Commissioning measurements for photon beam data on three TrueBeam linear accelerators, and comparison with Trilogy and Clinac 2100 linear accelerators.

This study presents the beam data measurement results from the commissioning of three TrueBeam linear accelerators. An additional evaluation of the measured beam data within the TrueBeam linear accelerators contrasted with two other linear accelerators from the same manufacturer (i.e., Clinac and Trilogy) was performed to identify and evaluate any differences in the beam characteristics between the machines and to evaluate the possibility of beam matching for standard photon energies. We performed a comparison of commissioned photon beam data for two standard photon energies (6 MV and 15 MV) and one flattening filter-free ("FFF") photon energy (10 FFF) between three different TrueBeam linear accelerators. An analysis of the beam data was then performed to evaluate the reproducibility of the results and the possibility of "beam matching" between the TrueBeam linear accelerators. Additionally, the data from the TrueBeam linear accelerator was compared with comparable data obtained from one Clinac and one Trilogy linear accelerator models produced by the same manufacturer to evaluate the possibility of "beam matching" between the TrueBeam linear accelerators and the previous models. The energies evaluated between the linear accelerator models are the 6 MV for low energy and the 15 MV for high energy. PDD and output factor data showed less than 1% variation and profile data showed variations within 1% or 2 mm between the three TrueBeam linear accelerators. PDD and profile data between the TrueBeam, the Clinac, and Trilogy linear accelerators were almost identical (less than 1% variation). Small variations were observed in the shape of the profile for 15 MV at shallow depths (< 5 cm) probably due to the differences in the flattening filter design. A difference in the penumbra shape was observed between the TrueBeam and the other linear accelerators; the TrueBeam data resulted in a slightly greater penumbra width. The diagonal scans demonstrated significant differences in the profile shapes at a distance greater than 20 cm from the central axis, and this was more notable for the 15 MV energy. Output factor differences were found primarily at the ends of the field size spectrum, with observed differences of less than 2% as compared to the other linear accelerators. The TrueBeam's output factor varied less as a function of field size than the output factors for the previous models; this was especially true for the 6 MV. Photon beam data were found to be reproducible between different TrueBeam linear accelerators well within the accepted clinical tolerance of ± 2%. The results indicate reproducibility in the TrueBeam machine head construction and a potential for beam matching between these types of linear accelerators. Photon beam data (6 MV and 15 MV) from the Trilogy and Clinac 2100 showed several similarities and some small variations when compared to the same data measured on the TrueBeam linear accelerator. The differences found could affect small field data and also very large field sizes in beam matching considerations between the TrueBeam and previous linear accelerator models from the same manufacturer, but should be within the accepted clinical tolerance for standard field sizes and standard treatments.

Evaluation of an implantable MOSFET dosimeter designed for use with hypofractionated external beam treatments and its applications for breast and prostate treatments.

PURPOSE: An implantable metal-oxide semiconductor field effect transistors-based dosimeter has recently been developed for the in vivo monitoring of hypofractionated radiotherapy. This DVS-HFT dosimeter is designed for fraction sizes of 340-950 cGy and can also be used for bis in die fraction monitoring. The current work reports on the testing and evaluation of this dosimeter, including both its basic characteristics as well as its performance during simulated clinical treatment plans. METHODS: The authors tested the dose rate dependence of this dosimeter (300 MU/min versus 600 MU/min), the treatment time dependence (4 min per treatment versus up to 60 min per treatment), and the dose and energy dependence (6 and 18 MV irradiations of 700-900 cGy per fraction). Additionally, they irradiated the detectors in-phantom with breast and prostate hypofractionated treatments. RESULTS: The detectors showed no significant dose rate, treatment time, energy, or dose dependence. Furthermore, the detectors were found to perform within manufacturer tolerances for all hypofractionated treatments examined, accurately reporting the measured dose (average disagreement of - 0.65%). CONCLUSIONS: These dosimeters appear well suited for in vivo monitoring of hypofractionated radiotherapy doses, and thereby, have the potential to improve patient care.

The Dose Verification System (DVS) for cancer patients receiving radiation therapy.

The Dose Verification System (DVS) is the first implantable radiation dosimeter designed for in situ measurement of dose delivered to the tissue being irradiated. The success of radiation therapy is predicated on maximizing tumor cell death and minimizing normal tissue toxicity. Tumor control increases with the delivery of appropriate radiation doses to the target area. These doses have been determined from in vitro and animal studies, which generated specific dose-response data. However, there has not been a practical system available to ensure that the appropriate dose was being delivered in situ to monitor the daily patient dose during radiation therapy. Studies have shown that dose variations can occur. Recently completed pivotal clinical studies using the DVS found a greater than 7% (positive or negative) change in cumulative dose in seven out of 36 (19%) breast cancer patients; and six out of 29 (21%) and eight out of 19 (42%) patients during large-field and boost irradiation of the prostate. The device is an important step to enable physicians to expand the concept of individualization of therapy.

The observed variance between predicted and measured radiation dose in breast and prostate patients utilizing an in vivo dosimeter.

PURPOSE: Report the results of using a permanently implantable dosimeter in radiation therapy: determine specific adverse events, degree of migration, and acquire dose measurements during treatment to determine difference between expected and measured dose. METHODS AND MATERIALS: The Dose Verification System is a wireless, permanently implantable metal-oxide semiconductor field-effect transistor dosimeter using a bidirectional antenna for power and data transfer. The study cohort includes 36 breast (33 patients received two devices) and 29 prostate (21 patients received two devices) cancer patients. A total of 1,783 and 1,749 daily dose measurements were obtained on breast and prostate patients, respectively. The measurements were compared with the planned expected dose. Biweekly computed tomography scans were obtained to evaluate migration and the National Cancer Institute's Common Toxicity Criteria, version 3, was used to evaluate adverse events. RESULTS: Only Grade I/II adverse events of pain and bleeding were noted. There were only four instances of dosimeter migration of >5 mm from known factors. A deviation of > or =7% in cumulative dose was noted in 7 of 36 (19%) for breast cancer patients. In prostate cancer patients, a > or =7% deviation was noted in 6 of 29 (21%) and 8 of 19 (42%) during initial and boost irradiation, respectively. The two patterns of dose deviation were random and systematic. Some causes for these differences could involve organ movement, patient movement, or treatment plan considerations. CONCLUSIONS: The Dose Verification System was not associated with significant adverse events or migration. The dosimeter can measure dose in situ on a daily basis. The accuracy and utility of the dose verification system complements current image-guided radiation therapy and intensity-modulated radiation therapy techniques.

Technical evaluation of radiation dose delivered in prostate cancer patients as measured by an implantable MOSFET dosimeter.

PURPOSE: To perform a comparison of the daily measured dose at depth in tissue with the predicted dose values from treatment plans for 29 prostate cancer patients involved in a clinical trial. METHODS AND MATERIALS: Patients from three clinical sites were implanted with one or two dosimeters in or near the prostatic capsule. The implantable device, known as the DVS, is based on a metal-oxide-semiconductor field effect transistor (MOSFET) detector. A portable telemetric readout system couples to the dosimeter antenna (visible on kilovoltage, computed tomography, and ultrasonography) for data transfer. The predicted dose values were determined by the location of the MOSFET on the treatment planning computed tomography scan. Serial computed tomography images were taken every 2 weeks to evaluate any migration of the device. The clinical protocol did not permit alteration of the treatment parameters using the dosimeter readings. For some patients, one of several image-guided radiotherapy (RT) modalities was used for target localization. RESULTS: The evaluation of dose discrepancy showed that in many patients the standard deviation exceeded the previous values obtained for the dosimeter in a phantom. In some patients, the cumulative dose disagreed with the planned dose by > or =5%. The data presented suggest that an implantable dosimeter can help identify dose discrepancies (random or systematic) for patients treated with external beam RT and could be used as a daily treatment verification tool for image-guided RT and adaptive RT. CONCLUSION: The results of our study have shown that knowledge of the dose delivered per fraction can potentially prevent over- or under-dosage to the treatment area and increase the accuracy of RT. The implantable dosimeter could also be used as a localizer for image-guided RT.

Technical aspects and evaluation methodology for the application of two automated brain MRI tumor segmentation methods in radiation therapy planning.

The purpose of this study was to design the steps necessary to create a tumor volume outline from the results of two automated multispectral magnetic resonance imaging segmentation methods and integrate these contours into radiation therapy treatment planning. Algorithms were developed to create a closed, smooth contour that encompassed the tumor pixels resulting from two automated segmentation methods: k-nearest neighbors and knowledge guided. These included an automatic three-dimensional (3D) expansion of the results to compensate for their undersegmentation and match the extended contouring technique used in practice by radiation oncologists. Each resulting radiation treatment plan generated from the automated segmentation and from the outlining by two radiation oncologists for 11 brain tumor patients was compared against the volume and treatment plan from an expert radiation oncologist who served as the control. As part of this analysis, a quantitative and qualitative evaluation mechanism was developed to aid in this comparison. It was found that the expert physician reference volume was irradiated within the same level of conformity when using the plans generated from the contours of the segmentation methods. In addition, any uncertainty in the identification of the actual gross tumor volume by the segmentation methods, as identified by previous research into this area, had small effects when used to generate 3D radiation therapy treatment planning due to the averaging process in the generation of margins used in defining a planning target volume.