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Objective To compare the whole-body equivalent doses from volumetric modulated arc therapy (VMAT) and static intensity-modulated radiotherapy (IMRT) for patients with cervical cancer.Methods Nine patients with cervical cancer admitted to our hospital in 2014 were included in this study.Both VMAT and IMRT were planned for each patient.Each patient's personal dose equivalent (Hp (10)) was measured using thermoluminescent dosimeters placed at the xiphoid process and glabella during IMRT and VMAT.The whole-body equivalent doses were estimated based on the results measured at the xiphoid process and compared between the VMAT and IMRT techniques.The paired t test was used for difference analysis.Results The Hp (10) values measured at the xiphoid process and glabella of every patient were lower for VMAT than for IMRT.At a prescribed dose of 50 Gy,if the mean Hp (10) values measured at the xiphoid process were considered to represent the whole-body equivalent doses,the whole-body equivalent doses for VMAT and IMRT were 364 mSv and 538 mSv,respectively.Conclusions VMAT results in a lower whole-body equivalent dose to patients compared with IMRT.The decreased whole-body equivalent dose delivered by VMAT may reduce the likelihood of a radiation-induced secondary malignancy.
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Objective To investigate the predictive value of dose?volume histograms ( DVHs ) of organs at risk ( OARs ) including the bladder, rectum, and small intestine in volumetric modulated arc therapy ( VMAT) plans for cervical cancer. Methods A total of 100 VMAT plans for cervical cancer were assigned into the learning group. The correlation of the anatomical information with the V30 , V40 , and V50 values of the bladder, rectum, and small intestine was evaluated in the group. The support vector regression ( SVR) algorithm was used to establish the correspondence between the anatomical information and the DVHs of OARs. The DVHs of OARs in the verification group containing 20 VMAT plans were predicted based on the anatomical information. Results The DVHs of the bladder, rectum, and small intestine were likely to be influenced mainly by the spatial relationship between these OARs and target volume. In the verification group, the prediction errors of V30,V40 and V50 by SVR algorithm were-2.4%±3. 5%,-2.5%±3. 8%, and-1.5%±4. 9% for the bladder, 0.5%±2. 6%,-1.5%±5. 1%, and-2.0%±7. 4% for the rectum, and-2.9%± 5. 3%, 2.7%±7. 7%, and 5.3%±11. 1% for the small intestine, respectively. Conclusions After learning the correlation between the anatomical information and the DVHs of OARs from prior VMAT plans for cervical cancer, SVR algorithm can precisely predict the DVHs of the bladder, rectum, and small intestine based on the anatomical information.
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Objective To investigate the impact of oral contrast agent for assisting in outlining the small bowel on pelvic volumetric modulated arc therapy (VMAT) dose in patients with cervical cancer.Methods Nine cervical cancer patients for postoperative radiotherapy underwent CT scans,and the target volumes and organs at risk including the small bowel were contoured.The VMAT plan was designed for each case.Then another plan was generated by re-calculating the radiation dose after changing the electron density of the small bowel.The first plan (plan A) was the conventional VMAT plan,and the second one (plan B) specified the electron density of the small bowel.Paired t-test was used to compare the dose distribution between the two plans.Results The Dg8,D5o,conformity index,and homogeneity index of plans A and B were 4 989.1 vs.5 000.1 cGy (P =0.026),5 208.6 vs.5 191.6 cGy (P =0.005),0.766 vs.0.765 (P =0.920),and 0.081 vs.0.074(P =0.055),respectively.The volumes of the small bowel receiving at least 30 Gy for plans A and B were 309.3 vs.314.3 cm3(P =0.207),while bladder V45 of the two plans was 52.4％ vs.51.1％ (P =0.168).To achieve the same prescribed dose,plan A and plan B needed 893.3 MU and 865.8 MU (P =0.093).Conclusions The contrast agent filling the small bowel does not lead to a significant increase in the pelvic VMAT dose in patients with cervical cancer after surgery.