Research Paper Related To Intensity Modulated Radiotherapy In Nasopharyngeal Carcinoma

Intensity-modulated radiation therapy (IMRT) is a highly conformal and sophisticated treatment modality. Because of the high dose conformation in the target volume and minimum dose in the organs at risk in IMRT, we should make mandatory accurate dose verification, both in terms of absolute dose in points and relative dose distributions. But there is still a 3% or 5% deviation between planned dose and measured dose. Our paper investigated some characteristic factors of beam, such as beam number, total segment number, average beam width and average beam weight and discussed the affection of beam characteristic on absolute dose verification in step and shoot IMRT. 40 patients' IMRT absolute dose verifications were performed at The University of Maryland Medical Centre. We applied Bivariate correlation method of linear correlation to determine the relation between measured dose deviation and beam characteristic, total segment number was significantly related to the absolute value of measured dose deviation (correlation coefficient is 0.520 p=0. 019) . Then these data were calculation by Stepwise method of linear regression. Between the absolute value of dose difference(Y) and total segment number(X), there exited a significant positive correlation. Y=3.98X+0.604 (F=6. 654, p=0. 019). When combining with total segment number(X1) and Average beam width(X2), P value closed to 0.05, Y=3. 984X1 -0.777X2 +2.54 (F=3. 536 p=0. 052). In two 9 beam patients, their total segment numbers were more than 90 and their absolute values of dose difference were more than 4. 5. Our study showed both total segment number and average beam width had an affection on the measured dose of the ion chamber. We should not apply more segment number in IMET planIntensity-modulated radiation therapy (IMRT) plan was produced traditionally through the intensity optimization, which ignore constrains imposed by multileaf collimator and result in more segments than the number of intensity levels. A new inverse planning technique called direct aperture optimization (DAO) can allow user to pre-specify the number of apertures to deliver from each beam direction and optimize simultaneously both shapes and the weights of the apertures. Therefore, direct aperture optimization can produces highly efficient treatment deliveries that maintain the full dosimetric benefits of IMRT. Nasopharynx is one of the sites where 3D-CRT and IMRT can play a major role in improving the therapeutic ratio. We applied direct aperture optimization technique to perform IMRT plans of nasopharyngeal carcinoma. DAO inverse planning system spent about 40 minutes to 60 minutes for each IMRT plan of nasopharyngeal carcinoma with 7 beams and 7 apertures for each beam and did a good IMRT plan with good target coverage, good homogeneity index and safe doses in critical normal tissue and organs. Because parotid is an important benefit part in IMRT of nasopharyngeal carcinoma, we investigated the IMRT plan of nasopharyngeal carcinoma with sparing unilateral parotid and added plan tumor volume (PTV) margin for parotid gland. We regarded the IMRT plan of nasopharyngeal carcinoma with sparing just only unilateral parotid can improve the coverage of clinical tumor volume (CTV) and solved the problem when tumor closed one parotid and avoid neither good parotid (closed to bigger lesion) dose and nor good plan. Add PTV margin for parotid were benefit to preserving parotid function and decreasing the uncertainty of anatomic changes of parotid during radiotherapy, but the IMRT plan should be under good target coverage as possible as.Purpose: To evaluate the feasibility, recent result of the on nasopharyngeal carcinoma (NPC) and observe the acute complication. Materials and methods: Forty patients with NPC were treated first by simultaneous modulated accelerated radiation therapy (SMART). Only primary lesion and upper neck were treated by SMART, and Meddle and low neck were received conventional radiotherapy. We give gross tumor volume (GTV) and clinical tumor volume (CTV) of nasopharyngeal carcinoma with different dose. Primary tumor: GTV-T: 70Gy/32f/6.4w, 2. 19Gy/f. CTV1: 62Gy/32f/6. 4w, 1. 90Gy/f. CTV2 : 56Gy/32f/6. 4w, 1. 75Gy/f. Lymph nodes: GTV-N : 70Gy/32f/6. 4w, 2. 19Gy/f . CTV2: 56Gy/32f/6. 4w, 1. 75Gy/f. 14 patients with III staging and 17 patients with IV staging were received 2 cycle inducement chemotherapy.Results: Each target volumes covered by 95% isodose were more than 99%, The mean homogeneity index of GTV was 1.22(1.11 - 1.31). The mean conformal index of GTV was 0. 82 (0. 75-0. 87) . Doses of All of risk at organ were under the safe range. There was no Grade 4 acute toxicity in all patients. After radiotherapy, Complete recovery (CR): 29, Partial recovery (PR):11. Patients were followed up at a median follow-up time of 27 months. One was died from distant metastasis. One and two years local recurrence-free survival rate were 96.2%. One and two years distant metastasis-free rate were 94.8%. One and two years survival rate were 97. 5%.Conclusions: The technique of SMART improves the advanced of intensity modulated radiotherapy. It increased the fractional and total dose for tumor, decreased the fractional and total dose of the normal tissues and organs, shorted the treatment time, have a good recent result and the complication of radiotherapy is able to endure. We think the technique of SMART is very good treatment method for nasopharyngeal carcinoma.Purpose: To investigate prospectively the feasibility and efficacy of dose escalation using three-dimensional conformal radiotherapy (3D-CRT) boost technique for locally recurrent nasopharyngeal carcinoma (NPC) in a randomized study.Materials and methods: Thirty-six patients with locally recurrent NPC were treated between August 1999 and August 2002 at our institution. Eligibility criteria for this randomized trial were as follows: (1) locally recurrent NPC after prior radical radiotherapy (68-72 Gy); (2) interval between first radiation and local recurrence of ≥6 months; and (3) no cervical lymph node involvement and no distant metastasis. Patients were treated with external-beam radiotherapy using small shaped fields to 50 Gy/25 fractions/5 weeks, followed by a 3D-CRT boost to the gross tumor region. Patients were randomized to three boost dose levels: 16Gy (4 Gy×4 fractions) for Group I; 20 Gy (4 Gy×5 fractions) for Group II; and 24Gy (4 Gy×6 fractions) for Group III. All boost doses were delivered as 3 fractions per week. Twelve patients were enrolled in each group. Median follow-up was 27 months (range 14-44 months). Results: Treatment was well tolerated (no grade IV toxicity in any groups) and there was no significant difference among the three groups in acute and late toxicity (p > 0.05). Overall 3-year survival rate was 65%, 3-year local recurrence-free survival rate was 45%, and 3-year distant metastasis rate was 10%. The local-recurrence-free survival was significantly higher (72%) for the high-dose Group III than for Groups I and II (37% and 28%, respectively, p=0.047). The 3-year distant metastases rates were 17%, 0% and 18% for Group I, II, III respectively (p = 0.35). There was no significant difference in the 3-year overall survival rate among the three groups (72%, 59%, and 82%, respectively, p=0.60). Univariate analysis revealed that skull base invasion (p = 0. 017) and pathology (p = 0. 0006) were significant prognostic factors foroverall survival rate.Conclusions: Re-irradiation with high-dose 3D-CRT boost technique results in high local control rate and acceptable toxicity in patients with recurrent NPC. Dose escalation to the boost volume to 74Gy (54Gy+24Gy boost) results in improved recurrence-free survival compared to lower doses.Purpose: To evaluate the cranial nerve (CN) palsy associated with nasopharyngeal carcinoma (NPC), factors influencing neurologic outcome of radiation therapy (RT), and patterns and time course of neurologic recovery of CN palsy.Materials and Methods: Between July 1987 and July 1989, 93 patients, who presented with CN palsy at the time of diagnosis of NPC, were studied. All patients underwent external-beam RT using either Cobalt-60 or 6 MV photon beams to a dose of 69Gy - 84Gy at 2Gy/fraction. The time course and pattern of neurologic recovery (complete, partial, or none) from CN palsy were evaluated. Factors including age, sex, stage, histology, incidence and distribution of types of CNs involved, duration of CN palsy, time course of tumor response during RT were correlated with the patterns and the time course of neurologic CN recovery using univariate and multivariate analysis. Results: CN palsy most commonly involved the CN V (38%), CN VI (26%), and CN XII (11%) accounting for majority of the cases (75%). The time course of CN recovery was variable and protracted. Most patients showed significant improvement upon completion of RT with 51%, 19% and 30% complete, partial and no recovery, respectively, and further improvement 6 months after RT with 58%, 17% and 25% respectively. CNs V, VI, and XII account for 75% cases with no recovery (NR). Recovery was best in CNs II, IX and XI (100%, 100% and 87% respectively), and worst in CNs IV, VII and XII, showing 67%, 60% and 40% no recovery. Neurologic CN recovery correlated significantly with pre-therapy duration of CN palsy (p = 0. 002), neurologic symptom improvement during RT (p = 0.041) and the time course of clinical tumor regression (p = 0.037) . Age, sex, T-stage, N-stage, histology, anterior vs. posterior CN palsies, and base of skull involvement, were not significant. Only pre-therapy duration of CN palsy was confirmed by multivariate analysis (0=0.037, X~2=6. 259, p=0. 015) Conclusions: Based upon our limited data, most patients with CN palsyrespond well to RT. The time course of neurologic recovery is variable and can be protracted indicating the need for continuous and close neurologic surveillance. The poorer neurologic outcome associated with longer duration of CN symptoms may be related to more severe long-term CN compression resulting in irreversible damage. The better neurologic outcome with fast tumor regression and faster improvement of CN symptoms during RT likely indicates rapid "decompression" of CN by tumor response to treatment.