Dosimetric Comparison Between Volumetric Modulated Arc Therapy And Intensity Modulated Radiotherapy For Different Tumor Volume And Different Lesion Length Of Esophageal Cancer

Objective: To compare the dosimetric differences between volumetricmodulated arc therapy (VMAT) and static intensity modulated radiotherapy(IMRT) for different tumor volume and different lesion length of esophagealcancer.Methods: Fifty patients with biopsy-proven thoracic esophageal cancerwere selected in this study from January2012to October2013, including18cases located in the upper thorax,21cases in the middle thorax and11casesin the lower thorax. All patients were required to be localized by CT scannerand the target area was delineated under a unified standard. The ElektaOncentra4.1Planning System was adopted to design both VMAT and IMRTplans (VMAT with a single arc and IMRT with five fields) for fifty patientswho were diagnosed with esophageal cancer in different tumor volume anddifferent lesion length. The dose-volume histograms were used to provide thequantitative comparison between VMAT and IMRT plans. Dosimetriccomparisons between VMAT and IMRT plans were analyzed to evaluate (1)coverage, conformity and homogeneity of PTV;(2) sparing of OARs;(3)monitor units (MUs) and delivery time.Results:(1) For GTV volume≤15cm3group, VMAT plan led to a lowerPTV HI. The PTV CI of VMAT and IMRT plans were similar. The PTVD100、D95、V95and V90of VMAT plan were higher than IMRT plan, whilethe PTV D90and V105were lower than IMRT plan. When comparing VMATwith IMRT plan, V5and mean lung dose (MLD) of lungs, V40and Dmean ofheart, V5and V10of healthy tissue (defined as the volume of the body minusPTV, B-P) were slightly higher for VMAT plan.（2）For15~55cm3group， the HI and CI of PTV by VMAT and IMRT plans were not significantlydifferent. VMAT plan provided superior target volume coverage in terms ofD100, V95and V90compared to IMRT plan. VMAT plan resulted in aslightly higher V30for lungs and lower V10for lungs. When comparingVMAT with IMRT plan, V40of the spinal cord, V40and Dmean of heart, V5and V30of B-P were higher for VMAT plan.（3）For GTV volume≥55cm3group，the HI and CI of PTV by IMRT and VMAT were not significantlydifferent. The D90and V100in the PTV of VMAT plan were lower thanIMRT plan, with a lower V10、V15for lungs and higher V5for B-P.（4）Forlesion length≤5cm group, VMAT plan had lower CI and HI in the PTV,compared to IMRT plan. The PTV D100、D95、V95and V90of VMAT planwere higher than IMRT plan, while the PTV D90and V105were lower thanIMRT plan. When comparing VMAT with IMRT plan, V5、V30and meanlung dose (MLD) of lungs, V30、V40and Dmean of heart, V5、V10and V30of B-P were slightly higher for VMAT plan.（5）For5~9cm group，VMATplan had superior CI and HI in the PTV, compared to IMRT. The PTV V95and V90of VMAT plan were higher than IMRT plan, while the PTV D90waslower than IMRT plan. V40and Dmean of heart, V5and V10of B-P wereslightly higher for VMAT plan when compared with IMRT plan.（6）Forlesion length≥9cm group, the HI and CI of PTV by IMRT and VMAT werenot significantly different. The D90and V100in the PTV of VMAT plan werelower than IMRT plan. VMAT plan led to a lower V10、V15for lungs andhigher V30for lungs and higher V5for B-P.（7）When compared with IMRTplan, VMAT plan reduced the monitor units by an average of11.3%(428.54vs.483.25，P=0.012) and18.1%(481.77vs.588.29, P＜0.001) in the15~55cm3group and≥55cm3group, and by an average of16.1%(425.86vs.507.31, P=0.001) and16.0%(476.97vs.567.98, P=0.001) in the5~9cmgroup and≥9cm group. However, VMAT plan provided an average of10.4%and14.4%more monitor units than IMRT plan in the tumor volume≤15cm3group and lesion length≤5cm group. The average monitor units forVMAT plan were428.61and436.43compared to IMRT plan (388.28, P=0.039and381.52, P<0.001, respectively) in the≤15cm3group and≤5cm group.Conclusion: VMAT plan provided superior target volume coveragecompared to IMRT plan, especially in a small target volume esophageal cancer.VMAT plan can reduce the volume of hot spot and cold spot, and improve theuniformity of the target. Although VMAT plan was not superior to IMRT planin the sparing of OARs, the technique was very successful in reducingdelivery time. Compared with VMAT plan, the monitor units weresignificantly reduced by IMRT plan. Individualized treatment is the optimaltreatment according to specific condition of patients with poor heart andpulmonary functions.