Intensity-modulated Radiotherapy Beam Research Articles

Using Scorecards to Tune Ethos Directive Templates: An Adaptive Radiation Therapy Individualized Approach-Cervix Dosimetric Planning Study

The Adaptive Radiation Therapy Individualized Approach-Cervix clinical trial uses predefined clinical directive templates (CDTs) combined with RapidPlan dose-volume histogram estimations (DVHe) to guide plan optimization in the Ethos treatment planning system. The dosimetric scorecard is a scoring tool that quantifies improvements in plan quality after physicians have precisely expressed their complete clinical intent. To our knowledge, this is the first study to use the dosimetric scorecard tool to tune an Ethos CDT to improve resulting plan quality. Iterative replanning was used to modify the draft CDT (CDT-1) in Ethos 1.1 to generate a new CDT (CDT-2) that maximized the clinical consensus scorecard's total score compared with CDT-1. CDT-2 was established, and resulting plans were compared with and without a DVHe. Additional fixed field intensity modulated radiation therapy beam geometries were compared between CDT-1 and CDT-2, both with DVHe. After obtaining favorable results when comparing CDT-1 versus CDT-2 for 2 test cases, 10 additional cases were retrospectively identified and tested. CDT-2 reduced organ at risk doses without compromising planning target volume coverage in the initial test cases. When combined with DVHe, CDT-2 marginally outperformed CDT-1. Plan quality further improved with a 19-field geometry. In the expanded analysis, CDT-2 achieved higher scores than CDT-1 in most cases, with the 19-field approach showing superiority. Optimization and calculation time increased by 1.9 minutes, monitor unit (MU)/field decreased by 44.4, whereas beam-on time increased by 2.8 minutes when increasing fields to 19 from 9. Reoptimization with Ethos 1.1 Maintenance Release 1 resulted in decreased MU and minimal score changes. The scorecard is an effective tool to adjust an Ethos CDT to improve the average calculated plan quality. It also allowed for easy evaluation of the dosimetric impact of other planning parameters (beam arrangements and use of DVHe) to identify the best approach. Using a finely tuned CDT is expected to improve planning efficiency and decrease intrainstitutional plan quality variability, benefiting cone beam computed tomography-guided adaptive radiation therapy.

Nasopharyngeal carcinoma in a young adolescent with unilatral palatal palsy and neck mass – A rare case report

Less than 1% of all head and neck neoplasms are juvenile nasopharyngeal angiofibromas, a cancer almost exclusively found in adolescent males. Here we present a case report of 14 year old male presented with neck swelling, nasal discharge mixed with blood, right sided proptosis and right sided palatal palsy where we performed CECT scan of the patient which showed homogenous opacity over nasopharynx extending to soft palate and posteriorly to C1 vertebra and DNE was performed. Later patient was planned for DNE along with biopsy which came out to be undifferentiated non-keratinized squamous cell carcinoma grade III. Further patient received external beam intensity modulated radiation therapy with complete response to treatment.

Delta4-based Dosimetric Error Detection in Volumetric-modulated Arc Therapy: Clinical Significance and Implications.

Volumetric-modulated arc therapy (VMAT) is an efficient method of administering intensity-modulated radiotherapy beams. The Delta4 device was employed to examine patient data. The utility of the Delta4 device in identifying errors for patient-specific quality assurance of VMAT plans was studied in this research. Intentional errors were purposely created in the collimator rotation, gantry rotation, multileaf collimator (MLC) position displacement, and increase in the number of monitor units (MU). The results show that when the characteristics of the treatment plans were changed, the gamma passing rate (GPR) decreased. The largest percentage of erroneous detection was seen in the increasing number of MU, with a GPR ranging from 41 to 92. Gamma analysis was used to compare the dose distributions of the original and intentional error designs using the 2%/2 mm criteria. The percentage of dose errors (DEs) in the dose-volume histogram (DVH) was also analyzed, and the statistical association was assessed using logistic regression. A modest association (Pearson's R-values: 0.12-0.67) was seen between the DE and GPR in all intentional plans. The findings indicated a moderate association between DVH and GPR. The data reveal that Delta4 is effective in detecting mistakes in treatment regimens for head-and-neck cancer as well as lung cancer. The study results also imply that Delta4 can detect errors in VMAT plans, depending on the details of the defects and the treatment plans employed.

A tomographic reconstruction algorithm for cross-sectional imaging of IMRT beams from six projections

Objective. Patient-specific Quality Assurance (QA) measurements are of key importance in radiotherapy for safe and efficient treatment delivery and allow early detection of clinically relevant errors. Such QA processes remain challenging to implement for complex Intensity Modulated Radiation Therapy (IMRT) radiotherapy fields delivered using a multileaf collimator (MLC) which often feature small open segments and raise QA issues similar to those encountered in small field dosimetry. Recently, detectors based on long scintillating fibers have been proposed to measure a few parallel projections of the irradiation field with good performance for small field dosimetry. The purpose of this work is to develop and validate a novel approach to reconstruct MLC-shaped small irradiation fields from six projections. Approach. The proposed field reconstruction method uses a limited number of geometric parameters to model the irradiation field. These parameters are iteratively estimated with a steepest descent algorithm. The reconstruction method was first validated on simulated data. Real data were measured with a water-equivalent slab phantom equipped with a detector made of 6 scintillating-fiber ribbons placed at 1 m from the source. A radiochromic film was used to acquire a reference measurement of a first dose distribution in the slab phantom at the same source-to-detector distance and the treatment planning system (TPS) provided the reference for another dose distribution. In addition, simulated errors introduced on the delivered dose, field location and field shape were used to evaluate the ability of the proposed method to efficiently identify a deviation between the planned and delivered treatments. Main results. For a first small IMRT segment, 3%/3 mm, 2%/2 mm and 2%/1 mm gamma analysis conducted between the reconstructed dose distribution and the dose measured with radiochromic film exhibited pass rates of 100%, 99.9% and 95.7%, respectively. For a second and smaller IMRT segment, the same gamma analysis performed between the reconstructed dose distribution and the reference provided by the TPS showed pass rates of 100%, 99.4% and 92.6% for the 3%/3 mm, 2%/2 mm and 2%/1 mm gamma criteria, respectively. Gamma analysis of the simulated treatment delivery errors showed the ability of the reconstruction algorithm to detect a 3% deviation between the planned and delivered doses, as well as shifts lower than 7 mm and 3 mm when considering an individual leaf and a whole field shift, respectively. Significance. The proposed method allows accurate tomographic reconstruction of IMRT segments by processing projections measured with six scintillating-fiber ribbons and is suitable for water-equivalent real-time small IMRT segments QA.

Assessment of Treatment Plan Quality between Flattening Filter and Flattening Filter Free Photon Beam for Carcinoma of the Esophagus with IMRT Technique.

As compared to the flattened photon beam, removing the flattening filter (FF) from the head of a gantry decreases the average energy of the photon beam and increases the dose rate, leading to an impact on the quality of treatment plans. This study aimed to compare the quality of intensity-modulated radiation therapy (IMRT) treatment plans for esophageal cancer with and without a flattened filter photon beam. In this analytical study, 12 patients, who had already been treated with a 6X FF photon beam, were treated based on new IMRT methods using a 6X the flattening filter-free (FFF) photon beam. Both 6X FF IMRT and 6X FFF IMRT plans used identical beam parameters and planning objectives. All plans were evaluated with planning indices and doses for organs at risk (OARs). Insignificant dose variation was for HI, CI, D98%, and V95% between FF and FFF photon beam IMRT plans. FF-based IMRT plan delivered a 15.51 % and 11.27% higher mean dose to both lungs and heart than the FFF plan, respectively. The integral dose (ID) for the heart and lungs was 11.21% and 15.51%, respectively, less in the IMRT plan with an FFF photon beam. In contrast to the FF photon beam, a filtered photon beam-oriented IMRT plan provides significant OAR sparing without losing the quality of the treatment plan. High monitor units (MUs), low ID, and Beam on Time (BOT) are major highlights of the IMRT plan with FFF beam.

Comparison of Dose Calculation Algorithms for Accelerated Partial Breast Intensity Modulated Radiation Therapy

<h3>Purpose/Objective(s)</h3> Accelerated partial breast irradiation (APBI) using intensity modulated radiation therapy (IMRT) has been introduced recently as an alternative treatment to whole breast irradiation for early-stage breast cancer after lumpectomy. Plan dose volume constraints for IMRT APBI are complex, requiring a more conformal and homogenous dose distribution compared to traditional tangential beam based whole breast planning. Anisotropic Analytical Algorithm (AAA) has been widely used for photon dose calculation. An Advanced Dose Calculation algorithm (AXB) is known to achieve comparable accuracy to Monte Carlo (MC) algorithm, the golden standard dose calculation, in heterogeneous media. However, the clinical assessment of AXB has been lacking. As a preliminary study, we investigated the dosimetric differences between the AAA, AXB and MC calculations on APBI IMRT. <h3>Materials/Methods</h3> Six patients with left breast cancer who previously received APBI IMRT were analyzed for this study. All patients received 30 Gy in 5 fractions with a multi beam IMRT technique using AAA 15.6 in the planning system. The following dose volume constraints were used for acceptable plan criteria based on the APBI IMRT Florence trial and all 6 cases previously treated met these criteria: For target (lumpectomy PTV), V28.5 Gy=100%, maximum dose to target < = 105% and V105% <= 2%. For critical organs, uninvolved breast with V15 Gy < 25%, ipsilateral lung volume with V10 Gy < 20%, contralateral breast maximal dose < 1 Gy, heart with V3 Gy < 10%. For a dosimetric comparison, plans were generated with AXB 15.6, reporting dose to medium, for each corresponding AAA plan by re-optimizing with the same dose constraints. After that, AXB plans were re-calculated with MC algorithm using XVMC and compared to AXB. <h3>Results</h3> The re-calculated plans using AXB for the same monitor units with an identical beam setup from AAA plans did not meet the acceptable dose volume criteria. For re-optimized plans with AXB, target conformity index, V28.5Gy and critical organs met the criteria but maximum dose and V105% were still higher than AAA plans (107-110% vs. 104-105.5% for max dose; <i>p</i>=0.02, 2.5- 5.0% vs. 0-2% for V105; <i>p</i> <0.001). The plan comparison between AXB and MC calculations showed similarity in dose distributions and hotspot area, and minimum difference in dose volume histogram. <h3>Conclusion</h3> The present data is the first report to assess the AXB for APBI IMRT. All 6 plans needed the re-optimization for AXB from plans with AAA to comply with the dose volume constraints. However hot spot size was better with AAA plans. MC calculation confirmed the dose distribution and hot spot area produced by AXB. Therefore, the clinical use of AXB for APBI IMRT will need careful evaluation due to a discrepancy in dose distributions and hot spot sizes between AAA and AXB calculations.

Preliminary Study on the Use of Fricke Gel Dosimeter for Verification of IMRT Beam Delivery

The goal of intensity-modulated radiation therapy (IMRT) is to deliver a uniform dose to the tumor with minimal margins around the target, in order to increase local control of the disease while reducing secondary effects. The research performed in this work has shown the potential usefulness of the Fricke-gel dosimeter as a quality assurance (QA) tool to verify IMRT treatments produced by inverse treatment planning. First, the 3D integrating Fricke-gel dosimeter was successfully compared to an accepted dosimetric tool. It was then used to measure relative 3D dose distributions of simple treatment plans with multiple square or rectangular fields and specific inverse-planned IMRT treatment plans. By combining the CT anatomical information and the plan contours with the gel-measured data, it was possible to display the contours on the measured dose and the measured isodose lines on the CT, in addition to measuring dose-volume histograms (DVH) for the plans. This demonstrated the usefulness of the gel dosimeter as a QA tool for IMRT and inverse planning.

The Fraction Size Sensitivity of Late Genitourinary Toxicity: Analysis of Alpha/Beta (α/β) Ratios in the CHHiP Trial

Moderately hypofractionated external beam intensity modulated radiation therapy (RT) for prostate cancer is now standard-of-care. Normal tissue toxicity responses to fraction size alteration are nonlinear: the linear-quadratic model is a widely used framework accounting for this, through the α/β ratio. Few α/β ratio estimates exist for human late genitourinary endpoints; here we provide estimates derived from a hypofractionation trial. The CHHiP trial randomized 3216 men with localized prostate cancer 1:1:1 between conventionally fractionated intensity modulated RT (74 Gy/37 fractions (Fr)) and 2 moderately hypofractionated regimens (60 Gy/20 Fr and 57 Gy/19 Fr). RT plan and suitable follow-up assessment was available for 2206 men. Three prospectively assessed clinician-reported toxicity scales were amalgamated for common genitourinary endpoints: dysuria, hematuria, incontinence, reduced flow/stricture, and urine frequency. Per endpoint, only patients with baseline zero toxicity were included. Three models for endpoint grade ≥1 (G1+) and G2+ toxicity were fitted: Lyman Kutcher-Burman (LKB) without equivalent dose in 2 Gy/Fr (EQD2) correction [LKB-NoEQD2]; LKB with EQD2-correction [LKB-EQD2]; LKB-EQD2 with dose-modifying-factor (DMF) inclusion [LKB-EQD2-DMF]. DMFs were age, diabetes, hypertension, pelvic surgery, prior transurethral resection of prostate (TURP), overall treatment time and acute genitourinary toxicity (G2+). Bootstrapping generated 95% confidence intervals and unbiased performance estimates. Models were compared by likelihood ratio test. The LKB-EQD2 model significantly improved performance over LKB-NoEQD2 for just 3 endpoints: dysuria G1+ (α/β=2.0 Gy; 95% confidence interval [CI], 1.2-3.2 Gy), hematuria G1+ (α/β=0.9 Gy; 95% CI, 0.1-2.2 Gy) and hematuria G2+ (α/β=0.6 Gy; 95% CI, 0.1-1.7 Gy). For these 3 endpoints, further incorporation of 2 DMFs improved on LKB-EQD2: acute genitourinary toxicity and prior TURP (hematuria G1+ only), but α/β ratio estimates remained stable. Inclusion of EQD2-correction significantly improved model fitting for dysuria and hematuria endpoints, where fitted α/β ratio estimates were low: 0.6 to 2 Gy. This suggests therapeutic gain for clinician-reported GU toxicity, through hypofractionation, might be lower than expected by typical late α/β ratio assumptions of 3 to 5 Gy.

Emerging Role of Carbon Ion Radiotherapy in Reirradiation of Recurrent Head and Neck Cancers: What Have We Achieved So Far?

Administering reirradiation for the treatment of recurrent head and neck cancers is extremely challenging. These tumors are hypoxic and radioresistant and require escalated radiation doses for adequate control. The obstacle to delivering this escalated dose of radiation to the target is its proximity to critical organs at risk (OARs) and possible development of consequent severe late toxicities. With the emergence of highly sophisticated technologies, intensity-modulated radiotherapy (IMRT) and stereotactic body radiotherapy have shown promising outcomes. Proton beam radiotherapy has been used for locally recurrent head and neck cancers because of its excellent physical dose distribution, exploring sharp Bragg peak properties with negligible entrance and exit doses. To further improve these results, carbon ion radiotherapy (CIRT) has been explored in several countries across Europe and Asia because of its favorable physical properties with minimal entrance and exit doses, sharper lateral penumbra, and much higher and variable relative biological efficacy, which cannot be currently achieved with any other form of radiation. Few studies have described the role of CIRT in recurrent head and neck cancers. In this article, we have discussed the different aspects of carbon ions in reirradiation of recurrent head and neck cancers, including European and Asian experiences, different dose schedules, dose constraints of OARs, outcomes, and toxicities, and a brief comparison with proton beam radiotherapy and IMRT.

A hybrid optimization strategy for deliverable intensity-modulated radiotherapy plan generation using deep learning-based dose prediction.

To propose a clinically feasible automatic planning solution for external beam intensity-modulated radiotherapy, including dose prediction via a deep learning and voxel-based optimization strategy. The dose distribution of patients was predicted using a U-Net-based deep learning network based on the patient's anatomy information. One hundred seventeen patients with nasopharyngeal cancer (NPC) and 200 patients with rectal cancer were enrolled in this study. For NPC cases, 94 cases were included in the training dataset, 13 in the validation dataset, and 10 in the testing dataset. For rectal cancer cases, 172 cases were included in the training set, 18 in the validation set, and 10 in the testing set. A voxel-based optimization strategy, "Voxel," was proposed to achieve treatment planning optimization by dividing body voxels into two parts: inside planning target volumes (PTVs) and outside PTVs. Fixed dose-volume objectives were attached to the total objective function to realize individualized planning intended as the "hybrid" optimizing strategy. Automatically generated plans were compared with clinically approved plans to evaluate clinical gains, according to dosimetric indices and dose-volume histograms (DVHs). Similarities were found between the DVH of the predicted dose and clinical plan, although significant differences were found in some organs at risk. Better organ sparing and suboptimal PTV coverage were shown using the voxel strategy; however, the deviations in homogeneity indices (HIs) and conformity indices (CIs) of the PTV between automatically generated plans and manual plans were reduced by the hybrid strategy ([manual plans]/[voxel plans[/[hybrid plans]: HI of PTV70 [1.06/1.12/1.02] and CI of PTV70 [0.79/0.58/0.76]). The optimization time for each patient was within 1 min and included fluence map optimization, leaf sequencing, and control point optimization. All the generated plans (voxel and hybrid strategy) could be delivered on uRT-linac 506c (United Imaging Healthcare, Shanghai, China). Deliverable plans can be generated by incorporating a voxel-based optimization strategy into a commercial treatment planning system (TPS). The hybrid optimization method shows the benefit and clinical feasibility in generating clinically acceptable plans.

Glioblastoma radiotherapy using Intensity modulated Radiotherapy (IMRT) or proton Radiotherapy\u2014GRIPS Trial (Glioblastoma Radiotherapy via IMRT or Proton BeamS): a study protocol for a multicenter, prospective, open-label, randomized, two-arm, phase III study

BackgroundRadiation therapy is an integral part of the multimodal primary therapy of glioblastomas. As the overall prognosis in this tumor entity remains unfavorable, current research is focused on additional drug therapies, which are often accompanied by increases in toxicity. By using proton beams instead of photon beams, it is possible to protect large parts of the brain which are not affected by the tumor more effectively. An initial retrospective matched-pair analysis showed that this theoretical physical benefit is also clinically associated with a reduction in toxicity during therapy and in the first few months thereafter.Methods/designThe GRIPS trial is a multicenter, prospective, open-label, randomized, two-arm, phase III study using either intensity modulated photon radiation techniques (standard arm) or proton beam radiotherapy (experimental arm). Additionally, patients are stratified according to "fractionation scheme" (normofractionated/hypofractionated), "subventricular zone involvement" (yes/no) and concurrent chemotherapy (yes/no) and the planned case number is 326 patients.Radiation therapy is performed with a dose of 30 × 2 Gy(RBE) or 33 × 1.8 Gy(RBE), or for patients treated according to the hypofractionation protocol with 15 × 2.67 Gy(RBE). A possible administration of additional chemotherapy (concurrent or adjuvant) or tumor treating fields is applied in dosage and frequency according to the therapy standard outside of this study. The primary endpoint is the cumulative rate of toxicity CTC grade 2 and higher in the first 4 months. Secondary endpoints include overall survival, progression-free survival, quality of life, and neurocognition.DiscussionAim of the GRIPS study is to prospectively assess whether the theoretical physical advantage of proton beam radiotherapy will translate into a clinical reduction of toxicity during and in the first months after therapy.Trial registrationClinicalTrials (NCT): NCT04752280.

A Systematic Review on Intensity Modulated Radiation Therapy for Mediastinal Hodgkin's Lymphoma.

Secondary malignant neoplasms (SMNs) and cardiovascular diseases induced by chemotherapy and radiotherapy represent the main cause of excess mortality for early-stage Hodgkin lymphoma patients, especially when the mediastinum is involved. Conformal radiotherapy techniques such as Intensity-Modulated Radiation Therapy (IMRT) could allow a reduction of the dose to the organs-at-risk (OARs) and therefore limit long-term toxicity. We performed a systematic review of the current literature regarding comparisons between IMRT and conventional photon beam radiotherapy, or between different IMRT techniques, for the treatment of mediastinal lymphoma. IMRT allows a substantial reduction of the volumes of OARs exposed to high doses, reducing the risk of long-term toxicity. This benefit is conterbalanced by the increase of volumes receiving low doses, that could potentially increase the risk of SMNs. Treatment planning should be personalized on patient and disease characteristics. Dedicated techniques such as "butterfly" VMAT often provide the best trade-off.

Error detection model developed using a multi‐task convolutional neural network in patient‐specific quality assurance for volumetric‐modulated arc therapy

In patient-specific quality assurance (QA) for static beam intensity-modulated radiation therapy (IMRT), machine-learning-based dose analysis methods have been developed to identify the cause of an error as an alternative to gamma analysis. Although these new methods have revealed that the cause of the error can be identified by analyzing the dose distribution obtained from the two-dimensional detector, they have not been extended to the analysis of volumetric-modulated arc therapy (VMAT) QA. In this study, we propose a deep learning approach to detect various types of errors in patient-specific VMAT QA. A total of 161 beams from 104 prostate VMAT plans were analyzed. All beams were measured using a cylindrical detector (Delta4; ScandiDos, Uppsala, Sweden), and predicted dose distributions in a cylindrical phantom were calculated using a treatment planning system (TPS). In addition to the error-free plan, we simulated 12 types of errors: two types of multileaf collimator positional errors (systematic or random leaf offset of 2mm), two types of monitor unit (MU) scaling errors (±3%), two types of gantry rotation errors (±2° in clockwise and counterclockwise direction), and six types of phantom setup errors (±1mm in lateral, longitudinal, and vertical directions). The error-introduced predicted dose distributions were created by editing the calculated dose distributions using a TPS with in-house software. Those 13 types of dose difference maps, consisting of an error-free map and 12 error maps, were created from the measured and predicted dose distributions and were used to train the convolutional neural network (CNN) model. Our model was a multi-task model that individually detected each of the 12 types of errors. Two datasets, Test sets 1 and 2, were prepared to evaluate the performance of the model. Test set 1 consisted of 13 types of dose maps used for training, whereas Test set 2 included the dose maps with 25 types of errors in addition to the error-free dose map. The dose map, which introduced 25 types of errors, was generated by combining two of the 12 types of simulated errors. For comparison with the performance of our model, gamma analysis was performed for Test sets 1 and 2 with the criteria set to 3%/2mm and 2%/1mm (dose difference/distance to agreement). For Test set 1, the overall accuracy of our CNN model, gamma analysis with the criteria set to 3%/2mm, and gamma analysis with the criteria set to 2%/1mm was 0.92, 0.19, and 0.81, respectively. Similarly, for Test set 2, the overall accuracy was 0.44, 0.42, and 0.95, respectively. Our model outperformed gamma analysis in the classification of dose maps containing a single type error, and the performance of our model was inferior in the classification of dose maps containing compound errors. A multi-task CNN model for detecting errors in patient-specific VMAT QA using a cylindrical measuring device was constructed, and its performance was evaluated. Our results demonstrate that our model was effective in identifying the error type in the dose map for VMAT QA.

Proton therapy for patients with esophageal cancer: History, characteristics, clinical outcome and future direction of proton beam therapy.

After the second war, Wilson who participated in development of the atomic bomb in Los Alamos studied peaceful use of atomic energy and proposed a property of proton beam that has potential to treat cancer. According to his proposal, the first patient was treated with proton beam therapy at the University of California Berkley in 1954. The first series of proton beam therapy for patients with esophageal cancer was reported from Japan in 1993. After that many proton facilities in Japan reported the clinical outcome of patients with esophageal cancer. Many dosimetric and clinical studies showed proton beam therapy for esophageal cancer was less toxic than photon beam therapy, however there is a paucity of randomized trials and evidence that proton beam therapy has clearly superior survival compared to photon therapy. Only one randomized trial has been conducted to study less toxicity for proton beam compared with intensity modulated radiotherapy (IMRT), which was stopped early because toxicities of IMRT were higher. A phase III study comparing overall survival between proton beam therapy and IMRT is now activated. A cost reduction for proton therapy is necessary to facilitate patient care and establishment of clinical evidence.

Oncologic outcomes in the era of modern radiation therapy using FIGO 2018 staging system for cervical cancer

BackgroundThe recently published ASTRO cervical cancer guidelines recommend the use of modern radiotherapy. Imaging is now incorporated in the updated FIGO 2018 staging with a new stage IIIC. This study aims to evaluate the oncologic outcomes and predictors of survival using FIGO 2018 staging in a cohort of patients treated in an era of high-precision image-guided radiotherapy. MethodsWe performed a retrospective cohort study of 216 adult cervical cancer patients treated with definitive chemoradiotherapy between 2010 and 2018. Eligible patients had non-metastatic cervical cancer treated at a single academic institution. All patients had pre-treatment MRI and CT/PET. Treatment protocol consisted of external beam intensity-modulated radiotherapy and 3D image-guided brachytherapy. Kaplan-Meier curves were used for survival analysis. Multivariate cox proportional-hazards model was performed to identify potential prognostic factors. ResultsMedian age at diagnosis was 50 and median BMI was 26.4 kg/m2. Median follow-up time was 44.3 months. Five-year overall survival (OS), disease-free survival and loco-regional disease-free survival rates were 76.8%, 68.5% and 82.6%, respectively. FIGO 2018 showed better OS discrimination compared to FIGO 2009 classification. OS was increasingly worse with positive pelvic and para-aortic nodes (p < 0.001). In a multivariate prediction model, performance status (p = 0.044) and FIGO 2018 classification (stage III p = 0.016; stage IVA p = 0.010) were predictors of mortality; FIGO 2018 classification (stage III p = 0.003; stage IVA p = 0.001) was a predictor of any recurrence; MRI tumor diameter (p ≤ 0.001) and nodal metastases (p = 0.024) were predictors of loco-regional recurrence. ConclusionsIntegration of state-of-the-art imaging in cervical cancer staging and in radiotherapy planning leads to good loco-regional control rates, however distant recurrence remains an important issue. FIGO 2018 staging better reflects patient prognosis, highlighting the need for new treatment strategies for stage IIIC cervical cancer.

PP35 Presentation Time: 11:30 AM: An Organ at Risk Dosimetric Comparison of HDR Multicatheter Brachytherapy versus External Beam Intensity Modulated Accelerated Partial Breast Irradiation

Purpose: Accelerated partial breast irradiation (APBI) is an adjuvant treatment option for select patients following partial mastectomy for early-stage breast cancer. Multiple APBI techniques have been described for both external beam radiation therapy (EBRT) and high dose rate (HDR) brachytherapy. Given the differences in these treatment techniques, we aimed to compare radiation dose to adjacent organs at risk (OARs) between 8 fraction HDR multicatheter interstitial brachytherapy and 5 fraction external beam intensity modulated radiation therapy (IMRT).

Measurement of surface dose in an MR-Linac with optically stimulated luminescence dosimeters for IMRT beam geometries.

This study aims to measure the surface dose on an anthropomorphic phantom for intensity-modulated radiation therapy (IMRT) plans treated in a 1.5T magnetic resonance (MR)-Linac. Previous studies have used Monte Carlo programs to simulate surface dose and have recognized high surface dose as a potential limiting factor for the MR-Linac; however, to our knowledge surface dose measurement for clinical plans has not yet been published. Given the novelty of the MR-Linac, it is important to perform in vivo measurements of a potentially dose-limiting factor such as surface dose when moving forward for clinical use. Optically stimulated luminescence dosimeters (OSLDs) were used on an anthropomorphic phantom. Intensity-modulated radiation therapy plans were generated to treat a near-surface breast tumor in the phantom. The tumor was treated with 2, 3, 5, 7, and 9 beam IMRT plans with a 1.5T MR-Linac using a 7-MV photon beam. The plans were generated in a Monte Carlo treatment planning system (TPS) capable of modeling magnetic field effects. The surface dose was sampled in seven locations on the surface surrounding the planning target volume (PTV), and in two different OSLD configurations with the dosimeters measuring water equivalent depths of 0.16 and 0.64mm. The TPS was used to estimate the doses at the OSLD locations. In addition, MR images were taken of a pork belly with and without an OSLD placed anteriorly placed to determine the effect of an OSLD on image fidelity. For the 3, 5, 7, and 9-beam configurations, surface doses were approximately half that of the prescription dose to the simulated tumor, although the magnitude of the skin dose relative to the prescription is certainly also dependent on individual patient anatomy. The general trend for both TPS and measurements was that the greater the number of beams, the lower the skin doses and dose readings; also, with increasing numbers of beams, doses at shallow depths become lower relative to deeper depths. The MR images showed that the presence of the OSLD did not induce clinically relevant geometric distortions or intensity differences. To our knowledge, this study is the first of its kind to experimentally measure the surface dose in an MR-Linac for IMRT plans. This study has explored the use of OSLDs to measure in vivo surface dose in a clinical setting. OSLDs may be used to measure skin dose clinically when there are concerns of skin radiation burns and near-surface toxicity. Optically stimulated luminescence dosimeters are promising devices for in vivo surface dosimetry in an MR-Linac.

Operating a treatment planning system using a deep-reinforcement learning-based virtual treatment planner for prostate cancer intensity-modulated radiation therapy treatment planning.

In the treatment planning process of intensity-modulated radiation therapy (IMRT), a human planner operates the treatment planning system (TPS) to adjust treatment planning parameters, for example, dose volume histogram (DVH) constraints' locations and weights, to achieve a satisfactory plan for each patient. This process is usually time-consuming, and the plan quality depends on planer's experience and available planning time. In this study, we proposed to model the behaviors of human planners in treatment planning by a deep reinforcement learning (DRL)-based virtual treatment planner network (VTPN), such that it can operate the TPS in a human-like manner for treatment planning. Using prostate cancer IMRT as an example, we established the VTPN using a deep neural network developed. We considered an in-house optimization engine with a weighted quadratic objective function. Virtual treatment planner network was designed to observe an intermediate plan DVHs and decide the action to improve the plan by changing weights and threshold dose in the objective function. We trained the VTPN in an end-to-end DRL process in 10 patient cases. A plan score was used to measure plan quality. We demonstrated the feasibility and effectiveness of the trained VTPN in another 64 patient cases. Virtual treatment planner network was trained to spontaneously learn how to adjust treatment planning parameters to generate high-quality treatment plans. In the 64 testing cases, with initialized parameters, quality score was 4.97 (±2.02), with 9.0 being the highest possible score. Using VTPN to perform treatment planning improved quality score to 8.44 (±0.48). To our knowledge, this was the first time that intelligent treatment planning behaviors of human planner in external beam IMRT are autonomously encoded in an artificial intelligence system. The trained VTPN is capable of behaving in a human-like way to produce high-quality plans.

Application of Two-Dimensional Detector Arrays to the Delivery Quality Assurance in Breast IMRT

Most two-dimensional (2D) detector arrays used for the verification of the intensity-modulated radiotherapy (IMRT) dose distribution comprise diode detectors or ion chamber detectors. These detectors show different sensitivities depending on the angle of incidence of the IMRT beam on the detector. In this study, the effect of the radiation beam’s angle of incidence onto the detector was analyzed in order to find an optimal 2D detector array setup position for delivery quality assurance in breast IMRT. For breast IMRT plans, comprising mostly tangential fields, the dose distribution produced with true composite beams was measured by arranging 2D detector array devices at various angles. The change in dosimetric accuracy was then assessed as a function of the radiation beam’s angle of incidence. A total of 72 dose distributions were measured and analyzed for 12 breast IMRT plans. Both the diode detector array and the ion chamber array showed a higher gamma passing ratio in the sagittal dose distribution measurement, where the beam’s angle of incidence was relatively larger. This study indicates that using a 2D detector array placed at a relatively large angle of incidence offers a more accurate verification of the IMRT dose distribution.

EBRT Modality-Specific Treatment Outcome of Cervical Cancer Patients for Real-World Practice

Purpose: To compare the clinical outcome while treating cervical cancer patients with intensity modulated radiation therapy (IMRT) versus 3-dimensional conformal radiation therapy (3DCRT). Methods: Analyzed a very large dataset from real-world practice using the National Cancer Database (NCDB) for FIGO IB-IIIB inoperable cervical cancer patients treated with chemoradiation from 2004 to 2014. Patients who received initial treatment with external beam radiation therapy (EBRT), either IMRT or 3DCRT, of 40-60Gy dose were included. Patients who received EBRT boost were stratified based on treatment modality (IMRT or 3DCRT for initial and boost). Also considered another group where EBRT is followed by brachytherapy, i.e. the standard of care. IBM-SPSS was used for statistical analysis; p-value &lt;0.05 was considered statistically significant. Results: Median age of the eligible patient population was 53 years and the median follow-up was 24.4 months. Analysis revealed that the median OS was 36.1 months for IMRT versus 51.2 months for 3DCRT (p &lt;0.05); 2- and 5-year OS were 7% and 9%, higher for 3DCRT (p &lt;0.007). Conclusion: This study demonstrates 3DCRT was better than IMRT for OS when no brachytherapy boost was considered. However, 3DCRT and IMRT did not make any difference in OS when brachytherapy boost was used. Therefore, it is important to use brachytherapy boost whenever possible for treatment of inoperable cervical cancer patients with curative intent.