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Reproducibility of target volumes generated using uncoached 4-dimensional CT scans for peripheral lung cancer.

van der Geld YG, Lagerwaard FJ, van Sörnsen de Koste JR, Cuijpers JP, Slotman BJ, Senan S - Radiat Oncol (2006)

Bottom Line: No significant volumetric differences were observed between the two PTVs (t-Test p = 0.60).The average displacement of the center of mass between corresponding PTVs was 1.4 +/- 1.0 mm, but differences in position were 2.0 mm or greater in 5 cases (19%).In nearly all patients with stage I lung cancer, the PTV derived from a single uncoached 4DCT achieves dosimetric coverage that is similar to that achieved using two such consecutive scans.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiation Oncology, VU University medical center, Amsterdam, The Netherlands. y.vandergeld@vumc.nl

ABSTRACT

Background: 4-dimensional CT (4DCT) scans are increasingly used to account for mobility during radiotherapy planning. As variations in respiratory patterns can alter observed motion, with consequent changes in the generated target volumes, we evaluated the reproducibility of 4D target volumes generated during repeat uncoached quiet respiration.

Methods: A retrospective analysis was performed on two successive scans (4DCT1 and 4DCT2) generated at the same scanning session for 26 patients with peripheral lung cancer treated with stereotactic radiotherapy (SRT). The volume and position of planning target volumes (PTV4DCT1 and PTV4DCT2) contoured on both scans were compared, and a dosimetric analysis performed. A SRT plan optimized for each PTV was sequentially applied to the other PTV, and coverage by the 80% isodose was evaluated. Color intensity projections (CIP) were used to evaluate regions of underdosage.

Results: No significant volumetric differences were observed between the two PTVs (t-Test p = 0.60). The average displacement of the center of mass between corresponding PTVs was 1.4 +/- 1.0 mm, but differences in position were 2.0 mm or greater in 5 cases (19%). Coverage of both PTVs by the 80% prescription isodose exceeded 90% for all but one patient. For the latter, the prescription isodose covered only 82.5% of PTV4DCT1. CIP analysis revealed that the region of underdosage was an end-inspiratory position occupied by the tumor for only 10-20% of the respiratory cycle.

Conclusion: In nearly all patients with stage I lung cancer, the PTV derived from a single uncoached 4DCT achieves dosimetric coverage that is similar to that achieved using two such consecutive scans.

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Related in: MedlinePlus

Left panel: Coronal reconstruction of the end-expiration phase bin of patient 13, showing both PTV4DCT1(violet contour) and PTV4DCT2 (pink contour). Colorwash displays of the 80%, 60% and 20% isodoses show the most caudal area of PTV4DCT1 to lie in the 20% isodose area. Right panel: A corresponding color intensity projection in the same patient with the color bar providing time-related positional information (white = 100% presence; blue = 90%; green = 50%; orange = 10%). This indicates that the most caudal PTV region represents a site occupied by the tumor for 10–20% of the respiratory cycle.
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Figure 2: Left panel: Coronal reconstruction of the end-expiration phase bin of patient 13, showing both PTV4DCT1(violet contour) and PTV4DCT2 (pink contour). Colorwash displays of the 80%, 60% and 20% isodoses show the most caudal area of PTV4DCT1 to lie in the 20% isodose area. Right panel: A corresponding color intensity projection in the same patient with the color bar providing time-related positional information (white = 100% presence; blue = 90%; green = 50%; orange = 10%). This indicates that the most caudal PTV region represents a site occupied by the tumor for 10–20% of the respiratory cycle.

Mentions: Treatment planning was performed using the 8–12 non-coplanar beam setup arrangement used for the clinical treatment of the patient. Beam portals were adjusted to both PTV4DCT1 and PTV4DCT2, respectively. When satisfactory target coverage was obtained for PTV4DCT1, the mean coverage of PTV4DCT2 by the resulting 80% prescription isodose was 97.8 ± 2.3%. Alternatively, the mean coverage of PTV4DCT1 was 97.0 ± 3.8% when planning was based on coverage of PTV4DCT2 (Table 2). The mean dose-volume histogram of PTV coverage in all 26 patients is shown in Figure 1. In all but one patient, the 80% prescription isodose covered >90% of the PTV4DCT (Figure 2). In this latter patient (no. 13), only 82.5% of PTV4DCT1 was covered when the plan was based upon PTV4DCT2. The shift between the center of mass of both 4DCT scans was 3.7 mm in this patient, with a 19% volume difference between both PTV's4DCT (Figure 2). The left panel of Figure 2 illustrates the inadequate coverage of the PTV4DCT1, and the encompassing 20% isodose suggests a major underdosage at the lower border of the PTV4DCT1. The CIP image that was generated from the 4DCT1 at the same level, however, illustrates that the inadequate PTV coverage was at an end-inspiratory GTV position, occupied by the tumor for only 10–20% of the respiratory cycle (Figure 2, right panel).


Reproducibility of target volumes generated using uncoached 4-dimensional CT scans for peripheral lung cancer.

van der Geld YG, Lagerwaard FJ, van Sörnsen de Koste JR, Cuijpers JP, Slotman BJ, Senan S - Radiat Oncol (2006)

Left panel: Coronal reconstruction of the end-expiration phase bin of patient 13, showing both PTV4DCT1(violet contour) and PTV4DCT2 (pink contour). Colorwash displays of the 80%, 60% and 20% isodoses show the most caudal area of PTV4DCT1 to lie in the 20% isodose area. Right panel: A corresponding color intensity projection in the same patient with the color bar providing time-related positional information (white = 100% presence; blue = 90%; green = 50%; orange = 10%). This indicates that the most caudal PTV region represents a site occupied by the tumor for 10–20% of the respiratory cycle.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1636642&req=5

Figure 2: Left panel: Coronal reconstruction of the end-expiration phase bin of patient 13, showing both PTV4DCT1(violet contour) and PTV4DCT2 (pink contour). Colorwash displays of the 80%, 60% and 20% isodoses show the most caudal area of PTV4DCT1 to lie in the 20% isodose area. Right panel: A corresponding color intensity projection in the same patient with the color bar providing time-related positional information (white = 100% presence; blue = 90%; green = 50%; orange = 10%). This indicates that the most caudal PTV region represents a site occupied by the tumor for 10–20% of the respiratory cycle.
Mentions: Treatment planning was performed using the 8–12 non-coplanar beam setup arrangement used for the clinical treatment of the patient. Beam portals were adjusted to both PTV4DCT1 and PTV4DCT2, respectively. When satisfactory target coverage was obtained for PTV4DCT1, the mean coverage of PTV4DCT2 by the resulting 80% prescription isodose was 97.8 ± 2.3%. Alternatively, the mean coverage of PTV4DCT1 was 97.0 ± 3.8% when planning was based on coverage of PTV4DCT2 (Table 2). The mean dose-volume histogram of PTV coverage in all 26 patients is shown in Figure 1. In all but one patient, the 80% prescription isodose covered >90% of the PTV4DCT (Figure 2). In this latter patient (no. 13), only 82.5% of PTV4DCT1 was covered when the plan was based upon PTV4DCT2. The shift between the center of mass of both 4DCT scans was 3.7 mm in this patient, with a 19% volume difference between both PTV's4DCT (Figure 2). The left panel of Figure 2 illustrates the inadequate coverage of the PTV4DCT1, and the encompassing 20% isodose suggests a major underdosage at the lower border of the PTV4DCT1. The CIP image that was generated from the 4DCT1 at the same level, however, illustrates that the inadequate PTV coverage was at an end-inspiratory GTV position, occupied by the tumor for only 10–20% of the respiratory cycle (Figure 2, right panel).

Bottom Line: No significant volumetric differences were observed between the two PTVs (t-Test p = 0.60).The average displacement of the center of mass between corresponding PTVs was 1.4 +/- 1.0 mm, but differences in position were 2.0 mm or greater in 5 cases (19%).In nearly all patients with stage I lung cancer, the PTV derived from a single uncoached 4DCT achieves dosimetric coverage that is similar to that achieved using two such consecutive scans.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiation Oncology, VU University medical center, Amsterdam, The Netherlands. y.vandergeld@vumc.nl

ABSTRACT

Background: 4-dimensional CT (4DCT) scans are increasingly used to account for mobility during radiotherapy planning. As variations in respiratory patterns can alter observed motion, with consequent changes in the generated target volumes, we evaluated the reproducibility of 4D target volumes generated during repeat uncoached quiet respiration.

Methods: A retrospective analysis was performed on two successive scans (4DCT1 and 4DCT2) generated at the same scanning session for 26 patients with peripheral lung cancer treated with stereotactic radiotherapy (SRT). The volume and position of planning target volumes (PTV4DCT1 and PTV4DCT2) contoured on both scans were compared, and a dosimetric analysis performed. A SRT plan optimized for each PTV was sequentially applied to the other PTV, and coverage by the 80% isodose was evaluated. Color intensity projections (CIP) were used to evaluate regions of underdosage.

Results: No significant volumetric differences were observed between the two PTVs (t-Test p = 0.60). The average displacement of the center of mass between corresponding PTVs was 1.4 +/- 1.0 mm, but differences in position were 2.0 mm or greater in 5 cases (19%). Coverage of both PTVs by the 80% prescription isodose exceeded 90% for all but one patient. For the latter, the prescription isodose covered only 82.5% of PTV4DCT1. CIP analysis revealed that the region of underdosage was an end-inspiratory position occupied by the tumor for only 10-20% of the respiratory cycle.

Conclusion: In nearly all patients with stage I lung cancer, the PTV derived from a single uncoached 4DCT achieves dosimetric coverage that is similar to that achieved using two such consecutive scans.

Show MeSH
Related in: MedlinePlus