3 Results
3.1 Post-implant dosimetry
The mean ± standard deviation of post-implant D90 (the doses delivered to 90% of the target volume) of the patients was 115.1 ± 19.9 Gy, and higher than the prescribed dose for each patient. The V100 (the percentage of target volume that receives at least 100% of the prescribed dose) was more than 85% for every patient with a median of 94.5% ranging from 87.7 to 96.1, and the mean ± standard deviation of V150 (the percentage of target volume that receives at least 150% of the prescribed dose) was 50.2% ± 11.7%.
3.2 Local control
During the follow-up, the local control rate was 7/7. No recurrent lesion was found in the patients undergoing surgery combined with brachytherapy. In patients treated with sole brachytherapy, 4/5 were radiological partial response and 1/5 was radiological complete response. In those reaching radiological partial response, 3/4 were pathological complete response. Among all 5 patients undergoing sole brachytherapy, local control condition was also described as the changes of tumor maximum diameter, MR signal evaluation and pathological examination by core-needle aspiration as follow.
3.2.1 Tumor maximum diameter
There was only one lesion in every patient. And the tumor maximum diameter at first visit, 2 months’ follow-up, 6 months’ follow-up and last follow-up were demonstrated in Figure 2. All the lesions were stable at the first follow-up, and reached partial regression or complete regression at 6 months’ follow-up (Figure 3).
3.2.2 MR signal evaluation
Of the patients treated with sole brachytherapy, 3/5 underwent MR examination before and after the brachytherapy. The MR were performed no more than 1 month before the pre-operative or post-operative biopsy. All lesions presented hyper-intense compared with muscle in the pre-operative T2 weighted images, and 2 lesions turned to hypo-intense and 1 lesion turned to isointense compared with muscle in the post-operative T2 weighted images (Figure 4).
3.2.3 Core-needle aspiration
Pathological examination by core-needle aspiration was performed on 3/4 of the lesion reaching partial regression, and specimens from at least five spots in the radiological tumor volume were taken under the guidance of the far-infrared navigation guidance system mentioned before. No tumor cell was found in all the specimens (Figure 5). Thus, all the patients receiving core-needle aspiration were regarded as pathological complete regression.
3.3 Side effects or toxicity
No operative complication such as cerebrospinal fluid leakage, hematoma or infection was observed. Radiation related acute toxicity, including dry desquamation, edema and erythema on skin were observed in all the patients, while 6/7 were classified as RTOG grade 1 and 1/7 was classified as RTOG grade 2, and no RTOG grade 3 or 4 toxicity were observed. None experienced late toxicity. Notably, no radiation related growth retardation and secondary cancer were observed.