Clinical study of the necessity of replanning before the 25th fraction during the course of intensity-modulated radiotherapy for patients with nasopharyngeal carcinoma.
ABSTRACT To quantify the target and normal structures on dose distributing variations during intensity-modulated radiotherapy (IMRT) and to assess the value of replanning for nasopharyngeal carcinoma (NPC) patients.
Twenty-eight NPC patients treated with IMRT were recruited. The IMRT was delivered in 33 fractions, to 70 to 76Gy, to the gross tumor volume (GTV). Before the 25th fraction of IMRT, a new simulation computed tomography (CT) scan was acquired for all patients. According to the dose constraint criterion in the Radiation Therapy Oncology Group (RTOG) 0225 protocol, the replanning was generated on the new simulation CT. With the Quality Assessment Center of a CORVUS 6.3 treatment planning system, a phantom plan was generated for each patient by applying the beam configurations of the initial plan to the anatomy of the new simulation CT. The dose-volume histograms of the phantom plan were compared with the replanning.
The percentage of prescription dose delivered to the clinical target volume (CTV1) was significantly increased by 4.91% +/- 10.89%, whereas the maximum dose to the spinal cord, mean dose to the left parotid, and V30 to the right parotid were significantly decreased by 5.00 +/- 9.23Gy, 4.23 +/- 10.03Gy, and 11.47% +/- 18.89% respectively in the replanning, compared with the phantom plan (p < 0.05). Based on the dose constraint criterion in the RTOG0225 protocol, 50% of phantom plans (14/28) were out of limit for the dose to the normal critical structures, whereas no plan was out of limit in replanning (p < 0.001).
Replanning for patients with NPC before the 25th fraction during IMRT helps to ensure adequate dose to the target volumes and safe doses to critical normal structures.
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ABSTRACT: To analyze the patterns of locoregional failure in patients with head-and-neck cancer treated with inverse planning intensity-modulated radiotherapy (IMRT). Between February 1997 and December 2000, 165 patients with histologically confirmed head-and-neck cancer were treated using a parotid-sparing inverse planning IMRT protocol. Thirty-nine patients who received either palliative repeat irradiation or IMRT as a boost were excluded from this analysis, leaving 126 patients for this analysis. Of the 126 patients, 30 were women and 96 were men (median age 56 years, range 13-84). Fifty-two patients (41%) received definitive IMRT. Of the 52 patients, 17 were treated with RT alone and 35 with concurrent cisplatin-based chemotherapy regimens. Seventy-four patients (59%) received postoperative IMRT. The median follow-up was 26 months (range 12-55). IMRT was used only in the upper neck for salivary sparing. The lower neck was treated with a conventional AP low-neck port abutted to the inferior IMRT dose distribution border. The radiation dose was prescribed to the two clinical target volumes (CTVs) according to the assumed risk of containing disease. The mean dose for definitive IMRT patients was 72.64 +/- 4.83 Gy to CTV1 and 64.34 +/- 5.15 Gy to CTV2. The mean dose to CTV1 and CTV2 in postoperative cases was 68.53 +/- 4.71 Gy and 60.95 +/- 5.33 Gy, respectively. The locations of failure were analyzed. Seventeen locoregional failures (persistent or recurrent disease) were found. Of these 17 failures, 9 (53%) were inside CTV1. One failure (6%) was marginal to CTV1 but inside CTV2. One failure (6%) occurred outside CTV1 but inside CTV2. Another failure was marginal to CTV2. Of the 17 failures, 5 (28%) were found outside of the IMRT field and in the lower neck. Dose-volume histogram analysis revealed that for all but 1 patient, the recurrent/persistent disease within the CTVs received comparable or superior dose coverage relative to the CTV. The 2-year actuarial locoregional control rate was 85%, and the ultimate locoregional control rate after surgical salvage was 89%. We observed no dermal failure and only one marginal failure in the region adjacent to the spared parotid glands. We have shown that the target definition and coverage for patients treated with IMRT for parotid sparing is adequate. The predominant tumor failure within CTV1 may imply the need to identify patients with radioresistant tumor subvolumes (such as hypoxic regions) within the CTV. This information would assist in discriminating a subgroup of tumors for a more aggressive and target-specific therapeutic approach.International Journal of Radiation OncologyBiologyPhysics 03/2003; 55(2):312-21. · 4.52 Impact Factor
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ABSTRACT: This study was designed to demonstrate the feasibility of 3-dimensional (3D) treatment planning in patients with carcinoma of the nasopharynx, and to explore its potential therapeutic advantage over the traditional 2-dimensional (2D) approach in this disease. Qualitative and quantitative comparisons between the two techniques were made for the boost portion of the treatment (19.8 Gy of a total 70.2 Gy treatment schedule) in 10 previously untreated patients and for the entire treatment in 5 patients with locally recurrent disease. The 2D and 3D plans were compared in each patient using dose-volume histograms (DVH's), tumor control probabilities (TCP's), normal tissue complication probabilities (NTCP's), and a new biologic figure of merit that describes the probability of uncomplicated control. Although there was no attempt to optimize the 3D treatment approach by using this method throughout the total treatment course (rather than for the boost only), it was still found that for each of the endpoints examined the 3D approach resulted in improved plans. An average of 22% of the target volume was underdosed at the 95% isodose level with the 2D plans compared to 7% with the 3D plans. The improved treatment planning by 3D increased the mean dose to the tumor volume by an average of 13% over 2D planning. The dose to normal structures such as the mandible and parotid glands was reduced with the 3D plans while the brain stem and spinal cord remained within tolerance limits. The probability of uncomplicated tumor control was increased by an average of 15% with 3D treatment planning compared to the 2D approach. Our findings demonstrate the potential of 3D planning for improving the treatment of carcinoma of the nasopharynx, but prospective studies are required to define the true clinical advantages of this methodology.International Journal of Radiation OncologyBiologyPhysics 05/1991; 20(4):823-33. · 4.52 Impact Factor
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ABSTRACT: Many patients with head-and-neck (H&N) cancer have tumor shrinkage and/or weight loss during the course of radiotherapy. We conducted this retrospective study to determine the dosimetric effects of repeat computed tomography (CT) imaging and replanning during the course of intensity-modulated radiotherapy (IMRT) on both normal tissues and target volumes. A retrospective chart review identified 13 patients with H&N cancer treated with IMRT who had repeat CT imaging and replanning during the course of radiotherapy. The first IMRT plan for each patient was generated based on the original planning CT scan acquired before the start of treatment. Because of tumor shrinkage or weight loss during radiotherapy, a second CT scan was acquired, and a new plan was generated and used to complete the course of IMRT. CT-CT fusion was used to correct patient positioning differences between the scans. By using a commercial inverse IMRT planning system, a hybrid IMRT plan was generated for each patient by applying the beam configurations of the first IMRT plan (including the intensity profile of each beam) to the anatomy of the second CT scan. The dose-volume histograms of the actual and hybrid IMRT plans were compared using analysis of variance methods for repeated measures. All patients had locally advanced, nonmetastatic Stage III or IV disease, including 6 nasopharynx, 6 oropharynx, and 1 unknown primary site. All patients were treated with concurrent platinum-based chemotherapy. When replanning vs. not replanning was compared, the hybrid IMRT plans (without replanning) demonstrated reduced doses to target volumes and increased doses to critical structures. The doses to 95% (D95) of the planning target volumes of the gross tumor volume (PTVGTV) and the clinical target volume (PTVCTV) were reduced in 92% of patients, by 0.8-6.3 Gy (p=0.02) and 0.2-7.4 Gy (p=0.003), respectively. The maximum dose (Dmax) to the spinal cord increased in all patients (range, 0.2-15.4 Gy; p=0.003) and the brainstem Dmax increased in 85% of patients without replanning (range, 0.6-8.1 Gy; p=0.007). Repeat CT imaging and replanning during the course of IMRT for selected patients with H&N cancer is essential to identify dosimetric changes and to ensure adequate doses to target volumes and safe doses to normal tissues. Future prospective studies with larger sample sizes will help to determine criteria for repeat CT imaging and IMRT replanning for H&N cancer patients undergoing radiotherapy.International Journal of Radiation OncologyBiologyPhysics 03/2006; 64(2):355-62. · 4.52 Impact Factor