Application of aSi-kVCBCT for Volume Assessment and Dose Estimation: An Offline Adaptive Study for Prostate Radiotherapy

Document Type: Research Articles

Authors

1 Department of Radiation Oncology, Yashoda Hospital, Hyderabad, India.

2 Research and Development Centre, Bharathiar University, Coimbatore, India.

3 Department of Radiation Oncology, All India Institute of Medical Sciences, New Delhi, India.

Abstract

Objective: The purpose of this study is to develop a method to estimate the dose using amorphous silicon detector
panel cone beam computed tomography (aSi-kVCBCT) for the OARs and targets in prostate radiotherapy and to compare
with the actual planned dose. Methods: The aSi-kVCBCT is used widely in radiotherapy to verify the patient position
before treatment. The advancement in aSi-kVCBCT combined with adaptive software allows us to verify the dose
distribution in daily acquired CBCT images. CBCT images from 10 patients undergoing radical prostate radiotherapy
were included in this study. Patients received total dose of 65Gy in 25 fractions using volumetric modulated arc therapy
(VMAT). aSi-kVCBCT scans were acquired before daily treatment and exported to smart adapt software for image
adaptation. The planning CT is adapted to daily aSi-kVCBCT images in terms of HU mapping. The primary VMAT
plans were copied on to the adapted planning CT images and dose was calculated using Anisotropic Analytic Algorithm
(AAA). The DVH is then used to evaluate the volume changes of organs at risk (OAR), the actual dose received by
OARs, CTV and PTV during a single fraction. Results: The normalized volume of the bladder and rectum ranged
from 0.70–1.66 and 0.70–1.16 respectively. The cumulative mean Sorensen–Dice coefficient values of bladder and
rectum were 0.89±0.04 and 0.79±0.06 respectively. The maximum dose differences for CTV and PTV were 2.5% and
-4.7% and minimum were 0.1% and 0.1% respectively. Conclusion: The adapted planning CT obtained from daily
imaging using aSi-kVCBCT and SmartAdapt® can be used as an effective tool to estimate the volume changes and
dose difference in prostate radiotherapy.

Keywords

Main Subjects