Comparison of two planning techniques (FiF/IMRT) for postoperative radiation therapy of prostate cancer

Abstract

Introduction: Within the past two decades, we made significant progress in radiation therapy for prostate cancer. At UH Rijeka IMRT became the technique of choice for radiation therapy following radical prostatectomy since 2016. Previously, an advanced 3-DCRT technique using the field-in-field (FiF) method was used for dose distribution optimization around target volumes and organs-at-risk. This research has been performed to investigate the influence of planning technique choice (FiF or IMRT) on coverage of target volumes with prescribed dose and organs-at-risk sparing. Materials and methods: Comparison of dose distributions calculated using FiF and IMRT techniques was performed retrospectively for ten patients who underwent postoperative radiotherapy. The prescribed dose for all patients was delivered using IMRT, and for this research, we also calculated dose distributions using the FiF technique. For FiF and IMRT techniques, we used linear accelerator photon beams. To determine the influence of planning technique on dose distribution parameters related to target volumes (GTV, CTV, PTV1, PTV2) were analyzed. For organs-at-risk sparing evaluation (rectum, bladder, femoral heads), we used dose-volume constraints. Results and discussion: The analysis of parameters related to target volumes has shown that most of them had no statistically significant difference (V100%(GTV), V100%(CTV), V95%(PTV2), V95%(PTV1)). For both planning techniques, internationally set dose constraints were achieved. Statistically, we found a significant difference for V100%(PTV2), p=0,000534, and V100%(PTV1), p=0,042944 in favor of IMRT. A statistically significant difference (p=0,045966) was found for the volume of the rectum, which receives 40Gy, and for the volume of femoral heads, which receives 30Gy (p=0,000385), where the sparing is better for IMRT. For dose-volume constraints related to the bladder, no statistically significant differences were found. Conclusion: Results of this research show a statistically significant difference for V100% target volume coverage for PTV1 and PTV2, with better dose coverage accomplished by IMRT. Concerning organs-at-risk sparing, a statistically significant difference in favor of IMRT was found for rectum volume, which receives 40Gy. Expectedly, IMRT was superior to the FiF technique. However, differences between the two planning techniques were relatively small, which points to the fact that the FiF technique is viable as a technique of choice.

Keywords

• intensity-modulated radiation therapy
• field-in-field technique
• postoperative prostate cancer radiotherapy
• radiation dosimetry.