HIGH-DOSE-RATE BRACHYTHERAPY FOR CARCINOMA OF THE ORAL TONGUE

Purpose: The purpose of this study is to assess the feasibility of tre ating early-staged tongue cancer with high dose rate (HDR) remote afte rloading technique. Furthermore, a new figure of merit, the Geometry I ndex (GI), is introduced to quantify the quality of the implants. Meth ods and Materials: Between 1994 and 1995, eight patients with carcinom a of the oral tongue were treated solely with interstitial implant usi ng the HDR remote afterloading technique. Five patients had T1 NO dise ase and the remaining three had T2 NO disease. Elective neck treatment was withheld. The male-to-female ratio was 1:1, and the mean age 60 y ears (range: 32-72 years). The median follow-up time was 26 months (ra nge: 6-30 months). The afterloading catheters were positioned through the submandibular approach with the assistance of templates. Six patie nts had single planar implant and the remaining two had double planar implant. The median number of catheters inserted was 5 (range: 4-9). T he median dose given was 60 Gy in 10 fractions over 6 days. The interf raction interval was 7 h. Mandibular and maxillary shields were insert ed prior to treatment. Thomadsen ef al. introduced the use of Implant Quality Index (QI). We introduce a new parameter, GI, which is defined as ratio of the QI of the nonoptimized executed implant to the corres ponding QI value of the nonoptimized idealized implant. Results: The m ucositis lasted for 6 to 20 weeks (median: 10 weeks). There was no loc al failure up to a median follow-up of 26 months. Two patients develop ed ipsilateral neck node metastases at 2 and 4 months following implan t, respectively. One patient had involvement at level II and the other failed at level I to III. Both patients were salvaged by neck node di ssection and regionally remained in control. One patient with multiple nodal metastases and extracapsular spread developed biopsy-proven liv er metastases and succumbed 6 months following implant. One patient tr eated with double planar implant developed Grade 3 necrosis of the sof t tissue and bone. This complication is largely preventable now, as we have acquired more technical expertise. The mean GI values for the si ngle and double planar implants were 0.88 (range: 0.84-0.91) and 0.8, respectively. This correlates with our practical experience that it is more difficult to maintain a good geometry as double planar implant i s required. The GI gives a better view of the geometry of implant as i t compares the nonoptimized QI of the executed implant with its ideal counterpart. The failure to achieve a high GI in double planar implant s is presumed to relate to technical difficulties rather than variatio n in individual performance. Conclusion: Our preliminary experience in treating early-staged tongue cancer with the HDR remote afterloading technique is inspiring, as it gives a local control rate of 100% with acceptable morbidity. Further studies are eagerly awaited to delineate the optimum schedule for this modality of treatment. It is hoped that the GI values, which represents the skills of insertion, could be rou tinely reported so that treatment results between different centers co uld be compared in a more precise manner. (C) 1997 Elsevier Science In c.