Intensity-modulated Treatment Research Articles

2D antiscatter grid and scatter sampling based CBCT method for online dose calculations during CBCT guided radiation therapy of pelvis.

Online dose calculations before the delivery of radiation treatments have applications in dose delivery verification, online adaptation of treatment plans, and simulation-free treatment planning. While dose calculations by directly utilizing CBCT images are desired, dosimetric accuracy can be compromised due to relatively lower HU accuracy in CBCT images. In this work, we propose a novel CBCT imaging pipeline to enhance the accuracy of CBCT-based dose calculations in the pelvis region. Our approach aims to improve the HU accuracy in CBCT images, thereby improving the overall accuracy of CBCT-based dose calculations prior to radiation treatment delivery. An in-house developed quantitative CBCT pipeline was implemented to address the CBCT raw data contamination problem. The pipeline combines algorithmic data correction strategies and 2D antiscatter grid-based scatter rejection to achieve high CT number accuracy. To evaluate the effect of the quantitative CBCT pipeline on CBCT-based dose calculations, phantoms mimicking pelvis anatomy were scanned using a linac-mounted CBCT system, and a gold standard multidetector CT used for treatment planning (pCT). A total of 20 intensity-modulated treatment plans were generated for five targets, using 6 and 10 MV flattening filter-free beams, and utilizing small and large pelvis phantom images. For each treatment plan, four different dose calculations were performed using pCT images and three CBCT imaging configurations: quantitative CBCT, clinical CBCT protocol, and a high-performance 1D antiscatter grid (1D ASG). Subsequently, dosimetric accuracy was evaluated for both targets and organs at risk as a function of patient size, target location, beam energy, and CBCT imaging configuration. When compared to the gold-standard pCT, dosimetric errors in quantitative CBCT-based dose calculations were not significant across all phantom sizes, beam energies, and treatment sites. The largest error observed was 0.6% among all dose volume histogram metrics and evaluated dose calculations. In contrast, dosimetric errors reached up to 7% and 97% in clinical CBCT and high-performance ASG CBCT-based treatment plans, respectively. The largest dosimetric errors were observed in bony targets in the large phantom treated with 6 MV beams. The trends of dosimetric errors in organs at risk were similar to those observed in the targets. The proposed quantitative CBCT pipeline has the potential to provide comparable dose calculation accuracy to the gold-standard planning CT in photon radiation therapy for the abdomen and pelvis. These robust dose calculations could eliminate the need for density overrides in CBCT images and enable direct utilization of CBCT images for dose delivery monitoring or online treatment plan adaptations before the delivery of radiation treatments.

Radiomics Breakthrough Could Spark the Head and Neck Cancer Radiotherapy Revolution

Radiomics, the method by which digital images could be transformed into mineable data, opens new horizons for biomedical research and in particular in oncology, for diagnostic, predictive and prognostic purposes. The use of artificial intelligence (AI) algorithms in the radiomics algorithm makes radiomics and AI two inseparable, intricate domains. AI defined as machine capability of imitating human intelligence, has already been implemented on a large scale in oncology and radiotherapy. One of the two main branches (the virtual one) of machine learning depending on the application, artificial intelligence is involved both in the diagnostics processes as well as treatment planning, – dose delivery and radiotherapy quality assurance (QA). Head and neck cancer (HNC), although it is the 6th malignancy in incidence worldwide, is redoubtable due to the high rate of therapeutic failures, especially of loco-regional recurrence. Although intensity-modulated treatment techniques have brought benefits especially in limiting the toxicities associated with irradiation, AI and especially radiomics, due the possibility to extract data from high-resolution medical imaging in order to build predictive diagnostic and prognostic models, could upgrade the technological revolution in HNC radiotherapy at a higher level. Beyond the already intensively studied diagnostic applications, radiomics could be useful for predicting the response to radio-chemotherapy, anticipating treatment related toxicities and for pre-therapeutic evaluation of the need for adaptive radiotherapy (ART). Clinical-radiomic models have superior predictive power and the delta variation of radiomic features could be a biomarker still less evaluated. Due to characteristics of modern radiotherapy which includes as standard the image guided radiotherapy (IGRT) concept using the computer tomography (CT) simulator and Cone Beam CT (CBCT) to ensure the accuracy of the patient’s positioning during the treatment, radiomics in radiotherapy could be the spearhead of the translation radiomics in daily clinical routine and of the HNC RGRT concept development.

Efficiency enhancements of a Monte Carlo beamlet based treatment planning process: implementation and parameter study

Objective. The computational effort to perform beamlet calculation, plan optimization and final dose calculation of a treatment planning process (TPP) generating intensity modulated treatment plans is enormous, especially if Monte Carlo (MC) simulations are used for dose calculation. The goal of this work is to improve the computational efficiency of a fully MC based TPP for static and dynamic photon, electron and mixed photon-electron treatment techniques by implementing multiple methods and studying the influence of their parameters. Approach. A framework is implemented calculating MC beamlets efficiently in parallel on each available CPU core. The user can specify the desired statistical uncertainty of the beamlets, a fractional sparse dose threshold to save beamlets in a sparse format and minimal distances to the PTV surface from which 2 × 2 × 2 = 8 (medium) or even 4 × 4 × 4 = 64 (large) voxels are merged. The compromise between final plan quality and computational efficiency of beamlet calculation and optimization is studied for several parameter values to find a reasonable trade-off. For this purpose, four clinical and one academic case are considered with different treatment techniques. Main results. Setting the statistical uncertainty to 5% (photon beamlets) and 15% (electron beamlets), the fractional sparse dose threshold relative to the maximal beamlet dose to 0.1% and minimal distances for medium and large voxels to the PTV to 1 cm and 2 cm, respectively, does not lead to substantial degradation in final plan quality compared to using 2.5% (photon beamlets) and 5% (electron beamlets) statistical uncertainty and no sparse format nor voxel merging. Only OAR sparing is slightly degraded. Furthermore, computation times are reduced by about 58% (photon beamlets), 88% (electron beamlets) and 96% (optimization). Significance. Several methods are implemented improving computational efficiency of beamlet calculation and plan optimization of a fully MC based TPP without substantial degradation in final plan quality.

Контроль качества планов с модуляцией интенсивности (volumetric modulated arc therapy - vmat) в лучевой терапии на линейном ускорителе vitalbeam

The importance of medical physics methods in modern radiation therapy is shown. The types of irradiation used in radiation therapy are considered. At each stage, it is necessary to maintain high accuracy of all procedures. One of the significant stages is the treatment planning, where the quality control of the plan is carried out to ensure the accuracy of the treatment of the patient. The process of quality control of radiation plans in radiation therapy with intensity modulation (Volumetric Modulated Arc Therapy - VMAT) on the VitalBeam linear accelerator is presented. The widely used method of quality control on the portal detector (Electronic Portal Imaging Device, EPID) of the radiation therapy plan with intensity modulation (Volumetric Modulated Arc Therapy - VMAT) is considered. Comparison of dose distribution that is the overlapping of dose distribution contours. Isodose lines and a dose-volume histogram for a plan with intensity modulation are presented and the main dimensional geometries used in clinical practice for dosimetric examination of treatment plans are described. Intensity modulated plan gamma analysis (VMAT) and gamma analysis criteria are defined. As well as the coverage of the physical volume of exposure. Quality control of dosimetric distributions of the intensity modulated treatment plan (VMAT) on the VitalBeam linear accelerator was assessed.

Five Fraction External Beam Partial Breast Irradiation: A User's Guide.

Mature follow up from multiple randomized trials have demonstrated the safety and efficacy of external beam partial breast irradiation (PBI) for appropriately selected patients with early stage breast cancer. Despite this evidence, external beam PBI remains underutilized. In this user guide we outline patient selection, workflow, and address possible challenges to aid in implementation of evidence-based external beam PBI. Review of the current guidelines for PBI suitability, surgical considerations, treatment technique, simulation, contouring, and treatment planning, citing the latest published literature to support PBI utilization. Prospective data supports the use of 30 Gy in 5 fractions delivered with intensity modulated radiation therapy on a daily or every other day basis for a significant proportion of early stage breast cancer patients. The surgical cavity must be clearly visualized on treatment planning scan, recommend 3-5 weeks post-operatively, and the recommended clinical target volume expansion on the surgical cavity is 0.5-1.0 cm. A planning target volume expansion, based on motion management and image guidance, of 0.5-1.0 cm should be used. Organ at risk dose constraints of heart V3Gy ≤10% and contralateral breast Dmax ≤1 Gy are often achievable. Five fraction external beam PBI is a highly effective treatment with very limited toxicity for patients with early stage breast cancer following breast conserving surgery. Commonly utilized intensity modulated treatment planning techniques with plan delivery on standard linear accelerators results significant normal tissue sparing and makes implementation feasible at most radiation oncology centers.

Comparison of non-coplanar optimization of static beams and arc trajectories for intensity-modulated treatments of meningioma cases

Two methods for non-coplanar beam direction optimization, one for static beams and another for arc trajectories, were proposed for intracranial tumours. The results of the beam angle optimizations were compared with the beam directions used in the clinical plans. Ten meningioma cases already treated were selected for this retrospective planning study. Algorithms for non-coplanar beam angle optimization (BAO) and arc trajectory optimization (ATO) were used to generate the corresponding plans. A plan quality score, calculated by a graphical method for plan assessment and comparison, was used to guide the beam angle optimization process. For each patient, the clinical plans (CLIN), created with the static beam orientations used for treatment, and coplanar VMAT approximated plans (VMAT) were also generated. To make fair plan comparisons, all plan optimizations were performed in an automated multicriteria calculation engine and the dosimetric plan quality was assessed. BAO and ATO plans presented, on average, moderate global plan score improvements over VMAT and CLIN plans. Nevertheless, while BAO and CLIN plans assured a more efficient OARs sparing, the ATO and VMAT plans presented a higher coverage and conformity of the PTV. Globally, all plans presented high-quality dose distributions. No statistically significant quality differences were found, on average, between BAO, ATO and CLIN plans. However, automated plan solution optimizations (BAO or ATO) may improve plan generation efficiency and standardization. In some individual patients, plan quality improvements were achieved with ATO plans, demonstrating the possible benefits of this automated optimized delivery technique.

Harnessing benefit of highly conformal RT techniques for lymphoma patients.

This status article describes current state-of-the-art radiotherapy for lymphomas and new emerging techniques. Current state-of-the-art radiotherapy is sophisticated, individualised, CT-based, intensity-modulated treatment, using PET/CT to define the target. The concept of involved site radiotherapy should be used, delineating the target using the exact same principles as for solid tumours. The optimal treatment delivery includes motion management and online treatment verification systems, which reduce intra- and interfractional anatomical variation. Emerging radiotherapy techniques in lymphomas include adaptive radiotherapy in MR- and CT-based treatment systems and proton therapy. The next generation linear accelerators have the capability to deliver adaptive treatment and allow relatively quick online adaptation to the daily variations of the anatomy. The computer systems use machine leaning to facilitate rapid automatic contouring of the target and organs-at-risk. Moreover, emerging MR-based planning and treatment facilities allow target definition directly from MR scans and allow intra-fractional tracking of structures recognisable on MR. Proton facilities are now being widely implemented. The benefits of proton therapy are due to the physical properties of protons, which in many cases allow sparing of normal tissue. The variety of techniques in modern radiotherapy means that the radiation oncologist must be able to choose the right technique for each patient. The choice is mainly based on experience and standard protocols, but new systems calculating risks for the patients with a specific treatment plan and also systems integrating clinical factors and risk factors into the planning process itself are emerging.

Operational Insights From the Longitudinal Analysis of a Linear Accelerator Machine Log.

PurposeThis study aimed to perform a longitudinal analysis of linear accelerator (linac) technical faults reported with a cloud-based Machine Log system in use in a busy academic clinic and derive operational insights related to linac reliability, clinical utilization, and performance.MethodsWe queried the Machine Log system for the following parameters: linac type, number of reported technical faults, types of fault, number of faults where the linac was disabled, and estimated clinical downtime. The number of fractions treated and monitor units (MU) delivered were obtained from the record and verify system as metrics of linac utilization and to normalize the number of reported linac faults, facilitating inter-comparison. Two Varian TrueBeam C-arm linacs (Varian Medical Systems, Palo Alto, CA), one Varian 21iX C-arm linac (Varian Medical Systems, Palo Alto, CA), and one newly installed Varian Halcyon ring gantry linac (Varian Medical Systems, Palo Alto, CA) were evaluated. The linacs were studied over a 30-month period from September 2017 to March 2020. ResultsOver 30 months, comprising 677 clinical days, 1234 faults were reported from all linacs, including 153 “linac down” events requiring rescheduling or cancellation of treatments. The TrueBeam linacs reported nearly twice as many imaging, multileaf collimator (MLC), and beam generation faults per fraction, and MU as the Halcyon. Halcyon experienced fewer beam generation/steering, accessory, and cooling-related faults than the other linacs but reported more computer and networking issues. Although it employs a relatively new MLC design compared to the C-arm linacs and delivers primarily intensity-modulated treatments, Halcyon reported fewer MLC faults than the other linacs. The 21iX linac had the fewest software-related faults but was subject to the most cooling-related faults, which we attributed to extensive use of this linac for treatment techniques with extended beam-on times.ConclusionsA longitudinal analysis of a cloud-based Machine Log system yielded operational insights into the utilization, performance, and technical reliability of the linacs in use at our institution. Several trends in linac sub-system reliability were identified and could be attributed to either age, design, clinical use, or operational demands. The results of this analysis will be used as a basis for designing linac quality assurance schedules that reflect actual linac usage and observed sub-system reliability. Such a practice may contribute to a clinic workflow subject to fewer disruptions from linac faults, ultimately improving efficiency and patient safety.

Intensity-Modulated Radiation Therapy and Intensity-Modulated Proton Therapy—2 Effective Treatment Modalities for Nasopharyngeal Cancer

Intensity-Modulated Radiation Therapy and Intensity-Modulated Proton Therapy—2 Effective Treatment Modalities for Nasopharyngeal Cancer

Optimizing Adjuvant Stereotactic Radiotherapy of Motor-Eloquent Brain Metastases: Sparing the nTMS-Defined Motor Cortex and the Hippocampus.

Brain metastases can effectively be treated with surgical resection and adjuvant stereotactic radiotherapy (SRT). Navigated transcranial magnetic stimulation (nTMS) has been used to non-invasively map the motor cortex prior to surgery of motor eloquent brain lesions. To date, few studies have reported the integration of such motor maps into radiotherapy planning. The hippocampus has been identified as an additional critical structure of radiation-induced deficits. The aim of this study is to assess the feasibility of selective dose reduction to both the nTMS-based motor cortex and the hippocampi in SRT of motor-eloquent brain metastases. Patients with motor-eloquent brain metastases undergoing surgical resection and adjuvant SRT between 07/2014 and 12/2018 were retrospectively analyzed. The radiotherapy treatment plans were retrieved from the treatment planning system (“original” plan). For each case, two intensity-modulated treatment plans were created: the “motor” plan aimed to reduce the dose to the motor cortex, the “motor & hipp” plan additionally reduce the dose to the hippocampus. The optimized plans were compared with the “original” plan regarding plan quality, planning target volume (PTV) coverage, and sparing of organs at risk (OAR). 69 plans were analyzed, all of which were clinically acceptable with no significant differences for PTV coverage. All OAR were protected according to standard protocols. Sparing of the nTMS motor map was feasible: mean dose 9.66 ± 5.97 Gy (original) to 6.32 ± 3.60 Gy (motor) and 6.49 ± 3.78 Gy (motor & hipp), p<0.001. In the “motor & hipp” plan, dose to the ipsilateral hippocampi could be significantly reduced (max 1.78 ± 1.44 Gy vs 2.49 ± 1.87 Gy in “original”, p = 0.003; mean 1.01 ± 0.92 Gy vs. 1.32 ± 1.07 Gy in “original”, p = 0.007). The study confirms the results from previous studies that inclusion of nTMS motor information into radiotherapy treatment planning is possible with a relatively straightforward workflow and can achieve reduced doses to the nTMS-defined motor area without compromising PTV coverage. Furthermore, we demonstrate the feasibility of selective dose reduction to the hippocampus at the same time. The clinical significance of these optimized plans yet remains to be determined. However, with no apparent disadvantages these optimized plans call for further and broader exploration.

Measuring foetal dose from tomotherapy treatments.

Treating pregnant women in the radiotherapy clinic is a rare occurrence. When it does occur, it is vital that the dose received by the developing embryo or foetus is understood as fully as possible. This study presents the first investigation of foetal doses delivered during helical tomotherapy treatments. Six treatment plans were delivered to an anthropomorphic phantom using a tomotherapy machine. These included treatments of the brain, unilateral and bilateral head-and-neck, chest wall, and upper lung. Measurements of foetal dose were made with an ionisation chamber positioned at various locations longitudinally within the phantom to simulate a variety of patient anatomies. All measurements were below the established limit of 100 mGy for a high risk of damage during the first trimester. The largest dose encountered was 75 mGy (0.125% of prescription dose). The majority of treatments with measurement positions less than 30 cm fell into the range of uncertain risk (50 - 100 mGy). All treatments with measurement positions beyond 30 cm fell into the low risk category (< 50 mGy). For the cases in this study, tomotherapy resulted in foetal doses that are at least on par with, if not significantly lower than, similar 3D conformal or intensity-modulated treatments delivered with other devices. Recommendations were also provided for estimating foetal doses from tomotherapy plans.

Myths, facts and scope of spinal cord tolerance dose revision in Intensity modulated SIB treatment of locally advanced head and neck cancer: A dosimetrical and radiobiological demonstration

PurposeTo explore the possibility of revising the spinal cord tolerance dose in Simultaneously Integrated Boost (SIB) intensity modulated treatment plan of locally advanced head and neck (H&N) cancer and assessment of achieved planning gain due to the revision. In SIB regimen, the Organ at Risk (OARs) tolerance dose is equally distributed throughout the treatment. Clinicians have usually considered the spinal cord tolerance to be the same as in conventional technique. However, in SIB fractionation regimen with intensity modulation treatment, the spinal cord may receive a physical dose of 45Gy, with much lesser dose per fraction than 2Gy per fraction. So when the dose of spinal cord is distributed throughout the treatment, the tolerance dose limit of physical dose can be considered higher than the usual conventional dose limits. In this study, an attempt has been made to explore the possibilities of dose escalation and treatment planning benefits while exploiting this “Window of Opportunity (WoO)” of increase in spinal cord and Planning Risk Volume (PRV) spinal cord tolerance dose. Material and methodsA total of 12 patients CT data set along with approved structure set of H&N cancer used for treatment planning in. Three independent SIB VMAT plans named as SPC, SPR and SPDE were generated for the 12 patients. First plan (SPC) was generated by considering standard spinal cord tissue constraint of maximum dose of 45Gy and PRV spinal cord maximum dose 50Gy as per QUANTEC summary and second plan (SPR) was generated considering spinal cord tissue constraint of maximum dose 52.50Gy and PRV spinal cord maximum dose 56.35Gy while optimization and dose calculation. The objectives for rest of the Organ at Risk (OAR) were kept same in both the plans during optimization and dose calculation. The SPC plan was copied for creation of third plan (SPDE) in which dose was escalated by increasing dose per fraction for target volumes such that dose to spinal cord reached a maximum dose of 52.50Gy and PRV spinal cord maximum dose of 56.35Gy. In this plan there have been changes to only dose per fraction, however dose optimization and dose calculation have not been performed. Radiobiological parameters TCP and NTCP were also calculated by using indigenously developed software. ResultsConsidering the increase of spinal cord tolerance dose as “window of opportunity”, a sufficient escalation in physical dose, Biological Effective Dose (BED) and Tumor Control Probability (TCP) was observed for all target volumes with acceptable level of NTCP values. ConclusionSufficient dose escalation and increased in TCP for target volumes or effective planning benefits can be achieved by revising the spinal cord tolerance dose in intensity modulated SIB treatment of locally advanced H&N cancers.

PO-1101: Intensity-modulated radiotherapy treatment of anal cancer: single-institution outcomes

PO-1101: Intensity-modulated radiotherapy treatment of anal cancer: single-institution outcomes

Dosimetric comparison of intensity-modulated radiotherapy (IMRT) and RapidArc in low grade mucoepidermoid carcinoma of the salivary gland: a single institutional experience

AbstractPurpose:To report a single-institution experience of intensity-modulated radiotherapy (IMRT) and RapidArc treatment plans for the patients treated with low grade mucoepidermoid carcinoma (MEC) of the salivary gland while sparing the organs at risk (OARs) within tolerance limits.Material and Methods:Twenty-five patients with MEC were selected to develop and analyse the treatment plans using both of the techniques. Dose distributions were calculated using Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA). Plans were generated to deliver the dose of 6000 cGy in 30 fractions. For IMRT, seven angle plans were used and for RapidArc, two half arcs were used with the same 6 MV photon beam. Quality of treatment plans was evaluated by using parameters such as, coverage, conformity index (CI), homogeneity index (HI), gradient index (GI), unified dosimetry index (UDI), dose volume histogram, delivery time and OARs sparing for IMRT and RapidArc plans.Results:The analysis revealed that IMRT and RapidArc coverages are 0·90 and 0·94, respectively; CIs are 1·15 and 1·10, respectively; HIs are 1·12 and 1·07, respectively; GIs are 0·94 and 0·98, respectively. Average UDI values for RapidArc and IMRT are 1·09 and 1·11, respectively. Integral dose comparison shows better OAR sparing for RapidArc. RapidArc plans have the shorter beam on time (45%) in comparison with IMRT plans.Conclusion:Planning constraints were achieved in both techniques. However, RapidArc showed better quality treatment plan, OARs sparing and shorter delivery time as compared to IMRT.

Abstract B21: Factors affecting outcomes in patients with squamous cell carcinoma of oropharynx

Abstract Objective: To study factors affecting outcomes such as overall survival (OS) and locoregional control (LRC), in patients with squamous cell carcinomas of oropharynx treated with definitive radiation therapy (RT), with or without concurrent chemotherapy. Method: Retrospective analysis of 83 patients with squamous cell carcinoma of oropharynx treated with definitive radiation therapy at University of Mississippi Medical Center. All patients were treated to 70 Gy utilizing intensity-modulated radiation treatment. Stage III and IV patients also received concurrent chemotherapy with weekly cisplatin. Chi-square test was used to test the goodness of fit, OS and LRC comparing races were generated by using log rank test and Kaplan-Meier method. The covariables associated with the OS and LRC were determined by multivariate Cox regression model. Hazards ratio (HR) was used to estimate time to event outcome with associated 95% confidence intervals (CIs) and P values. Median follow-up for the entire group was 39 months. Results: Of the total 83 eligible patients 51.8% were black, 48.5% were white, and 2.4% wee other. Stage distribution (per American Joint Committee on Cancer-AJCC 7th Ed) between blacks vs. whites for Stage I and II was 50% vs. 50%; for Stage III, 41.6% vs. 58.3%; and for Stage IV, 55.2% vs. 41.8%. In the univariate analysis, insurance, HPV/p16, body mass index (BMI), and race are the variables that affected the outcomes. In the multivariate analysis, HPV/p16, BMI, race, and tonsil subsite are shown to be significant. Age, gender, income level, employment, distance from facility, smoking, alcohol, and marital status are not shown to be significant. LRC for black patients was 49% vs. 72% in white patients (P = 0.022). Three-year OS for black patients was 49.2% vs. 66% for white patients (P = 0.010). HR for black patients was 0.13 with 95% CI 0.03- 0.61 (P= 0.009); HR for white patients was 0.24 with 95% CI 0.56- 1.06 (P= 0.061). OS for Stage IV black patients was 28% vs. 82% for white patients (P=0.006). In this cohort, HPV/p16 black positive patients were 75%, black negative 33%, white positive 87%, and white negative 50%, respectively. HR for HPV/p16 positive was 0.23 with 95% CI 0.07-0.71(P = 0.01). HR for tonsil subsite was 0.37 with 95% CI 0.15-0.91 (P=0.031). HR for BMI was 5.27 with 95% CI 1.79-15.5 (P = 0.003). The race, HPV/p16, BMI, and tonsil subsite were all independently associated with worse OS on multivariate analysis. HR for black patients was 0.16 with 95% CI 0.03-0.73 (P= 0.019), HR for HPV/p16 positive was 0.24 with 95% CI 0.07-0.73 (P = 0.013), HR for tonsil subsite was 0.41 with 95% CI 0.17-0.99 (P = 0.048), and HR for BMI was 5.59 with 95% CI 1.90-16.39 (P= 0.002). Race, HPV/p16, BMI, and tonsil subsite were all independently associated with worse locoregional failure on multivariate analysis. Conclusion: Among all the covariables examined, race, HPV/p16 status, BMI, and tonsil subsite were shown to be affecting the locoregional and overall survival outcomes. Racial factor appears to be more significant in patients with Stage IV disease. Citation Format: Mary R. Nittala, Eldrin Bhanat, Srinivasn Vijayakumar, Madhava R. Kanakamedala. Factors affecting outcomes in patients with squamous cell carcinoma of oropharynx [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; 2019 Apr 29-30; Austin, TX. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_2):Abstract nr B21.

Pilot study: protective effect on mucosal tissue using dental waterjet and dexpanthenol rinsing solution during radiotherapy in head and neck tumor patients

Radiogenic side effects are frequently seen in patients undergoing radiotherapy for head and neck tumors. Intensified dental and mucosal care reduce oral hygienic deficits. The aim of this study was the optimization of mouth hygiene using dexpanthenol rinsing solution applied with a dental waterjet system (DWS). 30 consecutive head and neck tumor patients (44–75 years) were analyzed, who received intensity-modulated radiation treatment (IMRT; total dose range: 54–66 Gy) with helical Tomotherapy HiArt II. The group under investigation (n = 10) additionally received a professional DWS using dexpanthenol mouthrinse (Bepanthen). The first control group received dexpanthenol mouthrinse alone. The second control group only performed the standardized mouth hygiene protocol. Grade of xerostomia, taste, dysphagia, thrush, and mucositis was evaluated on a daily basis. 29 of 30 patients completed radiation therapy. Change in taste occurred in all patients in all groups, however, with a delay in the study group. The occurrence of grade III stomatitis and Xerostomia grade II was significantly reduced in the study arm. No patient suffered from grade III xerostomia in the study arm versus four patients in the control groups. Dysphagia grade II was observed significantly less frequent in the study group (p = 0.0004). Thrush occurrence showed a delay in the study group. Our study underlines the importance of an intensified mouth hygiene during radiation therapy. The combination of dexpanthenol rinsing solution + DWS reduces the incidence of high-grade early side effects which often lead to a reduced quality of life and abortion of the treatment.

Automated intensity modulated treatment planning: The expedited constrained hierarchical optimization (ECHO) system.

To develop and implement a fully automated approach to intensity modulated radiation therapy (IMRT) treatment planning. The optimization algorithm is developed based on a hierarchical constrained optimization technique and is referred internally at our institution as expedited constrained hierarchical optimization (ECHO). Beamlet contributions to regions-of-interest are precomputed and captured in the influence matrix. Planning goals are of two classes: hard constraints that are strictly enforced from the first step (e.g., maximum dose to spinal cord), and desirable goals that are sequentially introduced in three constrained optimization problems (better planning target volume (PTV) coverage, lower organ at risk (OAR) doses, and smoother fluence map). After solving the optimization problems using external commercial optimization engines, the optimal fluence map is imported into an FDA-approved treatment planning system (TPS) for leaf sequencing and accurate full dose calculation. The dose-discrepancy between the optimization and TPS dose calculation is then calculated and incorporated into optimization by a novel dose correction loop technique using Lagrange multipliers. The correction loop incorporates the leaf sequencing and scattering effects into optimization to improve the plan quality and reduce the calculation time. The resultant optimal fluence map is again imported into TPS for leaf sequencing and final dose calculation for plan evaluation and delivery. The workflow is automated using application program interface (API) scripting, requiring user interaction solely to prepare the contours and beam arrangement prior to launching the ECHO plug-in from the TPS. For each site, parameters and objective functions are chosen to represent clinical priorities. The first site chosen for clinical implementation was metastatic paraspinal lesions treated with stereotactic body radiotherapy (SBRT). As a first step, 75 ECHO paraspinal plans were generated retrospectively and compared with clinically treated plans generated by planners using VMAT (volumetric modulated arc therapy) with 4 to 6 partial arcs. Subsequently, clinical deployment began in April, 2017. In retrospective study, ECHO plans were found to be dosimetrically superior with respect to tumor coverage, plan conformity, and OAR sparing. For example, the average PTV D95%, cord and esophagus max doses, and Paddick Conformity Index were improved, respectively, by 1%, 6%, 14%, and 15%, at a negligible 3% cost of the average skin D10cc dose. Hierarchical constrained optimization is a powerful and flexible tool for automated IMRT treatment planning. The dosimetric correction step accurately accounts for detailed dosimetric multileaf collimator and scattering effects. The system produces high-quality, Pareto optimal plans and avoids the time-consuming trial-and-error planning process.

Application of failure mode and effects analysis to optimization of linac quality controls protocol.

To apply Failure Mode and Effects Analysis (FMEA) to optimize linac quality control (QC) protocol in order to ensure patient safety and treatment quality, taking maximum advantage of the available resources. Each parameter tested by the QC was considered as a potential failure mode (FM). For each FM, likelihood of occurrence (O), severity of effect (S), and lack of detectability (D) were evaluated and corresponding Risk Priority Number (RPN) was calculated from the product of three indexes. The scores were assigned using two methods: (a) A survey submitted to the medical physicists; (b) A semi-quantitative analysis (SQA) performed through: simulation of FMs in the treatment planning system; studies reported in literature; results obtained by the QC data analysis. A weighted RPN for all FMs was calculated taking into account both the methods. For each linac, the tests were then sorted by their frequency and the RPN value. A high variability was found in the scores of the survey, although in many it was reduced in RPN values, highlighting the more relevant tests as on beam output and imaging system. Integrating these results with those obtained by SQA, the RPN-based ranking of tests has been provided considering the specific use of the accelerator: for example, more accurate tests on dose modulation and multileaf collimator speed were required in linacs where intensity-modulated treatment is performed, while, more specific tests on couch and jaw position indicators were necessary where treatments with multiple isocenters and/or junctions between adjacent fields were often delivered. Failure Mode and Effects Analysis is a useful tool to prioritize the linac QCs, taking into account the specific equipment and clinical practice. The integration of SQA and survey results reduces subjectivity of the FMEA scoring and allows to optimize linac QCs without "losing" the expertise and experience of medical physicists and clinical staff.

A Molecular Dynamics Approach for Optimizing Beam Intensities in IMPT Treatment Planning

This paper uses a molecular dynamics (MD) method for intensity-modulated proton therapy treatment planning optimization to overcome the problem of gradient-based optimization methods such as quasi-Newton, which is sensitive to starting conditions and is easily trapped in local minima. We implemented a molecular dynamics (MD) method and a quasi-Newton method for plan optimization. Three types of cancer cases, prostate, head-and-neck and lung cancer, were tested with three starting different initial conditions. Overall, the MD method consistently resulted in solutions with lower objective function values (OFVs) compared to those from the quasi-Newton algorithm. Furthermore, the MD method converged on the same OFV regardless of its initial starting points used for the prostate cancer case.

168. Evaluation of a machine QA software tool for MLC performance checks

PurposeOne of the main requirement for a correct intensity modulated treatment (IMRT) delivery, is a periodic check of Multileaf Collimator (MLC) parameters. In some Treatment Planning System (TPS), the Dosimetric Leaf Gap (DLG) is one of the most important parameter for the correct calculation of dose distribution when using dynamic MLC. The purpose of this work is to evaluate the feasibility and time saving in using a dedicated machine quality assurance (QA) software tool to monitor over time the DLG parameter and leaves positions. MethodsTwo 6 MV Linac equipped with a 120 leaf MLC were compared to check the measured constancy of the DLG and leaves positions through use of a 3D diode array equipped with a dedicated machine QA software tool. The MLC checks were performed at 50° and 320° gantry angles due to phantom’s plate geometry. In this way it was possible also to verify gravity effects on leaves banks. The analysis was carried out with a version of picket fence test implemented in the software. ResultsThe Veroli mean DLG values was 2,0 ± 0.4 mm for 50° gantry angle and 2.1 ± 0.5 mm for 320° gantry angle. The Rieti mean DLG values was 1.9 ± 0.1 for 50° gantry angle and 2.0 ± 0.1 mm for 320° gantry angle. The check on the leaves movement has shown gravity effect on two different angles. In particular the Rieti DLG value carried out at gantry 50° was 1.6 ± 0.1 mm when there was a problem to leaf motor. ConclusionThe picket fence test, originally used with radiographic film to check the reproducibility of leaf gap, is extended in this machine QA software tool, including checks for gap width and leaf positions. This tool can be used as a routine MLC QA check for mean leaf deviation, DLG, and absolute positions of the leaves.