Setup Errors In Radiotherapy Research Articles

Impact of dose distribution on rotational setup errors in radiotherapy for prostate cancer.

This study aimed to assess the impact of rotational setup errors on the target volume's dose distribution during radiotherapy for prostate cancer. A 6D robotic couch was used to describe the rotational setup error, and the dosage change in the target volume was analyzed using the planning evaluation factors. Treatment plans for three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT), and volumetric modulated arc radiotherapy (VMAT) were established after contouring the target volume and surrounding normal tissues on tomography obtained from the humanoid phantom. A 6D robotic couch was employed in the radiation room to describe the rotational setup errors of ±1° to ±5° in roll, yaw, and pitch, and cone beam computed tomography (CBCT) images were obtained. Furthermore, the dose distribution was extracted from the 3DCRT, IMRT, and VMAT treatment plans, dose mapping was performed on CBCT that depicts the rotational setup error. Target coverage(TC) decreased by 0.39% to 2.17% in roll, 0.43% to 2.59% in yaw, and 0.70% to 4.12% in pitch, respectively. In the comparison using the Radiation Therapy Oncology Group (RTOG) protocol criteria, when the rotational setup error of VMAT pitch was -2° or more, more than +1°, a target coverage of 95% or lower was shown, indicating the greatest effect among rotational setup errors. Furthermore, in 3DCRT, IMRT, and VMAT, the rotational setup error showed the greatest effect in pitch, and the dose change was larger in VMAT than in 3DCRT and IMRT. Therefore, specific rotational error due to pitch during radiotherapy for prostate cancer requires special consideration. Moreover, the more sophisticated and complex algorithms, such as VMAT, applied, the greater the dose change of target coverage due to rotational error; therefore, caution is required.

Evaluation of setup errors of immobilization device for radiation therapy in companion animals.

Intensity-modulated radiotherapy (IMRT), which allows generating steep dose gradients, is a beneficial treatment for companion animals with adjacent target and risk organs. IMRT is essential for high setup accuracy for avoiding overdose to risk organs, and optimal radiotherapy is important for evaluating the setup accuracy of companion animals. To use an immobilization device to evaluate setup errors in radiotherapy for companion animals. We calculated setup errors in radiotherapy for 386 animals (dogs and cats; 3,261 registration images) that underwent radiotherapy between 2016 and 2022. The companion animals were immobilized with a customized bite block and vacuum lock device. A quantile-quantile plot with 95% confidence interval (CI) was used to evaluate the histogram of the setup errors, and the systematic and random setup errors were calculated for each region (brain, head and neck, chest and abdomen, pelvis, and spine). The setup error in each direction presented an extremely narrow-interval histogram, with the following lower and upper 95% CIs: cranial-caudal (-0.08, -0.06 cm); left-right (-0.04, -0.02 cm); and dorsal-ventral (-0.13, -0.11 cm). The mean systematic setup error was 0.16 cm (range: 0.12-0.36 cm), and the random error was 0.15 cm (range: 0.08-0.34 cm). The pelvis showed the highest systematic and random setup errors (mean: 0.36 and 0.23 cm, respectively). The use of an immobilization device enables highly accurate radiotherapy for companion animals (95% CI < 0.15 cm).

Impact of Cold Weather on Setup Errors in Radiotherapy

Objective To investigate the influence of cold weather on setup errors of patients with chest and pelvic disease in radiotherapy. Methods The image-guided data of the patients were collected from the Radiotherapy Center of Cancer Hospital Affiliated to Guangxi Medical University from October 2020 to February 2021. During this period, the cold weather days were December 15, 16, and 17, 2020, and January 7 and 8, 2021. For body fixation in radiotherapy, an integrated plate and a thermoplastic mold were employed in 18 patients with chest disease, while an integrated plate and a vacuum pad were applied in 19 patients with pelvic disease. All patients underwent cone beam computed tomography (CBCT) scans in the first five treatments and once a week thereafter. The obtained data were registered to the planning CT image to get the setup errors of the patient in the translational direction including X, Y, and Z axes and rotational direction including RX, RY, and RZ. Then, the Mann–Whitney U test was performed. The expansion boundary values of the chest and pelvis were calculated according to the formula MPTV=2.5∑+0.7δ. Results A total of 286 eligible results of CBCT scans were collected. There were 138 chest CBCT scans, including 26 taken in cold weather and 112 in usual weather, and 148 pelvic CBCT scans, including 33 taken in cold weather and 115 in usual weather. The X-, Y-, and Z-axis translational setup errors of patients with chest disease in the cold weather group were 0.16 (0.06, 0.32) cm, 0.25 (0.17, 0.52) cm, and 0.35 (0.21, 0.47) cm, respectively, and those in the usual weather group were 0.14 (0.08, 0.29) cm, 0.23 (0.13, 0.37) cm, and 0.18 (0.1, 0.35) cm, respectively. The results indicated that there was a statistical difference in the Z-axis translational error between the cold weather group and the usual weather group (U = 935.5; p=0.005 < 0.05), while there was no statistical difference in the rotational error between the two groups. The external boundary values of X, Y, and Z axes in the cold weather group were 0.57 cm, 0.92 cm, and 0.99 cm, respectively, and those in the usual weather group were 0.57 cm, 0.78 cm, and 0.68 cm, respectively. There was no significant difference in the translational and rotational errors of patients with pelvic disease between the cold weather group and the usual weather group (p < 0.05). The external boundary values of X, Y, and Z axes were 0.63 cm, 0.79 cm, and 0.68 cm in the cold weather group and 0.61 cm, 0.79 cm, and 0.61 cm in the usual weather group, respectively. Conclusion The setup error of patients undergoing radiotherapy with their bodies fixed by an integrated plate and a thermoplastic mold was greater in cold weather than in usual weather, especially in the ventrodorsal direction.

Analysis of the setup errors and residual errors for ExacTrac X-ray image-guidance system for radiotherapy of somal tumors

Objective To retrospectively analyze the setup error in radiotherapy of somal tumors and body metastases using the ExacTrac X-ray portal image, and to evaluate the feasibility and effectiveness of 6D setup error correction in body radiotherapy. Methods The translational and rotational setup errors were calculated by registering the bony structures on the ExacTrac X- setup images to that of the digitally reconstructed setup images, and the corresponding residual errors were calculated together. Results The translational and rotational setup errors in the x (left-right), y (superior-inferior), z (anterior-posterior) and Rx (sagittal), Ry (transverse), Rz (coronal) directions were(2.27±2.02)mm, (4.49±2.52)mm, (2.27±1.37) mm and (1.02±0.73)°, (0.67±0.68)°, (0.76±0.84)°, respectively. The residual translational and rotational setup errors in the x(r), y(r), z(r) and Rx(r), Ry(r), Rz(r) directions were(0.27±0.48)mm, (0.37±0.45)mm, (0.22±0.30)mm and (0.17±0.33)°, (0.14±0.34)°, (0.16±0.28)°respectively. Conclusions Besides the translational setup errors, a certain amount of rotational setup errors exist in radiotherapy of somal tumors and body metastases. By using the 6D setup error correction of the ExacTrac system, a translational less than 0.4 mm and rotational setup errors less than 0.2° could be achieved. Key words: ExacTrac X-ray image-guidance system; 6 degree-of-freedom treatment couch; Setup errors; Residual errors

Feasibility and effectiveness of self-made tiltable treatment couch in minimizing setup errors of radiotherapy for thoracic and abdominal tumors

Objective A self-made tiltable treatment couch was adopted for CT simulation positioning and radiotherapy to evaluate the feasibility and effectiveness to minimize the setup errors. Methods Twenty-two patients with thoracic and abdominal tumors receiving radiotherapy in Department of Radiation Oncology, Peking Union Medical College between March and September 2016 were recruited in this study. All patients were randomly divided into the experimental (n=11) and control groups (n=11). In the study group, the tiltable treatment couch was adopted to switch the patients from the standing position to the supine position, and conventional supine position was utilized in the control group. All patients received CT positioning under spontaneous breathing. Image registration was performed according to the standard recommendations of IGRT group. The image registration data for the translational and rotation errors of CBCT were recorded and analyzed. The setup errors were calculated by four-parameter model between two groups. Results In the experimental group, the translational error of the x direction was (-0.012±0.128) cm with a variation range of (0.29-0.70 cm), (0.272±0.123) cm for the y direction (0.23-0.70 cm) and (0.089±0.105) cm for the z direction (0.14-0.53 cm), respectively. In the control group, the translational error of the x direction was (0.006±0.198) cm (0.27-0.75 cm), (-0.108±0.396) cm for the y direction (0.56-2.08 cm) and (-0.096±0.176) cm for the z direction (0.34-0.89 cm), respectively. Conclusions Application of the self-made tiltable treatment couch can enhance the setup reproducibility and reduce the setup errors, especially in the y direction during radiotherapy for the thoracic and abdominal tumors. Key words: Radiotherapy planning; Setup error; Tiltable treatment couch

Setup errors in radiation therapy for thoracic tumor patients of different body mass index.

PurposeTo assess the setup errors in radiation therapy for thoracic tumors patients of different somatotypes, and to seek an individualized mathematical basis for defining the planning target volume (PTV).MethodsSixty patients with thoracic tumors were divided into four somatotypes according to their body mass index (BMI), and their body positions were setup by two groups of technicians independently. CT simulations were performed and the reconstructed radiography was digitally generated as reference images for location verification and error measurement. By setting positioning error ranges, the within‐range positioning correction rate was compared among groups.ResultsPosition setups for patients in the emaciated group, moderate group, and overweight group were relatively stable (with minor setup error differences between the two groups of technicians). In emaciated group, moderate group, overweight group, and obese group, setup errors in the right–left direction (R‐L) were 2.2 ± 1.3 mm, 2.2 ± 1.6 mm, 3.9 ± 3.1 mm, and 8.8 ± 3.5 mm, respectively; whereas the setup errors in the four groups in the superior–inferior(S‐I) direction were 2.4 ± 1.8 mm, 2.1 ± 1.9 mm, 3.2 ± 2.6 mm, and 5.4 ± 3.5 mm, and in the anterior–posterior (A‐P) direction were 2.2 ± 1.7 mm, 1.9 ± 1.9 mm, 3.2 ± 2.9 mm, and 6.2 ± 4.2 mm, respectively. Moreover, in the moderate group, the positioning correction rate in the three directions (R‐L, S‐I, and A‐P) was 20%, 9%, 8% within the error range of 5–10 mm, and 3%, 0%, 1% with a more than 10 mm error range. However, in overweight group and obese group, the positioning correction rate in these three directions (also with a more than 10 mm error range) was 23%, 27%, 19% and 21%, 16%, 23%, respectively.ConclusionsIn radiation therapy for patients with thoracic tumors, the definition of PTV should be individualized. Meanwhile, with the increase in BMI, positioning correction rate has a tendency to rise too.

Robustness of VMAT and 3DCRT plans toward setup errors in radiation therapy of locally advanced left-sided breast cancer with DIBH

PurposeThe aim of our study was to evaluate and compare the robustness of treatment plans produced using the volumetric modulated arc-therapy (VMAT) and the standard three-dimensional conformal radiotherapy (3DCRT) techniques by estimating perturbed doses induced by localization offsets for deep inspiration breath-hold (DIBH) in locally advanced breast cancer radiation therapy. MethodsTwenty patients with left breast carcinoma requiring radiation therapy were analysed in this planning study. Robust VMAT plans regarding minimum CTV doses and standard 3DCRT plans were produced, and perturbed doses were calculated in accordance with localization values from the weekly offline imaging protocol. Offsets from 5 weeks were summed to a perturbed overall treatment plan. Dose criteria for evaluation were coverage and homogeneity of the target, as well as doses to organs at risk. ResultsVMAT plans resulted in significantly better target coverage compared to 3DCRT, as well as lowered doses to heart and left anterior descending artery, while the perturbed doses were less variable for VMAT than 3DCRT plans. Homogeneity was significantly improved in VMAT plans. The statistical analysis taking all organs into account found that VMAT plans were more robust than 3DCRT to localization offsets (p = .001). The overall mean setup-deviation for the DIBH-patients was less than 2 mm in all directions. ConclusionsVMAT plans were more robust on average than conventional 3DCRT plans for DIBH when localization errors were taken into consideration. The combination of robust VMAT planning and DIBH generally improves the homogeneity and target doses.

Influence of lower limb movements on setup errors in radiotherapy for rectal cancer using kilovoltage cone-beam CT (KV-CBCT)

Objective To investigate the influence of fixation of both lower limbs with negative pressure vacuum cushion and fixation of both ankles with self-made foam mat on setup errors in radiotherapy for rectal cancer. Methods A total of 12 patients with rectal cancer were enrolled in 2014 and randomly divided into group A (using negative pressure vacuum cushion) and group B (using self-made foam mat). An offline registration analysis was performed for the images of 108 times (A, B group of 54 times) of kilovoltage cone-beam CT (CBCT) before and after treatment. Grey scale translation error registration was used, and the results of registration were analyzed. The setup errors in x-axis (left-right direction), y-axis (cranial-caudal direction), and z-axis (anterior-posterior direction) were compared between the two groups. Results There was no significant difference in the absolute setup error in the y-axis between the two groups (2.13±0.64 mm vs.2.61±1.17 mm, P=0.399), while group A showed significantly lower absolute setup errors in the x-axis and z-axis than group B (x-axis: 1.51±0.28 mm vs. 2.70±1.05 mm, P=0.039; with an error rate of 7.41% vs. 42.59%; z-axis: 1.10±0.29 mm vs. 2.37±0.71 mm, P=0.002; with an error rate of 1.85% vs. 35.19%). Conclusions In the radiotherapy positioning for rectal cancer, fixation of both lower limbs with negative pressure vacuum cushion effectively avoids the translation and rotation of both lower limbs, reduces absolute setup errors, and has higher accuracy than fixation of both ankles with self-made foam mat. Key words: Tomography, X-ray computed, cone beam, kilovolt; Negative pressure vacuum cushion fixation; Self-made foam mat fixation; Set-up error; Rectal neoplasms/radiotherapy

Margin evaluation of translational and rotational set-up errors in intensity modulated radiotherapy for cervical cancer.

A clinical target volume (CTV) to planning target volume (PTV) margin recipes was routinely used to ensure dose was actually delivered to target for all (most) patients. Currently used margin recipes were associated with only translational set-up errors in radiotherapy. However, when set-up errors extended to six-degree (6D) scope (three translational and three rotational set-up errors), margin recipe should be re-evaluated. The purpose of this study was to investigate dosimetric changes of targets (both CTV and PTV) coverage when 6D set-up errors were introduced and testify the practicability of currently used margin recipe in radiotherapy. A total number of 105 cone beam computer tomography scans for ten patients with cervical cancer were derived prior to treatment delivery and 6D set-up errors were acquired with image registration tools. Target coverage was evaluated retrospectively for 6D set-up errors introduced plan with 6 mm CTV to PTV margin. Target coverage of PTV showed significant decreases (3.3 %) in set-up errors introduced plans compared with original plans. But CTV coverage was not susceptible to these set-up errors. A tendency of coverage decrease for PTV along with distance away from treatment was testified, from −0.2 to −6.2 %. However, CTV seems changed less, from −0.2 to −0.8 %. The result indicate that a CTV to PTV margin of 6 mm was sufficient to take into account 6D set-up errors for most patients with cervical cancer. Future research suggests a smaller margin to further improve both tumor coverage and organs at risk sparing.

Effectiveness of a Patient-Specific Immobilization and Positioning System to Limit Interfractional Translation and Rotation Setup Errors in Radiotherapy of Prostate Cancers

Objective: To evaluate the effectiveness of a patient-specific immobilization and positioning device in prostate radiotherapy. Methods: Eighty patients were immobilized and positioned by a patient-specific device. Prostate translations and rotations were estimated from daily cone beam computed tomography scans using a contour-based approach assisted by auto-registration and quantified by the group mean GM, systematic Σ and random σ' errors. Dosimetric impacts of residual prostate rotations where the translation errors were corrected were evaluated by robustness plan analysis. Results: Using the patient-specific immobilization alone without online image-guidance, the GM, Σ and σ' of the prostate translations were 0.8, 1.7, and 1.5 mm (left-right; LR), 0.8, 2.1, and 1.9 mm (superior-inferior; SI), and 0.5, 1.7 and 1.5 mm (anterior-posterior; AP), while for the prostate rotations they were 0.0°, 0.6°, and 0.7° (pitch), 0.2°, 0.5°, and 0.6° (roll), and 0.2°, 0.5°, and 0.6° (yaw). The resulting van Herk’s margin was 5.8 (LR), 7.3 (SI) and 5.8 (AP) mm. With adaptive online image-guidance based on estimates from the first 5 fractions, Σ were reduced by 0.7 - 1.2 mm for the prostate translations, resulting in a margin reduction by 2 - 3.5 mm. Changes of Σ and σ' in the prostate rotations were insignificant regardless of translation corrections. Dosimetric impacts of residual rotation errors were negligible if a 2 mm margin was applied. Conclusions: Our patient-specific immobilization system can effectively limit the prostate translations and rotations, which is important without 6D treatment couches or using ultrasound image-guidance without rotational corrections.

Comparation of set-up errors between two different body positions in precision radiotherapy for esophageal cancer

Objective To compare the effect of set-up errors to two different body positions that are putting arms on the side of the body (A group) or placing arms folded across the elbow on forehead (B group) in esophageal cancer' fraction radiotherapy.Methods By using case-control study,all supine patients were divided into the A group and the B group.After patients were fixed by thermoplastic membrane,they were located by spiral CT and treated by using IGRT.During treatmwnt,there were three cone-beam CT scans in the first week and then at least one scan weekly.We obtained the linear set-up errors data by using bone registration with manual proofreading in 3 directions that were left and right (x),head and feet (y),abdomen and back (z) by using CBCT.Means were compared by using independent sample t-test,and ratios were compared by chi-square test.Results Every group had 11 cases that the A group had 92 people times and the B group had 87 people times.Absolute set-up errors of two different positions:only x-axis,the mean of the A group was (2.46 ± 1.79) mm.But the mean of the B group was (1.91 ± 1.71)mm,which was significantly less than the A group (P =0.036).Relative set-up errors of two groups:only y-axis,the mean of the B group was (1.91 ± 4.12) mm.The A group was (0.09 ± 3.90) mm,which was significantly less than the B group (P =0.003).There was no significant difference of three-dimensional set-up errors (P=0.751).And there was no significant difference in absolute weekly set-up errors or weekly three-dimensional set-up errors in radiotherapy (P ＞ 0.05).Conclusions The each of two body positions in esophageal cancer' fraction radiotherapy has advantage and disadvantage for set-up errors,but they were in control and didn't affect the radiotherapy planning.We can choose appropriate treatment position according to clinical practice. Key words: Esophageal neoplasms/radiotherapy ; Position ; Set-up error

Prevention of gross setup errors in radiotherapy with an efficient automatic patient safety system

Treatment of the wrong body part due to incorrect setup is among the leading types of errors in radiotherapy. The purpose of this paper is to report an efficient automatic patient safety system (PSS) to prevent gross setup errors. The system consists of a pair of charge‐coupled device (CCD) cameras mounted in treatment room, a single infrared reflective marker (IRRM) affixed on patient or immobilization device, and a set of in‐house developed software. Patients are CT scanned with a CT BB placed over their surface close to intended treatment site. Coordinates of the CT BB relative to treatment isocenter are used as reference for tracking. The CT BB is replaced with an IRRM before treatment starts. PSS evaluates setup accuracy by comparing real‐time IRRM position with reference position. To automate system workflow, PSS synchronizes with the record‐and‐verify (R&V) system in real time and automatically loads in reference data for patient under treatment. Special IRRMs, which can permanently stick to patient face mask or body mold throughout the course of treatment, were designed to minimize therapist's workload. Accuracy of the system was examined on an anthropomorphic phantom with a designed end‐to‐end test. Its performance was also evaluated on head and neck as well as abdominalpelvic patients using cone‐beam CT (CBCT) as standard. The PSS system achieved a seamless clinic workflow by synchronizing with the R&V system. By permanently mounting specially designed IRRMs on patient immobilization devices, therapist intervention is eliminated or minimized. Overall results showed that the PSS system has sufficient accuracy to catch gross setup errors greater than 1 cm in real time. An efficient automatic PSS with sufficient accuracy has been developed to prevent gross setup errors in radiotherapy. The system can be applied to all treatment sites for independent positioning verification. It can be an ideal complement to complex image‐guidance systems due to its advantages of continuous tracking ability, no radiation dose, and fully automated clinic workflow.PACS number: 87.55.Qr

Feasibility study of real‐time planning for stereotactic radiosurgery

3D rotational setup errors in radiotherapy are often ignored by most clinics due to inability to correct or simulate them accurately and efficiently. There are two types of rotation-related problems in a clinical setting. One is to assess the affected dose distribution in real-time if correction is not applied and the other one is to correct the rotational setup errors prior to the initiation of the treatment. Here, the authors present the analytical solutions to both problems. (1) To assess the real-time dose distribution, eight stereotactic radiosurgery (SRS) cases were used as examples. For each plan, two new sets of beams with different table, gantry, and collimator angles were given in analytical forms as a function of patient rotational errors. The new beams simulate the rotational effects of the patient during the treatment setup. By using one arbitrary set of beams, SRS plans were recomputed with a series of different combinations of patient rotational errors, ranging from (-5°, -5°, -5°) to (5°, 5°, 5°) (roll, pitch, and yaw) with an increment of 1° and compared with those without rotational errors. For each set of rotational errors, its corresponding equivalent beams were computed using the analytical solutions and then used for dose calculation. (2) To correct for the rotational errors, two new sets of table, gantry, and collimator angles were derived analytically to validate the previously published derivation. However, in the derivation, a novel methodology was developed and two sets of table, gantry, and collimator angles were obtained in analytical forms. The solutions provide an alternative approach to rotational error correction by rotating the couch, gantry, and collimator rather than the patient. For demonstration purpose, the above-derived new beams were implemented in a treatment planning system (TPS) to study the rotational effects on the SRS cases. For each case, the authors have generated ten additional plans that accounted for different rotations of the patient. They have found that rotations have an insignificant effect on the minimal, maximum, mean doses, and V80% of the planning target volume (PTV) when the rotations were relatively small. This was particularly true for the small and near-spherical targets. They, however, did change V95% significantly when the rotations approached 5°. The theory has been validated with clinical SRS cases and proven to be practical and viable. The preliminary results demonstrate that the rotational effects are patient-specific and depend on several important factors, such as the PTV size, the PTV location, and the beam configuration. The solutions given in this paper are of great potential values in clinical applications. They have derived the analytical solutions to a new set of table, gantry, and collimator angles for a given treatment beam configuration as a function of patient rotational errors. One solution was used to assess the dosimetric effects of an imperfect patient setup and the other one was used to correct for the setup errors without rotating the patient. Compared to the widely adopted method of rotation effect assessment by importing the rotational CT images into TPS, the equivalent beam approach is simple and accurate. The analytical solutions to correcting for rotational setup errors prior to treatment were also derived. Based on the initial clinical investigations, they firmly believe that clinically viable real-time treatment planning and adaptive radiation therapy are feasible with this novel method.

Set-up errors in radiotherapy for oesophageal cancers – Is electronic portal imaging or conebeam more accurate?

PurposeTo compare kV computed tomography (CBCT) with electronic portal imaging (EPI) and evaluate set-up variations in the anterior–posterior (AP), right–left (LR) and cranio-caudal (CC) directions and rotational variations: pitch, roll, and yaw, for oesophageal cancer patients treated with radical radiotherapy. Methods and materialsTwenty patients with locally advanced oesophageal cancer treated with chemoradiation were consented for this prospective ethics approved protocol. Patients were positioned using skin marks/tattoos, kV-CBCT scans (XVI) and EPI’s were performed prior to treatment and registered to the planning CT scans and digitally reconstructed radiographs, respectively. XVI data was used to adjust patient setups before treatment delivery. A total of 122 EPI pairs and 207 CBCT scans were analysed. The systematic and random errors were calculated. ResultsThe systematic and random errors (mm) for XVI were 1.3, 1.7, 1.4 and 2.6, 3.9, 2.0 in RL, CC and AP direction, respectively, with EPI of similar magnitude. There was no correlation between the 2 modalities of imaging as 31.7% of all image pairs were discordant >3mm and 12.5% >5mm. XVI identified rotations >3° in 44 images. ConclusionsEPI results in different position correction for verification of radiotherapy in oesophageal malignancies when compared with CBCT. CBCT verification offers adequate 3D volumetric image quality to improve the accuracy of treatment delivery for oesophageal malignancies in radiotherapy and should be used for image guidance.

PhaseI/II clinical trial of dose escalation using daily on-line cone beam CT guided radiotherapy combined with active breath control after transcatheter arterial chemoembolization for hepatocellular carcinoma

e15654 Background: The radiation dose is the key factor to improve survival of patients with hepatocellular carcinoma (HCC). The optimal way to increase radiation dose is to reduce uncertainties of target mainly due to respiratory motion and setup error in radiotherapy. Our previous study demonstrated that lipiodol can be a reliable surrogate of direct tumor targeting in Kv- cone beam CT(CBCT) for patients with good lipiodol embolization. Relying on lipiodol,the daily on-line CBCT guidance with ABC is feasible. By reducing geometric position uncertainty, as well as liver movement, the technique of ABC combined with on-line CBCT guidance can permit CTV(clinical target volume)-PTV(planning target volume) margin reduction and dose escalation. The purpose of the study is to apply the new technique for clinical application and investigate the dose escalation, toxicities and response of liver tumors with the technique combined with chemoembolization(TACE). Methods: 20 HCC patients with Child-Pugh A liver function score were treated by daily on-line CBCT guided radiotherapy relying on lipiodol combined with ABC after TACE. After current doses of 45Gy/ 9 fractions,3 fractions/weeks were delivered,the scheduled dose escalation ranged from 5 to 20Gy. Each mean liver dose not reached 23G y, V30 ( the percentage of normal liver volume with radiation dose≥30 Gy) less than 28%. Results: The planned dose escalation was finished in all subgroups. None of these patients developed Grade 2 or greater liver toxicity except two patients developed Grade 2 gastrointestinal complications and one had grade 1 acute liver toxicity.The overall immediate tumor response rate was 76.3%. 1-year overall survival rate was 80.5%. Conclusions: The technique of daily on-line CBCT guided radiotherapy combined with ABC after TACE is a safe and effective treatment which can reduce CTV-PTV margin significantly and increase target precision greatly. With the technique combined with TACE, the total irradiation dose above 65Gy is feasible in daily fraction of 5Gy. No significant financial relationships to disclose.

Study of Interfractional and Intrafractional Set-up Errors in Radiotherapy Utilizing KV Cone Beam Computed Tomography

Study of Interfractional and Intrafractional Set-up Errors in Radiotherapy Utilizing KV Cone Beam Computed Tomography

X-ray Volumetric Imaging (XVI) to Redefine Radiotherapy Margins for Locally Advanced Pancreatic Cancer (LAPC)

Introduction: LAPC responds poorly to current therapies, with a 15–25% response rate to chemoradiation. The location of the pancreas makes safe escalation of tumour radiation dose, without a differential reduction in dose to normal tissues, difficult. The study aimed to quantify inter- and intra-fraction organ motion, bony set-up errors in radiotherapy for LAPC and redefine planning margins for use in dose-escalation studies.

The potential impact of the tension of the pelvic muscles on set-up errors in radiotherapy for pelvic malignancies

The purpose of the study reported here was to evaluate the potential impact of the tension of pelvic muscles on set-up errors. Twenty-nine consecutive patients with rectal cancer were included. The treatment simulation of the lateral beam in prone position was performed twice–with relaxed and next with maximally tense pelvic muscles. During the second simulation, the couch was moved so as to align the centre of the beam with the actual position of the skin mark tattooed during the first simulation. The bony landmarks on both images of corresponding lateral fields were matched. The beam's centre displacement and the rotation were measured using the beam image taken in relaxed position as a reference. The absolute values were used in calculation of the mean. For the anterior–posterior direction, the mean value of displacements was 15.3 mm, standard deviation (SD) 6.9 mm and the maximal value 37 mm. For the cranial–caudal direction, the mean value was 4.4 mm, SD 4 mm and the maximal value 17 mm. The mean rotation of the pelvis was 5.3 degrees, SD 2.4 degrees and maximal rotation 11 degrees. The majority of displacements were in the posterior (86%) and caudal (55%) directions. The majority of rotations were clockwise (76%). It was shown that pelvic muscle tension was the reason for anal verge displacements and mispositionings of the shielding block. This results in set-up inaccuracy, especially in the anterior–posterior direction, shielding block mispositioning and anal verge displacement.

Eine schnelle Bildkorrelationsmethode zur Überprüfung der Patientenlagerung in der Strahlentherapie

Accuracy of patient positioning is an important aspect in radiation therapy. The present paper presents a new procedure for the determination of set-up errors in radiotherapy, which is based on a special form of the Fast Fourier Transform (FFT), i. e., the Fast Hartley Transform (FHT). The use of this method allows to compare in short time verification and simulator films, and to calculate the translation vector or the in-plane rotation of the patient. Standard deviations <1 mm for shifting measurements and <1 degree for measurements of the rotation were detected, provided that the positioning remained within the common clinical range. The present results were in good agreement with data obtained using a landmark-based method.

When should systematic patient positioning errors in radiotherapy be corrected?

One way to reduce patient set-up errors in radiotherapy is to measure the position during the first N treatment fractions, and to do an unconditional correction of the set-up position once at the (N + 1)th fraction. This strategy is known as the ‘no action level’ protocol. The question is when to do the correction, i.e. what is the optimum value of N? We determine N by minimizing the expectation value of the total quadratic set-up error taken over all fractions. A central assumption that we make is that there is no time trend in the patient set-up. The result is a simple formula for the value of N, which is proportional to the square root of the total number of fractions, and to the ratio of the execution (delivery) error and preparation error. We also provide a formula for cases where the measurement error is not negligible. For typical cases the optimum value is N = 4. Because the optimum is shallow, the exact choice of N is uncritical.