Probe into rational target volume of nasopharyngeal carcinoma having been treated with conventional radiotherapy / 中华放射肿瘤学杂志

ABSTRACT

Objective To analyze the local control rate and the desimetric patterns of local recurrence in nasopharyngeal carcinoma(NPC)patients having been treated with standardized conventional radiotherapy and to evaluate the delineation of rational target volume.Methods From Jan.2000 to Dec.2000,476 patients with untreated NPC were treated by standardized conventional radiotherapy alone at the Sun Yat-sen University Cancer Center.The radiation ports were designed on a X-ray simulator.The nasopharyngeal lesion demonstrated by CT scan and the subclinical spread regions adjacent to the nasopharynx were defined as the target volume.Kaplan- Meier method was used to calculate the cumulative local recurrence rate.For patients with locad recurrence,the primary and recurrent local tumor volumes(V_(nx),V_(recur))were delineated with three-dimensional treatment planning system(3DTPS),and the dataset of radiation ports and delivered prescription dose to the 3DTPS were transferred according to the first treatment.The dose of radiation received by V_(recur)was calculated and analyzed with dose- volume histogram(DVH).Local recurrence was classified as:1.“in-port”with 95% or mere of the recurrence volume((recur)_V_(95))was within the 95% isedase;2.“marginal”with 20% to95% of _(recur)V_(95)within the 95% isedese; 3.“outside”with only less than 20% of _(recur)_V_(95)within the 95% isodose curve.Results With the median follow- up of 42.5 months(range 8～54 months),52 patients developed local recurrence.The 1-,2-,3 and 4-year cumulative local failure rate was 0.6%,3.9%,8.7% and 11.5%,respectively.Among the 42 local recurrent patients who could be analyzed by 3DTPS,52% were in-port,40% were marginal and 7% were outside.For most of the marginal recurrence and all the outside recurrence patients,the main reason of recurrence were related to the unreasonable design of the radiation port and inaccuracy in the interpretation image findings.Conclusions The outcome of better local control rate and the dosimetric pattern of local recurrence show that the target volume is reasonable for NPC in Sun Yat-sen University Cancer Center.Enhancing the capability of correct interpretation of images,accurate design of the radiation pouts and making most useful molecular or functional imaging techniques to escalate the local radiation dose are promising ways to improve the local control further and better.