56) in the non-spacer group and the spacer group, respectively. The max of VL was 2.24 ± 0.19 mm versus 2.89 ± 0.62 mm (P = 0.19), respectively.ConclusionsOur findings suggest that maximum intrafractional prostate motion during VMAT-SBRT was larger in patients with hydrogel spacer injection in the superior and anterior directions. Since this difference seemed not to disturb the dosimetric advantage of the hydrogel spacer, we do not recommend routine avoidance of the hydrogel spacer use.

Dosimetric Effects of Differences in Multi-Leaf Collimator Speed on SBRT-VMAT for Central Lung Cancer Patients.

Purpose: We aimed to investigate the effects of different multi-leaf collimator (MLC) speed constraints in volumetric modulated radiotherapy (VMAT) on the robustness of treatment plans for central lung cancer patients. Method and Materials: Twenty patients with central lung tumor who underwent stereotactic body radiotherapy (SBRT) with the VMAT technique at our hospital were included in this retrospective study. The reference plans were created with 3 different MLC speed constraints (Plan A: 0.1 cm/deg., Plan B: 0.3 cm/deg., and Plan C: 0.5 cm/deg.) with a 50-Gy/8Fr, planning target volume (PTV) D95% prescription. In each of these plans, setup errors from 1 to 5 mm were intentionally added in the direction of the central organ at 1-mm intervals (300 plans [20 cases × 3 MLC speeds × 5 error plans] were created in total). Each plan was then calculated by the same beam conditions as each reference plan. The actual average MLC speed and dose difference between the reference plan and the error-added plan were then calculated and compared among the 3 MLC speeds. Results: In the reference plans, the actual average MLC speeds were 0.25 ± 0.04, 0.34 ± 0.07, and 0.39 ± 0.12 cm/deg. for Plan A, Plan B, and Plan C, respectively (P < .05). For PTV and OARs, many dose indices tended to improve as the MLC speed increased, while no significant differences were observed among the 3 MLC speed constraints. However, in assessments of robustness, no significant differences in dose difference were observed among the 3 MLC speed constraints for most of the indices. Conclusions: When necessary, increasing the MLC speed constraint with a priority on improving the quality of the dose distribution is an acceptable approach for central lung cancer patients.

Significance of ovarian transposition in the preservation of ovarian function for young cervical cancer patients undergoing postoperative volumetric modulated radiotherapy.

BackgroundThis paper aimed to evaluate the effectiveness of ovarian transposition (OT) and the dose constraint for preserving ovarian function in young cervical cancer patients who underwent postoperative volumetric modulated arc therapy (VMAT).MethodsA retrospective analysis was conducted of young cervical cancer patients who accepted postoperative VMAT in the Affiliated Cancer Hospital of Nanjing Medical University from September 2015 to September 2018. VMAT plans for OT and non-OT patients were compared, and the patients’ ovarian function was followed up. The transposed position of the ovaries and the radiation dose constraint were further explored using a receiver operator characteristic (ROC) curve.ResultsA total of 51 young patients (age ≤40 years) were included in the study, 32 of whom underwent OT and 19 of whom did not. For these OT and non-OT patients, the homogeneity index (HI), conformity index (CI), organs at risk (OARs), average number of monitor units (MUs), and mean treatment time were similar and showed no statistically significant difference (P≥0.05). Through follow-up studies, the number of patients with preserved ovarian function was found to be 22 (out of 32) and 0 (out of 19) in the OT and non-OT patients, respectively. The minimal distance for preserving ovarian function was determined as 2.1 cm between the center of a transposed ovary and the planning target volume (PTV) margin. The optimal limited radiation doses were estimated as maximum dose (Dmax) 9.8 Gy and mean dose (Dmean) 4.6 Gy, respectively.ConclusionsOT shows no negative effects on dose distribution, target region conformity, protection of OARs, or treatment efficacy and is therefore a reliable method in the preservation of ovarian function for young cervical cancer patients undergoing postoperative radiotherapy using the VMAT technique. Specifically, when the distance between the center of a transposed ovary and the PTV margin is more than 2.1 cm, and the radiation dose is limited to a Dmax of less than 9.8 Gy and a Dmean of less than 4.6 Gy, the function of transposed ovaries may be preserved.

Consideration of Margin in SRS/SRT Plans for Brain Metastases Treatment With Volumetric Modulated Radiotherapy

It is well known that when treating brain metastases tumors local control depends not only on the amount of dose delivered but also on the margin to the clinical target volume in SRS/SRT treatment. The margin is commonly thought to be contributed from uncertainties of planning/treatment delivery, such as setup, imaging and target contouring, etc. It is defined as the margin expanding clinical target volume (CTV) to plan target volume (PTV). This margin, however, is the intended planning margin (PM) of clinicians. When considering contribution to the local control/toxicities from margin, it should be the delivery margin (DM), which is defined as the volume between CTV and the isodose surface at the minimum dose to PTV. The DM is contributed both from the high dose region outside of PTV and from the PM. The former has been ignored in current clinical practice though it is also a crucial part to affect the local control and treatment toxicities since this part is the high dose region in normal tissue but low dose region for the target.To access the contribution from the high dose region outside of PTV, two indexes were proposed: the modified conformity index (mCI) and modified Paddick confirmity index (mPCI). mCI = Vmin/PTV = CI + Vextra/PTV, where Vmin is the volume of brain tissue received the minimum dose to PTV or more and Vextra is the volume of brain tissue received the dose between the minimum dose to PTV and the prescribed dose. mPCI = TV2min/(PTV*Vmin), where TVmin is the target volume that is covered by the minimum dose to PTV. This retrospective study evaluated the DM with mCI, mPCI, V12 Gy, etc. for volumetric modulated radiotherapy (VMAT) planning techniques in 50 clinically treated brain metastasis cases.After implementing a set of planning techniques conformity has largely improved in the retrospective plans. Comparing the clinically treated plans with the retrospective study plans, the average CI and mCI were decreased by (6.5 ± 4.1)% and (28.1 ± 5.7)%, and the PCI and mPCI have been increased by (8.9 ± 2.9)% and (17.2 ± 2.8)% respectively (all data is expressed as ± std). The V12 (normal tissue volume irradiated within 12 Gy) was reduced by more than 35%. Comparison of historic data from 3D conformal, Dynamic conform arc and VMAT was made, and it showed that the typical CI decreased about 36% from the pioneer modality of SRS/SRT (1.67 ± 0.07) to the latest modality, VMAT (1.07 ± 0.05). This indicates that the more conformal is treatment plan the smaller the DM margin.Proposed mCI and mPCI to evaluate the DM in SRS/SRT plans for BM treatment with VMAT. Implementation of a set of planning techniques in VMAT largely improved the conformity of the VMAT plans. Comparison of CI from the progress of treatment modalities showed that the DM has been reduced 36% and its clinical impact on local control/toxicity is unknown.D. Wang: None. A.S. DeNittis: None.

Predicting the Optimal Bladder Volume to Minimize the Dose to the Organs at Risk in Carcinoma Cervix Treated With Modern Radiotherapy.

Whilst planning external beam radiotherapy (EBRT) for carcinoma cervix, bladder volume is an important consideration in deciding dose to other organs at risk (OARs). Though conformal techniques like volumetric-modulated radiotherapy (VMAT) have reduced the dose received by the OARs, there is still scope for improvement by utilizing other techniques. Planning with a full bladder is one such strategy that pushes a part of the bladder wall and the bowel away from the planning target volume (PTV). This is complicated by the fact that holding urine becomes increasingly more difficult along the course of pelvic radiotherapy. This makes the bladder volume threshold important to reduce the doses received by the OARs. We aim to assess the optimal bladder volume to spare OARs in patients with carcinoma cervix treated with VMAT.The data of 81 patients of carcinoma cervix stage IB2-IVB treated with EBRT using VMAT followed by brachytherapy was prospectively collected in this study. The patients were advised to void and drink 500 ml of water, 30 minutes following which, a simulation scan was acquired. The target was contoured according to the Japanese Clinical Oncology Group guidelines and OARs in line with Radiation Therapy Oncology Group guidelines. Constraints to the bowel, bladder, rectum, and sigmoid were V45 < 195cc, V45 < 35%, V45 < 45% and V45 < 45% respectively. A dose of 50.4 Gy in 28 fractions was prescribed to the PTV using VMAT. The generated plans were analyzed and acceptable plans were finalized for treatment with higher priority to PTV coverage while minimizing the OAR doses. The bladder volumes at simulation and the doses received by the OARS were correlated using Pearson's correlation. A receiver operating characteristic (ROC) curve was constructed to find the cut-off value of the bladder volume which facilitated achieving the dose constraints to the significantly correlated OARs with acceptable specificity and sensitivity.A correlational analysis of the bladder volume with the OAR dose constraints revealed that there was a significant negative weak correlation with the V45 Gy of the bladder and the bowel. A ROC curve was constructed assessing bladder volume against the achievability of the bladder dose constraint. The area under the curve was 0.78 showing a fairly accurate relationship between the variables. A bladder volume of 270cc is noted to be the best cut-off to achieve the bladder dose constraint with a sensitivity and specificity of approximately 75% and 80% respectively. The curve for bladder volume and achievability of bowel constraints yielded a curve with poor accuracy and an area under the curve of 0.64 and so further analysis for the same was abandoned given the low sensitivity and specificity of the attained cut-off (approximately 65%).Increasing bladder volume has reduced the doses received by bowel and bladder. A volume of 270cc is to be aimed at to achieve the V45 Gy of the bladder in patients of carcinoma cervix being treated with VMAT.S. Kombathula: None. J. Pandjatcharam: None. D. Kannikanti: None. A. Menon: None. J.M. Mathew: None. T. Elumalai: None. M. Sinnatamby: None.

Change in dysphagia and laryngeal function after radical radiotherapy in laryngo pharyngeal malignancies - a prospective observational study.

Intensity modulated radiotherapy (IMRT) has the perceived advantage of function preservation by reduction of toxicities in the treatment of laryngo-pharyngeal malignancies. The aim of the study was to assess changes in dysphagia from baseline (i.e. prior to start of treatment) at three and six months post treatment in patients with laryngo-pharyngeal malignancies treated with radical radiotherapy ± chemotherapy. Functional assessment of other structures involved in swallowing was also studied. 40 patients were sampled consecutively. 33 were available for final analysis. Dysphagia, laryngeal edema, xerostomia and voice of patients were assessed at baseline and at three and six months after treatment. Radiation was delivered with simultaneous integrated boost (SIB) using volumetric modulated radiation therapy (VMAT). Concurrent chemotherapy was three weekly cisplatin 100 mg/m2. Proportion of patients with dysphagia rose significantly from 45.5% before the start of treatment to 57.6% at three months and 60.6% at six months post treatment (p = 0.019). 67% patients received chemotherapy and addition of chemotherapy had a significant correlation with dysphagia (p = 0.05, r = -0.336). Severity of dysphagia at three and six months correlated significantly with the mean dose received by the superior constrictors (p = 0.003, r = 0.508 and p = 0.024, r = 0.391) and oral cavity (p = 0.001, r = 0.558 and p = 0.003, r = 0.501). There was a significant worsening in laryngeal edema at three and six months post treatment (p < 0.01) when compared to the pre-treatment examination findings with 60.6% of patients having grade two edema at six months. Significant fall in the mean spoken fundamental frequency from baseline was seen at 6 months (p = 0.04), mean fall was 21.3 Hz (95% CI: 1.5-41 Hz) with significant increase in roughness of voice post treatment (p = 0.01). There was progressive worsening in dysphagia, laryngeal edema and voice in laryngo-pharyngeal malignancies post radical radiotherapy ± chemotherapy.

Advanced radiotherapy technique in hepatocellular carcinoma with portal vein thrombosis: Feasibility and clinical outcomes.

In Thailand, individuals with hepatocellular carcinoma (HCC) who develop portal vein tumor thrombosis (PVTT) have a restricted treatment option because to the extent of the disease, poor underlying liver function, and non-coverage of immuno/targeted therapy. Radiotherapy (RT) plays an increasingly important function in these patients. To investigate the feasibility, efficacy, and adverse event rates, we performed a retrospective analysis of patients with HCC with PVTT who underwent 3-dimensional conformal radiation (3DCRT), intensity-modulated radiation (IMRT), volumetric-modulated radiotherapy (VMAT), and stereotactic body radiotherapy (SBRT) in a single-institution. To examine clinical results in terms of overall survival (OS), local control (LC), response of primary tumor and PVTT, hepatic and gastrointestinal adverse reaction, and prognosis variables for OS and LC. Between July 2007 and August 2019, non-metastatic HCC with PVTT patients treated with RT were retrospectively reviewed and evaluated. The analysis included data from 160 patients. The mean age of the patients was 60.8 years ((95% CI 58.2-62.0). The median diameter of the tumor was 7.7 cm (range: 1-24.5). 85 (54.5%) individuals had PVTT in the main or first branch. At 1.8-10 Gy per fraction, the mean biologically effective dose (BED) as α/β ratio of 10 was 49.6 (95% CI 46.7-52.5) Gy10. The median survival time was 8.3 (95% CI 6.1-10.3) months. Survival rates at one and two years were 39.6% and 17.1%, respectively. Estimated incidence of local failure using competing risk analysis were 24% and 60% at 1 and 2 years, respectively. The overall response rate was 74%, with an 18.5 percent complete response rate. In multivariate analysis, tumor size, overall response, and radiation dose were all significant prognostic variables for OS. Hepatic unfavorable events of grade 3 and 4 were for 14.1% of the total. There was no occurrences of grade 3-4 gastrointestinal toxicity, either acute or late. Additionally, there were no treatment-related mortality. Advanced RT is regarded as a safe and effective therapeutic option for HCC with PVTT. Overall survival was clearly related to tumor size, radiation dose, and tumor/PVTT response. Individuals with BED 56 Gy10 had significantly better overall survival than patients with BED 56 Gy10. A prospective randomized trial is required to validate these outcomes in order to corroborate these findings.

An Investigation of Non-Coplanar Volumetric Modulated Radiation Therapy for Locally Advanced Unresectable Pancreatic Cancer Using a Trajectory Optimization Method.

PurposeThis study was conducted in order to develop a trajectory optimization algorithm for non-coplanar volumetric modulated arc therapy (VMAT) and investigate the potential of organs at risk (OARs) sparing in locally advanced pancreatic cancer patients using non-coplanar VMAT.Methods and MaterialsFirstly, a cost map that represents the ray–OAR voxel intersections at each source position was generated using a ray-tracing algorithm. A graph search algorithm was then used to determine the least-cost path from the cost map. Lastly, full arcs or partial arcs were selected based on the least-cost path to generate the non-coplanar VMAT (ncVMAT) trajectories. Clinical coplanar VMAT (coVMAT) plans for 11 patients diagnosed with locally advanced unresectable pancreatic cancer (LAPC) receiving 45 to 70 Gy in 25 fractions were replanned using non-coplanar VMAT trajectories. Both coplanar and non-coplanar plans were normalized to cover 95% of the PTV45 Gy volume with a prescription dose of 45 Gy. The conformity index (CI), homogeneity index (HI), PTV coverage, and dose to the OARs were compared between coVMAT and ncVMAT plans.ResultsWith ncVMAT, the mean coverage of PTV50 Gy, PTV54 Gy, PTV60 Gy, and PTV70 Gy increased significantly. The mean conformity index of PTV45 Gy, PTV54 Gy, and PTV70 Gy was also improved in the ncVMAT plans. Compared with coVMAT plans, the ncVMAT plans resulted in significantly lower doses to the spinal cord, bilateral kidneys, stomach, and duodenum. The maximum dose to the spinal cord decreased by 6.11%. The mean dose to the left and right kidneys decreased by an average of 5.52% and 11.71%, respectively. The D max, D mean, and D 15% of the stomach were reduced by an average of 7.45%, 15.82%, and 16.79%, separately. The D 15% and D mean of the duodenum decreased 6.38% and 5.64%, respectively.ConclusionA trajectory optimization algorithm was developed for non-coplanar VMAT. Compared with conventional coplanar VMAT, non-coplanar VMAT resulted in improved coverage and conformity to the targets. The sparing of OARs was significantly improved in non-coplanar VMAT compared with coVMAT plans for locally advanced pancreatic cancer.

Volumetric Modulated Arc Therapy Craniospinal Re-Irradiation of Adulthood Medulloblastoma Leptomeningeal Disease

For the first time in the English medical literature we present two adulthood clinical cases with medulloblastoma leptomeningeal disease (LMD) in which we have performed second craniospinal irradiation (re-CSI) using bias volumetric-modulated arc therapy (VMAT) technique. In this article we present bias volumetric-modulated arc therapy (VMAT) technique for repeated CSI (re-CSI) in two patients with adulthood medulloblastoma leptomeningeal disease (LMD). In both clinical cases (case1/case2) with adulthood medulloblastoma LMD, re-CSI has been performed using the bias VMAT technique in the area of the spinal cord up to total dose (TD) - 24 Gy/32 Gy; cauda equina up to TD- 28 Gy/38 Gy; in the cerebellum up to TD- 24 Gy/28 Gy; both cerebral hemispheres up to TD- 26 Gy/32 Gy and the cerebral ventricles up to TD-30 Gy/38 Gy with daily dose (DD)-1.8 Gy (17/21fractions). We describe in detail the stages of dosimetry planning of this radiotherapy technique, presenting its advantages and disadvantages, the observed early radiation toxicity and the possible treatment outcome. Volumetric-modulated radiotherapy with bias dose VMAT technique in adulthood medulloblastoma patients achieves improved dose homogeneity at the junction of the fields, increased compliance with the target volume and minimized dose to the organs at risk (OARs).

Dosimetric comparison of constant dose rate volumetric modulated arc therapy (CDR-VMAT) and intensity-modulated radiation therapy (IMRT) for gallbladder cancer

AbstractAim:To study the feasibility of constant dose rate volumetric modulated arc therapy (CDR-VMAT) in radiotherapy for gallbladder cancer by comparing dosimetric parameter suggested by International Commission on Radiation Units and Measurements-83 (ICRU-83) with step and shoot intensity-modulated radiation therapy (SS IMRT).Methods:For this study, we selected 21 post-operative gallbladder cancer patients, which were treated with the IMRT technique from 2016 to 2019. For each patient, we generated SS IMRT plan and CDR-VMAT plan and were dosimetrically compared by parameters suggested by ICRU-83 for PTV. Homogeneity Index (HI) and Conformity Index (CI) were also calculated. For evaluation of Organ at Risk (OAR), we compared the mean doses, volume doses to the right kidney, left kidney, both kidneys combined, liver and max dose to the spinal cord. Monitor units (MUs) and treatment delivery time were also compared.Results:On comparing, we found that CDR-VMAT plans were highly conformed as CI and PCI (CI define by Paddick) were found more (0·98 ± 0·01 vs. 0·97 ± 0·03 and 0·86 ± 0·05 vs. 0·85 ± 0·05) than IMRT plans but not statistically significant. Better dose HI was found for IMRT plans with statistical significant difference (p &lt; 0·001). The tumour coverage was found similar 98·24% and 97·83% for SS IMRT and CDR-VMAT, respectively. For D2%, the maximum dose to PTV was significantly lower in IMRT (p = 0·001). D50% and mean dose to PTV were also comparable to IMRT with no statistically significant difference. The OAR parameters were comparable in both the techniques. The mean doses and volume doses V10, V20 and V30 to the right kidney, left kidney and liver were also comparable with no significant difference (p &gt; 0·05) was noted among them. However, the maximum dose to the spinal cord was significantly less in CDR-VMAT (21·1 Gy vs. 25·1Gy) than SS IMRT with p = 0·006. More MUs were associated with the CDR-VMAT technique, but shorter treatment delivery time than the IMRT technique.Conclusions:On dosimetric comparison of two treatment techniques, we conclude that CDR-VMAT can be a valid option in radiotherapy as it achieved highly conformed dose distribution, comparable tumour coverage and OAR sparing as IMRT technique for gallbladder cancer.

Error detection using a convolutional neural network with dose difference maps in patient-specific quality assurance for volumetric modulated arc therapy

The aim of this study was to evaluate the use of dose difference maps with a convolutional neural network (CNN) to detect multi-leaf collimator (MLC) positional errors in patient-specific quality assurance for volumetric modulated radiation therapy (VMAT). A cylindrical three-dimensional detector (Delta4, ScandiDos, Uppsala, Sweden) was used to measure 161 beams from 104 clinical prostate VMAT plans. For the simulation used error-free plans plus plans with two types of MLC error were introduced: systematic error and random error. A total of 483 dose distributions in a virtual cylindrical phantom were calculated with a treatment planning system. Dose difference maps were created from two planar dose distributions from the measured and calculated dose distributions, and these were used as the input for the CNN, with 375 datasets assigned for training and 108 datasets assigned for testing. The CNN model had three convolution layers and was trained with five-fold cross-validation. The CNN model classified the error types of the plans as “error-free,” “systematic error,” or “random error,” with an overall accuracy of 0.944. The sensitivity values for the “error-free,” “systematic error,” and “random error” classifications were 0.889, 1.000, and 0.944, respectively, and the specificity values were 0.986, 0.986, and 0.944, respectively. This approach was superior to those based on gamma analysis. Using dose difference maps with a CNN model may provide an effective solution for detecting MLC errors for patient-specific VMAT quality assurance.

Impact of radiopacified bone cement on radiotherapy dose calculation.

Background and purposeRadiopacifiers are introduced to bone cements to provide the appearance of bone in kilovoltage (kV) radiographic images. For higher energy megavoltage (MV) radiotherapy treatment beams, however, these radiopacifiers do not cause a bone-like perturbation of dose. This study therefore aimed to determine the impact of the barium-contrasted plastic-based cement materials on radiotherapy dose calculations.Materials and methodsThe radiological properties of a physical sample of bone cement were characterised by computed tomography (CT) imaging and transmission measurements. Monte Carlo simulations of percentage depth-dose profiles were performed to determine the possible dose error for MV treatment beams. Dose differences were then investigated for clinical volumetric modulated radiotherapy treatment plans, with and without density overrides applied.ResultsDifferences of up to 7% were observed at the downstream interface of a 0.6 cm thick bone cement layer, compared to bone. Differences in planning target volume dose-volume metrics varied between −0.5% and 2.0%.ConclusionBefore planning radiotherapy treatments for patients who have undergone cranioplasty, every effort should be made to identify whether a radiopacified bone cement has been implanted. Density overrides should be applied to minimise dose calculation errors, whenever bone cement is used.