Adaptive IG-IMRT for Prostate Cancer


Authors: J. Vaňásek 1;  K. Odrážka 1,2,3;  M. Doležel 1,3;  I. Kolářová 1
Authors‘ workplace: Oddělení klinické a radiační onkologie, Multiscan s. r. o., Pardubická krajská nemocnice a. s., Pardubice 1;  1. a 3. lékařská fakulta, Univerzita Karlova v Praze 2;  Katedra radiační onkologie IPVZ, Praha 3
Published in: Klin Onkol 2011; 24(5): 361-366
Category: Original Articles

Overview

Backgrounds:
Adaptive image-guided intensity-modulated radiation therapy (IG-IMRT) is a perspective method for the treatment of localized prostate cancer. Validate optimal protocols for IG-IMRT using kilovoltage cone-beam CT (CBCT) are required.

Patients and Methods:
Seventy-six patients with prostate cancer were treated using adaptive IG-IMRT. Based on the CBCT performed during the first 10 fractions of radiotherapy, an average prostate position in relation to the pelvic bones was determined in antero-posterior AP, supero-inferior SI, and right-left axes. An adapted treatment plan for the second phase of the treatment included an isocenter shift into its average position (correction of the systematic error Σ). A margin between a clinical and planned target volume (CTV-PTV) was adjusted according to the magnitude of random error σ. During the second phase of radiotherapy, set-up of patients was performed daily on pelvic bones using kilovoltage skiagraphic imaging in two projections (kV-kV). Follow-up CBCTs were repeated once a week.

Results:
An average isocenter position differed from the position of a reference planning CT isocenter in at least one axis in 63 patients (83%). Major changes were recorded in AP axis – shift ≥ 2 mm in 33 patients (43%), shift ≥ 5 mm in 7 patients (9%). PTV for the second phase of radiotherapy was in the range of 6–10 mm in AP axis, 6–8  mm in SI axis, and 6 mm in RL axis. Mean σ value in the AP axis was smaller in patients with a specific diet compared to patients without the diet (2.2 mm vs. 2.7  mm, p = 0.05). We evaluated 446 follow-up CBCT images from the second phase of radiotherapy (66 patients had 6 CBCT, 10 patients had 5 CBCT). Set-up error exceeding CTV-PTV margin occurred in 4 cases with no more than once per patient. Safety margin was sufficient in 72/76 patients (95%).

Conclusion:
IG-IMRT protocol integrating CBCT and kV-kV imaging provided adequate coverage of the target volume and proved to be compatible with departmental workflow. Margin reduction around the CTV is a prerequisite for dose escalation aimed at a intraprostatic lesion.

Key words:
prostate cancer – radiation therapy – adaptive – image guidance – IMRT

The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study.

The Editorial Board declares that the manuscript met the ICMJE “uniform requirements” for biomedical papers.

Submitted:
16. 2. 2011

Accepted:
15. 3. 2011


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Paediatric clinical oncology Surgery Clinical oncology
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