Dosimetric contribution of ovoid in the cervical cancer brachy radiotherapy through the intracavity combined with interstitial technique / 中华放射医学与防护杂志

ABSTRACT

Objective:To discuss the dosimetric contribution of the ovoid in the cervical cancer brachytherapy through the intracavity combined with interstitial(IC/IS)technique.Methods:The data on 20 patients with FIGO(2009)stageⅡ A, Ⅱ B or Ⅲ Bcervical cancer treated with radical radiotherapy in China-Japan Union Hospital of Jilin University during 2015-2017 was collected. External irradiation treatment was 45 Gy/1.8 Gy× 25 fractions. Brachytherapy was MRI-guided IC/IS brachytherapy with a prescription of 28 Gy/7 Gy× 4 fractions. All of 20 patients developed two kinds of plans, the ovoid group and the non-ovoid group. The original MRI-guided brachytherapy treatment plan was set(80 fractions)to the ovoid group. As contrast model that removed the ovoid and consisted of tandem combined with needles set to the non-ovoid group was built, and the same physicist designed the plan to make the dose of D90% for high-risk clinical target volume(HR-CTV)similar to the ovoid group. The dosimetric differences of the D90% and D98% for HR-CTV, D90% and D98% for intermediate-risk clinical target volume(IR-CTV)and D2 cm 3 for the bladder, rectum, sigmoid colon and small intestines between two groups of plans were analyze by paired t-test. Results:Compared with the ovoid group, the non-ovoid group showed no significant difference on HR-CTV D90%( P>0.05), but the HR-CTV D98%(6.99±0.60 vs. 6.78±0.76), IR-CTV D90%(4.71±0.58 vs. 4.26±0.57) and D98%(3.77±0.58 vs. 3.26±0.59) of the non-ovoid group decreased significantly( t=3.906, 9.860, 8.636, P<0.05). The sigmoid colon showed no significant difference( P>0.05), while the bladder (5.29±0.67 vs. 4.92±0.74), rectum (3.72±0.69 vs. 3.35±0.92) and small intestines (3.05±1.37 vs. 2.98±1.34) D2 cm 3of the non-ovoid group decreased significantly( t=8.758, 7.543, 8.059, P<0.05). Conclusions:Ovoid is very important for IC/IS technique in cervical cancer brachytherapy. Reasonable optimization of the dose weight ratio of the ovoid and the needle can bring better clinical benefits.