2756 - How Adaptive Radiotherapy Benefits for Cervical Cancer Patients: A Clinical Exploration Based on Daily FBCT
Presenter(s)
Y. Guo1, T. Li1,2, X. Yang1, W. Ye1, and S. Huang1; 1Sun Yat-sen University Cancer Center, GuangZhou, GuangDong, China, 2National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, 518116, China, Shenzhen, Guangdong, China
Purpose/Objective(s): To investigate the changes of the targets and organs at risk (OARs) during external radiation therapy in patients with cervical cancer, and to explore the necessity and applicability of adaptive radiotherapy.
Materials/Methods: Five cervical patients were retrospectively analyzed, and guided by daily Fan beam CT (FBCT) for radiotherapy. Targets were GTVnd (the positive lymph node areas), CTV1(the primary tumor and the whole uterus), CTV2 (the vagina), and CTV3 (the distal lymph node areas). The OARs included the rectum, bladder, small intestine, sigmoid colon, colon kidney, and pelvic bone. The Planning Clinical Target Volume (PTV) was formed by expanding the border 5 mm in all directions of the GTVnd/CTV, and the prescribed dose of PTVs was 45-60Gy/25 times. All patients had 3 plans: plans that were treated for the patients during the whole course of radiotherapy (PlanT), PlanT calculated on daily FBCTs (PlanF), which was the actual dose of the patients, and adaptive plans with corrected targets and OARs (PlanA) on daily FBCTs.
Results: There were 255 plans for 5 patients (5 PlanTs, 125 PlanFs and 125 PlanAs). All targets (GTVnd, CTV1, CTV2, CTV3) exhibited an overall decreasing trend during radiotherapy, with the GTVnd showing a maximum shrinkage of 76.68% for one patient. The fluctuations of the OARs were significant, with the bladder demonstrating a maximum volume change of 83.9%. As bladder volume increased, the bladder dose (V30Gy, V35Gy, V40Gy, V45Gy) showed corresponding increases (R = 0.19, P = 0.035), while the Rectum (V35Gy, V40Gy, V45Gy, V50Gy, Dmean) decreased (R = -0.176, P = 0.05). It was found that: as the bladder volume increased >20% the doses delivered to the small bowel and sigmoid colon were significantly decreased (minimum reduction: 5.89%, maximum reduction: 18%). Among 125 PlanF sessions of the 5 patients, the proportion with D95% < Prescription*95% were 1.6% (2/125) for GTVnd, 34.4% (43/125) for CTV1, 42.4% (53/125) for CTV2, and 1.6% (2/125) for CTV3. PlanT demonstrated better coverage in D95% and D98% for GTVnd, CTV2, and CTV3 compared to PlanF (P < 0.05), with no significant differences from PlanF plans. For the OARs, PlanF delivered more dose than PlanT in the Rectum (V30Gy, V35Gy, V40Gy, V45Gy, V50Gy, Dmean), the Sigmoid Colon (V30Gy, V40Gy, V45Gy, Dmean), and Pelvic bone (V30Gy, V40Gy, V50Gy) (P < 0.05). In addition, both PlanF and PlanT had more doses of OARs than PlanA (P < 0.05).
Conclusion: The CTV1 and CTV2 should be paid more attention to cervical cancer radiotherapy. Adaptive radiotherapy for cervical cancer could not only improve target coverage, but also reduce radiation exposure to bladder, bowel, and other OARs, effectively decreasing the likelihood of radiotherapy-related adverse effects.