Comparative dosimetric study of two strategies of intensity-modulated radiotherapy in nasopharyngeal cancer
- Department of Radiation Therapy and Oncology, China Medical University Hospital, Taichung, Taiwan (China)
- Department of Radiation Therapy and Oncology, China Medical University Hospital, Taichung, Taiwan (China) and School of Medicine, China Medical University, Taichung, Taiwan (China) and School of Medical Technology and Engineering, National Yang-Ming University, Taipei, Taiwan (China)
This study compared the target volume coverage and normal tissues sparing of simultaneous integrated boost (SIB-IMRT, 1-phase) and sequential-IMRT (2-phase) for nasopharyngeal carcinoma (NPC). Fourteen consecutive patients with newly diagnosed primary NPC were enrolled in this study. The CT images were transferred to a commercial planning system for structural delineation. The gross tumor volume (GTV) included gross nasopharyngeal tumor and involved lymph nodes of more than 1-cm diameter. The clinical target volume (CTV) modeled two regions considered to represent different risks. CTV1 encompassed the GTV with 5-10-mm margin of adjacent tissues. CTV2 encompassed ipsilateral or contralateral elective nodal regions at risk of harboring microscopic tumor. A commercial IMRT treatment planning system (Eclipse Version 7.1) was used to provide treatment planning. Seven fixed-gantry (0{sup o}, 50{sup o}, 100{sup o}, 150{sup o}, 210{sup o}, 260{sup o}, 310{sup o}) angles were designated. The 14 patients were treated with sequential-IMRT, and treatment was then replanned with an SIB strategy to compare the dosimetric difference. For the sequential strategy, the dose delivered to CTV1/CTV2 in the first course was 54 Gy (1.8 Gy x 30 Fr); while CTV1 was boosted by an additional 16.2 Gy (1.8 Gy x 9 Fr) in the second course. For SIB-IMRT, the dose prescribed to CTV1 was 69.7 Gy (2.05 Gy x 34 Fr); 56.1 Gy was given to CTV2 (1.65 Gy x 34 Fr). A statistical analysis of the dose-volume-histogram of target volumes and critical organs was performed. Paired Student's t-test was used to compare the dosimetric differences between the two techniques. The mean dose to CTV1 was 101.7 {+-} 2.4% and 102.3 {+-} 3.1% of the prescribed dose for SIB-IMRT and sequential-IMRT, respectively. The mean CTV2 dose was 109.8 {+-} 4.7% of the prescribed dose for SIB-IMRT and 112.6 {+-} 6.0% of the prescribed dose for sequential-IMRT. The maximal dose to the spinal cord was 4489 {+-} 495 cGy and 3547 {+-} 767 cGy for SIB and sequential-IMRT (p = 0.0001), respectively. The maximal dose to brain stem was significantly higher using SIB technique (5284 {+-} 551 cGy) than sequential-IMRT (4834 {+-} 388 cGy) (p = 0.0001). The mean dose to the parotid gland and ear apparatus was significantly lower using SIB-IMRT. The mean dose to the right/left parotids was 2865 {+-} 320 cGy/2903 {+-} 429 cGy and 3567 {+-} 534 cGy/3476 {+-} 489 cGy for SIB and sequential-IMRT, respectively (p = 0.0001). Target coverage was the same for both techniques; the dose distribution in the elective nodal area with SIB was superior to that with sequential-IMRT. SIB-IMRT provides better sparing of parotid gland and inner ear structures. Extra caution should be taken when applying SIB-IMRT since critical organs close to the boost volume may receive higher doses.
- OSTI ID:
- 20783348
- Journal Information:
- Medical Dosimetry, Vol. 30, Issue 4; Other Information: DOI: 10.1016/j.meddos.2005.07.001; PII: S0958-3947(05)00146-9; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0958-3947
- Country of Publication:
- United States
- Language:
- English
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