ABSTRACT
Purpose The aim of this study is to investigate the feasibility of prostate stereotactic body radiation therapy treatment with a newly developed Varian HalcyonTM 2.0 machine by comparing radiotherapy plans with previously delivered CyberKnife G4 plans created with the previous version of CyberKnife Treatment Planning System Multiplan 4.6.1. Methods Fifteen previously treated prostate stereotactic body radiation therapy treatment CyberKnife plans were re-planned retrospectively according to the Radiation Therapy Oncology Group 0938 protocol on a HalcyonTM 2.0 machine with a prescription of 3625 cGy in five fractions. Results All re-plans on a HalcyonTM 2.0 were able to meet the Radiation Therapy Oncology Group 0938 protocol goals and constraints. The re-plans decreased the maximum dose to skin and urethra, mean doses to the bladder and rectum, and also improve the conformity index and the Planning Target Volume coverage. However, D1cc to the rectum, D1cc and D10% to the bladder increased with no statistically significant differences (p > 0.05) with the re-plans. Conclusion The HalcyonTM 2.0 can generate stereotactic body radiation therapy treatment prostate plans created based on the Radiation Therapy Oncology Group 0938 protocol by delivering adequate coverage to the target while sparing healthy tissues.
ABSTRACT
Concurrent treatment of the prostate and the pelvic lymph nodes encounters the problem of the prostate gland moving independently from the pelvic lymph nodes on a daily basis. The purpose of this study is to develop a leaf-tracking algorithm for adjustment of IMRT portals without requirement of online dose calculation to account for daily prostate position during concurrent treatment with pelvic lymph nodes. A leaf-shifting algorithm was developed and programmed to adjust the positions of selected MLC leaf pairs according to prostate movement in the plane perpendicular to each beam angle. IMRT plans from five patients with concurrent treatment of the prostate and pelvic lymph nodes were selected to test the feasibility of this algorithm by comparison with isocenter-shifted plans, using defined dose endpoints. When the prostate moved 0.5, 1.0, and 1.5 cm along the anterior/posterior direction, the average doses to 95% of the prostate (D95%) for the iso-shift plans were similar to the MLC-shift plans, (54.7, 54.4, and 54.1 Gy versus 54.5, 54.3, and 53.9 Gy, respectively). The corresponding D95% averages to the pelvic lymph nodes were reduced from the prescription dose of 45 Gy to 42.7, 38.3, and 34.0 Gy for iso-shift plans (p = 0.04 for each comparison), while the D95% averages for the MLC-shift plans did not significantly differ from the prescription dose, at 45.0, 44.8, and 44.5 Gy. Compensation for prostate movement along the superior/inferior direction was more complicated due to a limiting MLC leaf width of 1.0 cm. In order to concurrently treat the prostate and pelvic lymph nodes with the prostate moving independently, shifting selected MLC leaf pairs may be a more practical adaptive solution than shifting the patient.