Implementation of daily image-guided radiation therapy using an in-room CT scanner for prostate cancer isocentre localization

Online adaptive planning methods for intensity-modulated radiotherapy

Online adaptive radiation therapy aims at adapting a patient's treatment plan to their current anatomy to account for inter-fraction variations before daily treatment delivery. As this process needs to be accomplished while the patient is immobilized on the treatment couch, it requires time-efficient adaptive planning methods to generate a quality daily treatment plan rapidly. The conventional planning methods do not meet the time requirement of online adaptive radiation therapy because they often involve excessive human intervention, significantly prolonging the planning phase. This article reviews the planning strategies employed by current commercial online adaptive radiation therapy systems, research on online adaptive planning, and artificial intelligence's potential application to online adaptive planning.

Review of ultrasound image guidance in external beam radiotherapy: I. Treatment planning and inter-fraction motion management

In modern radiotherapy, verification of the treatment to ensure the target receives the prescribed dose and normal tissues are optimally spared has become essential. Several forms of image guidance are available for this purpose. The most commonly used forms of image guidance are based on kilovolt or megavolt x-ray imaging. Image guidance can also be performed with non-harmful ultrasound (US) waves. This increasingly used technique has the potential to offer both anatomical and functional information.This review presents an overview of the historical and current use of two-dimensional and three-dimensional US imaging for treatment verification in radiotherapy. The US technology and the implementation in the radiotherapy workflow are described. The use of US guidance in the treatment planning process is discussed. The role of US technology in inter-fraction motion monitoring and management is explained, and clinical studies of applications in areas such as the pelvis, abdomen and breast are reviewed. A companion review paper (O'Shea et al 2015 Phys. Med. Biol. submitted) will extensively discuss the use of US imaging for intra-fraction motion quantification and novel applications of US technology to RT.

Seminal vesicle interfraction displacement and margins in image guided radiotherapy for prostate cancer

Background

To analyze interfraction motion of seminal vesicles (SV), and its motion relative to rectal and bladder filling.

Methods and Materials

SV and prostate were contoured on 771 daily computed tomography “on rails” scans from 24 prostate cancer patients undergoing radiotherapy. Random and systematic errors for SV centroid displacement were measured relative to the prostate centroid. Margins required for complete geometric coverage of SV were determined using isotropic expansion of reference contours. SV motion relative to rectum and bladder was determined.

Results

Systematic error for the SV was 1.9 mm left-right (LR), 2.9 mm anterior-posterior (AP) and 3.6 mm superior-inferior (SI). Random error was 1.4 mm (LR), 2.7 mm (AP) and 2.1 mm (SI). 10 mm margins covered the entire left SV and right SV on at least 90% of fractions in 50% and 33% of patients and 15 mm margins covered 88% and 79% respectively. SV AP movement correlated with movement of the most posterior point of the bladder (mean R² = 0.46, SD = 0.24) and rectal area (mean R² = 0.38, SD = 0.21).

Conclusions

Considerable interfraction displacement of SV was observed in this cohort of patients. Bladder and rectal parameters correlated with SV movement.

Influence of acquisition parameters on MV-CBCT image quality

The production of high quality pretreatment images plays an increasing role in image‐guided radiotherapy (IGRT) and adaptive radiation therapy (ART). Megavoltage cone‐beam computed tomography (MV‐CBCT) is the simplest solution of all the commercially available volumetric imaging systems for localization. It also suffers the most from relatively poor contrast due to the energy range of the imaging photons. Several avenues can be investigated to improve MV‐CBCT image quality while maintaining an acceptable patient exposure: beam generation, detector technology, reconstruction parameters, and acquisition parameters. This article presents a study of the effects of the acquisition scan length and number of projections of a Siemens Artiste MV‐CBCT system on image quality within the range provided by the manufacturer. It also discusses other aspects not related to image quality one should consider when selecting an acquisition protocol. Noise and uniformity were measured on the image of a cylindrical water phantom. Spatial resolution was measured using the same phantom half filled with water to provide a sharp water/air interface to derive the modulation transfer function (MTF). Contrast‐to‐noise ratio (CNR) was measured on a pelvis‐shaped phantom with four inserts of different electron densities relative to water (1.043, 1.117, 1.513, and 0.459). Uniformity was independent of acquisition protocol. Noise decreased from 1.96% to 1.64% when the total number of projections was increased from 100 to 600 for a total exposure of 13.5 MU. The CNR showed a∓5% dependence on the number of projections and 10% dependence on the scan length. However, these variations were not statistically significant. The spatial resolution was unaffected by the arc length or the sampling rate. Acquisition parameters have little to no effect on the image quality of the MV‐CBCT system within the range of parameters available on the system. Considerations other than image quality, such as memory storage, acquisition speed, and individual projection image quality, speak in favor of the use of a coarse sampling rate on the short scan.

PACS numbers: 87.57.C‐; 87.57.nf

Australian radiation therapists rank technology-related research as most important to radiation therapy

Background and purpose: Research is increasingly important in radiation therapy, but radiation therapists (or therapy radiographers) (RTs) are relatively new to research and may have difficulty defining research topics. Our aim was to identify the group interests and focus research priorities of Australian RTs. Although not measured, an additional aim was to make RTs more aware of the relevance of RT research.

Materials and methods: An Australia-wide Delphi process was used, examining the problems related to patient care, working with colleagues, and radiotherapy in general, that RTs experienced in their daily work. In an initial study, 374 problems were identified. These were translated into 53 research areas which were prioritised in the second stage of the study. Agreement between groups was analysed using a hierarchical cluster procedure and post hoc Scheffe multiple comparisons.

Results: There were three groups of responders with varying degrees of research interest. There was agreed high importance (p > 0.01) for the technical aspects of radiation therapy, such as image guidance, intensity-modulated radiation therapy (IMRT) and patient positioning. There was significant disagreement (p < 0.001 to p = 0.023) between groups on the importance of patient care research.

Conclusions: The strong interest in technical research is consistent with the rapid influx of technology, particularly in imaging. The disagreement on patient-related research may be of concern. The list of potential research areas specific to radiation therapy will be useful for new RT researchers to consider.