Purpose: The purpose of this study is to evaluate the dosimetric performance of online adaptive radiotherapy (ART) compared to image guided radiation therapy (IGRT) for cervical cancer.
Methods: Online ART for cervical cancer is routinely conducted at our institution on a CT-Linac manufactured by United Imaging Healthcare, which integrates a fan-beam CT (FBCT) with the linac to provide diagnostic quality image for IGRT and adaptive planning. For each adaptive fraction, daily FBCT is obtained and registered to the original planning CT. Original contours of GTVs and CTVs are then rigidly transferred or deformed to the daily FBCT. OARs are generated by auto segmentation. After physician reviewed and adjusted the contours, PTVs are generated by a patient-specific margin which is smaller than original plan. The adaptive plan is automatically optimized and evaluated using same set of clinical goals as original plan and then the treatment is delivered according to the new approved plan. To evaluate the dosimetric performance of online ART, two cervical cancer cases, with 12 and 18 adaptive fractions respectively, are included in this study. The original plan is recalculated on daily FBCT to represent IGRT dose distribution. Subsequently, the differences in target coverage and organs at risk (OARs) sparing between ART and IGRT are analyzed.
Results: Compared with IGRT, ART improved PTV coverage by 1.81% to 31.07%. For OARs, ART achieved 8.72% to 63.23% lower dose in femoral heads V30 and 1.70% to 7.94% lower dose in pelvic bone V30. The difference in D2cc of rectum, sigmoid and small bowel and pelvic bone V10 are either small or insignificant.
Conclusion: Compared with IGRT, ART for cervical cancer can improve coverage of dose on targets and reduce the dose of OARs significantly.
Radiation Therapy, Image-guided Therapy, Dose Volume Histograms