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J. Poder
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P2.14 - Radiotherapy (ID 715)
- Event: WCLC 2017
- Type: Poster Session with Presenters Present
- Track: Radiotherapy
- Presentations: 1
- Moderators:
- Coordinates: 10/17/2017, 09:30 - 16:00, Exhibit Hall (Hall B + C)
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P2.14-010 - The Time-Weighted Mid-Ventilation Technique: Reducing Planning Target Volumes For Patients Undergoing Lung Stereotactic Body Radiotherapy. (ID 9165)
09:30 - 09:30 | Author(s): J. Poder
- Abstract
Background:
Stereotactic Body Radio Therapy (SBRT) is a curative treatment option for patients diagnosed with primary lung cancer, who are deemed unsuitable for surgical resection. Currently, the most commonly used contouring method utilises 4D-CT delineated Internal Target Volumes (ITVs). This takes into account the tumour positions throughout all phases of the respiratory cycle but can result in unnecessarily large Planning Target Volumes (PTVs). The time-weighted mid-ventilation (TWMV) method is an alternative contouring method in which the gross tumour volume (GTV) is contoured on a single 3D-CT structure from the 4D dataset at the phase closest to its time-weighted average position. We hypothesise that the TWMV method will result in significantly smaller PTV and treated lung volumes when compared with the ITV method
Method:
5 consecutive lung SBRT patients who participated in a Phase 2 Clinical Trial were contoured with the ITV method using Velocity Advanced Imaging software (v.3.2.0). The PTVs and irradiated lung volumes were recorded. The GTVs were then re-contoured both manually on each phase of the 4D-CT and automatically using deformable image registration (DIR). The time-weighted average tumour position was determined and PTV volumes generated from the phase closest to this position using patient-specific margins described by Wolthaus et al. Finally, PTVs and treated lung volumes were recorded and compared with those from the ITV plans.
Result:
There was close agreement in both manual and automatic contouring methodologies for the time-weighted average position, with a three-dimensional vector error between the GTV centroids of 1.6mm ± 0.8 mm (1 SD). The manual contouring methods resulted in the same phase from the 4DCT being used for the mid-ventilation approach for all 5 patients. Using the mid-ventilation approach, the PTV volumes decreased by an average of 24.5% (range 19.8% - 33.7%), corresponding to an average decrease in irradiated healthy lung of 17.1cc ± 6.5cc. The decrease in PTV volume was greater for patients with a larger cranio-caudal tumour motion, with a linear relationship found between the two (R[2] = 0.995).
Conclusion:
For patients undergoing lung SBRT, contouring using the TWMV method resulted in a significant decrease in both PTVs and irradiated lung volumes compared with the ITV method. DIR for implementation of the mid-ventilation technique was feasible and reproducible. Application of this technique may improve the therapeutic ratio, and enable dose escalation for treatment of patients with unfavourable lung function to reduce lung toxicities.
