Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_9_3205 - Anatomically Corrected DVH Metrics Accounting for Intrafraction Motion of Esophagus in Dorsal Spine SBRT

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Anatomically Corrected DVH Metrics Accounting for Intrafraction Motion of Esophagus in Dorsal Spine SBRT
A. Karuppusamy1, V. Shankar1, C. Haritha2, A. Bhange1, V. N. Bhaskar1, S. Maurya1, P. Ganeshan1, B. ajai Kumar3, S. Mutha4, R. Purohit5, K. Chigurupalli5, H. Vyas5, and P. Deepanjali5; 1HCG Cancer Center, Mumbai, India, 2CR Reddy Cancer Center, Nellore, Nellore, India, 3HCG Cancer Center, Bengaluru, India, 4Inlaks & Budhrani Hospital, Pune, India, 5Geetanjali Cancer Center, Udaipur, India

Purpose/Objective(s): The oesophageal circumference varies markedly on sequential axial CT images, a reflection of the physiological motion due to respiration and swallowing which can lead to unanticipated increase in the volume of oesophagus receiving high doses. The predictive value of metrics “corrected” for this anatomic reality using accumulated doses deposited would be better than doses derived from “traditional” DVH-based metrics. Purpose of the study is to characterise the impact of relative motion of oesophagus on the radiation doses to the oesophagus in patients treated with single fraction dorsal spine SBRT.

Materials/Methods: Ten patients who underwent single fraction dorsal spine SBRT for Radio-resistant metastases from Thyroid, RCC and melanoma (n-2,6,2) were chosen for study. All patients underwent bodyfix immobilization & 4D-CT simulation. 2 conformal VMAT arcs were planned using unflat beams & Monte carlo optimisation. Prescription dose for all plans was 18 Gy to cover 90% of target volume using normal tissue and target constraints from RTOG-0631. Treatment was delivered on C-Arm linac using 6 DOF robotics & intra-fraction imaging. The Target volume and the normal structures including oesophagus were delineated in one of the 4D datasets and intensity based deformable image registration algorithm with limitless degree of freedom was used to sequentially deform the structures to nearest-neighbour phases among the 10 phases. A moving voxel dose from VMAT plan generated on the original bin is propagated through the 4D dose space using DIR and the fraction dose to that voxel on oesophagus is accumulated. Parameters analysed for each voxel on 4-D Datasets included (1) the Motion patterns of oesophagus - magnitude of the extreme displacements (median) in all planes and (2) reconstructed motion- perturbed Max dose and Threshold doses to oesophagus were analysed in 2 scenarios – Static and total accumulated.

Results: Median intrafraction right-left, Antero-posterior shifts of the oesophagus for below carina vertebral targets was 2.5 mm (range, 1-3 mm),2.7mm (range,2.2 – 3.3mm) and Above carina vertebral targets was 2.5 mm (range, 1-3 mm),2.7mm (range,2.2 – 3.3mm). For Below carinal vertebral targets,the median percentage increase in accumulated doses compared to static doses for esophageal Maximum dose, dose to 0.03 cm3, 1cm3 ,5 cm3 was 1.2%,1.8%, 3.4%, and 5%, respectively (p-0.03). No difference in static and accumulated doses were observed for above carinal vertebral targets. Two cases of significant late esophageal toxicity were observed for targets below carina.

Conclusion: It is safe to use the ITV of the esophagus for dorsal spine SBRT. Deformable dose accumulation reveals that the delivered maximum dose & threshold dose to the esophagus is typically higher than indicated on the static plan. Improved calculations of the delivered dose through deformable dose accumulation has the potential to improve the correlation between dose and tumor response and normal tissue complications.

Author Disclosure: A. Karuppusamy: None. V. Shankar: None. A. Bhange: None. V.N. Bhaskar: None. P. Ganeshan: None. B. ajai Kumar: Partner; Health care Global Enterprises, India. Partnership; Health Care Global Enterprises, India. CEO; Health Care Global Enterprise. S. Mutha: None. K. Chigurupalli: None. H. Vyas: None. P. Deepanjali: None.

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