Use of Implanted Markers and Interportal Adjustment With Real-Time Tracking Radiotherapy System to Reduce Intrafraction Prostate Motion

Abstract

Purpose: Interportal adjustment was applied to patients with prostate cancer using three fiducial markers and two sets of fluoroscopy in a real-time tumor-tracking radiotherapy (RTRT) system. The incidence of table position adjustment required to keep intrafractional uncertainty within 2.0 mm was investigated in this study. Methods and Materials:The coordinates of the center of gravity of the three fiducial markers were measured at the start of every portal irradiation in intensity-modulated radiotherapy (IMRT) with seven ports. The table position was adjusted to the planned position if the discrepancy was larger than 2.0 mm in the anterior-posterior (AP), cranio-caudal (CC), or left-right (LR) directions. In total, we analyzed 4541 observations in 20 patients who received 70 Gy in 30 fractions (7.6 times a day in average). Results:The incidence of table position adjustment at 10 minutes from the initial set-up of each treatment was 14.2%, 12.3%, and 5.0% of the observations in the AP, CC, and LR directions, respectively. The accumulated incidence of the table position adjustment was significantly higher at 10 minutes compared to that at 2 minutes for AP (p=0.0033) and CC (p=0.0110) but not LR (p=0.4296). An adjustment greater than 5 mm was required at least once in the treatment period in 11 (55%) patients. Conclusions:Interportal adjustment of table position was required in more than 10% of portal irradiations during the 10-minute period after initial set-up to maintain treatment accuracy within 2.0 mm.

Biological effect of dose distortion by fiducial markers in spot‐scanning proton therapy with a limited number of fields: A simulation study

“…Simulation setup Figure 1 shows the water phantom geometry, coordinate system, and beam directions. The phantom size (38× 20×20 cm 3 ) was determined based on the average anatomical measurements of water equivalent length made from computed tomography scans of 10 prostate cancer patients' pelvises. Clinical target volume (CTV) was defined as prostate and its size ranges from 28 to 74 cm 3 (44 cm 3 on average) over the 10 patients.…”

“…During irradiation, continuous target tracking by a fluoroscopic X-ray system is useful for respiratory moving tumors 1 . It has been reported that even the prostate can undergo more than 10 mm of intra-fractional motion during 1 minute 2 , which suggests that real-time tracking is also beneficial for the prostate 3 . Due to their high opacity, gold markers have been used with great effect especially for the cases of liver and prostate with the targets surrounded by water-equivalent tissues.…”

Prospective Phase II Study of Image-guided Local Boost Using a Real-time Tumor-tracking Radiotherapy (RTRT) System for Locally Advanced Bladder Cancer

“…We have also found that a method using multiple gold markers with frequent correction of the table position during RT is useful to reduce the error due to intrafractional organ motion (24). We inserted more than three markers around the tumor bed to be covered in the image-guided boost in principle, since the bladder wall is so flexible.…”

Early results of urethral dose reduction and small safety margin in intensity-modulated radiation therapy (IMRT) for localized prostate cancer using a real-time tumor-tracking radiotherapy (RTRT) system

“…Patients are asked to void a few hours before every radiotherapy. The details of this procedure were as reported [6,8]. …”

“…This system can maintain accuracy within nearly 2 mm during radiotherapy by reducing the intra-fractional as well as inter-fractional errors, and it could also be called on-line image-guided radiotherapy with intra-fractional correction (intra-IGRT) [6]. We have not yet encountered any situation in which the precision of intra-IGRT would be required rather than non-intra-IGRT technologies that do not improve intra-fractional accuracy but do improve inter-fractional accuracy (inter-IGRT).…”