Impact of immobilization system angle, body mass index and breast size on breast radiotherapy accuracy using EPID-only setup.

BackgroundSet-up errors are an inherent part of radiation treatment process. Coverage of target volume is a direct function of set-up margins, which should be optimized to prevent inadvertent irradiation of adjacent normal tissues. The aim of this study was to evaluate three-dimensional (3D) set-up errors and propose optimum margins for target volume coverage in head and neck radiotherapy.MethodsThe dataset consisted of 93 pairs of orthogonal simulator and corresponding portal images on which 558 point positions were measured to calculate translational displacement in 25 patients undergoing conventional head and neck radiotherapy with antero-lateral wedge pair technique. Mean displacements, population systematic (Σ) and random (σ) errors and 3D vector of displacement was calculated. Set-up margins were calculated using published margin recipes.ResultsThe mean displacement in antero-posterior (AP), medio-lateral (ML) and supero-inferior (SI) direction was -0.25 mm (-6.50 to +7.70 mm), -0.48 mm (-5.50 to +7.80 mm) and +0.45 mm (-7.30 to +7.40 mm) respectively. Ninety three percent of the displacements were within 5 mm in all three cardinal directions. Population systematic (Σ) and random errors (σ) were 0.96, 0.98 and 1.20 mm and 1.94, 1.97 and 2.48 mm in AP, ML and SI direction respectively. The mean 3D vector of displacement was 3.84 cm. Using van Herk's formula, the clinical target volume to planning target volume margins were 3.76, 3.83 and 4.74 mm in AP, ML and SI direction respectively.ConclusionThe present study report compares well with published set-up error data relevant to head and neck radiotherapy practice. The set-up margins were <5 mm in all directions. Caution is warranted against adopting generic margin recipes as different margin generating recipes lead to a different probability of target volume coverage.

Background: Set-up errors are errors which are inevitable in radiotherapy. However, they should be kept to a minimum to achieve the maximum radiation dose to a tumour as to maximise treatment efficacy. This study aims to quantify those errors and assess if they remain within the tolerance limit of 5 mm in all directions. This study will also determine the adequacy of the margins for set up error for 3DCRT of rectal cancers at University of Malaya Medical Centre (UMMC).Methods: A total of 20 rectal cancer patients (July 2018 to May 2019) who were treated with radiotherapy amounting to a total of 119 CBCT images were included in the study. Population systematic errors and random setup errors were calculated.Results: Population systematic errors and random setup errors in the vertical, longitudinal and lateral direction were tabulated in Table 1. There is a large deviation (>5 mm) noted in some patients’ setup between the first 3 days and the next successive day of imaging. Clinical target volume (CTV) to planning target volume (PTV) margin were calculated using Van Herk’s margin recipe (M=2.5Σ+0.7σ). The margins were 5.0 mm, 6.2 mm, and 4.0 mm for vertical, longitudinal and lateral directions, respectively. The systematic error for the population was 1.1 mm, 0.9 mm, 0.9 mm in the vertical, longitudinal and lateral directions respectively, while the random error is 3.2 mm, 5.7 mm and 2.5 mm in the vertical, longitudinal and lateral directions respectively.Conclusion: All of the patients involved in the study were within tolerance limits at some point in their treatment. The results demonstrated that a larger margin is needed in the longitudinal direction. Weekly CBCT is also necessary after the initial 3-day imaging to ensure that patients are kept within the tolerance limits.

Purpose: This study was to determine the impact of the body-mass factors on magnitude of setup displacements in patients treated with pelvic intensity modulated radiotherapy (IMRT) for gynecological cancer.Methods: Using the alignment data of daily on-line On Board Imaging (OBI) from image-guided radiotherapy (IGRT), the clinical data of 22 patients treated with pelvic IMRT for cervical or endometrial cancer was analyzed. Body-mass factors included body weight, body height, body mass index (BMI), waist circumference, waist thickness, hip circumference and hip thickness. Setup displacements for each patient were assessed by four components: namely systemic error (SE), and random error (RE), through three translational directions and couch rotation (CR). The median values for the body-mass factors were used as cutoff points to divide the groups. The Mann-Whitney U test was conducted to assess the predictive role of these factors for the set-up errors.Results: Population SE and RE were 2.8 mm, 2.6 mm, 2.4 mm and 1.7 mm, 1.4 mm, 1.3 mm in the superior-inferior (SI), anterior-posterior (AP) and medial-lateral (ML) directions, respectively. The SE and RE for rotation (CR) was 0.33 and 0.25 degree. Larger waist circumference (WC) was significantly correlated with greater SI-SE (p = 0.02), and CR-RE (p = 0.013), whereas larger hip circumference (HC) with greater SI-RE (p = 0.045), and CR-RE (p = 0.018). Higher BMI was associated with greater, CR-RE (p = 0.006). Body height correlated with AP-SE (p = 0.036).Conclusions: To reduce setup displacements in women with gynecological cancer requiring pelvic IMRT, the use of on-line IGRT should be recommended for those who have a WC ＞ 80.5 cm or a HC ＞ 88.8 cm, or a BMI ＞22.1 Kg/m^2.

Purpose: To evaluate two commercially available Head‐and‐Neck immobilization devices for daily treatment setup and their correlations to anatomy changes. The study represents an early implementation experience with the Orfit mask, which was new to our clinic. Method and Materials: Twenty‐one patients enrolled in an in‐house adaptive radiotherapy protocol 3171 using daily CT guided treatment were randomly assigned to one of two different thermoplastic masks: 5‐Point Efficast mask from Orfit (ORFIT Industries, Jericho, NY) or the extended S‐Board mask from Civco (CIVCO/MedTec, Orange City, IA). The daily setup displacements in each of the antero‐posterior(AP), supero‐inferior(SI), and medio‐lateral(ML) direction were determined using a 3D rigid image registration technique with the C2 vertebral body as the bony landmark. Systematic and random setup errors were computed for each group. The Pearson product‐moment correlation coefficient was used to determine the correlation between parotid shrinkage and the magnitudes of 3D displacements. Results: The random errors in AP, SI, and ML directions for Orfit mask (10 patients) were 0.13, 0.12, 0.11cm, and 0.12, 0.16, 0.11cm for the Civco mask (11 patients), respectively. The systematic errors were 0.20, 0.12, 0.16 cm for the Orfit mask, and 0.16, 0.16, 0.13 cm for the Civco mask, respectively. The Orfit mask significantly reduced the setup error in SI direction. However, in the AP and ML directions the systematic error increased with the Orfit mask, although the random errors were similar. The magnitude of the total (3D) shift was found to be correlated with the percent of parotid shrinkage for the Civco mask (p=0.026), but not for the Orfit mask. Conclusion: Although the Orfit mask reduced setup error in SI direction due to its head rest design, setup errors in AP and ML directions increased mainly due to increased systematic mask preparation errors. User training may be important.

Aim:In radiation therapy, accurate dose distribution in target volume requires accurate treatment setup. The set-up errors are unwanted and inherent in the treatment process. By achieving these errors, a set-up margin (SM) of clinical target volume (CTV) to planning target volume (PTV) can be determined. In the current study, systematic and random set-up errors that occurred during prostate cancer radiotherapy were measured by an electronic portal imaging device (EPID). The obtained values were used to propose the optimum CTV-to-PTV margin in prostate cancer radiotherapy.Materials and methods:A total of 21 patients with prostate cancer treated with external beam radiation therapy (EBRT) participated in this study. A total of 280 portal images were acquired during 12 months. Gross, population systematic (Σ) and random (σ) errors were obtained based on the portal images in Anterior–Posterior (AP), Medio-Lateral (ML) and Superior–Inferior (SI) directions. The SM of CTV to PTV were then calculated and compared by using the formulas presented by the International Commission on Radiation Units and Measurements (ICRU) 62, Stroom and Heijmen and Van Herk et al.Results:The findings showed that the population systematic errors during prostate cancer radiotherapy in AP, ML and SI directions were 1·40, 1·95 and 1·94 mm, respectively. The population random errors in AP, ML and SI directions were 2·09, 1·85 and 2·29 mm, respectively. The SM of CTV to PTV calculated in accordance with the formula of ICRU 62 in AP, ML and SI directions were 2·51, 2·68 and 3·00 mm, respectively. And according to Stroom and Heijmen, formula were 4·23, 5·19 and 5·48 mm, respectively. And Van Herk et al. formula were 4·96, 6·17 and 6·45 mm, respectively.Findings:The SM of CTV to PTV in all directions, based on the formulas of ICRU 62, Stroom and Heijmen and van Herk et al., were equal to 2·73, 4·98 and 5·86 mm, respectively; these values were obtained by averaging the margins in all directions.

Our aim was to evaluate liver transplant outcomes involving donors with high macrosteatosis grafts in the obese modern liver transplant recipient population. A high-steatosis graft was defined as donor graft macrosteatosis ≥30% on biopsy. Recipient obesity was defined as body mass index (BMI) >35 adjusted for ascites. Raw and adjusted recipient liver transplant survival were evaluated and compared between 4 cohorts: (1) high-steatosis graft in high-BMI recipient; (2) low-steatosis graft in high-BMI recipient; (3) high-steatosis graft in normal-BMI recipient; and (4) low-steatosis graft in normal-BMI recipient. After adjustment for multiple factors, recipient high-BMI remained an independent predictor of posttransplant mortality at 30 days (P < 0.0001) and persisted at 1 year (P = 0.009). A high-steatosis graft was the strongest independent predictor of mortality at 30 days (hazard ratio 2.05, 1.66-2.53; P < 0.0001) and that effect was diminished but persistent at 1 year (1.27, 1.10-1.46; P = 0.001). Recipient high-BMI and a high-steatosis graft are both significant independent and equally powerful predictors of mortality after modern liver transplant. High-steatosis grafts transplanted into obese recipients have the highest mortality. The increase in mortality associated with a high-steatosis graft into a normal-BMI recipient is similar in magnitude to a low-steatosis graft placed into a high-BMI recipient.

Objective To investigate the correlation between setup error and couch position error in radiotherapy. Methods A total of 25 patients with thoracic and abdominal tumors who recently finished image-guided radiotherapy were randomly selected. The data on couch position during treatment were obtained through the record validation system, and then the couch position error was calculated. The Pearson correlation analysis was used to investigate the correlation between setup error and couch position error during treatment. Results In the ≥5 setup errors among the 25 patients, the correlation coefficient between random setup error and random couch position error was 0.83(P=0.00), and the correlation coefficient between systematic setup error and systematic couch position error was 0.36(P=0.11). Conclusions In radiotherapy, the random setup error is highly correlated with the random couch position error, while a moderate or low correlation exists between the systematic setup error and the systematic couch position error. Key words: Radiotherapy; Setup error; Couch position; Correlation

Evaluation of set-up errors in head and neck radiotherapy using electronic portal imaging

Objective To study the real-time correction of setup error in intensity modulated radia-tion therapy (IMRT) for nasopharyngeal carcinoma (NPC) using an electronic portal imaging device (EP-ID), and to reduce systematic and random setup errors. Methods Thirty NPC patients treated by IMRT were enrolled into this study. During irradiation, three metal markers which embedded in the occlusal splint were used to monitor the setup error. Anterior and lateral isocentric electronic portal images were acquired before radiation and compared to digitally reconstructed radiographs. If the setup error in x-axis (right-left direction ) , y-axis ( superior-inferior direction) or z-axis ( anterior-posterior direction) exceeded 2 mm, real-time correction was performed before radiation and then the setup error after the correction were recorded. Results Before correction, 88.3% of all translational setup errors were less than 3 mm, and 99.1% less than 5 mm. Real-time correction was given to 16 patients who had translational setup errors more than 2 mm in one or two directions. The standard deviation of overall systematic and random setup errors after correction were obviously lower than those before correction. The M PTV value before correction was about 3 mm in the three directions and was only about 1.5 mm after correction. Conclusions In IMRT for NPC, Real-time correction of setup error using EPID and oeclusal splint method can improve the setup accuracy by reducing the systematic and random setup errors, and reduce the margin from CTV to PTV. Key words: Nasopharyngeal neoplasms/intensity modulation radiotherapy; Electronic portal ima-ging device; Setup error; Correction method

Background: The accuracy and precision of patient setup are important in radiotherapy. The thermoplastic mask is used to immobilize head and neck cancer patient. However, the mask is reused for low-income patients. Therefore, the setup error should be evaluated to approve that these patients remain in the exact position during treatment. Objective: To investigate setup errors with the use of thermoplastic masks in head and neck cancer patients and to compare setup errors of new and reused thermoplastic masks. Materials and Methods: Eighty patients who underwent volumetric modulated arc radiotherapy (VMAT) for head and neck cancer lesions were retrospectively evaluated. The setup error, population systematic error, and population random error were calculated. Subsequently, setup errors in patients using the new and reused thermoplastic masks were compared. Results: The population systematic error in the vertical, longitudinal, and lateral directions for new masks was 2.02, 2.27, and 2.13 mm, respectively, and that for reused masks was 2.37, 1.96, and 2.33 mm, respectively. The population random error in the vertical, longitudinal, and lateral direction for new masks was 1.46, 1.54, and 1.57 mm, respectively, and that for reused masks was 1.65, 1.63, and 1.87 mm, respectively. The results showed no statistically significant difference supported by p value &gt; 0.05 in the setup error between using the new and reused thermoplastic masks in all directions. Conclusion: For head and neck radiotherapy, the population setup errors were &lt; 3 mm in all directions. Moreover, thermoplastic masks can be reused in patients with head and neck cancer.

Precise Point Positioning (PPP) is an increasingly recognized precisely the GPS/GNSS positioning technique. In order to improve the accuracy of PPP, the error sources in PPP measurements should be reduced as much as possible and the ambiguities should be correctly resolved. The correct ambiguity resolution requires a careful control of residual errors that are normally categorized into random and systematic errors. To understand effects from two categorized errors on the PPP ambiguity resolution, those two GPS datasets are simulated by generating in locations in South Korea (denoted as SUWN) and Hong Kong (PolyU). Both simulation cases are studied for each dataset; the first case is that all the satellites are affected by systematic and random errors, and the second case is that only a few satellites are affected. In the first case with random errors only, when the magnitude of random errors is increased, L1 ambiguities have a much higher chance to be incorrectly fixed. However, the size of ambiguity error is not exactly proportional to the magnitude of random error. Satellite geometry has more impacts on the L1 ambiguity resolution than the magnitude of random errors. In the first case when all the satellites have both random and systematic errors, the accuracy of fixed ambiguities is considerably affected by the systematic error. A pseudorange systematic error of 5 cm is the much more detrimental to ambiguity resolutions than carrier phase systematic error of 2 mm. In the 2 nd case when only a portion of satellites have systematic and random errors, the L1 ambiguity resolution in PPP can be still corrected. The number of allowable satellites varies from stations to stations, depending on the geometry of satellites. Through extensive simulation tests under different schemes, this paper sheds light on how the PPP ambiguity resolution (more precisely L1 ambiguity resolution) is affected by the characteristics of the residual errors in PPP observations. The numerical examples recall the PPP data analysts that how accurate the error correction models must achieve in order to get all the ambiguities resolved correctly.

Set-Up Errors, Organ Motion, Tumour Regression and its Implications on Internal Target Volume–Planning Target Volume During Cervical Cancer Radiotherapy: Results From a Prospective Study

The evaluation of treatment-associated errors is important in the radiotherapy process, particularly those resulting related to patient setup. This research aimed to assess the interfractional setup errors and determine the Clinical Target Volume to Planning Target Volume (CTV to PTV) margin in patients undergoing 3-Dimensional Conformal Radiation Therapy (3DCRT) for head and neck cancer by means of electronic portal imaging device. In this analytical study, 300 portal images were acquired from 50 patients undergoing 3DCRT for head and neck cancer. Using the portal images of Lateral (LAT) and Antero-Posterior (AP) fields, population systematic (∑) and random (σ) errors were obtained in the lateral, longitudinal, and vertical directions. Finally, based on the International Commission on Radiation Units and Measurements (ICRU) Report 62's, Stroom's and Van Herk's methods, Planning target volume margins were determined. The translational shift ranges were 0-8.1 mm in the ML, 0-9 mm in the SI (AP), 0-8.8 mm in the SI (LAT), and 0-10 mm in the AP directions. The population systematic and random errors were respectively 3.230, 2.753, and 2.997 mm, and 1.476, 1.853, and 1.715 mm in X, Y, and Z directions. The calculated PTV margins using the ICRU-62, Stroom's, and Van Herk's formulae were ranging from 3.236-3.551, 6.605-7.493, and 7.932-9.108 mm, respectively. A PTV margin of 7.5-9.5 mm seems safe for ensuring adequate treatment volume coverage. In addition, the EPID is an effective equipment for verifying patient positioning and reducing treatment setup errors.

Purpose:To empirically derive margin formulas from existing clinical radiotherapy plans accounting for respiratory motion and setup uncertainties.Methods:We simulated realistic treatment scenarios, including respiratory motion and setup errors. Individual probability density functions (PDF) from respiratory data were used to simulate respiratory motion. Random (σ) and systematic (Σ) setup errors were modeled as Gaussian distributions. One‐dimensional dose profiles were extracted from existing radiotherapy plans and convolved with respiratory PDFs and random error distributions to produce blurred dose profiles. Each blurred dose profile was then shifted 1000 times by randomly sampling the simulated systematic error distribution. Margins were determined from the distance between the simulated treatment and the original 95% isodose level. An equation was fit for each (σ, Σ) combination to derive margin formulas for 90% of the population receiving 95% dose. This methodology can be applied to different tumor sites. Here, dose profiles were extracted from partial breast 3DCRT plans in the anterior‐posterior (AP) and superior‐inferior (SI) directions. Respiratory motion data was from healthy volunteers, and a clinically relevant range of random and systematic setup errors (standard deviations 1 – 4 mm) was determined from the literature.Results:The PBI margin formulas in the AP and SI directions for 95% dose coverage for 90% of the population were very similar: M= 0.68σ + 1.54Σ and M= 0.72σ + 1.50Σ, respectively. Systematic setup errors had the largest influence on required margin size, whereas realistic respiratory amplitude had minimal impact. The derived formulas resulted in a smaller systematic component than commonly‐used theoretical margin recipes.Conclusion:We have demonstrated a method to derive empirical margin formulas from existing patient radiotherapy plans, incorporating realistic respiratory motion and appropriate ranges of random and systematic error. Site‐specific margin formulas may be better suited to patient populations than theoretically derived, ideal geometry general margin formulas.

A service evaluation of on-line image-guided radiotherapy to lower extremity sarcoma: Investigating the workload implications of a 3 mm action level for image assessment and correction prior to delivery