The Applied Research Of Adaptive Radiotherapy In The Treatment Of Nasopharyngeal Carcinoma

Purpose: The aim of this study was to show the benefit of adaptive radiotherapy(ART)method by examining geometric and dosimetric changes.Material and Methods: seven patients with nasopharyngeal carcinoma treated with ARTwere recruited. All patients were treated with SIB-IMRT regimen (named IMRT).Allpatients had a second computed tomography scan after10fractions and a new planbased on this was initiated from fraction11(ART1).And a third CT scan after21fractions and a new plan based on this was initiated from fraction22(ART2).When thetreatment was finished,a fourth CT scan was made. geometric and dosimetric changesResults:1.The volumes of primary tumors and parotid glands regressed significantlyafter the teatment.The GTVnx and GTVnd mean volume shrunk to62.13％(42.94％～79.14％)，60.19％(33.02％～84.6％) of the initial plan respectively.The left and rightparotid volume compared with original treatment were reduced about39.41%（23.21%~58.57%）,35.48%（11.32%~53.76%）and the position of the parotid glandsshifted medially an average of4.5（1.6~9.2）mm during the plans.Parotid volume shrunk obviously in the first third time than the other two third timetreatment, the GTVnx and GTVnd were just the opposite and increasing treatment timeand tumor shrinkage had obvious relationship.2.In the aspect of target dosimetry, the maximum dose（Dmax）, minimum dose（Dmin）and average dose（Dmean）of GTVnx and GTVnd in the three plans were similar, and there was no significant difference (P>0.05).3.In the aspect of OAR dosimetry, the maximum dose（Dmax）of brainstem and spinalcord have no significant difference.ART1reduced mean dose to left parotid by0.42Gy（1.68%）(P=0.019) and right parotid by0.79Gy (3.04%)(P=0.013) over the IMRTalone. ART2further reduced the mean left parotid dose by0.86Gy or3.5%(P=0.001)and right parotid by1.04Gy or4.13%(P=0.035).Conclusions:The volumes of primary tumors and parotid glands regressed significantlyafter the teatment.Replanning does not result in significant dosimetric difference intargets.However,it could reduce the dose of parotid gland.It’s feasible that the revisedplan using off-line ART in the clinical course of radiotherapy could mitigate the sideeffects of radiotherapy.