Liver SBRTPTV dose prescription strategies for SBRT of metastatic liver tumours
Section snippets
Automatic plan generation with Cycle
In this study, plans are automatically generated using an in-house developed algorithm, designated Cycle. The algorithm has been described in detail in [3], [12], [13]. Here a short summary is given. Cycle aims at generating a treatment plan with the prescribed PTV isocentre dose, while strictly obeying the imposed constraint levels on the PTV dose inhomogeneity, OARs and other normal tissues. Cycle starts plan generation with an empty plan. Sequentially new beam directions are selected and
PTV evaluation
Results for the isocentre dose, PTV mean dose, DPTV,99% and gEUDPTV(a) comparisons are shown in Fig. 1. For a ⩾ −20 the gEUD(a) for the 65% strategy plans is on average higher than for the 80% strategy, with a considerable variation between individual patients. For a = −20 and a = −10 the increase for the 65% strategy is on average 1.4% (range −6.3% to 12.3%) and 4.8% (range −4.1% to 15.8%), respectively. The increase is significant for a ⩾ −10 (P < 0.01), for a ⩽ −20 and for the DPTV,99% both strategies
Discussion
The 65% strategy results in plans that have a considerably higher peak dose in the central part of the PTV (isocentre dose) than for the 80% strategy, at the cost of a somewhat lower dose in voxels close to the boundaries of the PTV. The OAR dose is on average the same for both strategies and within the applied planning constraint levels. The conformality as measured with the CI is somewhat higher for the 65% strategy, and within the limit of 1.4 as proposed by Timmerman et al. [10].
The
Conclusion
PTV dose maximisation for SBRT of liver metastases with an inhomogeneous PTV dose prescription strategy (65%) compared to a more homogeneous dose prescription strategy (80%) leads to plans with a higher peak dose and mean dose in the PTV at the cost of small parts with a somewhat lower dose close to the edges of the PTV. The dose in the OARs is the same for both strategies. On average, PTV dose delivery is superior with the 65% strategy. However, apart from the isocentre dose, for each applied
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Cited by (20)
Kilovoltage intrafraction motion monitoring and target dose reconstruction for stereotactic volumetric modulated arc therapy of tumors in the liver
2014, Radiotherapy and OncologyCitation Excerpt :The large CTV D95 reductions were caused by CTV motion relative to the central high dose region of the PTV. The CTV dose would be less susceptible to intrafraction motion if a uniform PTV dose were prescribed rather than a PTV dose that gradually decreased from 95% to 67% outside the CTV [5–10]. However, in order to be isotoxic a uniform PTV dose would mean a lower prescribed dose to the hypoxia-prone tumor center than with the peaked PTV dose prescription.
Stereotactic ablative body radiation therapy with dynamic conformal multiple arc therapy for liver tumors: Optimal isodose line fitting to the planning target volume
2014, Practical Radiation OncologyCitation Excerpt :Dose heterogeneities within the target for SABR are acceptable for targets that do not involve functional normal tissue to improve dose fall off outside of the targeted volume and help to spare nearby at risk organs.11 In addition, the more dose heterogeneity increases in the PTV, the more mean PTV dose increases.12 In our previous study of lung tumors, we concluded that the optimal percentage isodose value that fit to the PTV surface was a 60% isodose line,6 which was similar to the results obtained by Widder et al.7 In this study, we investigated the optimal plans for liver tumors and found that a 70% isodose value was the most suitable for liver tumors as it increased the dose to the PTV while sparing surrounding normal liver tissue.
Dosimetric impact of image-guided radiotherapy in liver stereotactic radiotherapy
2013, Journal of Medical Imaging and Radiation SciencesCitation Excerpt :IGRT can correct for these baseline shifts in the liver. The geometric impact of IGRT to reduce random and systematic uncertainties and planning target volume (PTV) margins has been previously described [9, 11–14], and it is expected that such uncertainties would have increased dosimetric impact in SBRT compared to standard fractionated radiotherapy [2]. In the absence of volumetric IGRT with or without intravenous contrast, the diaphragm [15–17] or inserted fiducials may be used as a surrogate for the liver tumor as they are easily visible on MV and kV orthogonal imaging.
Hypofraction radiotherapy of liver tumor using cone beam computed tomography guidance combined with active breath control by long breath-holding
2012, Radiotherapy and OncologyCitation Excerpt :Four hypofractional prescriptions were used: 6 Gy × 7 (n = 8), 10 Gy × 4 (n = 7), 5 Gy × 9 (n = 6), 4 Gy × 10 (n = 3). The dose was prescribed to the 80% isodose line encompassing the PTV with 6 MV photons [29]. Conformality was achieved by a minimum of five static beams.
Stereotactic radiation therapy and selective internal radiation therapy for hepatocellular carcinoma
2011, Cancer/RadiotherapieCitation Excerpt :Rotational techniques have also been described [30]. The dose is prescribed to the periphery of the PTV [31,32]. A lower isodose can be used to cover the microscopic extension, as mentioned.
Stereotactic Body Radiation Therapy for Liver Tumors: Impact of Daily Setup Corrections and Day-to-Day Anatomic Variations on Dose in Target and Organs at Risk
2009, International Journal of Radiation Oncology Biology PhysicsCitation Excerpt :Observed differences in target doses between a corrected setup and planning were then attributed to anatomic differences in the healthy tissues surrounding the target (radiologic path length differences) and to (small) uncertainties in the applied procedures. Target dose distributions were evaluated using TV coverages (percentage of the TV within the 12.5-Gy isodose volume) and calculated generalized equivalent uniform dose values (gEUD) with volume parameters a = −5 and a = −10 (16–19). Because of the high similarity of conclusions to be drawn from the a = −5 and a = −10 analyses, results are only shown for a = −5.