Analysis of dose to patient, spouse/caretaker, and staff, from an implanted trackable radioactive fiducial for use in the radiation treatment of prostate cancer

Review of ultrasound image guidance in external beam radiotherapy part II: intra-fraction motion management and novel applications

Imaging has become an essential tool in modern radiotherapy (RT), being used to plan dose delivery prior to treatment and verify target position before and during treatment. Ultrasound (US) imaging is cost-effective in providing excellent contrast at high resolution for depicting soft tissue targets apart from those shielded by the lungs or cranium. As a result, it is increasingly used in RT setup verification for the measurement of inter-fraction motion, the subject of Part I of this review (Fontanarosa et al 2015 Phys. Med. Biol. 60 R77-114). The combination of rapid imaging and zero ionising radiation dose makes US highly suitable for estimating intra-fraction motion. The current paper (Part II of the review) covers this topic. The basic technology for US motion estimation, and its current clinical application to the prostate, is described here, along with recent developments in robust motion-estimation algorithms, and three dimensional (3D) imaging. Together, these are likely to drive an increase in the number of future clinical studies and the range of cancer sites in which US motion management is applied. Also reviewed are selections of existing and proposed novel applications of US imaging to RT. These are driven by exciting developments in structural, functional and molecular US imaging and analytical techniques such as backscatter tissue analysis, elastography, photoacoustography, contrast-specific imaging, dynamic contrast analysis, microvascular and super-resolution imaging, and targeted microbubbles. Such techniques show promise for predicting and measuring the outcome of RT, quantifying normal tissue toxicity, improving tumour definition and defining a biological target volume that describes radiation sensitive regions of the tumour. US offers easy, low cost and efficient integration of these techniques into the RT workflow. US contrast technology also has potential to be used actively to assist RT by manipulating the tumour cell environment and by improving the delivery of radiosensitising agents. Finally, US imaging offers various ways to measure dose in 3D. If technical problems can be overcome, these hold potential for wide-dissemination of cost-effective pre-treatment dose verification and in vivo dose monitoring methods. It is concluded that US imaging could eventually contribute to all aspects of the RT workflow.

Estimation of effective imaging dose for kilovoltage intratreatment monitoring of the prostate position during cancer radiotherapy

Kilovoltage intratreatment monitoring (KIM) is a novel real-time localization modality where the tumor position is continuously measured during intensity modulated radiation therapy (IMRT) or intensity modulated arc therapy (IMAT) by a kilovoltage (kV) x-ray imager. Adding kV imaging during therapy adds radiation dose. The additional effective dose is quantified for prostate radiotherapy and compared to dose from other localization modalities. The software PCXMC 2.0 was used to calculate the effective dose delivered to a phantom as a function of imager angle and field size for a Varian On-Board Imager. The average angular effective dose was calculated for a field size of 6 cm × 6 cm. The average angular effective dose was used in calculations for different treatment scenarios. Treatment scenarios considered were treatment type and fractionation. For all treatment scenarios, (i.e. conventionally fractionated and stereotactic body radiotherapy (SBRT), IMRT and IMAT), the total KIM dose at 1 Hz ranged from 2-10 mSv. This imaging dose is less than the Navotek radioactive implant dose (64 mSv) and a standard SBRT cone beam computed tomography pretreatment scan dose (22 mSv) over an entire treatment regime. KIM delivers an acceptably low effective dose for daily use as a real-time image-guidance method for prostate radiotherapy.

Kilovoltage intrafraction monitoring for prostate intensity modulated arc therapy: first clinical results

PURPOSE

Most linear accelerators purchased today are equipped with a gantry-mounted kilovoltage X-ray imager which is typically used for patient imaging prior to therapy. A novel application of the X-ray system is kilovoltage intrafraction monitoring (KIM), in which the 3-dimensional (3D) tumor position is determined during treatment. In this paper, we report on the first use of KIM in a prospective clinical study of prostate cancer patients undergoing intensity modulated arc therapy (IMAT).

METHODS AND MATERIALS

Ten prostate cancer patients with implanted fiducial markers undergoing conventionally fractionated IMAT (RapidArc) were enrolled in an ethics-approved study of KIM. KIM involves acquiring kV images as the gantry rotates around the patient during treatment. Post-treatment, markers in these images were segmented to obtain 2D positions. From the 2D positions, a maximum likelihood estimation of a probability density function was used to obtain 3D prostate trajectories. The trajectories were analyzed to determine the motion type and the percentage of time the prostate was displaced ≥ 3, 5, 7, and 10 mm. Independent verification of KIM positional accuracy was performed using kV/MV triangulation.

RESULTS

KIM was performed for 268 fractions. Various prostate trajectories were observed (ie, continuous target drift, transient excursion, stable target position, persistent excursion, high-frequency excursions, and erratic behavior). For all patients, 3D displacements of ≥ 3, 5, 7, and 10 mm were observed 5.6%, 2.2%, 0.7% and 0.4% of the time, respectively. The average systematic accuracy of KIM was measured at 0.46 mm.

CONCLUSIONS

KIM for prostate IMAT was successfully implemented clinically for the first time. Key advantages of this method are (1) submillimeter accuracy, (2) widespread applicability, and (3) a low barrier to clinical implementation. A disadvantage is that KIM delivers additional imaging dose to the patient.

Quality assurance for nonradiographic radiotherapy localization and positioning systems: report of Task Group 147

New technologies continue to be developed to improve the practice of radiation therapy. As several of these technologies have been implemented clinically, the Therapy Committee and the Quality Assurance and Outcomes Improvement Subcommittee of the American Association of Physicists in Medicine commissioned Task Group 147 to review the current nonradiographic technologies used for localization and tracking in radiotherapy. The specific charge of this task group was to make recommendations about the use of nonradiographic methods of localization, specifically; radiofrequency, infrared, laser, and video based patient localization and monitoring systems. The charge of this task group was to review the current use of these technologies and to write quality assurance guidelines for the use of these technologies in the clinical setting. Recommendations include testing of equipment for initial installation as well as ongoing quality assurance. As the equipment included in this task group continues to evolve, both in the type and sophistication of technology and in level of integration with treatment devices, some of the details of how one would conduct such testing will also continue to evolve. This task group, therefore, is focused on providing recommendations on the use of this equipment rather than on the equipment itself, and should be adaptable to each user's situation in helping develop a comprehensive quality assurance program.

Tracking accuracy of a real-time fiducial tracking system for patient positioning and monitoring in radiation therapy

PURPOSE

In radiation therapy there is a need to accurately know the location of the target in real time. A novel radioactive tracking technology has been developed to answer this need. The technology consists of a radioactive implanted fiducial marker designed to minimize migration and a linac mounted tracking device. This study measured the static and dynamic accuracy of the new tracking technology in a clinical radiation therapy environment.

METHODS AND MATERIALS

The tracking device was installed on the linac gantry. The radioactive marker was located in a tissue equivalent phantom. Marker location was measured simultaneously by the radioactive tracking system and by a Microscribe G2 coordinate measuring machine (certified spatial accuracy of 0.38 mm). Localization consistency throughout a volume and absolute accuracy in the Fixed coordinate system were measured at multiple gantry angles over volumes of at least 10 cm in diameter centered at isocenter. Dynamic accuracy was measured with the marker located inside a breathing phantom.

RESULTS

The mean consistency for the static source was 0.58 mm throughout the tested region at all measured gantry angles. The mean absolute position error in the Fixed coordinate system for all gantry angles was 0.97 mm. The mean real-time tracking error for the dynamic source within the breathing phantom was less than 1 mm.

CONCLUSIONS

This novel radioactive tracking technology has the potential to be useful in accurate target localization and real-time monitoring for radiation therapy.