A Comparison Of Dosimetry And Late Toxicity For Conventional Or Intensity-modulated Radiation Therapy Of Early-breast Cancer After Breast-conserving Surgery

Objective: To observe the late radiation toxicities and compare the dosimetry ofconventional or intensity modulated radiation therapy of breast cancer after early-breastconserving surgery.Methods: Collect eighty-six women who were prescribed whole breastradiotherapy after tumor excision for early stage cancer between September2006andDecember2013in our department.64patients were treated with conventional radiationtherapy and22were treated with intensity modulated radiotherapy，called CRT groupand IMRT group respectively. Patients with CRT using conventional tangentialtechniques, IMRT patients acquired chest CT images, using5wilds reverse IMRTplanning program designed by Eclipse three-dimensional treatment planning system toget the best dosimetry program. All patients were treated with6MV photons, giving theplanning target volume(PTV)5040cGy in28fractions in6weeks. According to thesurgery scar scope and the depth of the tumor bed measured by ultrasound, usingelectronic wire9-12MeV plus1000cGy in5fractions to the tumour bed.86patientswere followed up during radiotherapy and at the end of three months after radiotherapy,evaluate the incidence of pneumonia and acute radiation dermatitis in patients andrecent cosmetic effect of ipsilateral breast after radiotherapy.10cases of breast cancer on the left side were selected from patients with IMRTrandomly, designing conventional radiotherapy plan by Eclipse three-dimensionaltreatment planning system, then integration and comparison of the two plans. Using PTV dose distribution and distribution of doses were compared to the CRT and IMRTplanning target volume,and assess the two treatment techniques by planning targetvolume dose uniformity index and conformal index. The dose volume histograms(DVH) was used for assess the heart, ipsilateral lung, contralateral breast in both ofthese three organs at risk in radiation treatment planning and the amount of irradiatedvolume were compared.Results: Through the86patients in the follow-up study found that acute radiationskin reactions in CRT group Grade0acute dermatitis occurred in2patients(3.1%),gradeI in36patients (56.3%), grade II in9patients (26.6%), grade III in2patients(12.5%)and grade IV in1patients (1.5%).In IMRT group, Grade0acute dermatitisoccurred in8patients(36.4%),grade I in12patients (54.5%), grade II in2patients(9.1%),there was no grade III and IV observed. The frequency of graded≥II dermatitiswas more in the patients with CRT than with IMRT，40.6%and9.1%respectively，p=0.001. In CRT group,Grade0radiation pneumonitis occurred in15patients(68.2%),grade I in27patients (27.3%), grade II in6patients (4.5%), grade III in1patients (1.6%).In IMRT group, Grade0radiation pneumonitis occurred in15patients(68.2%),grade I in27patients (27.3%), grade II in6patients (3.5%), acutedermatitis of grade III and IV were not observed，no differences were observed in twogroups. Excellent or good cosmetic outcome were95.3%in CRT group and95.5%inIMRT group(p=0.128).The PTV coverage in IMRT plan was similar to that of the conventional plan(98.9%vs98%), the difference was not statistically significant (p=0.218). The percentageof PTV receiving more than100%、105%、110%prescribed dose (V100%、 V105%、V110%) in IMRT group decreased than CRT group, the difference was statisticallysignificant (p=0.003, p=0.001,p=0.04). Dose distribution homogeneity indices(HI) ofCRT and IMRT were1.30±0.14and1.12±0.03, respectively, the difference wasstatistically significant (p=0.001). Dose distribution conformal indices(CI) of CRT andIMRT were1.30±0.14and1.12±0.03, respectively, with statistically significantdifferences (p=0.038). OAR assessment results: compared with the conventional plan, IMRT plans ipsilateral lung V20, V30, V40were lower (p=0.18, p=0.02, p=0.01), whileV5is increased (p=0.02); contralateral breast: IMRT plans V2, V3, V4, V5are more thanconventional scheme, the difference was statistically significant (p=0.005, p=0.008,p=0.03, p=0.04), there was no difference in V10(p=0.12); heart: compared with CRTplans, IMRT plans for V30, V40were lower, the difference was statistically significant(p=0.04, p=0.02), V5was increased (p=0.03), V20difference was not statisticallysignificance (p=0.18).Conclusions：Compared with CRT, IMRT can significantly reduce the incidence oflate radiation dermatitis and the probability of occurrence of radiation pneumonitis,there was no significant difference; CRT and IMRT techniques can obtain bettercosmetic results recently. The target volume dose uniformity and conformal propertiesof IMRT planning were better than CRT significantly, IMRT plans can reduce radiationdose and volume of ipsilateral lung, heart, contralateral breast and other organs at risksignificantly, but the low dose irradiated volume increases in contralateral breastsignificantly.