Room: Exhibit Hall | Forum 6
Purpose: We have previously demonstrated that high frequency percussive ventilation (HFPV) can significantly reduce thoracic motion; the aim of this follow up retrospective study is to investigate the potential dosimetric benefits due to gradient effects for HFPV during photon radiotherapy.
Methods: Five normal and HFPV chest wall breathing curves of volunteers that previously underwent HFPV were utilized to drive a thoracic motion phantom that held high resolution GafChromic EBT3 film. Simultaneously, a predetermined static MLC (multi leaf collimator) defined photon (6MV) field was chosen to irradiate each film with a dose of 300 cGy. All films were placed on the motion platform at 100 cm SSD with 2 cm buildup. The mean peak-to-peak amplitude of the normal and HFPV breathing curves were 19.20 mm (SD: 3.33) and 2.33 mm (SD: 0.82), respectively. We evaluated the dosimetric effects of normal and HFPV relative to static by measuring the Gamma Index, as defined by Low et al, with 3%/2mm and 10% threshold criteria. Furthermore, hot and cold spots, relative to static, for a set ROI (region of interest), were evaluated for each film.
Results: When compared to the static films, the mean Gamma Index passing rates for normal and HFPV breathing curves was 79.29% (SD: 4.65) and 99.72% (SD: 0.37), respectively. We observed hot spots that ranged between 17.14-20.00% for films irradiated with normal breathing curves and 5.71-8.57% for HFPV.
Conclusion: In this retrospective phantom study, our results suggest that high frequency percussive ventilation can significantly improve the gradient effects when utilized as a thoracic immobilization technique for photon radiotherapy.
Not Applicable / None Entered.