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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

Respiratory waveforms during image acquisition for both 4DCT scans at the level of tumor in patient 13. Images were reconstructed from acquisitions at two consecutive couch positions (table increments of 2 cm) as evidenced by the discontinuous waveforms. The RPM amplitude at the end-expiration tumor position was similar in both 4DCT scans (A), but a larger difference in respiratory amplitude was seen at the end-inspiratory tumor position (B).
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Figure 3: Respiratory waveforms during image acquisition for both 4DCT scans at the level of tumor in patient 13. Images were reconstructed from acquisitions at two consecutive couch positions (table increments of 2 cm) as evidenced by the discontinuous waveforms. The RPM amplitude at the end-expiration tumor position was similar in both 4DCT scans (A), but a larger difference in respiratory amplitude was seen at the end-inspiratory tumor position (B).

Mentions: In view of concerns about the reproducibility of target volumes derived from uncoached 4DCT scans that were post-processed using the RPM approach, PTV determination in our patients who underwent 3–5 fractions of non-gated curative SRT for lung cancer was based upon data from 2 successive planning 4DCT scans. This analysis of the repeat 4DCT scans in 26 patients revealed that volumetric and spatial differences in PTVs in excess of 10% and 2 mm, respectively, were observed in a fifth of patients. Despite the use of highly conformal stereotactic treatment planning using multiple treatment beams, potential variations in the breathing cycle between CT scanning sessions translated into substantial dosimetric differences in only a single patient. The discrepancy in target volumes for this particular patient may be explained by the 4DCT scanning technique used. We perform axial (cine) scans with table increments of 2 cm, and Figure 3 shows the reconstructed respiratory waveforms during image acquisition at the level of tumor in both 4DCT scans. For this small and mobile tumor, the 4DCT image reconstruction was derived from images that were acquired at two consecutive couch positions as evidenced by the discontinuous waveforms. Although the amplitude at the end-expiration tumor position (most cranial) was similar in both 4DCT scans (A), a larger difference in amplitude was seen during imaging at the end-inspiration tumor position (most caudal), which explains the discrepancy in the caudal border of both PTVs.


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)

Respiratory waveforms during image acquisition for both 4DCT scans at the level of tumor in patient 13. Images were reconstructed from acquisitions at two consecutive couch positions (table increments of 2 cm) as evidenced by the discontinuous waveforms. The RPM amplitude at the end-expiration tumor position was similar in both 4DCT scans (A), but a larger difference in respiratory amplitude was seen at the end-inspiratory tumor position (B).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Respiratory waveforms during image acquisition for both 4DCT scans at the level of tumor in patient 13. Images were reconstructed from acquisitions at two consecutive couch positions (table increments of 2 cm) as evidenced by the discontinuous waveforms. The RPM amplitude at the end-expiration tumor position was similar in both 4DCT scans (A), but a larger difference in respiratory amplitude was seen at the end-inspiratory tumor position (B).
Mentions: In view of concerns about the reproducibility of target volumes derived from uncoached 4DCT scans that were post-processed using the RPM approach, PTV determination in our patients who underwent 3–5 fractions of non-gated curative SRT for lung cancer was based upon data from 2 successive planning 4DCT scans. This analysis of the repeat 4DCT scans in 26 patients revealed that volumetric and spatial differences in PTVs in excess of 10% and 2 mm, respectively, were observed in a fifth of patients. Despite the use of highly conformal stereotactic treatment planning using multiple treatment beams, potential variations in the breathing cycle between CT scanning sessions translated into substantial dosimetric differences in only a single patient. The discrepancy in target volumes for this particular patient may be explained by the 4DCT scanning technique used. We perform axial (cine) scans with table increments of 2 cm, and Figure 3 shows the reconstructed respiratory waveforms during image acquisition at the level of tumor in both 4DCT scans. For this small and mobile tumor, the 4DCT image reconstruction was derived from images that were acquired at two consecutive couch positions as evidenced by the discontinuous waveforms. Although the amplitude at the end-expiration tumor position (most cranial) was similar in both 4DCT scans (A), a larger difference in amplitude was seen during imaging at the end-inspiration tumor position (most caudal), which explains the discrepancy in the caudal border of both PTVs.

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