Abstract
Purpose: Various factors cause geometric uncertainties during prostate radiotherapy, including interfractional and intrafractional patient motions, organ motion, and daily setup errors. This may lead to increased normal tissue complications when a high dose to the prostate is administered. More-accurate treatment delivery is possible with daily imaging and localization of the prostate. This study aims to measure the shift of the prostate by using kilovoltage (kV) cone beam computed tomography (CBCT) after position verification by kV orthogonal portal imaging (OPI). Methods: Position verification in 10 patients with prostate cancer was performed by using OPI followed by CBCT before treatment delivery in 25 sessions per patient. In each session, OPI was performed by using an on-board imaging (OBI) system and pelvic bone-to-pelvic bone matching was performed. After applying the noted shift by using OPI, CBCT was performed by using the OBI system and prostate-to-prostate matching was performed. The isocenter shifts along all three translational directions in both techniques were combined into a three-dimensional (3-D) iso-displacement vector (IDV). Results: The mean (SD) IDV (in centimeters) calculated during the 250 imaging sessions was 0.931 (0.598, median 0.825) for OPI and 0.515 (336, median 0.43) for CBCT, p- value was less than 0.0001 which shows extremely statistical significant difference. Conclusion: Even after bone-to-bone matching by using OPI, a significant shift in prostate was observed on CBCT. This study concludes that imaging with CBCT provides a more accurate prostate localization than the OPI technique. Hence, CBCT should be chosen as the preferred imaging technique.
Highlights
Prostate cancer is the second most common type of cancer and the fifth leading cause of cancer-related death in men worldwide.[1]
orthogonal portal imaging (OPI) and cone beam computed tomography (CBCT) were performed with the on-board imaging (OBI) system (Varian Medical Systems, Palo Alto, CA) consisting of a 125-kVp x-ray tube isocentrically mounted to the gantry of the Clinac
The results obtained by using CBCT cannot be compared with the results obtained by using OPI in this study or the results of other studies already published on imaging by using the OPI or CBCT technique for prostate cancer
Summary
Prostate cancer is the second most common type of cancer and the fifth leading cause of cancer-related death in men worldwide.[1] Prostate cancer can be managed by using surgery, chemotherapy, radiotherapy, and so on. Among these treatment options, radiotherapy is considered superior in terms of survival rate and side effects. Three-dimensional conformal radiotherapy (3-DCRT), intensity-modulated radiotherapy (IMRT), imaging-guided radiotherapy (IGRT), volumetric modulated arc therapy (VMAT) and intensity modulated proton therapy (IMPT) are various modern techniques by which prostate cancer can be treated.[2,3] All these modern radiotherapy techniques basically focus on lethal-dose delivery to the target volume and minimum dose delivery to the organs at risk (OAR).[4] In IMRT, propinquity between the prostate and the OAR such as the bladder and rectum often leads to highly
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