2237 - Evaluation of Biology-Guided Radiotherapy (BgRT) in Motion Phantom with Real Patient Breathing Patterns

H. Chen¹, D. Han¹, E. Draeger¹, W. Zhong¹, M. Lee¹, F. Guan¹, D. F. Hicks¹, H. S. M. Park¹, K. L. Johung¹, M. R. Young¹, G. Bal², D. J. Carlson¹, and Z. Chen¹; ¹Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT, ²RefleXion Medical, Inc., Hayward, CA

Purpose/Objective(s): Tumor motion management presents challenges due to the inherent inter- and intra-patient variation in breathing patterns. The aim of this phantom study was to assess the quality assurance (QA) passing rate of biology-guided radiotherapy (BgRT) in a motion phantom employing real patient breathing patterns. Materials/

Methods: A treatment plan was generated on a patient-specific quality assurance phantom, featuring a spherical target (2.2 cm) and a C-shaped OAR (3 cm). A biological tracking zone (BTZ) was delineated with 2 cm margin of target volume in both superior and inferior directions. A dose of 10 Gy was delivered for each fraction, with a conformity index of 1.06 and homogeneity index of 1.25. FDG was injected to achieve a desired activity concentration (AC) of 5 kBq/ml as the background, with a target-to-background AC ratio of 20:1. A real patient breathing waveform (PBW), derived from CT scan, was adapted to generate eight breathing patterns characterized by varying maximum amplitudes (1.5 cm, 2 cm, 2.5cm, and 3 cm) and breathing periods (3 s and 4 s) in the IEC-Y direction, thereby simulating diverse motion scenarios during the treatment session. Dosimetry validation was measured using a patient-specific quality assurance, with gamma passing criteria of 3%/3 mm (10% global dose threshold) and compared against commissioning data obtained from standard cos4 wave studies (amplitude of 1.5 cm and breathing period of 4 s).

Results: All patient-specific quality assurance phantom treatment sessions were delivered successfully. For a breathing period of 4 s, gamma passing rates showed a reduction from 99.0% (cos4 wave, amplitude of 1.5 cm) to 96.5% (PBW, amplitude of 1.5 cm). Corresponding gamma passing rates for amplitudes of 2 cm, 2.5 cm, and 3 cm were 95.5%, 91.3%, and 82.4%, respectively. With a breathing period of 3 s, only the session with 1.5 cm amplitude achieved a gamma passing rate of 92.6%, while all other QA failed when the amplitude exceeded 2 cm.

Conclusion: This phantom study indicated that the dosimetric accuracy of BgRT is sensitive to motion parameters like motion range and breathing period time. Further work will explore additional QA matrix to assess target coverage and investigate additional quantitative aspects of human respiratory waveforms on BgRT delivery accuracy. Abstract 2237 – Table 1

Gamma passing =90% (3%/3mm)		Amplitude (cm)
		1.5	2	2.5	3
Breathing period (second)	3	Yes	No	No	No
	4	Yes	Yes	Yes	No