engleski

Comparison of two planning techniques (F-IMRT/I- IMRT) for post-operative radiotherapy treatment of prostate cancer

Introduction: With the development of medical linear accelerator and algorithms for absorbed dose calculation and optimization, a great progress has been made in radiotherapy treatment of prostate cancer [1]. At UH Rijeka, since 2016, when the system for dose distribution optimisation based on Monte Carlo calculation has been clinically implemented, IMRT technique (inverse IMRT, I-IMRT) became the technique of choice for radiotherapy treatment following radical prostatectomy [2]. Previously, advanced 3-DCRT technique using field-in-field method was used for dose distribution optimisation around target volumes and organs-at-risk (forward IMRT, F-IMRT). This research has been performed with purpose of investigating how choice of planning technique (F-IMRT or I-IMRT) affects coverage of target volumes with prescribed dose and organs- at-risk sparing. Methods and materials: Comparison of dose distributions calculated using F-IMRT and I-IMRT techniques was done for 10 patients with indicated post-operative radiotherapy, and whose treatment was carried out at the Clinic for Radiotherapy and Oncology at UH Rijeka. Prescribed dose for all patients was delivered using I-IMRT technique, and for purpose of this research, dose distributions using F-IMRT technique were calculated. Absorbed dose of 46Gy was delivered to target volume PTV1 , created by adding a 0.7cm margin around lymph nodes (CTV) and 1.0cm around prostate bed (GTV). Additional 22Gy were delivered to target volume PTV2 with 1.0cm margin around prostate bed [2]. For I-IMRT and F-IMRT techniques, photon beams of linear accelerator equipped with a 160 leaf MLC were used. To determine the influence of planning technique on dose distribution, parameters related to target volumes (GTV, CTV, PTV1 , PTV2 ) were analysed. For organs-at-risk sparing (rectum, bladder, femoral heads), three dose- volume constraints were used. Results and discussion: By analysing parameters related to target volumes, most of them shown no statistical significance (V100%(GTV), V100%(CTV), V95%(PTV2 ), V95%(PTV1 ), D2%). For both planning techniques, internationally set [3] dose constraints were achieved: for GTV, V100%=98, 8±1, 3 (F-IMRT) and V100%=99, 9±0, 2 (I-IMRT), for CTV, V100%=99, 4±0, 9 (F-IMRT) and V100%=99, 4±0, 8 (I-IMRT), for PTV2 , V95%=99, 9±0, 2 (F- IMRT) and V95%=99, 7±0, 4 (I-IMRT), and for PTV1 , V95%=99, 3±0, 6 (F-IMRT) and V95%=99, 9±0, 1(I- IMRT). Statistically significant difference was found for V100%(PTV2 ), p=0, 000534 and V100% (PTV1 ), p=0, 042944 in favour of I-IMRT technique. For PTV2 , V100%=91, 6±3, 8 for F-IMRT and V100%=97, 9±1, 4 for I-IMRT and for PTV1 , V100%=93, 3±2, 0 for F-IMRT and V100%=95, 8±2, 5 for I-IMRT. Comparing the effect of planning technique to organs-at-risk sparing, statistically significant difference (p=0, 045966) was found for V40Gy for rectum where the sparing is better for I-IMRT technique. For dose- volume constraints related to bladder and femoral heads, no statistically significant difference was found. Conclusion: Results of this research show statistically significant difference for minimal absorbed dose delivered to target volumes PTV1 and PTV2 , with better dose coverage in favour of I-IMRT. Concern- Lib Oncol. 2020 ; 48(Suppl 1):73–143 90 ing organs-at-risk sparing, statistically significant difference in favour of I-IMRT was found for V40Gy for rectum. Expectedly, I-IMRT technique provided better results [4]. However, differences for two planning techniques (F-IMRT and I-IMRT) for analysed parameters are rather small which points to the fact that well-executed radiotherapy planning by using F-IMRT technique can be used as a technique of choice as well.

treatment planning ; radiotherapy

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