Comparison of intensity modulated radiation therapy (IMRT) treatment techniques for nasopharyngeal carcinoma

Abstract

SUMMARY We studied target volume coverage and normal tissue sparing of serial tomotherapy intensity modulated radiation therapy (IMRT) and fixed-field IMRT for nasopharyngeal carcinoma (NPC), as compared with those of conventional beam arrangements. Twelve patients with NPC (T2-4N1-3M0) at Mallinckrodt Institute of Radiology underwent computed tomography simulation. Images were then transferred to a virtual simulation workstation computer for target contouring. Target gross tumor volumes (GTV) were primary nasopharyngeal tumor (GTV NP ) with a prescription of 70 Gy, grossly enlarged cervical nodes (GTV LN ) with a prescription of 70 Gy, and the uninvolved cervical lymphatics [designated as the clinical tumor volume (CTV)] with a prescription of 60 Gy. Critical organs, including the parotid gland, spinal cord, brain stem, mandible, and pituitary gland, were also delineated. Conventional beam arrangements were designed following the guidelines of Intergroup (SWOG, RTOG, ECOG) NPC Study 0099 in which the dose was prescribed to the central axis and the target volumes were aimed to receive the prescribed dose ± 10%. Similar dosimetric criteria were used to assess the target volume coverage capability of IMRT. Serial tomotherapy IMRT was planned using a 0.86-cm wide multivane collimator, while a dynamic multileaf collimator system with five equally spaced fixed gantry angles was designated for fixed-beam IMRT. The fractional volume of each critical organ that received a certain predefined threshold dose was obtained from dose-volume histograms of each organ in either the three-dimensional or IMRT treatment planning computer systems. Statistical analysis (paired t-test) was used to examine statistical significance. We found that serial tomotherapy achieved similar target volume coverage as conventional techniques (97.8 ± 2.3% vs. 98.9 ± 1.3%). The static-field IMRT technique (five equally spaced fields) was inferior, with 92.1 ± 8.6% fractional GTV NP receiving 70 Gy ± 10% dose (P < 0.05). However, GTV LN coverage of 70 Gy was significantly better with both IMRT techniques (96.1 ± 3.2%, 87.7 ± 10.6%, and 42.2 ± 21% for tomotherapy, fixed-field IMRT, and conventional therapy, respectively). CTV coverage of 60 Gy was also significantly better with the IMRT techniques. Parotid gland sparing was quantified by evaluating the fractional volume of parotid gland receiving more than 30 Gy; 66.6 ± 15%, 48.3 ± 4%, and 93 ± 10% of the parotid volume received more than 30 Gy using tomotherapy, fixed-field IMRT, and conventional therapy, respectively (P < 0.05). Fixed-field IMRT technique had the best parotid-sparing effect despite less desirable target coverage. The pituitary gland, mandible, spinal cord, and brain stem were also better spared by both IMRT techniques. These encouraging dosimetric results substantiate the theoretical advantage of inverse-planning IMRT in the management of Publication of the International Union Against Cancer NPC. We showed that target coverage of the primary tumor was maintained and nodal coverage ...

PARP1 Is Overexpressed in Nasopharyngeal Carcinoma and Its Inhibition Enhances Radiotherapy

“…This reflects both the inaccessible location of the nasopharynx as well as the radiosensitivity of nasopharyngeal carcinoma cells. More recent advances in radiotherapy such as three-dimensional conformal radiotherapy and intension-modulated radiotherapy have helped to achieve good prognosis, in particular for early-stage nasopharyngeal carcinoma (6,7). For advanced nasopharyngeal carcinoma, however, treatment outcomes have been poor due to distant metastases and recurrence (8).…”

High-Risk Factors of Parotid Lymph Node Metastasis in Nasopharyngeal Carcinoma: A Case-Control Study

“…Mean dose of parotid was 55.3Gy [8] and ≥ grade II late xerostomia was 29.7 % [9]. With the development of radiation technique, parotid-sparing IMRT has decrease the dose distribution of parotid [10,11] and improved patients' quality of life, particularly xerostomia recovery [12]. However, with the use of parotid-sparing IMRT, parotid region recurrence has been reported.…”

Dose Planning Study of Target Volume Coverage with Intensity-Modulated Radiotherapy for Nasopharyngeal Carcinoma: Penang General Hospital Experience

“…This is especially so in stages III and IV disease where complicated target volumes which lie very close to critical organs like the spinal cord and brainstem making it impossible to be treated with adequate high dose with conventional 2D or 3DCRT. However, IMRT has been shown to be able to deliver high dose to the target areas despite these obstacles (Cheng et al, 2001;Waldron et al, 2003). The most important aim of RT is maximization of the therapeutic index which essentially means maximal radiation dose to the target volumes while delivering as little dose as possible to the organs at risk (OAR).…”

“…Clinically, this should be expected to translate to maximal local control and survival with as little toxicity as possible. Comparison of dosimetry for NPC treatment between 3DCRT to IMRT has been done in several studies and these studies have collectively shown advantages of IMRT over 3DRT with regards to tumour coverage and OARs (Cheng et al, 2001;Hunt et al, 2001;Kam et al, 2003;Kristensen et al, 2007). However, these studies were done with different protocols from that of our institution and included different total doses to different target volumes.…”