前列腺癌影像導引放射治療擺位誤差之劑量評估

Purpose: In prostate radiation therapy, inter-fractional organ motion/deformation has posed significant challenges on reliable daily dose delivery. To evaluate the set-up errors and dose impact at clinical target volume (CTV), planning target volume (PTV) coverage and critical organ with cone beam computed tomography (CBCT), image-guided radiation therapy (IGRT), volumetric modulated arc therapy (VMAT); off-line re-optimization and online re-positioning have been used clinically. Materials and Methods: Between 2011 and 2013, 12 patients with prostate cancer were treated with IGRT to a dose of 75.6 Gy with daily correction of the target position based on Elekta Synergy X-ray cone beam computed tomography system, image-guided radiation therapy practiced with VMAT. We captured each space coordinates in every fraction with dose redistribution to form a new dose distribution with the Pyton software. The real dose with recalculation and stacking with new three dimensional coordinates from each fraction were compared with initial plan. The dose at CTV, PTV coverage and critical organ were reevaluated. Results: The average shift of ML (medial-lateral), CC (cranio-caudal) and AP (anterior-posterior) were 2 mm±1 mm, 3 mm±3 mm and 4 mm±3 mm. The calculated systematic errors in ML, AP and CC direction were 0.8 mm, 2.0 mm and 1.6 mm. The calculated random errors in ML, AP and CC direction were 1.22 mm, 1.7 mm and 2.1 mm. The coverage of CTV and PTV with recalculation were significantly decreased from 100% to 96% and 97.5% to 86.9% respectively. There was no statistical difference in the dose to organ at risk. IGRT will be necessary in our study. Though CTV coverage decrease from 100% to 96%, but the PTV coverage decrease from 97.5% to 86.9% reaching statistical significance. Conclusions: IGRT would be beneficial for prostate cancer treatment with VMAT really. CBCT image guide VMAT in radiotherapy to prostate cancer not only shortened the treatment time but also decreased the uncertainty of set-up within each fraction. The specific dose to critical organs and tumor would be more exact compared with radiotherapy without IGRT. The less side effect and better tumor control might be expected in the future after proof of new randomized clinical trial.