Treatment planning and dosimetry of a multi-axis dynamic arc technique for prostate cancer: A comparison with IMRT.

PURPOSE

Intensity-modulated radiation therapy (IMRT) allows greater dose conformity to the tumor target. However, IMRT, especially static delivery, usually requires more time to deliver a dose fraction than conventional external beam radiotherapy (EBRT). The authors have been using a "two-axis dynamic arc therapy" (2A-DAT) technique for prostate cancer treatment to make a concave dose distribution to spare the rectum and bladder while working with limited time and human resources. The objectives of this study were to (1) clinically implement the 2A-DAT technique, (2) evaluate the dosimetry in comparison with IMRT, and (3) analyze the initial treatment outcome.

MATERIALS AND METHODS

The 2A-DAT consists of two dynamic arc therapies (DATs) with half rotation around two isocenters each in two separate symmetrical rhombi. Treatment planning is forward and on a trial-and-error basis. Thirty-four patients received 2A-DAT with a median prescribed dose of 70 Gy.

RESULTS

Although inferior in dose uniformity, the 2A-DAT provided equivalent sparing of normal structures to IMRT. Daily fraction delivery time for the 34 patients ranged from 6.4 to 9.6 minutes, with an average of 7.4 minutes. Five-year survival and five-year prostate specific autigen (PSA) failure-free survival were 89.3% and 79.5%, respectively. Three patients developed grade 2 proctitis.

CONCLUSION

This technique is a possible alternative to IMRT in EBRT of prostate cancer.