Online correction of catheter movement using CT in high-dose-rate prostate brachytherapy.

PURPOSE

To present a clinical procedure that readjusts catheters to its planned positions based on pretreatment computed tomography (CT) for patients undergoing high-dose-rate (HDR) prostate brachytherapy, and evaluate the magnitude and dosimetric impact of the adjustments.

METHODS AND MATERIALS

Patients received a pretreatment verification CT (vCT) before each fraction. The vCT dataset was imported to the treatment-planning system and fused to the planning CT (pCT) by rigid-body registration based on the implanted fiducials within the prostate. Catheter positions in the vCT were then compared with catheter positions in the pCT in a reconstructed plane through each catheter. Any catheter with difference in penetration larger than 3 mm was manually adjusted by a radiation oncologist before treatment. To evaluate treatment quality, the patient's plan was applied to the vCT off-line and dose delivered to prostate and normal structures were compared with their planned value.

RESULTS

Forty-four fractions of 13 consecutive patients were treated using this method. Thirty-nine fractions had at least one catheter adjusted before treatment. A total of 651 catheters were assessed, and 194 catheters (30%) were adjusted by an average amount of 5.8 ± 1.9 mm. In eight fractions the prostate D90 would have decreased by more than 10% from the planned value (with a maximum of 32%) if the catheter displacements were not rectified. After the adjustment, the maximum deviation of D90 was 10.6%. The improvement in D90 is 24% per 1 cm of time-averaged adjustment.

CONCLUSIONS

Interfraction catheter motion occurs without any particular pattern. Using pretreatment CTs and restoring each catheter to its planned position ensures that the delivered treatment closely matches the treatment plan and therefore enhances the overall quality of the HDR treatment. The procedure can be readily implemented in any clinical setting.