Dosimetric Comparison of Stereotactic Body Radiotherapy and Intensity-Modulated Radiotherapy to Deliver Hypofractionated Radiotherapy in Organ-Confined Prostate Cancer

We compared the dose conformity, homogeneity, dose to organs at risk, and remaining volume at risk of two radiotherapy techniques --stereotactic body radiotherapy and intensity-modulated radiotherapy (IMRT) to deliver hypofractionated radiotherapy in organ-confined prostate cancer. Eleven successive patients treated on the CyberKnife stereotactic robotic radiosurgical system were taken up for this study. The CT images, including the structures contoured, were imported through DICOM RT from the Multiplan (Accuray Inc., Sunnyvale, CA, USA) treatment planning system to the Plato Sunrise treatment planning system (Nucletron, The Netherlands) for creating IMRT treatment plans on the Linac. Treatment planning was done for five fractions, each fraction prescribed to a dose of 7.25 Gy to the planning target volume. Dose volume histograms were generated for the CyberKnife and Linac treatments for comparison. As per our protocol, a plan was considered adequate if at least 95% of planning target volume received the prescribed dose and satisfied the following constraints: a) volume of the rectum receiving 36Gy (V36) to < 1cc and b) volume of the bladder receiving 37Gy (V37) to < 10cc. Both the treatment techniques plans resulted in adequate planning target volume coverage (p value for D95, D90, D5, and V100% was 0.402, 0.97, 0.013, and 0.012, respectively). CyberKnife plans were more conformal (p value 0.001). Remaining volume at risk dose was significantly less in all CyberKnife plans at [V100% (p=0.01), V95% (p=.004), V90% (p=.001), V80% (p=0.02), V70 (p=0.03), V40% (p=0.021), and V30% (p=0.001)] dose levels. The mean dose to rectum was lower in the CyberKnife plans (The p value for V100%, V80%, V50% and V30% dose levels was 0.02, 0.0001, 0.0002, and 0.12, respectively). Categories: Radiation Oncology, Urology