Body Radiation Therapy Treatment Plans Research Articles

Evaluation of Flattening-Filter-Free and Flattening Filter Dosimetric and Radiobiological Criteria for Lung SBRT: A Volume-Based Analysis

The use of volumetric modulated arc therapy (VMAT) with flattening-filter-free (FFF) beams is becoming more prevalent in lung cancer stereotactic body radiotherapy (SBRT). The aim in this study was to assess the impact of dosimetric and radiobiological differences between FFF and flattening filter (FF) beams for lung SBRT based on the target volume. A total of 198 lung stereotactic body radiation therapy treatment plans with FFF beams and FF beams were retrospectively selected for this study. For all plans, the prescribed dose was 50 Gy/5 fractions, and the dose volume histogram (DVH) for the target and organs at risk (OAR) and the normal tissue complication probability (NTCP) of the lung were recorded and compared. Moreover, monitor units (MUs), the beam on-time and the treatment time were evaluated. The study was performed following the Radiation Therapy Oncology Group (RTOG) 0813 and 0915 protocols. No significant differences in D90, coverage rate (CR) or conformity index (CI) of the target were observed between FFF beams and FF beams (p>0.05). The D2, R50% and gradient index (GI) for the target improved with FFF beams compared with FF beams (p<0.05). FFF beams also significantly reduced the dose for the lung, heart, spinal cord, esophagus and NTCP of the lung (p<0.05), compared with FF beams. However, there was no significant difference in sparing of the trachea (p>0.05). The mean MUs, beam on-time and treatment time were 1871±278 MUs, 3.2 ±0.2 min and 3.9 ±0.3 min for FFF beams, and 1890±260 MUs, 4.2±0.3 min and 4.8 ±0.4 min for FF beams, respectively. The FFF beam technique for lung SBRT with VMAT results in a better dose fall-off, better dose-sparing of OAR, lower NTCP of the lung and a shorter beam on-time compared with the FF beam technique. Additionally, the improvement in target and OAR-sparing for FFF beams was increased with increasing target volume.

Scorecards: Quantifying Dosimetric Plan Quality in Pancreatic Ductal Adenocarcinoma Stereotactic Body Radiation Therapy

A scoring mechanism called the scorecard that objectively quantifies the dosimetric plan quality of pancreas stereotactic body radiation therapy treatment plans is introduced. A retrospective analysis of patients with pancreatic ductal adenocarcinoma receiving stereotactic body radiation therapy at our institution between November 2019 and November 2020 was performed. Ten patients were identified. All patients were treated to 36 Gy in 5 fractions, and organs at risk (OARs) were constrained based on Alliance A021501. The scorecard awarded points for OAR doses lower than those cited in Alliance A021501. A team of 3 treatment planners and 2 radiation oncologists, including a physician resident without plan optimization experience, discussed the relative importance of the goals of the treatment plan and added additional metrics for OARs and plan quality indexes to create a more rigorous scoring mechanism. The scorecard for this study consisted of 42 metrics, each with a unique piecewise linear scoring function which is summed to calculate the total score (maximum possible score of 365). The scorecard-guided plan, the planning and optimization for which were done exclusively by the physician resident with no prior plan optimization experience, was compared with the clinical plan, the planning and optimization for which were done by expert dosimetrists, using the Sign test. Scorecard-guided plans had, on average, higher total scores than those clinically delivered for each patient, averaging 280.1 for plans clinically delivered and 311.7 for plans made using the scorecard (P=.003). Additionally, for most metrics, the average score of each metric across all 10 patients was higher for scorecard-guided plans than for clinically delivered plans. The scorecard guided the planner toward higher coverage, conformality, and OAR sparing. A scorecard tool can help clarify the goals of a treatment plan and provide an objective method for comparing the results of different plans. Our study suggests that a completely novice treatment planner can use a scorecard to create treatment plans with enhanced coverage, conformality, and improved OAR sparing, which may have significant effects on both tumor control and toxicity. These tools, including the scorecard used in this study, have been made freely available.

Evaluation of commercial devices for patient specific QA of stereotactic radiotherapy plans.

Stereotactic radiotherapy (SRT) methods have become common for the treatment of small tumors in various parts of the body. Small field dosimetry has a unique set of challenges when it comes to the pre-treatment validation of a radiotherapy plan that involves film dosimetry or high-resolution detectors. Comparison of commercial quality assurance (QA) devices to the film dosimetry method for pre-treatment evaluation of stereotactic radiosurgery (SRS), fractionated SRT, and stereotactic body radiation therapy treatment plans have been evaluated in this study. Forty stereotactic QA plans were measured using EBT-XD film, IBA Matrixx Resolution, SNC ArcCHECK, Varian aS1200 EPID, SNC SRS MapCHECK, and IBA myQA SRS. The results of the commercial devices are compared to the EBT-XD film dosimetry results for each gamma criteria. Treatment plan characteristics such as modulation factor and target volume were investigated for correlation with the passing rates. It was found that all detectors have greater than 95% passing rates at 3%/3mm. Passing rates decrease rapidly for ArcCHECK and the Matrixx as criteria became more strict. In contrast, EBT-XD film, SNC SRS MapCHECK, and IBA myQA SRS passing rates do not decline as rapidly when compared to Matrix Resolution, ArcCHECK, and the EPID. EBT-XD film, SNC SRS MapCHECK, and IBA myQA SRS maintain greater than 90% passing rate at 2%/1mm and greater than 80% at 1%/1mm. Additionally, the ability of these devices to detect changes in dose distribution due to MLC positioning errors was investigated. Ten VMAT SBRT/SRS treatment plans were created with 6MV FFF or 10MV FFF beam energies using Eclipse 15.6. A MATLAB script was used to create two MLC positioning error scenarios from the original treatment plan. It was found that errors in MLC positioning were most reliably detected at 2%/1mm for high-resolution detectors and that lower-resolution detectors did not consistently detect MLC positioning errors.

Evaluation of flattening-filter-free and flattening filter dosimetric and radiobiological criteria for lung SBRT: A volume-based analysis.

The use of volumetric modulated arc therapy (VMAT) with flattening-filter-free (FFF) beams is becoming more prevalent in lung cancer stereotactic body radiotherapy (SBRT). The aim in this study was to assess the impact of dosimetric and radiobiological differences between FFF and flattening filter (FF) beams for lung SBRT based on the target volume. A total of 198 lung stereotactic body radiation therapy treatment plans with FFF beams and FF beams were retrospectively selected for this study. For all plans, the prescribed dose was 50 Gy/5 fractions, and the dose volume histogram (DVH) for the target and organs at risk (OAR) and the normal tissue complication probability (NTCP) of the lung were recorded and compared. Moreover, monitor units (MUs), the beam on-time and the treatment time were evaluated. The study was performed following the Radiation Therapy Oncology Group (RTOG) 0813 and 0915 protocols. No significant differences in D90, coverage rate (CR) or conformity index (CI) of the target were observed between FFF beams and FF beams (p>0.05). The D2, R50% and gradient index (GI) for the target improved with FFF beams compared with FF beams (p<0.05). FFF beams also significantly reduced the dose for the lung, heart, spinal cord, esophagus and NTCP of the lung (p<0.05), compared with FF beams. However, there was no significant difference in sparing of the trachea (p>0.05). The mean MUs, beam on-time and treatment time were 1871 ± 278 MUs, 3.2 ± 0.2min and 3.9 ± 0.3min for FFF beams, and 1890 ± 260 MUs, 4.2 ± 0.3min and 4.8 ± 0.4min for FF beams, respectively. The FFF beam technique for lung SBRT with VMAT results in a better dose fall-off, better dose-sparing of OAR, lower NTCP of the lung and a shorter beam on-time compared with the FF beam technique. Additionally, the improvement in target and OAR-sparing for FFF beams was increased with increasing target volume.

Planning Benchmark Study for Stereotactic Body Radiation Therapy of Liver Metastases: Results of the DEGRO/DGMP Working Group on Stereotactic Radiation Therapy and Radiosurgery

Our purpose was to investigate whether liver stereotactic body radiation therapy treatment planning can be harmonized across different treatment planning systems, delivery techniques, and institutions by using a specific prescription method and to minimize the knowledge gap concerning intersystem and interuser differences. We provide best practice guidelines for all used techniques. A multiparametric specification of target dose (gross target volume [GTV]D50%, GTVD0.1cc, GTVV90%, planning target volume [PTV]V70%) with a prescription dose of GTVD50%=3×20 Gy and organ-at-risk (OAR) limits were distributed with computed tomography and structure sets from 3 patients with liver metastases. Thirty-five institutions provided 132 treatment plans using different irradiation techniques. These plans were first analyzed for target and OAR doses. Four different renormalization methods were performed (PTVDmin, PTVD98%, PTVD2%, PTVDmax). The resulting 660 treatments plans were evaluated regarding target doses to study the effect of dose renormalization to different prescription methods. A relative scoring system was used for comparisons. GTVD50% prescription can be performed in all systems. Treatment plan harmonization was overall successful, with standard deviations for Dmax, PTVD98%, GTVD98%, and PTVDmean of 1.6, 3.3, 1.9, and 1.5 Gy, respectively. Primary analysis showed 55 major deviations from clinical goals in 132 plans, whereas in only <20% of deviations GTV/PTV dose was traded for meeting OAR limits. GTVD50% prescription produced the smallest deviation from target planning objectives and between techniques, followed by the PTVDmax, PTVD98%, PTVD2%, and PTVDmin prescription. Deviations were significant for all combinations but for the PTVDmax prescription compared with GTVD50% and PTVD98%. Based on the various dose prescription methods, all systems significantly differed from each other, whereas GTVD50% and PTVD98% prescription showed the least difference between the systems. This study showed the feasibility of harmonizing liver stereotactic body radiation therapy treatment plans across different treatment planning systems and delivery techniques when a sufficient set of clinical goals is given.

Monte Carlo as quality control tool of stereotactic body radiation therapy treatment plans.

The objective of this study was to verify the accuracy of treatment plans of stereotactic body radiation therapy (SBRT) and to verify the feasibility of the use of Monte Carlo (MC) as quality control (QC) on a daily basis. Using EGSnrc, a MC model of Agility™ linear accelerator was created. Various measurements (Percentage depth dose (PDD), Profiles and Output factors) were done for different fields sizes from 1x1 up to 40x40 (cm2). An iterative model optimization was performed to achieve adequate parameters of MC simulation. 40 SBRT patient's dosimetry plans were calculated by Monaco™ 3.1.1. CT images, RT-STRUCT and RT-PLAN files from Monaco™ being used as input for Moderato MC code. Finally, dose volume histogram (DVH) and paired t-tests for each contour were used for dosimetry comparison of the Monaco™ and MC. Validation of MC model was successful, as <2% difference comparing to measurements for all field's sizes. The main energy of electron source incident on the target was 5.8MeV, and the full width at half maximum (FWHM) of Gaussian electron source were 0.09 and 0.2 (cm) in X and Y directions, respectively. For 40 treatment plan comparisons, the minimum absolute difference of mean dose of planning treatment planning (PTV) was 0.1% while the maximum was 6.3%. The minimum absolute difference of Max dose of PTV was 0.2% while the maximum was 8.1%. SBRT treatment plans of Monaco agreed with MC results. It possible to use MC for treatment plans verifications as independent QC tool.

Lung Stereotactic Body Radiation Therapy (SBRT) dose gradient and PTV volume: a retrospective multi-center analysis

BackgroundThe treatment of lung lesions with stereotactic body radiation therapy calls for highly conformal dose, which is evaluated by a number of metrics. Lung stereotactic body radiation therapy clinical trials constrain a plans gradient index. The purpose of this work is to describe the dependence of clinically achievable dose gradient on planning target volume.MethodsThree hundred seventy-four lung stereotactic body radiation therapy treatment plans were retrospectively reviewed and selected for this study. The relationship between R50% and planning target volume size was observed and compared against the RTOG 0915 and 0813 constraints noting minor and major deviations. Then a least squares regression was used to determine the coefficients for a power functional form of the dependence of gradient measure (GM) on planning target volume size.ResultsOf the 317 peripheral lung SBRT plans, 142 exhibited no deviation, 135 exhibited a minor deviation, and 40 exhibited a major deviation according to the RTOG 0915 dosimetric.conformality and dose fall-off constraints. A plot of gradient measure versus planning target volume size for peripheral lesions, excluding RTOG 0915 major deviations, is fit with an power function of GM = 0.564 V0.215.ConclusionsUsing the PTV size and GM relationship we have characterized, treatment plans with PTV < 85 cm3 can be evaluated subjectively to our previously plans, and given a percentile GM. This relationship and evaluation is useful for volumetric modulated arc therapy lung stereotactic body radiation therapy treatment planning and quality control.

Dosimetric Comparison of Real-Time MRI-Guided Tri-Cobalt-60 Versus Linear Accelerator-Based Stereotactic Body Radiation Therapy Lung Cancer Plans.

Purpose:Magnetic resonance imaging–guided radiation therapy has entered clinical practice at several major treatment centers. Treatment of early-stage non-small cell lung cancer with stereotactic body radiation therapy is one potential application of this modality, as some form of respiratory motion management is important to address. We hypothesize that magnetic resonance imaging–guided tri-cobalt-60 radiation therapy can be used to generate clinically acceptable stereotactic body radiation therapy treatment plans. Here, we report on a dosimetric comparison between magnetic resonance imaging–guided radiation therapy plans and internal target volume–based plans utilizing volumetric-modulated arc therapy.Materials and Methods:Ten patients with early-stage non-small cell lung cancer who underwent radiation therapy planning and treatment were studied. Following 4-dimensional computed tomography, patient images were used to generate clinically deliverable plans. For volumetric-modulated arc therapy plans, the planning tumor volume was defined as an internal target volume + 0.5 cm. For magnetic resonance imaging–guided plans, a single mid-inspiratory cycle was used to define a gross tumor volume, then expanded 0.3 cm to the planning tumor volume. Treatment plan parameters were compared.Results:Planning tumor volumes trended larger for volumetric-modulated arc therapy–based plans, with a mean planning tumor volume of 47.4 mL versus 24.8 mL for magnetic resonance imaging–guided plans (P = .08). Clinically acceptable plans were achievable via both methods, with bilateral lung V20, 3.9% versus 4.8% (P = .62). The volume of chest wall receiving greater than 30 Gy was also similar, 22.1 versus 19.8 mL (P = .78), as were all other parameters commonly used for lung stereotactic body radiation therapy. The ratio of the 50% isodose volume to planning tumor volume was lower in volumetric-modulated arc therapy plans, 4.19 versus 10.0 (P < .001). Heterogeneity index was comparable between plans, 1.25 versus 1.25 (P = .98).Conclusion:Magnetic resonance imaging–guided tri-cobalt-60 radiation therapy is capable of delivering lung high-quality stereotactic body radiation therapy plans that are clinically acceptable as compared to volumetric-modulated arc therapy–based plans. Real-time magnetic resonance imaging provides the unique capacity to directly observe tumor motion during treatment for purposes of motion management.

4D VMAT, gated VMAT, and 3D VMAT for stereotactic body radiation therapy in lung

Four-dimensional volumetric modulated arc therapy (4D VMAT) is a treatment strategy for lung cancers that aims to exploit relative target and tissue motion to improve organ at risk (OAR) sparing. The algorithm incorporates the entire patient respiratory cycle using 4D CT data into the optimization process. Resulting treatment plans synchronize the delivery of each beam aperture to a specific phase of target motion. Stereotactic body radiation therapy treatment plans for 4D VMAT, gated VMAT, and 3D VMAT were generated on three patients with non-small cell lung cancer. Tumour motion ranged from 1.4–3.4 cm. The dose and fractionation scheme was 48 Gy in four fractions. A B-spline transformation model registered the 4D CT images. 4D dose volume histograms (4D DVH) were calculated from total dose accumulated at the maximum exhalation. For the majority of OARs, gated VMAT achieved the most radiation sparing but treatment times were 77–148% longer than 3D VMAT. 4D VMAT plan qualities were comparable to gated VMAT, but treatment times were only 11–25% longer than 3D VMAT. 4D VMAT's improvement of healthy tissue sparing can allow for further dose escalation. Future study could potentially adapt 4D VMAT to irregular patient breathing patterns.

Evaluation of pencil beam convolution and anisotropic analytical algorithms in stereotactic lung irradiation

The aim of this study was to evaluate differences in dose distributions in stereotactic body radiation therapy treatment plans for lung tumors calculated with pencil beam convolution (PBC) algorithm with modified Batho power law (MBPL) versus heterogeneity corrected anisotropic analytical algorithm (AAA) of the Varian Eclipse treatment planning system. The four-dimensional computed tomography images from 20 patients with lung cancer were used to create treatment plans. Plans used five to seven nonopposing coplanar 6 MV beams. Plans generated with the PBC algorithm and MBPL for tissue heterogeneity corrections were optimized to deliver 60 Gy in three fractions to at least 95% of the planned target volume, and the normal tissue doses for spinal cord, esophagus, heart, and ipsilateral bronchus were restricted to less than 18, 27, 30, and 30 Gy, respectively. Plans were recalculated with AAA, retaining identical beam arrangements, photon beam fluences, and monitor units. The pencil beam plans, designed to deliver 60 Gy, delivered on average 51.6 Gy when re-calculated with the AAA, suggesting a reduction of at least 10% to prescription dose is appropriate when calculating with the AAA.

Impact of tissue heterogeneity corrections in stereotactic body radiation therapy treatment plans for lung cancer

This study aims at evaluating the impact of tissue heterogeneity corrections on dosimetry of stereotactic body radiation therapy treatment plans. Four-dimensional computed tomography data from 15 low stage non-small cell lung cancer patients was used. Treatment planning and dose calculations were done using pencil beam convolution algorithm of Varian Eclipse system with Modified Batho Power Law for tissue heterogeneity. Patient plans were generated with 6 MV co-planar non-opposing four to six field beams optimized with tissue heterogeneity corrections to deliver a prescribed dose of 60 Gy in three fractions to at least 95% of the planning target volume, keeping spinal cord dose <10 Gy. The same plans were then regenerated without heterogeneity correction by recalculating previously optimized treatment plans keeping identical beam arrangements, field fluences and monitor units. Compared with heterogeneity corrected plans, the non-corrected plans had lower average minimum, mean, and maximum tumor doses by 13%, 8%, and 6% respectively. The results indicate that tissue heterogeneity is an important determinant of dosimetric optimization of SBRT plans.

SU-FF-T-633: Impact of Tissue Heterogeneity Corrections in Stereotactic Body Radiation Therapy Treatment Plans for Non Small Cell Lung Cancer Patients

Purpose: To study the effect of tissue heterogeneity corrections on the dosimetry of stereotactic body radiation therapy treatment plans for patients with non-small cell lung cancer. Materials and Methods: Data from 15 stage I non-small cell lung patients was used. Treatment planning was done with 6 MV non-opposing coplanar beams using Varian Eclipse TPS (PBC Algorithm with Modified Batho Power Law). Prescription dose was 60 Gy in 3 fractions with tissue heterogeneity corrections. Plans were normalized to deliver prescription dose to 95% of the planning target volume (PTV) maintaining the spinal cord dose under 10 Gy. Separate plans were generated by recalculating the optimized treatment plans without heterogeneity correction while keeping identical beam arrangements, monitor units, and fluences. Results: Compared with the heterogeneity corrected plans, the uncorrected plans had lower minimum, mean, and maximum tumor doses by at least 12.5%, 7.7%, and 6.0%. The PTV receiving less than prescription dose was significantly higher (>25%) in the uncorrected plans. The percentage of uninvolved lung volume receiving minimum doses of 10 Gy, 15 Gy, 20 Gy, and 30 Gy was ⩽ 10% for both treatment plans. However, the uncorrected plans calculated slightly less dose to normal lung. The average maximum spinal cord dose was 8.56 Gy and 9.73 Gy for corrected and uncorrected plans respectively. Conclusions: Treatment plans optimized with tissue heterogeneity corrections were generated to satisfy planning goals and constraints. Re-calculating such plans without tissue heterogeneity corrections and keeping identical conditions of beam and monitor units resulted in target underdosing because the planning system assumed that more tissue attenuation was present than is actually the case. By extension, failure to use tissue heterogeneity correction to plan complex beam arrangements to treat tumors within the lung will lead to delivery of higher doses than are prescribed to less than optimum dose distributions.

SU-FF-T-570: A Dosimetric Comparison as a Function of Respiration and Tumor Location in Stereotactic Body Radiation Therapy Treatment Plans For Patients with Non Small Cell Lung Cancer

Purpose: To calculate and compare doses to the tumor and normal tissues at full respiratory cycle, inhalation, and exhalation as a function of the tumor site and location within the thorax. Materials and Methods: 20 patients were scanned using 4D CT techniques. Treatment plans were created with five to seven 6 MV non-opposing coplanar beams using Varian Eclipse Treatment Planning System with tissue heterogeneity corrections for three respiratory phase combinations. A 7 mm margin was given to the internal target volume to create the planning target volume. The prescribed dose was 60 Gy in 3 fractions. Optimization goals and normal tissue constraints were the same as in the RTOG 0236 criteria. Statistical analysis used a mixed effect ANOVA model, and a 2-sided 0.05 alpha level was used for hypothesis testing. Results: Lower peripheral tumors had three times the displacement of the upper peripheral tumors. Central tumors received lower minimum doses than the peripheral tumors. When tumors were in the peripheral region, the uninvolved lung mean dose was significantly different for all phases of respiration (p=0.008), specially, when the tumors were in the upper peripheral region (p=0.04), and the doses were higher (>26%) in the lower peripheral region compared to the upper one for all phases of respiration. The V15, V20, and V30 for uninvolved lung were below 10%. Patients with central tumors received higher maximum doses in the esophagus than patients with peripheral tumors. For the ipsilateral bronchus, patients with central tumors received higher mean and maximum doses than patients with peripheral tumors. There were no statistical differences in the mean and maximum doses to the heart or to the spinal cord. Conclusions: Lesions in the lower part of the lung are more impacted by respiratory motion. Central lesions receive less tumor dose to preserve normal tissue dose limits.