ObjectiveTo compare the dosimetric differences among the double-arc volumetric-modulated arc therapy (VMAT), 7 field intensity-modulated radiotherapy (IMRT) and 3-dimensional conformal radiotherapy (3D-CRT) techniques in treatment planning for cervical cancer as adjuvant radiotherapy. MethodFifteen patients who underwent adjuvant chemotherapy for cervical cancer between March 1st and September 30th, 2013 were chosen to be our study subjects through random sampling. Under Pinnacle 9.2 planning system, the same CT image was designed through three different techniques:VMAT, IMRT and 3D-CRT. We then compared target zone fitness index, evenness index, D98%, D2%, D50% among those different techniques. Monitor unit (MU) and treatment time were also analyzed. ResultsThree techniques showed similar target dose coverage. The IMRT and VMAT plans achieved better target dose conformity, which reduced the V20 of the pelvic, the V50 of the rectum and bladder, as well as the V40/50 of the small intestine (P<0.05). The VMAT technique showed few dosimetric advantages over the IMRT technique. VMAT technique had the advantages of less MU (P>0.05) and shorter overall treatment time (P<0.01) compared with IMRT technique. ConclusionsThe IMRT and VMAT plans achieve similar dose distribution to the target, and are superior to the 3D-CRT plans, in adjuvant radiotherapy for cervical cancer. VMAT technique has the advantages of less MU and shorter overall treatment time.
ObjectiveCompare the two-degrade collimator (MLC) angle selection's impact on plan quality and operational efficiency for volumetric intensity-modulated radiotherapy (VMAT) in the treatment planning system, and to explore the scheme for treatment plan optimization. MethodsTwenty patients with nasopharyngeal carcinoma underwent the treatment between March and December 2013 were randomly selected and planned for SIBVMAT treatment with different parameters set in the range of 0-60°with 15°interval for collimator angles. Planned dose distribution to the target volumes, organs at risk, and monitor units were compared. ResultsAs the MLC angle increased, target conformal index and homogeneity index had a trend to became deteriorated. The optimal plans were 0°and 15°, while 45°and 60°plans gave poor protection for the organ at risk compare to other angle plans and the monitor units were significantly increased. ConclusionChange the MLC angle had visible impact on treatment plans,there was a trend to deteriorate with the MLC angle increased, but small changes in MLC angle range can theoretically reduce the influence from leakage radiation on the human body.