An immunocompetent rectal cancer model to study radiation therapy.

We describe a mouse model of rectal cancer (RC) involving rapid tumor organoid engraftment via orthotopic transplantation in an immunocompetent setting. This approach uses simple mechanical disruption to allow engraftment, avoiding the use of dextran sulfate sodium. The resulting RC tumors invaded from the mucosal surface and metastasized to distant organs. Histologically, the tumors closely resemble human RC and mirror remodeling of the tumor microenvironment in response to radiation. This murine RC model thus recapitulates key aspects of human RC pathogenesis and presents an accessible approach for more physiologically accurate, preclinical efficacy studies.

The effects of the orthopedic metal artifact reduction (O-MAR) algorithm on contouring and dosimetry of head and neck radiotherapy patients.

Metallic objects, such as dental fillings, cause artifacts in computed tomography (CT) scans. We quantify the contouring and dosimetric effects of Orthopedic Metal Artifact Reduction (O-MAR), in head and neck radiotherapy. The ease of organ contouring was assessed by having a radiation oncologist identify the CT data set with or without O-MAR for each of 28 patients that was easier to contour. The effect on contouring was quantified further by having the physician recontour parotid glands, previously drawn by him on the O-MAR scans, on uncorrected scans, and calculating the Dice coefficent (a measure of overlap) for the contours. Radiotherapy plans originally generated on scans reconstructed with O-MAR were recalculated on scans without metal artifact correction. The study was done using the Analytical Anisotropic Algorithm (AAA) dose calculation algorithm. The 15 patients with a planning target volume (PTV) extending to the same slice as the artifacts were used for this part of the study. The normal tissue doses were not significantly affected. The PTV mean dose and V95 were not affected, but the cold spots became less severe in the O-MAR corrected plans, with the minimum point dose on average being 4.1% higher. In 79% of the cases, the radiation oncologist identified the O-MAR scan as easier to contour; in 11% he chose the uncorrected scan and in 11% the scans were judged to have equal quality. A total of nine parotid glands (on both scans-18 contours in total) in 5 patients were recontoured. The average Dice coefficient for parotids drawn with and without O-MAR was found to be 0.775 +/- 0.045. The O-MAR algorithm does not produce a significant dosimetric effect in head and neck plans when using the AAA dose calculation algorithm. It can therefore be used for improved contouring accuracy without updating the critical structure tolerance doses and target coverage expectations.

Glomus tumors treated with stereotactic radiosurgery: A retrospective study.

BACKGROUND: Glomus tumors are difficult to manage surgically because they are vascular tumors that are topographically associated with important vascular and neuronal structures. Hence, there is a strong risk of incomplete resection and a high morbidity rate. In addition, they grow slowly. Recent treatments have increasingly involved a combination of surgical resection and radiosurgery. We present our experience in treating glomus tumors of the skull base with stereotactic radiosurgery as an upfront therapy. METHODS: We analyzed data from 13 consecutive patients with glomus tumors that were initially treated with stereotactic radiosurgery in our institute from February 2010 to April 2012. The tumor control rate, resolution of symptoms, and the complication rate were tabulated. RESULTS: All patients were female with a median age of 63 (mean 62.7+/-14.6 years). The median treatment dose was 25.8 Gy (27.6 Gy +/- 9.5 Gy) and the median tumor volume 10.4 mL (9.2 +/- 6.5). The median follow-up was 47.4 months (51.8+/-11.2 months, range 31-74). The tumor control rate was 92.3%; 46.7% of the patients had noticeable tumor shrinkage. This happened at a median interval of 17 months (18.7+/-6.8) after treatment. Most patients with tinnitus had resolution of their symptoms (87.5%). Four patients presented with new symptoms and four patients with worsening of pre-existing symptoms. The time course of symptomatic improvement followed that of tumor size reduction. However, there was no statistical correlation between the amount of tumor reduction and symptomatic relief. CONCLUSION: Stereotactic radiosurgery (SRS) is an effective upfront treatment option in the management of glomus tumors.

A special report of current state of the medical physicist workforce - results of the 2012 ASTRO Comprehensive Workforce Study.

The medical physics profession is undergoing significant changes. Starting in 2014, candidates registering for certification exams by the American Board of Radiology must have completed a CAMPEP-accredited residency. This requirement, along with tightened state regulations, uncertainty in future reimbursement, and a stronger emphasis on board certification, have raised questions concerning the state of the medical physics workforce and its ability to adapt to changing requirements. In 2012, ASTRO conducted a workforce study of the comprehensive field of radiation oncology. This article reviews the findings of the medical physics section of the study, including age and gender distribution, educational background, workload, and primary work setting. We also report on job satisfaction, the perceived supply and demand of medical physicists, and the medical physicists' main concerns pertaining to patient safety and quality assurance.

Early-stage breast cancer treated with 3-week accelerated whole-breast radiation therapy and concomitant boost.

PURPOSE: To report early outcomes of accelerated whole-breast radiation therapy with concomitant boost. METHODS AND MATERIALS: This is a prospective, institutional review board-approved study. Eligibility included stage TisN0, T1N0, and T2N0 breast cancer. Patients receiving adjuvant chemotherapy were ineligible. The whole breast received 40.5 Gy in 2.7-Gy fractions with a concomitant lumpectomy boost of 4.5 Gy in 0.3-Gy fractions. Total dose to the lumpectomy site was 45 Gy in 15 fractions over 19 days. RESULTS: Between October 2004 and December 2010, 160 patients were treated; stage distribution was as follows: TisN0, n = 63; T1N0, n = 88; and T2N0, n = 9. With a median follow-up of 3.5 years (range, 1.5-7.8 years) the 5-year overall survival and disease-free survival rates were 90% (95% confidence interval [CI] 0.84-0.94) and 97% (95% CI 0.93-0.99), respectively. Five-year local relapse-free survival was 99% (95% CI 0.96-0.99). Acute National Cancer Institute/Common Toxicity Criteria grade 1 and 2 skin toxicity was observed in 70% and 5%, respectively. Among the patients with ≥ 2-year follow-up no toxicity higher than grade 2 on the Late Effects in Normal Tissues-Subjective, Objective, Management, and Analytic scale was observed. Review of the radiation therapy dose-volume histogram noted that ≥ 95% of the prescribed dose encompassed the lumpectomy target volume in >95% of plans. The median dose received by the heart D05 was 215 cGy, and median lung V20 was 7.6%. CONCLUSIONS: The prescribed accelerated schedule of whole-breast radiation therapy with concomitant boost can be administered, achieving acceptable dose distribution. With follow-up to date, the results are encouraging and suggest minimal side effects and excellent local control.

Automating the initial physics chart checking process.

The initial physics chart check, an essential quality assurance process, verifies that the physician intent is properly expressed in the treatment plan, the treatment plan is reasonable, and the Record and Verify (RV) system properly captures the plan parameters. In this work the process was automated by characterizing the initial physics chart check as a universal set of steps, compartmentalized into intra-plan and inter-plan reviews. The intra-plan review confirms the diagnosis-prescription-plan correlation, and verifies transfer accuracy of the signed treatment plan parameters into the RV system. The inter-plan review tabulates all RV parameters for similar cases, and highlights outliers. The tabulation of RV parameters for similar cases enables a summation of experience across staff members, and facilitates a comparison using the Statistical Process Control (SPC) formalism. A summary sheet, added to each reviewed chart, automatically documents deviations noted during the review process. Forty-five patient charts were analyzed using the software. The length of time for the entire initial chart-checking process was reduced from about an hour to a few minutes. The code developed in this work allows the user to consider the big picture, trusting the software to track details.

Observation of interfractional variations in lung tumor position using respiratory gated and ungated megavoltage cone-beam computed tomography.

PURPOSE: To evaluate the use of megavoltage cone-beam computed tomography (MV CBCT) to measure interfractional variation in lung tumor position. METHODS AND MATERIALS: Eight non-small-cell lung cancer patients participated in the study, 4 with respiratory gating and 4 without. All patients underwent MV CBCT scanning at weekly intervals. Contoured planning CT and MV CBCT images were spatially registered based on vertebral anatomy, and displacements of the tumor centroid determined. Setup error was assessed by comparing weekly portal orthogonal radiographs with digitally reconstructed radiographs generated from planning CT images. Hypothesis testing was performed to test the statistical significance of the volume difference, centroid displacement, and setup uncertainty. RESULTS: The vertebral bodies and soft tissue portions of tumor within lung were visible on the MV CBCT scans. Statistically significant systematic volume decrease over the course of treatment was observed for 1 patient. The average centroid displacement between simulation CT and MV CBCT scans were 2.5 mm, -2.0 mm, and -1.5 mm with standard deviations of 2.7 mm, 2.7 mm, and 2.6 mm in the right-left, anterior-posterior and superior-inferior directions. The mean setup errors were smaller than the centroid shifts, while the standard deviations were comparable. In most cases, the gross tumor volume (GTV) defined on the MV CBCT was located on average at least 5 mm inside a 10 mm expansion of the GTV defined on the planning CT scan. CONCLUSIONS: The MV CBCT technique can be used to image lung tumors and may prove valuable for image-guided radiotherapy. Our conclusions must be verified in view of the small patient number.

Low-dose megavoltage cone-beam computed tomography for lung tumors using a high-efficiency image receptor.

We report on the capabilities of a low-dose megavoltage cone-beam computed tomography (MV CBCT) system. The high-efficiency image receptor consists of a photodiode array coupled to a scintillator composed of individual CsI crystals. The CBCT system uses the 6 MV beam from a linear accelerator. A synchronization circuit allows us to limit the exposure to one beam pulse [0.028 monitor units (MU)] per projection image. 150-500 images (4.2-13.9 MU total) are collected during a one-minute scan and reconstructed using a filtered backprojection algorithm. Anthropomorphic and contrast phantoms are imaged and the contrast-to-noise ratio of the reconstruction is studied as a function of the number of projections and the error in the projection angles. The detector dose response is linear (R2 value 0.9989). A 2% electron density difference is discernible using 460 projection images and a total exposure of 13 MU (corresponding to a maximum absorbed dose of about 12 cGy in a patient). We present first patient images acquired with this system. Tumors in lung are clearly visible and skeletal anatomy is observed in sufficient detail to allow reproducible registration with the planning kV CT images. The MV CBCT system is shown to be capable of obtaining good quality three-dimensional reconstructions at relatively low dose and to be clinically usable for improving the accuracy of radiotherapy patient positioning.

Integrating respiratory gating into a megavoltage cone-beam CT system.

We have previously described a low-dose megavoltage cone beam computed tomography (MV CBCT) system capable of producing projection image using one beam pulse. In this study, we report on its integration with respiratory gating for gated radiotherapy. The respiratory gating system tracks a reflective marker on the patient's abdomen midway between the xiphoid and umbilicus, and disables radiation delivery when the marker position is outside predefined thresholds. We investigate two strategies for acquiring gated scans. In the continuous rotation-gated acquisition, the linear accelerator (LINAC) is set to the fixed x-ray mode and the gantry makes a 5 min, 360 degree continuous rotation, during which the gating system turns the radiation beam on and off, resulting in projection images with an uneven distribution of projection angles (e.g., in 70 arcs each covering 2 degrees). In the gated rotation-continuous acquisition, the LINAC is set to the dynamic arc mode, which suspends the gantry rotation when the gating system inhibits the beam, leading to a slightly longer (6-7 min) scan time, but yielding projection images with more evenly distributed projection angles (e.g., approximately 0.8 degrees between two consecutive projection angles). We have tested both data acquisition schemes on stationary (a contrast detail and a thoracic) phantoms and protocol lung patients. For stationary phantoms, a separate motion phantom not visible in the images is used to trigger the RPM system. Frame rate is adjusted so that approximately 450 images (13 MU) are acquired for each scan and three-dimensional tomographic images reconstructed using a Feldkamp filtered backprojection algorithm. The gated rotation-continuous acquisition yield reconstructions free of breathing artifacts. The tumor in parenchymal lung and normal tissues are easily discernible and the boundary between the diaphragm and the lung sharply defined. Contrast-to-noise ratio (CNR) is not degraded relative to nongated scans of stationary phantoms. The continuous rotation-gated acquisition scan also yields tomographic images with discernible anatomic features; however, streak artifacts are observed and CNR is reduced by approximately a factor of 4. In conclusion, we have successfully developed a gated MV CBCT system to verify the patient positioning for gated radiotherapy.

Weighted expectation maximization reconstruction algorithms with application to gated megavoltage tomography.

We propose and investigate weighted expectation maximization (EM) algorithms for image reconstruction in x-ray tomography. The development of the algorithms is motivated by the respiratory-gated megavoltage tomography problem, in which the acquired asymmetric cone-beam projections are limited in number and unevenly sampled over view angle. In these cases, images reconstructed by use of the conventional EM algorithm can contain ring- and streak-like artefacts that are attributable to a combination of data inconsistencies and truncation of the projection data. By use of computer-simulated and clinical gated fan-beam megavoltage projection data, we demonstrate that the proposed weighted EM algorithms effectively mitigate such image artefacts.