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  4. Study On Dose Calculation for Patient Plan Using CBCT Images

Study On Dose Calculation for Patient Plan Using CBCT Images

h gong1, B Liu2 , B Qu1 , J Liu3 , Z Chi4 , S Xu1,* , (1) PLA General Hospital, Beijing, BJ, (2) Beihang University, Beijing, BJ, (3) Tangshan People's Hospital, Tangshan, Heibei, (5) Fourth Hospital of Hebei Medical University, Shijiazhuang, Hebei

Presentations

(Monday, 7/30/2018) 9:30 AM - 10:00 AM

Room: Exhibit Hall | Forum 1

Purpose: This study is to investigate the accuracy of two different methods for CBCT dose calculation, so as to explore the possibility of using CBCT images to implement the dose calculation for patients under clinical conditions.

Methods: The in-house software tool was used for deformable registration between CBCT and kVCT images, and mapping, etc. Then the plans of mapping CBCT were imported into the original planning system for dose re-calculation. The difference of dose distribution between kVCT and CBCT images using two methods for dose reâ‚‹calculation were analyzed in different sites of patients. The first method of dose calculation converts HU values to electron density using the HUâ‚‹ED curve for CBCT images. The second method includes the modification of CBCT HU values using histogram matching method firstly, and convertion using the HU-ED curve of kVCT.

Results: For all 27 patients, the Dmean of target using the two methods of CBCT were higher than those of kVCT doses. For head-neck and pelvic patients, the deviations were less than 1% and the dose distribution of CBCT using method 2 was closer to that of kVCT. For lung cancer, the deviation of Dmean in target between kVCT and CBCT using method 1 were bigger (＜3%) than that of method 2 with significant difference (p＜0.05). The deviations of Dmean for OARs (except for oral cavity) between CBCT and kVCT were less than 2% in the head-neck and pelvic patients. But the dosimetric parameters of lung tissue were similar to those of the target for lung cancer with significant difference (p＜0.05).

Conclusion: This study compared the accuracy of dose calculation using CBCT images. It could provide some clinical guidance for the selection of CBCT dose calculation in adptive radiotherapy.

Funding Support, Disclosures, and Conflict of Interest: Chinese Natural Science Fund(No. 61601012) Natural Key R&D Program of China(No.2017YFC0112100)

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