Purpose. The goal of the present study was to demonstrate risk factors affecting the interfractional variation in whole pelvic irradiation. Patients and methods. Daily image acquisitions of 101 patients with locally advanced pelvic malignancy were undertaken using a kilo-voltage orthogonal on-board imager. The baseline deviation (the shift between the initial treatment and each fraction; Value Base) and day-to-day variation (the shift between the previous treatment and each fraction; Value DD) were measured. The standard deviations (SD) along the x- (right-left), y- (cranial-caudal), and z- (anterior-posterior) axes (SD[x], SD[y], and SD[z], respectively), the 3D vector of the SD (SD[3D]), and the mean of 3D shift (mean[3D]) were calculated in each patient. Various clinical factors, lumbar pelvic balance and rotation, and the shift of 5 consecutive fractions from the initial treatment (Value 5Fx) were investigated as risk factors. Results. The prone set-up showed a larger mean Base[3D] than in the supine position (p =0 .063). A body mass index (BMI) ≥ 30 kg/m 2 resulted in the largest mean DD[3D] (p = 0.078) and SD DD[3D] (p = 0.058). All the SD 5Fx along the x-, y-, and z-axes had moderate linear relationships with SD Base and SD DD (p < 0.001). The SD 5Fx[3D] also had a moderate linear relationship with the mean Base[3D], mean DD[3D], SD Base[3D], and SD DD[3D] (p < 0.001). In multivariate analysis, the SD 5Fxhad the same significant relationship with SD Base and SD DD (p < 0.001). A BMI ≥ 30 kg/m 2 was associated with the largest SD DD[x] (p = 0.003). Conclusion. Close surveillance through high-quality and frequent image guidance is recommended for patients with extensive variations of the initial five consecutive fractions or obesity.
- Image-guided radiation therapy
- On-board imager
- Pelvic neoplasms
- Radiotherapy dosage
- Risk factors
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging