ABSTRACT
The purpose of this dosimetric study was to evaluate the effect of beam number and arrangement on the dose distribution with intensity-modulated radiation therapy in patients with nasopharyngeal cancer. Computed tomography data sets of seven patients who were treated for nasopharyngeal carcinoma at the Peter MacCallum Cancer Centre were used for the present dosimetric study. The dose planned was 70 Gy in 7 weeks for the gross nasopharyngeal and nodal disease and the biological equivalents of 60 Gy in 6 weeks for the high-risk and 50 Gy in 5 weeks for the low-risk nodal disease. A plan using seven fields was compared to that using nine fields in all patients. Plans were assessed on the dose to the planning target volume (PTV) and the degree of parotid sparing achieved by evaluating both dose-volume histograms (DVH) and axial slices. Seven fields (three anterior and four posterior) provide good PTV coverage and satisfactory parotid sparing in patients with localized nasopharyngeal lesions. Nine fields appear to be better for tumours with significant posterolateral parapharyngeal extension. Parotid sparing is consistently better with nine fields. Both DVH and axial slices need to be evaluated before accepting any plan.
Subject(s)
Carcinoma/radiotherapy , Nasopharyngeal Neoplasms/radiotherapy , Radiotherapy Planning, Computer-Assisted , Radiotherapy, Conformal , Carcinoma/diagnostic imaging , Humans , Nasopharyngeal Neoplasms/diagnostic imaging , Radiotherapy Dosage , Tomography, X-Ray ComputedABSTRACT
Intensity-modulated radiotherapy (IMRT) has been available at Peter MaCallum Cancer Centre (PMCC) since November 2000. The present report illustrates two cases of our early experience with IMRT. Case 1 is a 66-year-old man with a T(1)N(2)M(0) nasopharyngeal carcinoma treated with chemo-radiotherapy using parotid-sparing IMRT. Fourteen months following treatment he remains in complete remission, with salivary function assessed using a xerostomia-specific quality of life questionnaire, having returned to near pretreatment levels by 12 months. Case 2 is a 70-year-old man with a T(4)N(0)M(0) base of tongue squamous cell carcinoma treated with chemo-radiotherapy after refusing radical surgery. He had received subtotal nodal irradiation to 36 Gy in 1994 for Hodgkins disease stage IIA. A radical dose was still achievable despite previous irradiation without exceeding unacceptable spinal cord dose with IMRT. He remains in complete remission 14 months from his initial presentation without evidence of neurological toxicity. Intensity-modulated radiotherapy allows sparing of critical normal structures in the head and neck without compromising dose to the tumour. It is, therefore, desirable for several clinical applications and essential in some, if unacceptable compromises are not to be made.
Subject(s)
Carcinoma, Squamous Cell/radiotherapy , Carcinoma/radiotherapy , Nasopharyngeal Neoplasms/radiotherapy , Radiotherapy Planning, Computer-Assisted , Radiotherapy, Conformal , Tongue Neoplasms/radiotherapy , Aged , Combined Modality Therapy , Humans , MaleABSTRACT
Intensity-modulated radiation therapy (IMRT) is an exciting new advance in the practice of radiation oncology. It is the use of non-uniform radiation beams to achieve conformal dose distributions. As a result of the high initial capital costs and the time and complexity of planning, IMRT is not yet a widely available clinical treatment option. We describe the process involved in applying this new technology to a case of locally advanced nasopharyngeal cancer.
