Sha Chang

Large deformation three-dimensional image registration in image-guided radiation therapy

In this paper, we present and validate a framework, based on deformable image registration, for automatic processing of serial three-dimensional CT images used in image-guided radiation therapy. A major assumption in deformable image registration has been that, if two images are being registered, every point of one image corresponds appropriately to some point in the other. For intra-treatment images of the prostate, however, this assumption is violated by the variable presence of bowel gas. The framework presented here explicitly extends previous deformable image registration algorithms to accommodate such regions in the image for which no correspondence exists. We show how to use our registration technique as a tool for organ segmentation, and present a statistical analysis of this segmentation method, validating it by comparison with multiple human raters. We also show how the deformable registration technique can be used to determine the dosimetric effect of a given plan in the presence of non-rigid tissue motion. In addition to dose accumulation, we describe a method for estimating the biological effects of tissue motion using a linear-quadratic model. This work is described in the context of a prostate treatment protocol, but it is of general applicability.

Beam orientation selection for intensity-modulated radiation therapy based on target equivalent uniform dose maximization

PURPOSEnTo develop an automated beam-orientation selection procedure for intensity-modulated radiotherapy (IMRT), and to determine if a small number of beams picked by this automated procedure can yield results comparable to a large number of manually placed orientations.nnnMETHODS AND MATERIALSnThe automated beam selection procedure maximizes an unconstrained objective function composed of target equivalent uniform dose (EUD) and critical structure dose-volume histogram (DVH) constraints. Beam orientations are selected from a large feasible set of directions through a series of alternating fluence optimization and orientation alteration steps, until convergence to a stable orientation set. The fluence optimization step adjusts fluences to maximize the objective function. The orientation alteration step substitutes beams in the orientation set currently under consideration with beams of the parent set in the immediate angular vicinity; the altered orientation set is deemed current if it produces a higher objective function value in the fluence optimization step.nnnRESULTS AND CONCLUSIONSnIt is demonstrated, for prostate IMRT planning, that a modest number of appropriately selected beam orientations (3 or 5) can provide dose distributions as satisfactory as those produced by a large number of unselected equispaced orientations. Such selected beam orientations can reduce overall treatment time, thus making IMRT more clinically practical.

A carbon nanotube field emission multipixel x-ray array source for microradiotherapy application

The authors report a carbon nanotube (CNT) field emission multipixel x-ray array source for microradiotherapy for cancer research. The developed multipixel x-ray array source has 50 individually controllable pixels and it has several distinct advantages over other irradiation source including high-temporal resolution (millisecond level), the ability to electronically shape the form, and intensity distribution of the radiation fields. The x-ray array was generated by a CNT cathode array (5×10) chip with electron field emission. A dose rate on the order of >1.2 Gy∕min per x-ray pixel beam is achieved at the center of the irradiated volume. The measured dose rate is in good agreement with the Monte Carlo simulation result.

Modeling the dosimetry of organ-at-risk in head and neck IMRT planning: An intertechnique and interinstitutional study

PURPOSEnTo build a statistical model to quantitatively correlate the anatomic features of structures and the corresponding dose-volume histogram (DVH) of head and neck (HN) Tomotherapy (Tomo) plans. To study if the model built upon one intensity modulated radiation therapy (IMRT) technique (such as conventional Linac) can be used to predict anticipated organs-at-risk (OAR) DVH of patients treated with a different IMRT technique (such as Tomo). To study if the model built upon the clinical experience of one institution can be used to aid IMRT planning for another institution.nnnMETHODSnForty-four Tomotherapy intensity modulate radiotherapy plans of HN cases (Tomo-IMRT) from Institution A were included in the study. A different patient group of 53 HN fixed gantry IMRT (FG-IMRT) plans was selected from Institution B. The analyzed OARs included the parotid, larynx, spinal cord, brainstem, and submandibular gland. Two major groups of anatomical features were considered: the volumetric information and the spatial information. The volume information includes the volume of target, OAR, and overlapped volume between target and OAR. The spatial information of OARs relative to PTVs was represented by the distance-to-target histogram (DTH). Important anatomical and dosimetric features were extracted from DTH and DVH by principal component analysis. Two regression models, one for Tomotherapy plan and one for IMRT plan, were built independently. The accuracy of intratreatment-modality model prediction was validated by a leave one out cross-validation method. The intertechnique and interinstitution validations were performed by using the FG-IMRT model to predict the OAR dosimetry of Tomo-IMRT plans. The dosimetry of OARs, under the same and different institutional preferences, was analyzed to examine the correlation between the model prediction and planning protocol.nnnRESULTSnSignificant patient anatomical factors contributing to OAR dose sparing in HN Tomotherapy plans have been analyzed and identified. For all the OARs, the discrepancies of dose indices between the model predicted values and the actual plan values were within 2.1%. Similar results were obtained from the modeling of FG-IMRT plans. The parotid gland was spared in a comparable fashion during the treatment planning of two institutions. The model based on FG-IMRT plans was found to predict the median dose of the parotid of Tomotherapy plans quite well, with a mean error of 2.6%. Predictions from the FG-IMRT model suggested the median dose of the larynx, median dose of the brainstem and D2 of the brainstem could be reduced by 10.5%, 12.8%, and 20.4%, respectively, in the Tomo-IMRT plans. This was found to be correlated to the institutional differences in OAR constraint settings. Re-planning of six Tomotherapy patients confirmed the potential of optimization improvement predicted by the FG-IMRT model was correct.nnnCONCLUSIONSnThe authors established a mathematical model to correlate the anatomical features and dosimetric indexes of OARs of HN patients in Tomotherapy plans. The model can be used for the setup of patient-specific OAR dose sparing goals and quality control of planning results.The institutional clinical experience was incorporated into the model which allows the model from one institution to generate a reference plan for another institution, or another IMRT technique.

Feasibility of Breast Preserving Therapy with Single Fraction In Situ Radiotherapy Delivered Intraoperatively

BackgroundAccelerated partial breast irradiation (APBI) has gained widespread interest as a means of improving the convenience and availability of breast conserving radiotherapy. Intraoperative radiation therapy (IORT) is an APBI technique that delivers breast radiotherapy as a single dose at the time of partial mastectomy. We adapted the technique of Veronesi to deliver IORT prior to tumor excision to improve delivery to the region at risk and reduce the volume of normal tissue irradiated.MethodsPatients age ≥55 with ultrasonographically defined tumors ≤3xa0cm and invasive ductal carcinoma confirmed by core biopsy were eligible. Pre-operative ultrasound was performed at the time of needle localization and radiocolloid injection. IORT treatment planning was performed prior to surgery using ultrasound tumor definition, selecting cone size and electron energy to optimize dose distribution. In the operating room, the surgeon retracted the skin over the tumor, cone was placed and radiotherapy delivered. Standard partial mastectomy was then performed.ResultsTwenty-three patients were enrolled in the study. Eighteen patients completed IORT with 10 patients having successful IORT no additional local therapy necessary. In five patients, the intraoperative radiation therapy served as the boost and in three patients unsuspected larger tumors or multicentric disease necessitated a mastectomy. The majority of patients had a good to excellent cosmetic result.ConclusionsSingle fraction in situ IORT prior to partial mastectomy is feasible for patients with small breast cancers in achieving a good to excellent cosmetic result. Based on this early preliminary data, we plan to expand our feasibility trial.

Improving quality of patient care by improving daily practice in radiation oncology.

Radiation oncology is an ever-advancing, complex, technologically based specialty that has been thrust into the public spotlight because of recent reports of serious treatment delivery errors that have impacted the quality of patient care. Although quality assurance (QA) initiatives are already common place in radiation oncology, the continued complex technology and automation-based advances in radiotherapy have created new safety challenges. The ongoing evolution of safety challenges in radiation oncology requires corresponding evolution in workflow and QA programs to ensure the quality of patient care. We believe that the incorporation of QA themes into our daily practice will help to create safer patient environments. Practical QA approaches that can be readily incorporated and applied in the daily practice of radiation oncology include process engineering and human factors engineering, medical peer review, safety rounds, and software QA tools. Most importantly, we need to develop a culture of safety in which all team members work together to maximize the quality of our patient care.

Clinical experience with 3-dimensional surface matching-based deep inspiration breath hold for left-sided breast cancer radiation therapy

PURPOSEnThree-dimensional (3D) surface matching is a novel method to administer deep inspiration breath-hold (DIBH) radiation therapy for left-sided breast cancer to reduce cardiac exposure. We analyzed port (x-ray) films to assess patient setup accuracy and treatment times to assess the practical workflow of this system.nnnMETHODS AND MATERIALSnThe data from 50 left-sided breast cancer patients treated with DIBH were studied. AlignRT (London, UK) was used. The distance between the field edge and the anterior pericardial shadow as seen on the routine port films (dPORT), and the corresponding distance seen on the digitally reconstructed radiographs (DRR) from the planning (dDRR) were compared as a quantitative measure of setup accuracy. Variations of dPORT - dDRR over the treatment course were assessed. In a subset of 21 patients treated with tangential beams alone, the daily treatment durations were analyzed to assess the practical workflow of this system.nnnRESULTSnConsidering all 50 patients, the mean absolute systematic uncertainty between dPORT and dDRR was 0.20 cm (range, 0 to 1.22 cm), the mean systematic uncertainty was -0.07 cm (range, -1.22 to 0.67 cm), and their mean random uncertainty was 0.19 cm (range, 0 to 0.84 cm). There was no significant change in dPORT - dDRR during the course of treatment. The mean patient treatment duration for the 21 patients studied was 11 minutes 48 seconds. On intrapatient assessments, 15/21 had nonsignificant trends toward reduced treatment durations during their course of therapy. On interpatient comparisons, the mean treatment times declined as we gained more experience with this technique.nnnCONCLUSIONSnThe DIBH patient setup appears to provide a fairly reproducible degree of cardiac sparing with random uncertainties of ≈ 0.2 cm. The treatment durations are clinically acceptable and appear not to change significantly over time on an intrapatient basis, and to improve over time on an interpatient basis.

Dosimetric comparison of treatment planning systems in irradiation of breast with tangential fields

PURPOSEnThe objectives of this study are: (1) to investigate the dosimetric differences of the different treatment planning systems (TPS) in breast irradiation with tangential fields, and (2) to study the effect of beam characteristics on dose distributions in tangential breast irradiation with 6 MV linear accelerators from different manufacturers.nnnMETHODS AND MATERIALSnNine commercial and two university-based TPS are evaluated in this study. The computed tomographic scan of three representative patients, labeled as small, medium and large based on their respective chest wall separations in the central axis plane (CAX) were used. For each patient, the tangential fields were set up in each TPS. The CAX distribution was optimized separately with lung correction, for each TPS based on the same set of optimization conditions. The isodose distributions in two other off-axis planes, one 6 cm cephalic and the other 6 cm caudal to the CAX plane were also computed. To investigate the effect of beam characteristics on dose distributions, a three-dimensional TPS was used to calculate the isodose distributions for three different linear accelerators, the Varian Clinac 6/100, the Siemens MD2 and the Philips SL/7 for the three patients. In addition, dose distributions obtained with 6 MV X-rays from two different accelerators, the Varian Clinac 6/100 and the Varian 2100C, were compared.nnnRESULTSnFor all TPS, the dose distributions in all three planes agreed qualitatively to within +/- 5% for the small and the medium patients. For the large patient, all TPS agreed to within +/- 4% on the CAX plane. The isodose distributions in the caudal plane differed by +/- 5% among all TPS. In the cephalic plane in which the patient separation is much larger than that in the CAX plane, six TPS correctly calculated the dose distribution showing a cold spot in the center of the breast contour. The other five TPS showed that the center of the breast received adequate dose. Isodose distributions for 6 MV X-rays from three different accelerators differed by about +/- 3% for the small patient and more than +/- 5% for the large patient. For two different 6 MV machines of the same manufacturer, the isodose distribution agreed to within +/- 2% for all three planes for the large patient.nnnCONCLUSIONnThe differences observed among the various TPS in this study were within +/- 5% for both the small and the medium patients while doses at the hot spot exhibit a larger variation. The large discrepancy observed in the off-axis plane for the large patient is largely due to the inability of most TPS to incorporate the collimator angles in the dose calculation. Only six systems involved agreed to within +/- 5% for all three patients in all calculation planes. The difference in dose distributions obtained with three accelerators from different manufacturers is probably due to the difference in beam profiles. On the other hand, the 6 MV X-rays from two different models of linear accelerators from the same manufacturer have similar beam characteristics and the dose distributions are within +/- 2% of each other throughout the breast volume. In general, multi-institutional breast treatment data can be compared within a +/- 5% accuracy.

Image-guided microbeam irradiation to brain tumour bearing mice using a carbon nanotube x-ray source array

Microbeam radiation therapy (MRT) is a promising experimental and preclinical radiotherapy method for cancer treatment. Synchrotron based MRT experiments have shown that spatially fractionated microbeam radiation has the unique capability of preferentially eradicating tumour cells while sparing normal tissue in brain tumour bearing animal models. We recently demonstrated the feasibility of generating orthovoltage microbeam radiation with an adjustable microbeam width using a carbon nanotube based x-ray source array. Here we report the preliminary results from our efforts in developing an image guidance procedure for the targeted delivery of the narrow microbeams to the small tumour region in the mouse brain. Magnetic resonance imaging was used for tumour identification, and on-board x-ray radiography was used for imaging of landmarks without contrast agents. The two images were aligned using 2D rigid body image registration to determine the relative position of the tumour with respect to a landmark. The targeting accuracy and consistency were evaluated by first irradiating a group of mice inoculated with U87 human glioma brain tumours using the present protocol and then determining the locations of the microbeam radiation tracks using γ-H2AX immunofluorescence staining. The histology results showed that among 14 mice irradiated, 11 received the prescribed number of microbeams on the targeted tumour, with an average localization accuracy of 454 µm measured directly from the histology (537 µm if measured from the registered histological images). Two mice received one of the three prescribed microbeams on the tumour site. One mouse was excluded from the analysis due to tissue staining errors.

Quantification of the impact of multifaceted initiatives intended to improve operational efficiency and the safety culture: A case study from an academic medical center radiation oncology department

PURPOSEnWe have systematically been incorporating several operational efficiency and safety initiatives into our academic radiation oncology clinic. We herein quantify the impact of these initiatives on prospectively collected, clinically meaningful, metrics.nnnMETHODS AND MATERIALSnThe data from 5 quality improvement initiatives, each focused on a specific safety/process concern in our clinic, are presented. Data was collected prospectively: operational metrics recorded before and after implementation of the initiative were compared using statistical analysis. Results from the Agency for Health Care Research and Quality (AHRQ) patient safety culture surveys administered during and after many of these initiatives were similarly compared.nnnRESULTSn(1) Workload levels for nurses assisting with brachytherapy were high (National Aeronautics and Space Administration Task Load Index (NASA-TLX) scores >55-60, suggesting, overwork). Changes in work flow and procedure room layout reduced workload to more acceptable levels (NASA-TLX <55; P < .01). (2) The rate of treatment therapists being interrupted was reduced from a mean of 4 (range, 1-11) times per patient treatment to a mean <1 (range, 0-3; P < .001) after implementing standards for electronic communication and placement of monitors informing patients and staff of the treatment machine status (ie, delayed, on time). (3) The rates of replans by dosimetrists was reduced from 11% to 6% (P < .01) through a more systematic pretreatment peer review process. (4) Standardizing nursing and resident functions reduced patient wait times by ≈ 45% (14 min; P < .01). (5) Standardizing presimulation instructions from the physician reduced the number of patients experiencing delays on the simulator (>50% to <10%; P < .01). To assess the overall changes in patient safety culture, we conducted a pre- and postanalysis using the AHRQ survey. Improvements in all measured dimensions were noted.nnnCONCLUSIONSnQuality improvement initiatives can be successfully implemented in an academic radiation oncology department to yield measurable improvements in operations resulting in improvement in patient safety culture.