Image-Guided Adaptive Radiation Therapy of Intensity-Modulated Radiation for Cervical Cancer
|Keywords||cervical cancer intensity modulated radiation therapy the cone-beam tomography the position error Adaptive radiation therapy|
The article is to investigate optimized IMRT plan of cervical cancer;to measure setup errors for patient of cervical cancer in radiotherapy. It was investigated the feedback in treatment effects and the dose distribution for IMRT plan.And to discuss the feasibility of adaptive radiation therapy.Sixteen patients with postoperative cervical cancer were investigated. All the plans were normalized so that 95% of planning target volume (PTV) at least received 50 Gy. Different IMRT plans were generated for each patient and the parameters of plans were discussed for the quality of plans. A seven-field technique was best for dose of PTV and protection of organ at risks (OARs), moreover reduced treatment time than a five-field technique and a nine-field technique.Concentric ring technique improved comfortable of PTV and reduced irradiation volume.And no uniform set up of beams technique reduced irradiation volume but to increases the volume of low dose for intestine.The quality of the plan for the intension level 8 was to get close the intension level 10,and to further reduced the number of segments by 19.32%.The 16 patients of cervical cancer were received a total of 305 kilo-volt cone-beam computed tomography (kv-CBCT) scans, which evaluated the setup errors in left-to-right (X), in superior-to-inferir (Y) and in anterior-to-posterior (Z) .The isocenter of the initial plan (PLAN1) was changed according to the setup errors to simulate radiotherapy and then recalculated the dose distribution without changing the direction, shape and weight of fields,we would had the new plans (PLAN2 and PLAN3) .Then retracted the PTV from the original plan to get CTVx10, CTVx9, CTVx8, CTVx7, CTVx6, CTVx5, CTVx4, CTVx3, selected CTVx that agree with prescription dose , confirm the distance between CTVx and PTV, the minimum value was the margin from CTV to PTV. (1)The setup errors of 16 patients in X, Y and Z directions were(1.13±2.94) mm (,-1.63±7.13) mm(,-0.65±2.25) mm.(2) The distance between CTVx and PTV was 5,9 and 3mm in X, Y and Z directions According to 2.5∑+0.7σ.(3)Setup errors was not to increase obviously dose of rectum, intestine and femoral head, but bladder.(4) Transplantation plans displayed 99% of CTVx10- CTVx7 and received 95% of prescription dose, departed from standard of clinic.In order to protect normal tissues,we selected 7mm that was the minimum value of the margin from CTV to PTV.(5) The margin from CTV to PTV, that be to calculated by formula and Transplantation plans was difference.In fact, the margin from the result of transplantating plans would be confidence,because it represented practice of treatment.So that we selected the margin of 7mm for CTV to PTV.