Reproducibility Of Patient Setup Research Articles

Vacuum immobilisation reduces tumour excursion and minimises intrafraction error in a cohort study of stereotactic ablative body radiotherapy for pulmonary metastases

The purpose of this study is to assess the impact of a vacuum immobilisation system on reproducibility of patient set-up, interfraction stability and tumour motion amplitude. From February 2010 to February 2012 as part of a prospective clinical trial 12 patients with solitary pulmonary metastases had consecutive four-dimensional computed tomography (4DCT) scans performed with and without vacuum immobilisation. The displacement of the tumour centroid position was recorded in each of the 10 phases of the 4DCT reconstruction. A further six patients with seven metastases underwent single fraction stereotactic ablative body radiotherapy (SABR) during this period (a total of 19 targets) and were included in an analysis of positional reproducibility and intrafraction immobilisation. Couch shifts recorded in the medio-lateral (X), cranio-caudal (Y) and ventero-dorsal (Z) planes. For the 19 treatments delivered, the median (0-90% range) shift required immediately pretreatment was 1 mm (0-3) in the X-plane, 2 mm (0-6) in the Y-plane and 4 mm (0-8) in the Z-plane, respectively. The mean (+/- standard deviation) of mid-treatment shifts were 0.3 mm (+/- 0.7), 1.1 mm (+/- 2) and 0.8 mm (+/- 1.5) in the X, Y and Z planes, respectively. Mid-treatment shifts were <2 mm in all directions (P = < 0.001). The length of treatment time correlated to the required shifts in the Z plane (r(2) = 0.377, P = 0.005), but not in the X or Y planes (P = 0.198 and P = 0.653, respectively). In the subset of 12 patients who had two 4DCTs, the median (range) amplitude of tumour displacements in the X, Y and Z planes when immobilised were 0.9 mm (0.3-2.9), 2.6 mm (0.2-10.6) and 1.6 mm (0.5-5.5), respectively. Immobilisation reduced the volume of tumour displacement during respiration by a median of 52.6% (P = 0.021). Vacuum immobilisation reduces total tumour excursion, facilitates reproducible positioning and provides robust intrafractional immobilisation during SABR treatments for pulmonary metastases.

The Reproducibility of Patient Setup for Head and Neck Cancers Treated with Image-Guided and Intensity-Modulated Radiation Therapies Using Thermoplastic Immobilization Device

The reproducibility of patient setup is an important issue for head and neck cancers treated with intensity-modulated radiation therapy (IMRT). In this study, an image-guided radiation therapy (IGRT) system has been used to minimize the uncertainty of patient setup while standard thermoplastic masks were used to provide adequate immobilization for the head and neck. However, they do not provide sufficient immobilization of the shoulders, which is an important requirement in comprehensive nodal irradiation. Therefore, we investigated the setup and rotational shifts in head and neck cancer patients undergoing IMRT for which this immobilization device had been used together with an IGRT system. The setup and rotational shifts of patients were analyzed using the ExacTrac X-ray 6D IGRT system. The patients were classified as having head and neck tumors in the upper or lower regions. The upper neck nodes included lymph nodal level II while the lower neck nodes included lymph nodal levels III and IV. Clinical data from 227 treatment sessions of 12 head and neck cancer patients were analyzed. The random translational error in inter-and intra-fraction errors of the anterio-posterior (AP) direction might influence the rotational errors of pitch and roll in the upper region. At the same time, the random translational error in the inter-and intra-fraction errors of the AP direction might influence the rotational error of roll in the lower region. We believe that these random translational errors should be considered during treatment. We found variability in random translational errors for different regions in the anatomy of head and neck cancer patients due to rotational shifts. Depending on the location of the primary lesion or the selected nodal treatment targets, these relative positional variations should be considered when setup and rotational shifts are corrected with IGRT systems before treatment.

Robustness Against Interfraction Prostate Movement in Scanned Ion Beam Radiation Therapy

To assess the robustness of scanned ion beam treatment plans against the interfraction internal target motion and evaluate the limits of validity of target-based isocenter realignment for prostate cancer radiation therapy. For 12 prostate patients, scanned beam carbon ion treatment plans were prepared using 2 lateral opposed beams and the raster scanning technique with different clinical target volume (CTV) to planning target volume (PTV) margins (2-10 mm). Internal target motion of 2-15 mm in anteroposterior (AP), superoinferior (SI), and left-to-right (LR) directions was simulated by displacing the CTV contours with respect to the computed tomography data. The plans were recalculated with and without target-based isocenter realignment and the CTV coverage was assessed. For CTV shifts within the applied planning margin, the CI-98% is greater than 98.0%, both with and without isocenter realignment. Without realignment, because of the sharp lateral gradients, the CI-98% shows rapid fall as soon as the target shift exceeds the applied planning margin for all displacement directions. With isocenter realignment, the coverage improves notably for shifts in AP and SI directions and the CI-98% is restored to >95.0% for plans optimized with a 2-mm margin, >97% with a 3-mm margin, and >98% with larger margins. For large corrections, predominately in AP direction, cold spots in the CTV may occur. Their magnitude is dependent on the patients' individual anatomies. Within the physiological limits of internal prostate movement, target-based isocenter realignment results in improved CTV coverage for shifts in AP and SI directions exceeding the applied planning margin. Assuming optimal patient setup reproducibility (eg,immobilization, setup error correction, patient preparation protocols), hence negligible interfraction bone and soft-tissue variations, changes in traversed densities resulting from target-based realignment applied with a reduced planning margin do not induce significant dose deterioration in most of the cases.

Detection of setup uncertainties with 3D surface registration system for conformal radiotherapy of breast cancer

Aim To investigate the clinical application of a technique for patient set-up verification in breast cancer radiotherapy based on a 3D surface image registration system. Background Accurate and reproducible patient set-up is a prerequisite to correctly deliver fractionated radiotherapy. Various approaches are available to verify and correct patient setup for 3D image acquisition in a radiation treatment room. Materials and methods The study analyzed the setup reproducibility of 15 patients affected by breast cancer and candidates for conformal radiotherapy by using the AlignRT system (VisionRT, London, UK). At the initial setup, electronic portal imaging device (EPID) images were compared with Digitally Reconstructed Radiographs (DRRs) and a reference three-dimensional (3D) surface image was obtained by AlignRT. Surface images were acquired prior to every subsequent setup procedure. The systematic and random errors along longitudinal and vertical directions were measured and compared for the two systems. Results The procedure for surface registration, image acquisition and comparison with the reference image took less than 1 min on average. The T test for systematic error showed no significant difference between the 2 verification systems along the longitudinal ( p = 0.69) and vertical ( p = 0.67) axes. The T-test for random error showed a significant difference between the 2 systems along the vertical axis ( p = 0.05). Conclusion AlignRT is fast, simple, non-invasive and seems to be reliable in detecting patient setup errors. Our results suggest that it could be used to assess the setup reproducibility for breast cancer patients.

The role of a prone setup in breast radiation therapy.

Most patients undergoing breast conservation therapy receive radiotherapy in the supine position. Historically, prone breast irradiation has been advocated for women with large pendulous breasts in order to decrease acute and late toxicities. With the advent of CT planning, the prone technique has become both feasible and reproducible. It was shown to be advantageous not only for women with larger breasts but in most patients since it consistently reduces, if not eliminates, the inclusion of heart and lung within the field. The prone setup has been accepted as the best localizing position for both MRI and stereotactic biopsy, but its adoption has been delayed in radiotherapy. New technological advances including image-modulated radiation therapy and image-guided radiation therapy have made possible the exploration of accelerated fractionation schemes with a concomitant boost to the tumor bed in the prone position, along with better imaging and verification of reproducibility of patient setup. This review describes some of the available techniques for prone breast radiotherapy and the available experience in their application. The NYU prone breast radiotherapy approach is discussed, including a summary of the results from several prospective trials.

SU-GG-T-60: Clinical Implementation and Quality Assurance of a New HDR Applicator for Partial Breast Irradiation

Purpose/Objectives: To present clinical implementation and a method of quality assurance for a new HDR applicator of Strut-Adjusted Volume Implant (SAVI) for partial breast irradiation. Materials/Methods: The SAVI applicator has multi-peripheral struts that can be differentially loaded with the HDR source in order to achieve a conformai dose distribution to the lumpectomy cavity. The treatment plan is evaluated by a dose volume histogram (DVH) as follows: V90 > 90% or V95 > 95%, V150 < 50 cc, and V200 < 20 cc. Patients undergo a CAT scan guided simulation using an alpha cradle immobilization for reproducibility. The SAVI device status is verified using both 3D CT images and image fusion in addition to AP and lateral scout films. A self-developed Java program based on the AAPM TG-43 is used for the dose verification and uncertainty analysis. Results: Fifteen patients to date at Mercy Medical Center, Baltimore, Maryland were treated with SAVI device. The dosimetric data demonstrate the achievements of greater than 90% (95%) coverage for V90 (V95) at an average value of 97.9% (96.3%) while keeping a low V150 at 34.9 cc and V200 at 16.5 cc. Potential uncertainty induced by the SAVI applicator motion is evaluated to be a 3% variation in dose either by a 3-mm translation along the SAVI long axis or 3*deg; rotation from the SAVI applicator. Conclusion: The feature of multiple catheters of the SAVI applicator allows for optimal and conformai dose distribution around a lumpectomy cavity while minimizing the dose to adjacent normal structures such as skin and ribcage. Reproducible patient setup is important for assessing inter-fraction motion of the SAVI applicator. Multiple methods of AP and lateral scout films, 3D images, and CT image fusion are able to provide valuable information such as cavity variation, strut collapse or relative motion, and device shift.

Improved Fixation and Position Verification for Salivary Gland Sparing Head and Neck IMRT

Improved Fixation and Position Verification for Salivary Gland Sparing Head and Neck IMRT

WE‐B‐211A‐01: Strengths and Limitations of Anatomical and Spectroscopic MRI in Radiation Oncology Treatment Planning

Magnetic resonance imaging (MRI) is playing an increasingly important role in radiation oncology treatment planning. As compared to computed tomography (CT), MRI provides excellent soft tissue contrast making it ideal for imaging brain tumors. Other anatomical sites (e.g., prostate, pelvis, head and neck, extremities, abdomen, etc.) also benefit from the soft tissue contrast provided by MRI, but are limited by difficulties in reproducing CT patient positioning in the MRI as well as geometric distortions introduced within the MRI datasets. These issues will be described, along with techniques for their minimization and quantification. MRI is also a powerful and non‐invasive imaging modality to assess tissue motion, caused by a host of physiological processes (respiration, peristalsis, bladder and/or rectal filling, etc.). Clinical approaches to using MRI for motion management will be described.In addition to morphological imaging, magnetic resonance spectroscopic imaging (MRSI) provides a non‐invasive spatial mapping of abnormal tumor metabolism. This information may provide critically relevant assessment of the presence and extent of tumor activity, which may be substantially different from those considered to contain tumor based on T1 and T2 imaging. Many uncertainties remain: geometric and quantification accuracy of the acquired MRSI data due to magnetic field imperfections, lack of adequate anatomical details with MRSI images for registration with planning CT, and lacking essential DICOM objects hamper the incorporation of MRSI information into the treatment planning process. Clinical approaches to using MRSI for tumor target delineation will also be described.This lecture will outline the indications for MRI in radiation oncology treatment planning for both external beam and brachytherapy. Examples are provided for many anatomical sites, along registration of MRI datasets with PET/CT. Approaches that can be used to validate MRI applications will be provided, along with a description of the current limitations.Learning Objectives:1. Widespread applications of MRI in radiation oncology treatment planning2. Assessment of geometric distortion when MRI is utilized as one of several imaging modalities: reproducibility of patient setup and image distortion3. Application of MRI to quantify and validate motion management models4. Review obstacles to clinical utilization of magnetic resonance spectroscopic imaging (MRSI)Research sponsored by Siemens Medical Solutions

Reproducibility of patient setup by surface image registration system in conformal radiotherapy of prostate cancer

BackgroundThe reproducibility of patient setup for radiotherapy is based on various methods including external markers, X-rays with planar or computerized image acquisition, and, more recently, surface matching imaging. We analyzed the setup reproducibility of 16 patients affected by prostate cancer who underwent conformal radiotherapy with curative intent by using a surface image registration system.MethodsWe analyzed the setup reproducibility of 16 patients affected by prostate cancer candidates for conformal radiotherapy by using a surface image registration system. At the initial setup, EPID images were compared with DRRs and a reference 3D surface image was obtained by the AlignRT system (Vision RT, London, UK). Surface images were acquired prior to every subsequent setup procedure. EPID acquisition was repeated when errors > 5 mm were reported.ResultsThe mean random and systematic errors were 1.2 ± 2.3 mm and 0.3 ± 3.0 mm along the X axis, 0.0 ± 1.4 mm and 0.5 ± 2.0 mm along the Y axis, and 2.0 ± 1.8 mm and -0.7 ± 2.4 mm along the Z axis respectively. The positioning error detected by AlignRT along the 3 axes X, Y, and Z exceeded the value of 5 mm in 14.1%, 2.0%, and 5.1% measurements and the value of 3 mm in 36.9%, 13.6% and 27.8% measurements, respectively. Correlation factors calculated by linear regression between the errors measured by AlignRT and EPID ranged from 0.77 to 0.92 with a mean of 0.85 and SD of 0.13. The setup measurements by surface imaging are highly reproducible and correlate with the setup errors detected by EPID.ConclusionSurface image registration system appears to be a simple, fast, non-invasive, and reproducible method to analyze the set-up alignment in 3DCRT of prostate cancer patients.

Radiotherapy in Italy after Conservative Treatment of Early Breast Cancer. A Survey by the Italian Society of Radiation Oncology (AIRO)

The aim of surveys on clinical practice is to stimulate discussion and optimize practice. In this paper the current Italian radiotherapy practice after breast-conserving surgery for early breast cancer is described and adherence to national and international guidelines is assessed. Furthermore, results are compared with an earlier survey in northern Italy and international reports. A multiple-choice questionnaire sent to all 138 Italian radiation oncology centers. 48% of centers responded. Most performed breast-conserving surgery when tumor size was < or =3 cm. All centers routinely performed axillary dissection; 45 carried out sentinel node biopsy followed by axillary dissection when the sentinel node was positive. Most centers re-excised when resection margins were positive. The median interval between surgery and radiotherapy, when chemotherapy was not administered, was 60 days. Adjuvant chemotherapy was preferably administered before radiotherapy. Regional lymph nodes were never irradiated in 10 centers; in all others irradiation depended on the number of positive lymph nodes and/or involvement of axillary fat and/or tumor location in medial quadrants. All centers used standard fractionation; hypofractionated schemes were available in 6. Most centers used 4-6 MV photons. In 59 centers the boost dose of 10 Gy could be increased if margins were not negative. All centers ensured patient setup reproducibility. Treatment planning was computerized in 59 centers. The irradiation dose was prescribed at the ICRU point in 56 centers and portal films were made in 54 centers. Intraoperative radiotherapy was used in 4 centers: for partial breast irradiation in 1 and for boost administration in 3 centers. Although the quality of radiotherapy delivery has improved in Italy in recent years, approaches that do not conform to international standards persist.

Multimodality Image Fusion and Planning and Dose Delivery for Radiation Therapy

Image-guided radiation therapy (IGRT) relies on the quality of fused images to yield accurate and reproducible patient setup prior to dose delivery. The registration of 2 image datasets can be characterized as hardware-based or software-based image fusion. Hardware-based image fusion is performed by hybrid scanners that combine 2 distinct medical imaging modalities such as positron emission tomography (PET) and computed tomography (CT) into a single device. In hybrid scanners, the patient maintains the same position during both studies making the fusion of image data sets simple. However, it cannot perform temporal image registration where image datasets are acquired at different times. On the other hand, software-based image fusion technique can merge image datasets taken at different times or with different medical imaging modalities. Software-based image fusion can be performed either manually, using landmarks, or automatically. In the automatic image fusion method, the best fit is evaluated using mutual information coefficient. Manual image fusion is typically performed at dose planning and for patient setup prior to dose delivery for IGRT. The fusion of orthogonal live radiographic images taken prior to dose delivery to digitally reconstructed radiographs will be presented. Although manual image fusion has been routinely used, the use of fiducial markers has shortened the fusion time. Automated image fusion should be possible for IGRT because the image datasets are derived basically from the same imaging modality, resulting in further shortening the fusion time. The advantages and limitations of both hardware-based and software-based image fusion methodologies are discussed.

Accuracy of a commercial optical 3D surface imaging system for realignment of patients for radiotherapy of the thorax

Accurate and reproducible patient setup is a prerequisite to fractionated radiotherapy. To evaluate the applicability and technical performance of a commercial 3D surface imaging system for repositioning of breast cancer patients, measurements were performed in a rigid anthropomorphic phantom as well as in healthy volunteers. The camera system records a respiration-gated surface model of the imaged object, which may be registered to a previously recorded reference model. A transformation is provided, which may be applied to the treatment couch to correct the setup of the patient. The system showed a high stability and detected pre-defined shifts of phantoms and healthy volunteers with an accuracy of 0.40 ± 0.26 mm and 1.02 ± 0.51 mm, respectively (spatial deviation between pre-defined shift and suggested correction). The accuracy of the suggested rotational correction around the vertical axis was always better than 0.3° in phantom measurements and 0.8° in volunteers, respectively. Comparison of the suggested setup correction with that detected by a second and independently operated marker-based optical system provided consistent results. The results demonstrate that the camera system provides highly accurate setup corrections in a phantom and healthy volunteers. The most efficient use of the system for improving the setup accuracy in breast cancer patients has to be investigated in routine patient treatments.

SU‐FF‐J‐81: Importance of Daily Portal Imaging for Head and Neck IMRT Treatments

Purpose: To investigate the set up variation for head and neck IMRT patients based on daily portal imaging. Method and Materials: Reproducible patient setup is critical to accurate delivery of head and neck IMRT. At our institution, these patients are immobilized using a head‐neck‐shoulder thermoplastic immobilization system (S‐Type, Medtec) and a customized headrest. Orthogonal digital portal images are taken daily to check patient positioning and are compared with plan DRRs. Isocenter misalignments are corrected by the therapists using a couch shift, with a 3mm action level. Therapists also carefully examine patient positioning in the mask, especially shoulder position, and re‐position the patient in the mask if considered necessary. Isocenter shifts and frequency of patient repositioning were investigated by review of record‐and‐verify records for 15 patients. The magnitude of the shoulder respositioning was evaluated for 10 patients by comparing portal images and plan DRRs for a point 8cm inferior of isocenter, which is typically located at C2. Results: Isocenter discrepancies of 3mm or smaller were recorded for a median of 92.5% of fractions (range: 71.4 – 100%). Isocenter shifts larger than 5mm were only recorded twice (2 patients, 1 fraction each; 0.38% of all fractions). On the basis of pre‐treatment daily imaging, patients were repositioned in the immobilization mask before treatment for a median of 14% of fractions (range: 3–34%). Fifty nine percent of these repositioning were for a shoulder shift of less than 5mm. Thirty percent, however, were for shoulder shifts of 1cm or larger. Conclusion: With our current immobilization, daily isocenter positioning accuracy is excellent, while correct shoulder position is more variable. Frequent imaging of head and neck IMRT patients is essential to accurate delivery of therapy, with shoulder position an important factor.

Clinical Implications of New Innovations in Radiation Treatment Delivery.

The practice of radiation therapy involves accurately defining the target and precisely delivering the treatment. The end result is to maximize dose to the tumor and minimize dose to surrounding tissue. Many technical innovations in the delivery of radiation have been developed over the past few years. These developments essentially increase the precision of radiation delivery, but do not directly address the accuracy of target definition. These technical innovations can be broadly thought of as accomplishing two goals: first, to increase the reproducibility of patient setup, and second, to improve the dose homogeneity. The clinical implementation, concerns, and utility of these innovations are discussed.

Verification Films: A Study of the Daily and Weekly Reproducibility of Breast Patient Set-up in the START Trial

Verification of patient position in radiotherapy by the use of portal images is a current practice in most radiotherapy departments. All patients within the Standardisation of Breast Radiotherapy Trial (START) were required to have on-treatment verification images. Measurements of maximum lung and breast depth from these were used to provide details for the case-report forms. This study was undertaken to validate these measurements, assess the reproducibility of patients' set-up within the START trial and to compare reproducibility on a day-to-day basis with reproducibility over a longer period. Analysis also included a subjective assessment of image quality. Fifty-three patients from 29 departments were studied. Some centres used electronic portal imaging and others used film. Where film verification was the method of choice, information was collected about the type of film and cassette used. The correlation coefficients for inter- and intra-observer variability of breast and lung depth were 0.99. Comparing maximum breast depth on weekly and daily images, the median per cent standard deviation of breast depth was 4% and 3%, respectively. The mean standard deviation of breast depth for all patients, which gives an indication of the individual patient variability, was 5.5 +/- 2.2 mm for weekly and 3.9 +/- 1.5 mm for daily measurements. For lung depth, mean standard deviation was 6.8 +/- 2.5 mm for weekly and 6.8 +/- 2.8 mm for daily measurements. Images taken using Kodak X-omat V film were inferior to those taken with films in corresponding cassettes. Differences between lung depth measured in simulator and on the treatment unit were evident for many patients. There was little difference in the standard deviations of breast and lung depth for daily and weekly verification films on the treatment machine.

Development of Respiratory Motion Reduction Device System (RMRDs) for Radiotherapy in Moving Tumors

The internal target volume (ITV) for tumors in the abdomen or thorax includes sufficient margin for breathing-related movement of tumor volumes during treatment. Depending on the location of the tumor, the magnitude of the ITV margin extends from 1 to 3 cm, which increases substantially the volume of the irradiated normal tissue, hence resulting in an increase in normal tissue complication probability (NTCP). We developed a simple and handy method which can reduce ITV margins in patients with moving tumors: the respiratory motion reduction device system (RMRDs). The patient's clinical database was structured for moving tumor patients and patient set-up error measurement and immobilization device effects were investigated. The system is composed of the respiration presser device (RPD) utilized in the prone position and the abdominal strip device (ASD) utilized in the supine position, and the analysis program, which enables analysis of patient set-up reproducibility. It was tested for analyzing the diaphragm movement from patients with RMRDs, the magnitude of the ITV margin was determined and the dose-volume histogram (DVH) was computed using treatment planning software. The dose to normal tissue in patients with and without RMRDs was analyzed by comparing the fraction of the normal liver receiving 50% of the isocenter dose. Average diaphragm movement due to respiration was 16 +/- 1.9 mm in the case of the supine position, and 12 +/- 1.9 mm in the case of the prone position. When utilizing the RMRDs, which was personally developed in our hospital, the value was reduced to 5 +/- 1.4 mm, and in the case in which the belt immobilization device was utilized, the value was reduced to 3 +/- 0.9 mm. In the case where the strip device was utilized, the value was proven to reduce to 4 +/- 0.3 mm. As a result of analyzing the volume of normal liver where 50% of the prescription dose is irradiated in DVH according to the radiation treatment planning, the use of the RMRD can create a reduction of 30% to the maximum. Also by obtaining the digital image, the function of comparison between the standard image, automated external contour subtraction, etc. was utilized to develop a patient set-up reproducibility analysis program that can evaluate the change in patient set-up. Internal organ motion due to breathing can be reduced using RMRDs, which is simple and easy to use in the clinical setting. It can reduce the organ motion-related planning target volume margin, thereby decreasing the volume of irradiated normal tissue.

A dynamic supraclavicular field-matching technique for head-and-neck cancer patients treated with IMRT

A dynamic supraclavicular field-matching technique for head-and-neck cancer patients treated with IMRT

A dynamic supraclavicular field-matching technique for head-and-neck cancer patients treated with IMRT.

The conventional single-isocenter and half-beam (SIHB) technique for matching supraclavicular fields with head-and-neck (HN) intensity-modulated radiotherapy (IMRT) fields is subject to substantial dose inhomogeneities from imperfect accelerator jaw/MLC calibration. It also limits the isocenter location and restricts the useful field size for IMRT. We propose a dynamic field-matching technique to overcome these limitations. The proposed dynamic field-matching technique makes use of wedge junctions for the abutment of supraclavicular and HN IMRT fields. The supraclavicular field was shaped with a multileaf collimator (MLC), which was orientated such that the leaves traveled along the superoinferior direction. The leaves that defined the superior field border moved continuously during treatment from 1.5 cm below to 1.5 cm above the conventional match line to generate a 3-cm-wide wedge-shaped junction. The HN IMRT fields were optimized by taking into account the dose contribution from the supraclavicular field to the junction area, which generates a complementary wedge to produce a smooth junction in the abutment region. This technique was evaluated on a polystyrene phantom and 10 HN cancer patients. Treatment plans were generated for the phantom and the 10 patients. Dose profiles across the abutment region were measured in the phantom on films. For patient plans, dose profiles that passed through the center of the neck lymph nodes were calculated using the proposed technique and the SIHB technique, and dose uniformity in the abutment region was compared. Field mismatches of +/- 1 mm and +/- 2 mm because of imperfect jaw/MLC calibration were simulated, and the resulting dose inhomogeneities were studied for the two techniques with film measurements and patient plans. Three-dimensional volumetric doses were analyzed, and equivalent uniform doses (EUD) were computed. The effect of field mismatches on EUD was compared for the two match techniques. For a perfect jaw/MLC calibration, dose profiles for the 10 patients in the 3-cm match zone had an average inhomogeneity range of -1.6% to +1.6% using the dynamic-matching technique and -3.7% to +3.8% according to the SIHB technique. Measurements showed that dose inhomogeneities that resulted from 1-mm and 2-mm jaw/MLC calibration errors were reduced from as large as 27% and 45% with the SIHB technique to less than 2% and 5.7% with the dynamic technique, respectively. For -1-mm, -2-mm, +1-mm, and +2-mm jaw/MLC calibration errors, respectively, treatment plans for the 10 patients yielded average dose inhomogeneities of -5.9%, -3.0%, +2.7%, and +5.8% with the dynamic technique as compared to -22.8%, -11.1%, +9.8%, and +22.1% with the SIHB technique. Calculation based on a dose-volume histogram (DVH) showed that the SIHB technique resulted in larger changes in EUD of the PTV in the junction area than did the dynamic technique. Compared with the conventional SIHB technique, the dynamic field-matching technique provides superior dose homogeneity in the abutment region between the supraclavicular and HN IMRT fields. The dynamic feathering mechanism substantially reduces dose inhomogeneities that result from imperfect jaw/MLC calibration. In addition, isocenter location in the dynamic field-matching technique can be chosen for reproducible patient setup and for adequate IMRT field size rather than being dictated by the match position. It also allows angling of the supraclavicular field to reduce the volume of healthy lung irradiated, which is impractical with the SIHB technique. In principle, this technique should be applicable to any treatment site that requires the abutment of static and intensity-modulated fields.

60/Time trend of setup deviations during irradiation of patients with breast, prostate and gynecologic cancers

Purpose Evaluation of the time trend of setup deviations for patients treated with external beams. Materials and methods Analysis of time trend of setup deviations was carried out for patients irradiated for breast, prostate and gynecological cancers. Portal control technique was used to detect patients setup displacement for 18 patients with breast cancer (inverse hockey technique was applied), for 11 patients with gynecological cancers (box technique) and for 10 patients with prostate cancer (3 fields, AP and 2 wedge lateral fields). For breast cancer patients portals were made for photon field only. A total of 82, 129 and 112 portals were made or breast, gynecological and prostate patients respectively. For gynecological and prostate patients for 1 vertical and 1 lateral fields portals were taken. Simulator films were treated as reference ones. For each patient and each axis displacement as a function of time was investigated. The analysis of setup deviations as a function of time, the displacement were plotted against time along each of perpendicular axis. The linear fit of the resulting curve represents the trend of setup deviation with time. The slope of each linear curve fit was tested for statistical significance at the 95% confidence limit utilizing the T-test. Results Displacements with significant time trends were not detected. For 1 breast patient setup reproducibility was significantly gradually deteriorated – in the last week of treatment displacement reached the value of 8,5 mm (for mediolateral direction). For all other patients reaction level was nether exceeded. Conclusions Time trend of setup displacement were rarely observed among patients treated in our hospital. In only 1 of 20 cases the setup accuracy was significantly deteriorated during the whole treatment course.

An integrated treatment delivery system for CSRS and CSRT and clinical applications

An integrated treatment delivery system for conformal stereotactic radiosurgery (CSRS) and radiotherapy (CSRT) has been developed through a collaboration involving Siemens Medical Systems, Inc., Tyco/Radionics, Inc., and The University of Texas M. D. Anderson Cancer Center. The system consists of a 6-MV linear accelerator (LINAC) equipped with a Tyco/Radionics miniature multileaf collimator (mMLC). For the conventional SRS treatment, the circular collimator housing can be attached to the opening window of the mMLC. The treatment delivery system is integrated with a radiotherapy treatment planning system and a record-and-verify system. The purpose of this study is to report the characteristics, performance, benefits, and the clinical applications of this delivery system. The technical specifications of the LINAC and mMLC were tested, and all the specifications were met. The 80% to 20% penumbral width for each mMLC leaf is approximately 3 mm and is nearly independent of the off-axis positions of a leaf. The maximum interleaf leakage is 1.4% (1.1% on average) and the maximum intra-leaf leakage is 1.0% (0.9% on average). The leaf position precision is better than 0.5 mm for all the leaves. The integration of the SRS/SRT treatment planning system, mMLC, and LINAC has been evaluated successfully for transferring the patient treatment data file through radiotherapy treatment planning system to the patient information and treatment record-and-verify server and the mMLC controller. Subsequently, the auto-sequential treatment delivery for SRS, CSRS/CSRT, and the step-and-shoot intensity-modulated radiotherapy has also been tested successfully. The accuracy of dose delivery was evaluated for a 2-cm spherical target in a Radiological Physics Center SRS head phantom with GAFChromic films and TLD. Five non-coplanar arcs, using a 2-cm diameter circular collimator, were used for this simulation treatment. The accuracy to aim the center of the spherical target was within 0.5 mm and the deviation of dose delivery to the isocenter of the target was within 2% of the calculated dose. For the irregularly shaped tumor, a tissue-equivalent head phantom was used to evaluate the accuracy of dose delivery for using either geometric conformal treatment or IMRT The accuracy of dose delivery to the isocenter was within 2% and 3% of the calculated dose, respectively. From October 26, 1999 to September 30, 2002, we treated over 400 SRS patients and 70 SRT patients. Four representative cases are presented to illustrate the capabilities of this dedicated unit in performing conventional SRS, CSRS, and CSRT. For all the cases, the geometric conformal-plan dose distributions showed a high degree of conformity to the target shape. The degree of conformity can be evaluated using the target-volume-ratio (TVR). Our preferred TVR values for highly conformed dose distributions range from 1.6 to 2.0. The patient setup reproducibility for the Gill-Thomas-Cosman (GTC) noninvasive head frame ranges from 0.5 to 1 mm, and the head and neck noninvasive frame is within 2 mm. The integrated treatment delivery system offers excellent conformation for complicated planning target volumes with the stereotactic setup approach, ensuring that dose delivery can be achieved within the specified accuracy. In addition, the treatment time is comparable with that of single isocenter multiple-arc treatments. PACS number(s): 87.53.Kn, 87.53.Ly