Dose-guided radiation therapy with megavoltage cone-beam CT

UCSF Comprehensive Cancer Center, Department of Radiation Oncology, University of California San Francisco, 1600 Divisadero Street, Suite H1031, San Francisco, CA 94143, USA.
The British journal of radiology (Impact Factor: 2.03). 10/2006; 79 Spec No 1(special_issue_1):S87-98. DOI: 10.1259/bjr/60612178
Source: PubMed


Recent advances in fractionated external beam radiation therapy have increased our ability to deliver radiation doses that conform more tightly to the tumour volume. The steeper dose gradients delivered in these treatments make it increasingly important to set precisely the positions of the patient and the internal organs. For this reason, considerable research now focuses on methods using three-dimensional images of the patient on the treatment table to adapt either the patient position or the treatment plan, to account for variable organ locations. In this article, we briefly review the different adaptive methods being explored and discuss a proposed dose-guided radiation therapy strategy that adapts the treatment for future fractions to compensate for dosimetric errors from past fractions. The main component of this strategy is a procedure to reconstruct the dose delivered to the patient based on treatment-time portal images and pre-treatment megavoltage cone-beam computed tomography (MV CBCT) images of the patient. We describe the work to date performed to develop our dose reconstruction procedure, including the implementation of a MV CBCT system for clinical use, experiments performed to calibrate MV CBCT for electron density and to use the calibrated MV CBCT for dose calculations, and the dosimetric calibration of the portal imager. We also present an example of a reconstructed patient dose using a preliminary reconstruction program and discuss the technical challenges that remain to full implementation of dose reconstruction and dose-guided therapy.

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    • "On the other hand, patients with oesophageal cancer often have problems maintaining their calorie intake and it is not preferable to change their dietary habits. With the implementation of image-guided radiotherapy (IGRT) and dose recalculation based on the kilovoltage cone-beam computed tomography (kV CBCT), we can calculate the delivered dose to the target volume during treatment and eventually adjust treatment if necessary [10] [11]. This study has two main objectives: (1) to investigate the necessity of adaptive radiotherapy for patients with GEJ tumours in case of unaccounted stomach changes e.g. "
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    • "This recent adaptive radiotherapy (ART) strategy appears however complex, in particular to decide when and how many times to replan during the treatment course [11] [12]. In this context, a key step is the capability to monitor the cumulated dose received by the deformed OARs, fraction after fraction, then to compare this dose with the planned dose, and finally to decide whether or not to replan within a dose-guided adaptive radiotherapy strategy [13] [14]. Deformable image registration (DIR) is a keystone of the dose accumulation process (Figure 1). "
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    • "This analysis typically includes the calculation of dose-volume histograms, which plot the percentage of a previously-segmented volume in the image data receiving a certain dose from the treatment beams. One could define dose-guided radiotherapy (Chen et al. (2006)) as an extension of adaptive radiotherapy where dosimetric considerations are the basis for decisions about whether future treatment fractions should be reoptimized, readjusted or re-planned to compensate for dosimetric errors. In this paper, we present an integrated constrained nonrigid registration and automatic segmentation algorithm designed to meet the demands of IGRT. "
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