Planning Target Volume D95 Research Articles

Setup error of electronic portal image device in IMRT for thoracic tumors and its influence.

The aim of this study was to analyze the setup error of the electronics portal image device (EPID) in intensity-modulated radiation therapy (IMRT) for thoracic tumors and the influence on the outward expansion distance of the target area. A total of 202 patients with chest tumors admitted to our hospital from March 2016 to March 2018 were selected as the observation subjects. All patients were treated with IMRT. The original plan was developed based on the SM90 obtained by the planning target volume (PTV) expansion method, and the new plan was obtained by shifting the isocenter coordinates of the treatment plan according to the positioning error value obtained by EPID. Before the treatment, EPID scans were performed. The electronic radiation field images (ERIs) were registered with the digitally reconstructed radiographic images (DRRs) generated by the treatment planning system using the image registration software, and the setup errors in the X, Y, and Z directions were further measured. The PTV was developed according to ERIs, and the setup error was simulated to obtain the PTV with 95% internal target volume (ITV) reaching the prescribed dose under the condition of a setup error. The outward expansion distance of clinical target volume (CTV) → PTV was calculated. In this experiment, the setup errors in X, Y, and Z directions were (-2.00±1.16) mm, (0.16±1.14) mm, and (-0.55±1.16) mm, respectively. The systematic error in the Z direction was -3.00 mm, and the random error in the X direction was 3.30 mm. The CTV → PTV outward expansion distance was set as 7, 8 and 7 mm in the X direction, Y direction and Z direction, respectively. At this time, under the presence of setup error, the PTV D95 and the ITV V100 in the new plan were (62.23±3.85) Gy and (97.51±1.56) %, respectively, effectively ensuring that 95% ITV of 90% patients reached the prescribed dose. In contrast, the ITV D95 and ITV V100 in the presence of setup error were (56.11±5.26) Gy and (90.15±3.12) %, respectively, at a CTV → PTV outward expansion distance of 5 mm, which could not guarantee that 95% ITV of 90% patients reached the prescribed dose. In the presence of a setup error, the double-lung 5 Gy irradiation of the total heart volume (V5), the double-lung 20 Gy irradiation of the total heart volume (V20), mean lung dose (MLD), mean heart dose (MHD), and D1 cm3 of the new plan increased by 0.89%, 0.29%, 0.13%, 0.06%, and 5 Gy, respectively, compared with the original plan. In general, the first treatment of radiotherapy in thoracic tumors mostly has a certain degree of setup error, which is most evident in the X direction. When the CTV → PTV outward expansion distance is set at 7, 8, and 7 mm in the X direction, Y direction, and Z direction, respectively, it can effectively ensure that 95% ITV reach the prescribed dose in 90% of patients in the presence of a setup error. EPID helps to achieve the desired effect of radiotherapy, improves the efficacy of radiotherapy, and reduces the side effects caused by radiotherapy errors.

Pretreatment patient-specific quality assurance prediction based on 1D complexity metrics and 3D planning dose: classification, gamma passing rates, and DVH metrics

PurposeHighly modulated radiotherapy plans aim to achieve target conformality and spare organs at risk, but the high complexity of the plan may increase the uncertainty of treatment. Thus, patient-specific quality assurance (PSQA) plays a crucial role in ensuring treatment accuracy and providing clinical guidance. This study aims to propose a prediction model based on complexity metrics and patient planning dose for PSQA results.Materials and methodsPlanning dose, measurement-based reconstructed dose and plan complexity metrics of the 687 radiotherapy plans of patients treated in our institution were collected for model establishing. Global gamma passing rate (GPR, 3%/2mm,10% threshold) of 90% was used as QA criterion. Neural architecture models based on Swin-transformer were adapted to process 3D dose and incorporate 1D metrics to predict QA results. The dataset was divided into training (447), validation (90), and testing (150) sets. Evaluation of predictions was performed using mean absolute error (MAE) for GPR, planning target volume (PTV) HI and PTV CI, mean absolute percentage error (MAPE) for PTV D95, PTV D2 and PTV Dmean, and the area under the receiver operating characteristic (ROC) curve (AUC) for classification. Furthermore, we also compare the prediction results with other models based on either only 1D or 3D inputs.ResultsIn this dataset, 72.8% (500/687) plans passed the pretreatment QA under the criterion. On the testing set, our model achieves the highest performance, with the 1D model slightly surpassing the 3D model. The performance results are as follows (combine, 1D, and 3D transformer): The AUCs are 0.92, 0.88 and 0.86 for QA classification. The MAEs of prediction are 0.039, 0.046, and 0.040 for 3D GPR, 0.018, 0.021, and 0.019 for PTV HI, and 0.075, 0.078, and 0.084 for PTV CI. Specifically, for cases with 3D GPRs greater than 90%, the MAE could achieve 0.020 (combine). The MAPE of prediction is 1.23%, 1.52%, and 1.66% for PTV D95, 2.36%, 2.67%, and 2.45% for PTV D2, and 1.46%, 1.70%, and 1.71% for PTV Dmean.ConclusionThe model based on 1D complexity metrics and 3D planning dose could predict pretreatment PSQA results with high accuracy and the complexity metrics play a leading role in the model. Furthermore, dose-volume metric deviations of PTV could be predicted and more clinically valuable information could be provided.

A method for patient-specific DVH verification using a high-sampling-rate log file in an Elekta linac.

We have proposed a method for patient-specific dose-volume histogram (DVH) verification using a 40-ms high-sampling-rate log file (HLF) available in an Elekta linac. Ten prostate volumetric-modulated arc therapy plans were randomly selected, and systematic leaf position errors of ±0.2, ±0.4, or ±0.8mm were added to the 10 plans, thereby producing a total of 70 plans. An RTP file was created by interpolating each leaf position in the HLF to obtain values at each control point, which is subsequently exported to a treatment planning system. The isocenter dose calculated by the HLF-based plan to a phantom (Delta4 Phantom+) was compared to that measured by the diode in the phantom in order to evaluate the accuracy of the HLF-based dose calculation. The D95 of the planning target volume (PTV) was also compared between the HLF-based plans and the original plans with the systematic leaf position errors, the latter being referred to as theory-based plans. Sensitivities of the DVH parameters in the target, the rectum, and the bladder were also calculated with the varied systematic leaf position errors. The relative differences in the isocenter doses between the HLF-based calculations and the measurements among the 70 plans were 0.21%±0.67% (SD). The maximum relative differences in PTV D95 between the HLF-based and the theory-based plans among the 70 cases were 0.11%. The patient-specific DVH verification method detected a change in the target DVH parameters of less than 1% when the systematic leaf position error was ±0.2mm. It is therefore suggested that the proposed DVH verification method may simplify patient-specific dose quality assurance procedures without compromising accuracy and sensitivity.

The dosimetric error due to uncorrected tumor rotation during real-time adaptive prostate stereotactic body radiation therapy.

During prostate stereotactic body radiation therapy (SBRT), prostate tumor translational motion may deteriorate the planned dose distribution. Most of the major advances in motion management to date have focused on correcting this one aspect of the tumor motion, translation. However, large prostate rotation up to 30° has been measured. As the technological innovation evolves toward delivering increasingly precise radiotherapy, it is important to quantify the clinical benefit of translational and rotational motion correction over translational motion correctionalone. The purpose of this work was to quantify the dosimetric impact of intrafractional dynamic rotation of the prostate measured with a six degrees-of-freedom tumor motion monitoringtechnology. The delivered dose was reconstructed including (a) translational and rotational motion and (b) only translational motion of the tumor for 32 prostate cancer patients recruited on a 5-fraction prostate SBRT clinical trial. Patients on the trial received 7.25 Gy in a treatment fraction. A 5 mm clinical target volume (CTV) to planning target volume (PTV) margin was applied in all directions except the posterior direction where a 3 mm expansion was used. Prostate intrafractional translational motion was managed using a gating strategy, and any translation above the gating threshold was corrected by applying an equivalent couch shift. The residual translational motion is denoted as . Prostate intrafractional rotational motion was recorded but not corrected. The dose differences from the planned dose due to + , ΔD( + ) and due to alone, ΔD( ), were then determined for CTV D98, PTV D95, bladder V6Gy, and rectum V6Gy. The residual dose error due to uncorrected rotation, was then quantified: = ΔD( + ) - ΔD( ). Fractional data analysis shows that the dose differences from the plan (both ΔD( + ) and ΔD( )) for CTV D98 was less than 5% in all treatment fractions. ΔD( + ) was larger than 5% in one fraction for PTV D95, in one fraction for bladder V6Gy, and in five fractions for rectum V6Gy. Uncorrected rotation, induced residual dose error, , resulted in less dose to CTV and PTV in 43% and 59% treatment fractions, respectively, and more dose to bladder and rectum in 51% and 53% treatment fractions, respectively. The cumulative dose over five fractions, ∑D( + ) and ∑D( ), was always within 5% of the planned dose for all four structures for everypatient. The dosimetric impact of tumor rotation on a large prostate cancer patient cohort was quantified in this study. These results suggest that the standard 3-5 mm CTV-PTV margin was sufficient to account for the intrafraction prostate rotation observed for this cohort of patients, provided an appropriate gating threshold was applied to correct for translational motion. Residual dose errors due to uncorrected prostate rotation were small in magnitude, which may be corrected using different treatment adaptation strategies to further improve the dosimetricaccuracy.

Patient-Reported and Clinical Outcomes From 5-Fraction SBRT for Oligometastases: A Prospective Single-Institution Study

To describe the long-term outcomes of a 5-fraction normal tissue tolerance adapted strategy for the management of oligometastases (OM). Patients with histologically confirmed solid tumors, ≤5 extracranial metastases, suitable for a definitive approach for all metastatic lesions, at least one lesion suitable for Stereotactic Body Radiotherapy (SBRT), Eastern Coooperative Oncology Group Performance Status ≤2 were eligible. Treatment intervention was a 5-fraction (25-55 Gy) normal tissue adapted dosing strategy. The primary outcome was cumulative local progression rate at 12 months. Between March 2013 and January 2018, 137 patients started SBRT. Median follow-up was 35.7 months. In addition, 107 (78%) patients had a solitary OM. The mean planning target volume D95 was 39.6 (standard deviation, 8.8; biological effective dose using an alpha/beta ratio of 10, 70.8) Gy. Mean planning target volume D95 was highest for lung lesions (48.7 [standard deviation, 4.7]; biological effective dose using an alpha/beta ratio of 10, 96.1) Gy but was <40 Gy for all other anatomic sites. Two grade 3 toxicities (gastrointestinal bleed) were observed with stomach D0.05 30.3 Gy and 30.4 Gy. The cumulative local progression rate at 12 of 36 months was 16.1% (95% CI, 10-22) and 38.3% (95% CI 30-46.7); overall survival was 90% and 37%, and progression free survival was 58% and 19%, respectively. Mean symptom burden (Edmonton Symptom Assessment Total Score) worsened in patients with progressive disease (+8.8) at 12 months and was paralleled by changes in mean European Organization for Research and Treatment Quality of Life Core Questionnaire Summary Score and Global Health Quality of Life Score. Systemic therapy was initiated in 55% of patients at an average of 12.7 (standard deviation 12.4) months. If long-term progression free survival is the primary goal of therapy, SBRT for OM achieved this in <20% of patients attributable to a high risk of distant failure. Favorable local progression free survival is accompanied by preservation of quality of life, avoidance of symptom progression and reduced need of antineoplastic therapies at 12 months. Information on symptom burden, quality of life, as well as pattern of antineoplastic therapy use after progressive disease is useful to support conversations between patients, families, and health care providers. Strategies to improve patient selection and reduce distant progression rate remain a priority for further study.

Predicting personalised and progressive adaptive dose escalation to gross tumour volume using knowledge-based planning models for inoperable advanced-stage non-small cell lung cancer patients treated with volumetric modulated arc therapy

Objectives. Increased radiation doses could improve local control and overall survival of lung cancer patients, however, this could be challenging without exceeding organs at risk (OAR) dose constraints, especially for patients with advanced-stage disease. Increasing OAR doses could reduce the therapeutic ratio and quality of life. It is therefore important to investigate methods to increase the dose to target volume without exceeding OAR dose constraints. Methods. Gross tumour volume (GTV) was contoured on synthetic computerised tomography (sCT) datasets produced using the Velocity adaptive radiotherapy software for eleven patients. The fractions where GTV volume decreased compared to that prior to radiotherapy (reference plan) were considered for personalised progressive dose escalation. The dose to the adapted GTV (GTVAdaptive) was increased until OAR doses were affected (as compared to the original clinical plan). Planning target volume (PTV) coverage was maintained for all plans. Doses were also escalated to the reference plan (GTVClinical) using the same method. Adapted, dose-escalated, plans were combined to estimate accumulated dose, D99 (dose to 99%) of GTVAdapted, PTV D99 and OAR doses and compared with those in the original clinical plans. Knowledge-based planning (KBP) model was developed to predict D99 of the adapted GTV with OAR doses and PTV coverage kept similar to the original clinical plans; prediction accuracy and model verification were performed using further data sets. Results. Compared to the original clinical plan, the dose to GTV was significantly increased without exceeding OAR doses. Adaptive dose-escalation increased the average D99 to GTVAdaptive by 15.1Gy and 8.7Gy compared to the clinical plans. The KBP models were verified and demonstrated prediction accuracy of 0.4% and 0.7% respectively. Conclusion. Progressive adaptive dose escalation can significantly increase the dose to GTV without increasing OAR doses or compromising the dose to microscopic disease. This may increase overall survival without increasing toxicities.

Clinical results of dynamic tumor-tracking stereotactic body radiotherapy with real-time monitoring for liver tumors using a gimbal-mounted linac: A multi-institutional phase II study.

441 Background: Dynamic tumor-tracking (DTT) stereotactic body radiotherapy (SBRT) with real-time monitoring for liver tumors using a gimbal-mounted linac can decrease the normal liver dose and planning target volume (PTV) without sacrificing the target dose. We hypothesized that this method would yield excellent tumor control comparable to that by the conventional SBRT. We conducted a multi-institutional prospective phase II study to evaluate the safety and efficacy of DTT-SBRT for liver tumors (UMIN-CTR, UMIN000017886). Methods: The main eligibility criteria were as follows: (1) &lt; 4 liver tumors; (2) technical difficulties with percutaneous ablation therapies, inoperable lesions, or patient refusal to undergo surgery; (3) Eastern Cooperative Oncology Group performance status of 0–2; (4) Child-Pugh score of ≤8; and (5) respiratory motion of ≥10 mm. The primary endpoint was the local control rate (LC) at 2 years (expected endpoint: &gt; 90%), and the secondary endpoints were overall survival rate (OS), progression-free survival rate (PFS), and treatment-related toxicity. We performed DTT-SBRT with 40 Gy in 5 fractions prescribed to the PTV D95, and a maximum dose of 55−58 Gy using 7–9 static non-coplanar ports of the 6-MV beam was applied. The Kaplan-Meier analysis was performed to estimate the OS and LC. Treatment-related toxicity was scored according to the Common Terminology Criteria for Adverse Events v.4.0. Results: Forty-eight patients (48 tumors) were registered from four institutes and successfully treated between September 2015 and March 2019. Their median age was 74 years (range, 52–97). Thirty-nine tumors were hepatocellular carcinomas, and nine were metastatic liver tumors. The median tumor size was 5.8 ml (range, 0.7–64.1). At the time of data cutoff on March 31, 2021, the median follow-up period was 36.5 months (range, 3.0–62.4). The 2-year LC was 98.0%. Two-year OS and PFS were 88.8% and 55.1%, respectively. Recurrences were observed in 33 patients (68.5%). One patient (0.2%) had local recurrence, 30 (62.5%) developed new hepatic lesions outside of the irradiation field, and 9 (18.8%) had distant metastases. Grade 3 adverse events were observed in seven patients, including elevation of liver or biliary enzyme levels and hematopoietic adverse events. No treatment-related toxicity of grade 4 or higher was observed. Conclusions: Employing DTT-SBRT to treat liver tumors resulted in excellent LC with acceptable incidence of adverse events. This method will be a promising alternative therapy for patients who cannot receive surgery or percutaneous ablation therapy. To the best of our knowledge, this is the first phase II trial evaluating DTT-SBRT for liver tumors. Clinical trial information: UMIN000017886.

Sparing Functional Lung Using Optimized Volumetric Modulated Arc Therapy in Thoracic Radiation for Locally Advanced Non-Small Cell Lung Cancer

Chemoradiation (CRT) followed by maintenance durvalumab is the standard of care for locally advanced non-small cell lung cancer (NSCLC) but is limited by toxicity to normal lung tissue from radiotherapy and immunotherapy1. Many lung cancer patients have heterogeneous lung function as a result of the tumor and/or pre-existing co-morbidities2. We proposed Volumetric Modulated Arc Therapy (VMAT) could be used to spare the functional parts of the lung (FL) without exceeding organs at risk (OARs) constraints or compromising tumor coverage.Functional lung volumes were retrospectively contoured using 4D-CT ventilation maps for 32 patients with stage III NSCLC treated with CRT and maintenance durvalumab at a single institution from September 2017- October 2019. Functional lung volumes were created from 4D-CT data using methodology previously described3,4. Studies have shown 4D-CT ventilation maps generated from the changes in the density of lungs during the respiratory cycle correlate with pulmonary function tests and ventilation-perfusion imaging5. New VMAT plans were generated to spare the FL while also maintaining adequate planning target volume (PTV) coverage and without exceeding dose constraints to the OARs. The dosimetric values of the original plans were compared to the dosimetric values of the optimized plans using paired t-test or paired Wilcox rank-sum test as appropriate. Specifically, the PTV D95, heart mean, esophagus mean, spinal cord Dmax, as well as the FL mean, FL V5, FL V10, FL V20, and FL V30 were compared.Optimized plans had statically significant lower FL mean dose, FL V5, FL V10, FL V20, and FL V30 (all P values < 0.001). Numerically, the mean dose to the heart, mean dose to the esophagus, and spinal cord Dmax were lower in the optimized plan as compared to the original plan, though only the esophageal dose was statistically significant (P < 0.001). When comparing the PTV D95, the median for both plans were the same (60 Gy), though statistically lower (P = 0.032) in the optimized plan (range, 57-66.15) as compared to the original plan (range, 57-67.27). However, both plans provided adequate PTV coverage.We demonstrated the ability to optimize VMAT plans to avoid functional parts of the lung while maintaining adequate PTV coverage and meeting OAR constraints for locally advanced NSCLC. VMAT plans optimized to avoid functional lung can be created with minimal extra cost or change in treatment planning workflow as 4D-CT acquisition at time of simulation is standard practice, which is advantageous compared to other functional lung avoidance techniques, i.e., single photon emission computerized tomography (SPECT). Given already compromised lung function and risk of pulmonary toxicities from treatment, this work highlights a personalized approach to radiation treatment planning.

Overview of the Dosimetry of Free Breathing and Breath Hold Forward Intensity Modulated Treatments in a Large Clinical Series of Left-Sided Breast Cancer Patients

<h3>Purpose/Objective(s)</h3> To compare the dosimetry of a large clinical series of left-sided breast cancer patients treated with forward intensity modulated radiation therapy in free breathing (FB) or in breath hold (BH). <h3>Materials/Methods</h3> A total of 155 early-stage pT1c-T2N1 left breast carcinoma patients receiving whole breast irradiation were enrolled in this study. Computed tomography scans acquired in FB (75 patients) and in BH (82 patients) were exported to the treatment planning. Clinical target volume (CTV) and organs at risk (OARs) were contoured by an experienced radiation oncologist of the breast department; the planning target volume (PTV) was generated with an isotropic expansion of the CTV with a 3 mm margin in all directions, excluding the first 5 mm inside the body external contour. Patients were treated with a prescribed dose (Dp) of 50 Gy in 25 fractions. All plans were based on a tangential field in field technique with a 6 MV photon beam energy using two opposing tangential fields, each including 3 to 5 sub-segments. Treatment plans were optimized to achieve minimum 95% of the PTV covered by 95% isodose line and a mean dose () to the PTV equal to the Dp and keeping the organs at risk (OARs) doses as low as achievable. Dose volume histogram (DVH) endpoints for the PTV (D95, D98, Dm, Dmax), for heart and left lung (V5, V20, Dm) and for right lung and right breast (Dm and Dmax) were used to compare the dosimetry of FB and BH treatments. Data were analyzed with the Wilcoxon Cox test; <b>P</b> value < 0.05 was considered statistically significant. <h3>Results</h3> The analysis showed no significant difference for PTV D95, D98, Dm, Dmax, and volume (<b>P</b> = 0.329, <b>P</b> = 0.456, <b>P</b> = 0.566, <b>P</b> = 0.067, <b>P</b> = 0.482, respectively) between BH and FB groups. Comparing the dosimetry of OARs, we recorded significantly lower values for patients in the BH group: heart Dm (1.7 Gy vs 5.3 Gy), V5 (3.7% vs 26.0%) and V20 (0.4% vs 3.0%); left lung V5 (29.5% vs 38.0%) and V20 (13.6% vs 15.7%); right lung Dm (0.1% vs 2.5%), right breast Dm (0.2 Gy vs 1.7 Gy). While, a slight lower lung left Dm value (8.0 Gy vs 8.6 Gy), not statistically significant (<b>P</b> = 0.106) was registered for BH group. The OARs dosimetry obtained for the FB patients and the corresponding percentage difference obtained for the BH group is shown in the Table below. <h3>Conclusion</h3> The use of BH in the clinical practice may be the best option for left breast RT reducing the irradiation of heart, left lung, and of right lung and right breast, without compromising target coverage.

A preliminary investigation of re-evaluating the irradiation dose in hepatocellular carcinoma radiotherapy applying 4D CT and deformable registration.

PurposeTo investigate the effect of breathing motion on dose distribution for hepatocellular carcinoma (HCC) patients using four‐dimensional (4D) CT and deformable registration.MethodsFifty HCC patients who were going to receive radiotherapy were enrolled in this study. All patients had been treated with transarterial chemoembolization beforehand. Three‐dimensional (3D) and 4D CT scans in free breathing were acquired sequentially. Volumetric modulated arc therapy (VMAT) was planned on the 3D CT images and maximum intensity projection (MIP) images. Thus, the 3D dose (Dose‐3D) and MIP dose (Dose‐MIP) were obtained, respectively. Then, the Dose‐3D and Dose‐MIP were recalculated on 10 phases of 4D CT images, respectively, in which the end‐inhale and end‐exhale phase doses were defined as Dose‐3D‐EI, Dose‐3D‐EE, Dose‐MIP‐EI, and Dose‐MIP‐EE. The 4D dose (Dose‐4D‐3D and Dose‐4D‐MIP) were obtained by deforming 10 phase doses to the end‐exhale CT to accumulate. The dosimetric difference in Dose‐3D, Dose‐EI3D, Dose‐EE3D, Dose‐4D‐3D, Dose‐MIP, Dose‐EIMIP, Dose‐EEMIP, and Dose‐4D‐MIP were compared to evaluate the motion effect on dose delivery to the planning target volume (PTV) and normal liver.ResultsCompared with Dose‐3D, PTV D99 in Dose‐EI3D, Dose‐EE3D and Dose‐4D‐3D decreased by an average of 6.02%, 1.32%, 2.43%, respectively (P < 0.05); while PTV D95 decreased by an average of 3.34%, 1.51%, 1.93%, respectively (P < 0.05). However, CI and HI of the PTV in Dose‐3D was superior to the other three distributions (P < 0.05). There was no significant differences for the PTV between Dose‐EI and Dose‐EE, and between the two extreme phase doses and Dose‐4D (P> 0.05). Negligible difference was observed for normal liver in all dose distributions (P> 0.05).ConclusionsFour‐dimensional dose calculations potentially ensure target volume coverage when breathing motion may affect the dose distribution. Dose escalation can be considered to improve the local control of HCC on the basis of accurately predicting the probability of radiation‐induced liver disease.

Dosimetric impact of commercial CT metal artifact reduction algorithms and a novel in-house algorithm for proton therapy of head and neck cancer.

To compare the dosimetric impact of all major commercial vendors' metal artifact reduction (MAR) algorithms to one another, as well as to a novel in-house technique (AMPP) using an anthropomorphic head phantom. The phantom was an Alderson phantom, modified to allow for artifact-filled and baseline (no artifacts) computed tomography (CT) scans using teeth capsules made with metal amalgams or bone-equivalent materials. It also included a cylindrical insert that was accessible from the bottom of the neck and designed to introduce soft tissue features into the phantom that were used in the analysis. The phantom was scanned with the metal teeth in place using each respective vendor's MAR algorithm: OMAR (Philips), iMAR (Siemens), SEMAR (Canon), and SmartMAR (GE); the AMPP algorithm was designed in-house. Uncorrected and baseline (bone-equivalent teeth) image sets were also acquired using a Siemens scanner. Proton spot scanning treatment plans were designed on the baseline image set for five targets in the phantom. Once optimized, the proton beams were copied onto the different artifact-corrected image sets, with no reoptimization of the beams' parameters, to evaluate dose distribution differences in the different MAR-corrected and -uncorrected image sets. Dose distribution differences were evaluated by comparing dose-volume histogram (DVH) metrics, including planning target volume D95 and clinical target volume D99 coverages, V100, D0.03cc, and heterogeneity indexes, along with a qualitative and water equivalent thickness (WET) analysis. Uncorrected CT metal artifacts and commercial MAR algorithms negatively impacted the proton dose distributions of all five target shapes and locations in an inconsistent manner, sometimes overdosing by as much as 11.1% (D0.03) or underdosing by as much as 11.7% (V100) the planning target volumes. The AMPP-corrected images, however, provided dose distributions that consistently agreed with the baseline dose distribution. The dosimetry results also suggest that the commercial MAR algorithms' performances varied more with target location and less with target shape. Once relocated further from the metal, the target showed dose distributions that agreed more with the baseline for all commercial solutions, improving the overdosing by as much as 6%, implying inadequate HU correction from commercial MAR algorithms. In comparison to the baseline, HU profile shapes were considerably altered by commercial algorithms and reference values showed differences that represent stopping power percentage differences of 2.7-10%. The AMPP algorithm plans showed the smallest WET differences with the baseline (0.06cm on average), while the commercial image sets created differences that ranged from 0.11 to 0.54cm. Computed tomography metal artifacts negatively impacted proton dose distributions on all five targets analyzed. The commercial MAR solutions performed inconsistently throughout all targets compared to the metal-free baseline. A lack of CTV coverage and an increased number of hotspots were observed throughout all commercial solutions. Dose distribution errors were related to the proximity to the artifacts, demonstrating the inability of commercial techniques to adequately correct severe artifacts. In contrast, AMPP consistently showed dose distributions that best matched the baseline, likely because it makes use of accurate HU information, as opposed to interpolated data like commercial algorithms.

Interfraction Tumor Change During Stereotactic Radiotherapy For Large Brain Metastases And Importance Of Treatment Plan Modification During Treatment Period

We aimed to evaluate the magnetic resonance imaging (MRI) appearance changes during stereotactic radiotherapy (SRT) for large sized brain metastases, and analyze the lesions necessitating treatment plan modification. A total of 23 patients (27 lesions, >2 cm in tumor diameter) underwent SRT and all lesions were evaluated the appearance changes which had the necessity of the treatment plan modification. The prescribed dose and fraction were chosen based on the size of brain metastasis: for lesions between 2.1 and 3 cm or 5.1 and 10 cc, the total dose was 35 Gy in 5 fractions, and between 3.1 and 4 cm or 10.1 and 30 cc, the total dose was 40 Gy in 8 fractions. The dose was prescribed with the 80% isodose line covering the planning target volume (PTV). Usually, our plans were normalized so that PTV D95 or D98 was equal to the prescribed dose, and gross tumor volume (GTV) D99 (dose that covers 99% of the GTV) was planned to be more than 110% of the prescribed dose. The appearance change of tumor during SRT was evaluated using gadolinium-enhanced MRI. Usually, we conducted Gd-MRI for the evaluation and modification before or after 4th treatment. The reasons of the modification were classified into tumor reduction, tumor enlargement, displacement, and shape change. Tumor reduction was defined as a ≥1 mm reduction in the maximum tumor diameter and ≥10% reduction in the tumor volume on T1-weighted MRI during treatment period. Tumor enlargement was defined as a ≥1 mm enlargement in the tumor diameter in each direction and ≥10% enlargement in the tumor volume on T1-weighted MRI. Displacement was defined as a ≥1 mm shift of center of PTV except tumor reduction and tumor enlargement. Shape change was defined as a slightly change of GTV delineation that caused the decreased GTV D99 except the cases of tumor reduction, tumor enlargement, and displacement. Univariate analyses using the χ2 test were performed to determine the statistical significance of differences between lesions with and those without the modification. Among the 27 lesions, 55.6% required the treatment plan modification. The reasons were tumor reduction in 6 lesions, tumor enlargement in 3 lesions, displacement in 3 lesions, and shape change in 3 lesions. The planning target volume (PTV) size changed up to 43.0% and the shift of center of PTV was a maximum of 1.7 mm. The pathological status (adenocarcinoma vs others) and timing of steroid administration (prior vs after SRT start) were the predictive factors of tumor changes required the modification. As tumor changes might occur even during short period of SRT, the treatment plan evaluation and modification were important in SRT for large brain metastases.

Set-up error and dosimetric analysis of HexaPOD evo RT 6D couch combined with cone beam CT image-guided intensity-modulated radiotherapy for primary malignant tumor of the cervical spine.

PurposeTo investigate the set‐up error and consequent dosimetric change in HexaPOD evo RT 6D couch under image‐guided intensity‐modulated radiotherapy (IG‐IMRT) for primary malignant tumor of the cervical spine.MethodsTen cases with primary malignant tumor of the cervical spine were treated with intensity‐modulated radiotherapy (IMRT) in our hospital from August 2013 to November 2014. The X‐ray volumetric images (XVI) were scanned and obtained by cone‐beam CT (CBCT). The six directions (6D) of set‐up errors of translation and rotation were obtained by planned CT image registration. HexaPOD evo RT 6D couch made online correction of the set‐up error, and then the CBCT was conducted to obtain the residual error.ResultsWe performed set‐up error and dosimetric analysis. First, for the set‐up error analysis, the average error in three translation directions of 6D set‐up error of the primary tumor of the cervical spine was <2 mm, whereas the single maximum error (absolute value) is 7.0 mm. Among average errors of rotation direction, Rotation X (RX) direction 0.67° ± 0.04°, Rotation Y (RY) direction 1.06° ± 0.06°, Rotation Z (RZ) direction 0.78° ± 0.05°; and the single maximum error in three rotation directions were 2.8°, 3.8°, and 2.9°, respectively. On three directions (X, Y, Z axis), the extended distance from clinical target volume (CTV) to planning target volume (PTV) was 3.45, 3.17, and 3.90 mm by calculating, respectively. Then, for the dosimetric analysis, the parameters, including plan sum PTV D98 and D95, planning gross tumor volume D98 and D95, V100% of the plan sum were significantly lower than the treatment plan. Moreover, Dmax of the spinal cord was significantly higher than the treatment plan.Conclusion6D set‐up error correction system should be used for accurate position calibration of precise radiotherapy for patients with malignant tumor of the cervical spine.

Comparison of Volumetric Modulated Arc Therapy and Three-Dimensional Conformal Radiotherapy in Postoperative High-Grade Glioma: A Dosimetric Comparison

Introduction: We aimed to dosimetrically compare three-dimensional conformal radiotherapy (3D-CRT) and volumetric modulated arc therapy (VMAT) in terms of planning target volume (PTV) coverage, organ at risk (OAR) sparing, and conformity index (CI). Material and Methods: Planning data of 26 high grade glioma (HGG) patients were used. Prescribed dose for 3D-CRT was 46Gy in 23 fractions to low-risk PTV (LR-PTV) and 14 Gy in 7 fractions to high-risk PTV (HR-PTV). VMAT plans were conducted using 46 Gy in 30 fractions to LR-PTV and 60 Gy in 30 fractions to HR-PTV. Results: Tumor locations were frontal, parietal, temporal, and multi-lobed in 27%, 15%, 23%, and 35% of cases, respectively. Histology was glioblastoma multiform in 89% of patients. Mean values of PTV D95 (dose received by 95% volume) in 3D-CRT and VMAT were 96.6% and 98.8% for the LR-PTV and 97.3% and 99% for HR-PTV (p <0.001), respectively. Mean values of CI in 3D-CRT were 0.96 and 0.97 for LR-PTV and HR-PTV and 0.98 and 0.99 for LR-PTV and HR-PTV of VMAT (both p <0.001), respectively. Mean Dmax of right optic nerve (maximum point dose received by the organ) for 3D-CRT and VMAT were 31.59 and 25.57Gy (P=0.02). Mean Dmax for left optic nerve and optic chiasm were 28.81 and 22.14 Gy (P=0.019) and 42.24 and 37.12 Gy (P=0.055) respectively for 3D-CRT versus VMAT. Doses to other OARs were not statistically different between 3D-CRT and VMAT. Conclusion: VMAT achieved better coverage of the PTV and delivered fewer doses to bilateral optic nerve and chiasm.

VMAT Optimization and Dose Calculation in the Presence of Metallic Hip Prostheses.

Introduction:This research quantifies and compares the effect of hip prostheses on dose distributions calculated using collapsed cone convolution superposition and Monte Carlo (with and without correcting for the density of the implant and surrounding tissues). The use of full volumetric modulated arc therapy arcs versus volumetric modulated arc therapy arcs avoiding the hip implants (skip arcs) was also studied.Materials and Methods:Six prostate patients with hip prostheses were included in this study. The hip prostheses and the streaking artifacts on the computed tomography images were contoured by a single physician, and full volumetric modulated arc therapy arcs were created in the Pinnacle3 TPS. Copies of each plan were made, and the doses were recalculated with the densities of the prostheses and surrounding tissues overridden. The plans were then exported to Monaco and recalculated using a Monte Carlo dose calculation algorithm, with and without densities of the prosthesis and surrounding tissues overridden.Results:With density overrides, Pinnacle3 had a 4.4% error for ion chamber measurements. Monaco was within 0.2% of ion chamber measurement when density overrides were used. On average, when density overrides were used in Pinnacle3 for patient dose calculations, the planning target volume D95 value dropped from 99.3% to 82.7%. Monaco also showed decreased planning target volume coverage when plans were recalculated with correct density information. Full arc plans (with density overrides) for the patient with a bilateral prosthesis provided significant bladder sparing and some rectal sparing compared to skip arc plans.Conclusion:When planning for prostate patients with hip prostheses, correct density information for implants and surrounding tissues should be used to optimize the plan and ensure optimal accuracy. If available, a Monte Carlo algorithm should be used as a second check. Full arcs could be used to spare dose to organs at risk, while maintaining adequate planning target volume coverage, when using a Monte Carlo dose calculation algorithm.

Marginal Failures with Stereotactic Body Radiation Therapy(SBRT) for Early Stage Lung Cancer: Room for Improvement?

SBRT is an effective treatment for early stage non-small cell lung cancer (NSCLC). Prior series distinguish local from regional/distant recurrences, but detailed patterns of local failure are not well-described. We evaluate the location of local failures to provide further insight for treatment planning. Patients treated with SBRT for T1-2N0 NSCLC from 2007-2016 at a single institution were included. Prescribed dose was 48-54Gy in 3 to 5 fractions and planning target volume (PTV) margins were generally 5mm radially and 8mm superior/inferior. Site of first failure was classified as local, regional (hilar/mediastinal lymph nodes) or metastatic. For patients with a component of local failure, post-treatment diagnostic scans at time of recurrence were fused to the initial planning scan using rigid registration to lung features proximal to recurrence. The recurrence volume was delineated and compared to the treatment PTV. For each local failure, percent overlap of the PTV and recurrence volume was calculated. Distance from centroid (geometric center) of recurrence to PTV edge was measured in 3 planes and average distance was calculated. Local failures were categorized as: in-field failure (≥80% overlap or centroid >1cm inside PTV), marginal failure (20-80% overlap and centroid <1 cm inside/outside PTV), or involved lobe failure (overlap <20% or centroid >1cm outside PTV). Parametric statistics compared characteristics of recurrences. A total of 217 patients were treated with robotic radiosurgery (94%) or linac-based (6%) SBRT. 83% were T1 tumors, 69% upper lobe tumors, and 74% biopsy-proven malignancy. With a median follow-up of 20 months (range 0-98), 38% had progression of disease. 16% (N=34) had a component of local progression at time of first failure: 18 local only, 8 locoregional, 8 metastatic. 60% were pathologically confirmed. Of the local failures, 9 were classified as in-field, 15 marginal and 10 involved lobe. For in-field, marginal, and involved lobe failures there were differences in mean PTV/recurrence overlap (93% vs 43% vs 2%) and distance from centroid to PTV margin (1.39cm vs 0.56cm vs 1.78cm). For all local failures, PTV D95 was at least prescription dose. Marginal failures developed earlier than other local failures (mean 15 vs 25 months, p<0.05). Upper and lower lobe tumors had similar rates of local failure (16% vs 18%); however, 8 of the 11 local failures seen in lower lobe tumors were marginal failures compared to only 7 of 23 local failures in upper lobe tumors. Local progression is seen in roughly 16% of patients following SBRT. Marginal failures represent nearly half of these events, and appear to be of particular concern for lower lobe tumors. These findings highlight an opportunity to further evaluate margin size, motion management, and accuracy of dose calculations at the PTV margin to further improve local control in lung SBRT.

Towards abdominal MRI-based treatment planning using population-based Hounsfield units for bulk density assignment

This study investigates the dosimetric impact of using population-based Hounsfield units (HUs) and ICRU-based HUs as a function of the number of tissue segments for bulk density assignment toward MRI-based treatment planning in the abdomen. To avoid potential geometric differences between CT and MR images, CT images rather than MR images were chosen to simulate an MRI-only planning scenario. A retrospective study was performed utilizing 18 patients that had previously undergone stereotactic body radiation therapy for liver or pancreas cancer. HU values in the CT datasets were collected for various tissue types, and compared with the HUs derived from ICRU report 46. Doses were recalculated using the fluence obtained from clinical plans and with (1) homogeneous assignment, (2) ICRU-based HU assignment and (3) population-based HU assignment using three, four, five, nine or ten tissue segments. Dose-volume metrics for targets and organs-at-risk for all scenarios were compared with those obtained using the clinical CT. For the planning target volume (PTV) D99.9%, the mean differences from clinical CT plans were −2.1% ± 3.9%, −0.6% ± 0.3% and −0.1% ± 0.3% for homogeneity, ICRU-HUs and population-HUs using ten tissue segments, respectively. The population-HU method resulted in better dosimetric accuracy compared to the ICRU-HU method (p-value < 0.05). The dosimetric accuracy of homogeneity plans was comparable to that of both ICRU-HU and population-HU plans when targets were far from the lungs but deteriorated when targets were close to the lungs. As the number of tissue segments decreased, the dosimetric accuracy for PTV D99.9% reduced for the population-HU method, from −0.1% for ten tissue segments to −0.4% for three tissue segments, while no such dependence was observed for the ICRU-HU method. Hence, to generate a clinically acceptable plan when using MRI to synthesize CT in the abdomen for treatment planning, it might be sufficient for electron density assignment with either the population-HU or ICRU-HU method to only use three tissue segments.

Haploidentical hematopoietic SCT using helical tomotherapy for total-body irradiation and targeted dose boost in patients with high-risk/refractory acute lymphoblastic leukemia.

A novel conditioning regimen using helical tomotherapy (HT) was developed to deliver 10 Gy for total body irradiation (TBI) and simultaneously augment dose to 12 Gy for targeted dose boost to total marrow, central nervous system leukemia, and extramedullary disease sites in patients with high-risk or relapsed/refractory acute lymphoblastic leukemia (ALL) receiving haploidentical allogeneic hematopoietic stem cell transplantation (allo-HSCT). Fourteen patients were included, eight of these patients were in first complete remission (CR1), one was in CR2, one had a partial response and four patients had refractory disease at transplantation. The median delivered average dose was 11.395 Gy (range 10.06-12.17). The median planning target volume D95 was 8.2 Gy (range 7.52-9.01). The median delivered dose to skeleton bone with active bone marrow sites was 12.685 Gy (range 11.12-13.52). The results of this trial suggest that using HT TBI confers satisfactory immunosuppression and excellent eradication of malignant cells in patients with high-risk ALL undergoing allo-HSCT, especially in those with refractory ALL. After a median follow-up of 14.6 months (range 4-28), four patients experienced non-relapse mortality, ten patients are alive in durable CR including remission of extramedullary leukemic infiltration. One-year overall survival and disease-free survival rates post-transplantation were both 70.7%.

A modified formula for dose calculations of stereotactic ablative body radiotherapy for non–small cell lung cancer

To provide a modified formula consistent with the Monte Carlo (MC) algorithm for dose calculations during stereotactic ablative body radiotherapy for non–small cell lung cancer. Seventy CyberKnife treatment plans were calculated and analyzed by MC and ray-tracing (RT) algorithms, separately. Parameters of treatment plans were compared, and those associated with differences of dose distributions were analyzed to establish a modified formula. Gross tumor volume and tumor tracking volume (TTV) were defined as the evident disease on the sequences of the window width and level of the lung and the mediastinum. Additionally, the formula was validated by another 20 plans. The prescription dose of the 90 patients was 60 Gy/5f. The RT algorithm overestimated the planning target volume (PTV) D95 by an average of 8.59 Gy and the gross tumor volume D99 by an average of 5.84 Gy. The homogeneity index of PTV was underestimated by 0.11 on average, whereas the conformity index and new conformity index was underestimated by 0.05. The RT algorithm overestimated the dose distribution to the spinal cord by 2.23 Gy, the esophagus by 1.96 Gy, the trachea by 1.89 Gy, the left-sided bronchus by 1.77 Gy, the right-sided bronchus by 1.64 Gy, and the heart by 2.16 Gy. The average whole-lung dose volumes of lung tissues and dose volumes of V5 were overestimated by 2.69 Gy and 7.52%, respectively. A power function distribution (R2 = 0.8626) was confirmed between PTV D95 and TTV volumes. PTV D95 calculated by the MC algorithm could be computed easily with TTV and PTV D95 calculated by the RT algorithm based on the formula. The modified equation was more consistent with MC algorithm than with other formula, which could be a reference to those not accessible to the MC algorithm.

Dosimetric effect of uncorrected rotations in lung SBRT with stereotactic imaging guidance

PurposeTo evaluate the dosimetric impact of uncorrected rotations on the planning target volume (PTV) coverage for early stage non-small cell lung cancer patients treated with stereotactic body radiotherapy using Brainlab ExacTrac image guidance. MethodsTwenty-two patients were retrospectively selected. Two scenarios of uncorrected rotations were simulated with magnitude of 1°, 2°, 3° and 5°: (1) rotation around the treatment isocenter; and (2) roll and yaw rotations around a setup isocenter. The D95 of PTV from recalculated dose on the rotated CT was compared to that from the clinical plan. A logistic regression model was used to predict the probability of dose differences between recalculated and original plans that are less than 2% based on the rotation angle, PTV volume, and distance between the treatment and setup isocenter. ResultsLogistic regression model showed the uncorrected isocentric rotations of up to 2.5° in all directions have negligible dosimetric impact. For non-isocentric rotations, a rotational error of 2° may cause significant under-dose of the PTV. Statistically significant (p<0.05) parameters in the logistic regression model were angle for isocentric rotations, angle and distance for non-isocentric roll rotations, and angle, distance and the PTV volume for non-isocentric yaw rotations. ConclusionsThe severity of the dose deviations due to uncorrected rotations depends on the type and magnitude of the rotation, the volume of the PTV, and the distance between the treatment and setup isocenter, which should be taken into consideration when making clinical judgment of whether the rotational error could be ignored.