Parotid Gland Sparing Radiotherapy Technique Using 3-D Conformal Radiotherapy for Nasopharyngeal Carcinoma / 대한방사선종양학회지

ABSTRACT

PURPOSE: Although using the high energy photon beam with conventional parallel-opposed beams radio-therapy for nasopharyngeal carcinoma, radiation-induced xerostomia is a troublesome problem for patient. We conducted this study to explore a new parotid gland sparing technique in 3-D conformal radiotherap (3-D CRT) in an effort to prevent the radiation-induced xerostomia. MATERIALS AND METHODS: We performed three different planning for four clinically node-negative naso-phar yngeal cancer patients with different location of tumor(intracranial extension, nasal cavity extension, oropharyngeal extension, parapharyngeal extension), and intercompared the plans. Total prescription dos <. Was 70.2 Gy to the isocenter, For plan-A, 2-D parallel opposing fields, a conventional radiotherapy technique, were employed. For plan-B, 2-D parallel opposing fields were used up until 54 Gy an < 3 afterwards 3-D non-coplanar beams were used. For plan-C, the new technique, 54 Gy was delivered b r 3-D conformal 3-port beams (AP and both lateral ports with wedge compensator; shielding both superficial lobes of parotid glands at the AP beam using BEV) from the beginning of the treatment and early spinal cord block (at 36 Gy) was performed. And bilateral posterio r necks were treated with electron after 36 Gy. After 54 Gy, non-coplanar beams were used for cone-down plan. We intercompared dose statistic; Dmax, Dmin, Dmean, D95, D05, V95, V05, Volume receiving 46 Gy) and dose volume histograms (DVH) of tumor and normal tissues and NTCP values of parotid glands for the above three plans. RESULTS: For all patients, the new technique (plan-C) was comparable or superior to the other plans in target volume isodose distribution and dose statistics and it has more homogenous target volume, coverage. The new technique was most superior to the other plans in parotid glands sparing (volume receiving 46 Gy 100, 9 B, 69% for each plan-A, B and C). And it showed the lowest NTCP value of parotid glands in all patients (range of NTCP; 96-100%, 79-99%, 51-72% for each plan-A, B and C). CONCLUSION: We conclude that the new technique employing 3-D conformal radiotherapy at the beginning of radiotherapy and cone down using non-coplanar beams with early spinal cord block is highly recommended to spare parotid glands for node-negative nasopharygeal cancer patients.