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- Roland, Teboh, et al.
(författare)
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Tradeoffs for Assuming Rigid Target Motion in Mlc-Based Real Time Target Tracking Radiotherapy : A Dosimetric and Radiobiological Analysis
- 2010
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Ingår i: Technology in Cancer Research & Treatment. - : SAGE Publications. - 1533-0346 .- 1533-0338. ; 9:2, s. 199-210
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Tidskriftsartikel (refereegranskat)abstract
- We report on our assessment of two types of real time target tracking modalities for lung cancer radiotherapy namely (1) single phase propagation (SPP) where motion compensation assumes a rigid target and (2) multi-phase propagation (MPP) where motion compensation considers a deformable target. In a retrospective study involving 4DCT volumes from six (n=6) previously treated lung cancer patients, four-dimensional treatment plans representative of the delivery scenarios were generated per modality and the corresponding dose distributions were derived. The modalities were then evaluated (a) Dosimetrically for target coverage adequacy and normal tissue sparing by computing the mean GTV dose, relative conformity gradient index (CGI), mean lung dose (MLD) and lung V-20; (b) Radiobiologically by calculating the biological effective uniform dose ((sic)) for the target and organs at risk (OAR) and the complication free tumor control probability (P+). As a reference for the comparative study, we included a 40 Static modality, which was a conventional approach to account for organ motion and involved the use of individualized motion margins. With reference to the 4D Static modality, the average percent decrease in lung V-20 and MLD were respectively (13.1 +/- 6.9) % and (11.4 +/- 5.6) % for the MPP modality, whereas for the SPP modality they were (9.4 +/- 6.2) % and (7.2 +/- 4.7) %. On the other hand, the CGI was observed to improve by 15.3 +/- 13.2 and 9.6 +/- 10.0 points for the MPP and SPP modalities, respectively while the mean GTV dose agreed to better than 3% difference across all the modalities. A similar trend was observed in the radiobiological analysis where the P+ improved on average by (6.7 +/- 4.9) % and (4.1 +/- 3.6) % for the MPP and SPP modalities, respectively while the (sic) computed for the OAR decreased on average by (6.2 +/- 3.6) % and (3.8 +/- 3.5) % for the MPP and SPP tracking modalities, respectively. The (sic) calculated for the GTV for all the modalities was in agreement to better than 2% difference. In general, respiratory motion induces target displacement and deformation and therefore the complex MPP real time target tracking modality is the preferred. On the other hand, the SPP approach affords simplicity in implementation at the expense of failing to account for target deformation. Radiobiological and dosimetric analyses enabled us to investigate the consequences of failing to compensate for deformation and assess the impact if any on the clinical outcome. While it is not possible to draw any general conclusions on a small patient cohort, our study suggests that the two tracking modalities can lead to comparable clinical outcomes and as expected are advantageous when compared with the static conventional modality.
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| 2. |
- Su, F-C, et al.
(författare)
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Assessing four-dimensional radiotherapy planning and respiratory motion-induced dose difference based on biologically effective uniform dose.
- 2009
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Ingår i: Technology in Cancer Research & Treatment. - : SAGE Publications. - 1533-0346 .- 1533-0338. ; 8:3, s. 187-200
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Tidskriftsartikel (refereegranskat)abstract
- Four-dimensional (4D) radiotherapy is considered as a feasible and ideal solution to accommodate intra-fractional respiratory motion during conformal radiation therapy. With explicit inclusion of the temporal changes in anatomy during the imaging, planning, and delivery of radiotherapy, 4D treatment planning in principle provides better dose conformity. However, the clinical benefits of developing 4D treatment plans in terms of tumor control rate and normal tissue complication probability as compared to other treatment plans based on CT images of a fixed respiratory phase remains mostly unproven. The aim of our study is to comprehensively evaluate 4D treatment planning for nine lung tumor cases with both physical and biological measures using biologically effective uniform dose (D =) together with complication-free tumor control probability, P+. Based on the examined lung cancer patients and PTV margin applied, we found similar but not identical curves of DVH, and slightly different mean doses in tumor (up to 1.5%) and normal tissue in all cases when comparing 4D, P0%, and P50% plans. When it comes to biological evaluations, we did not observe definitively PTV size dependence in P+ among these nine lung cancer patients with various sizes of PTV. Moreover, it is not necessary that 4D plans would have better target coverage or higher P+ as compared to a fixed phase IMRT plan. However, on the contrary to significant deviations in P+ (up to 14.7%) observed if delivering the IMRT plan made at end-inhalation incorrectly at end-exhalation phase, we estimated the overall P+, PB, and PI for 4D composite plans that have accounted for intra-fractional respiratory motion.
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