Encrypted login | home

Program Information

A Dosimetric Investigationof Prostate IGRT Based On CT-On-Rails

G Shan

G Shan1*, L Chen2 , W Hu3 , C Ma2 , (1) Zhejiang Cancer Hospital, Hangzhou, Zhejiang, (2) Fox Chase Cancer Center, Philadelphia, PA, (3) Taizhou Central Hospital, Taizhou, Zhejiang


SU-I-GPD-J-69 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Image-guided radiation therapy (IGRT) has become routine treatment for prostate cancer. The aim of this work was to investigate the organ variation and dose distribution for prostate IGRT based on the in-room CT technique.

Methods: A Siemens CT-on-rails system was used for image-guided target localization for intensity-modulated radiation therapy (IMRT) of prostate cancer. CT-on-rails scans were performed before and after the IMRT treatment once a week under local IRB approval. A total of 15 original simulation CT scans and 98 post-treatment CT scans were contoured by the same oncologist to delineate the target, bladder and rectum. The volumes of bladder and rectum were measured in different fractions. IMRT plans were generated on the simulation CT. The same MUs, leaf sequences were used to compute the dose distributions in post-treatment CTs. These dose distributions indicated what the patients actually received by the IGRT procedure.

Results: The results show significant organ variations in some patients, which resulted in compromised dose coverage of the prostate target using the standard IGRT procedure based on anatomy matching (i.e., aligning patient anatomy with organ contours from the simulation CT). The volume of bladder and rectum varied by more than 50% in different fractions. About 7.1% of the treatment fractions exhibited poor target coverage (Dmin<65Gy vs. 76Gy prescription dose) while 27.6% and 26.5% of the treatment fractions violated our rectal criteria of V65Gy<17% and V40gy<35%, respectively.

Conclusion: This investigation showed that the current IGRT procedure for prostate cancer is still not ideal if only anatomy matching is used for target localization (mainly due to organ deformation). The target coverage may be compromised for some patients. Both the doses received by the target and normal tissues should be re-evaluated in analyzing the clinical outcome data for prostate dose escalation/fractionation trials based on IGRT dose delivery.

Contact Email: