Evaluation of radiotherapy techniques for radical treatment of lateralised oropharyngeal cancers : Dosimetry and NTCP.
OBJECTIVE
The aim of this study was to investigate potential advantages and disadvantages of three-dimensional conformal radiotherapy (3DCRT), multiple fixed-field intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) in terms of dose to the planning target volume (PTV), organs at risk (OARs) and normal tissue complication probability (NTCP) for delivering ipsilateral radiotherapy.


METHODS
3DCRT, IMRT and VMAT were compared in patients with well-lateralised primary tonsillar cancers who underwent primary radical ipsilateral radiotherapy. The following parameters were compared: conformity index (CI); homogeneity index (HI); dose-volume histograms (DVHs) of PTVs and OARs; NTCP, risk of radiation-induced cancer and dose accumulation during treatment.


RESULTS
IMRT and VMAT were superior to 3DCRT in terms of CI, HI and dose to the target volumes, as well as mandible and dose accumulation robustness. The techniques were equivalent in terms of dose and NTCP for the contralateral oral cavity, contralateral submandibular gland and mandible, when specific dose constraint objectives were used on the oral cavity volume. Although the volume of normal tissue exposed to low-dose radiation was significantly higher with IMRT and VMAT, the risk of radiation-induced secondary malignancy was dependant on the mathematical model used.


CONCLUSIONS
This study demonstrates the superiority of IMRT/VMAT techniques over 3DCRT in terms of dose homogeneity, conformity and consistent dose delivery to the PTV throughout the course of treatment in patients with lateralised oropharyngeal cancers. Dosimetry and NTCP calculations show that these techniques are equivalent to 3DCRT with regard to the risk of acute mucositis when specific dose constraint objectives were used on the contralateral oral cavity OAR.
Head and Neck Unit, Royal Marsden Hospital, Downs road, SM2 5PT, Sutton, Surrey, UK.|Head and Neck Unit, Royal Marsden Hospital, SW3 6JJ, London, UK.|The Institute of Cancer Research, SW3 6JB, London, UK.|The Institute of Cancer Research, SM2 5NG, Sutton, UK.
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McQuaid
Head and Neck Unit, Royal Marsden Hospital, Downs road, SM2 5PT, Sutton, Surrey, UK.|Head and Neck Unit, Royal Marsden Hospital, SW3 6JJ, London, UK.|The Institute of Cancer Research, SW3 6JB, London, UK.|The Institute of Cancer Research, SM2 5NG, Sutton, UK.
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Dunlop
Head and Neck Unit, Royal Marsden Hospital, Downs road, SM2 5PT, Sutton, Surrey, UK.|Head and Neck Unit, Royal Marsden Hospital, SW3 6JJ, London, UK.|The Institute of Cancer Research, SW3 6JB, London, UK.|The Institute of Cancer Research, SM2 5NG, Sutton, UK.
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Nill
Head and Neck Unit, Royal Marsden Hospital, Downs road, SM2 5PT, Sutton, Surrey, UK.|Head and Neck Unit, Royal Marsden Hospital, SW3 6JJ, London, UK.
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Franzese
Head and Neck Unit, Royal Marsden Hospital, Downs road, SM2 5PT, Sutton, Surrey, UK.|Head and Neck Unit, Royal Marsden Hospital, SW3 6JJ, London, UK.|The Institute of Cancer Research, SW3 6JB, London, UK.|The Institute of Cancer Research, SM2 5NG, Sutton, UK.
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Nutting
Head and Neck Unit, Royal Marsden Hospital, Downs road, SM2 5PT, Sutton, Surrey, UK.|Head and Neck Unit, Royal Marsden Hospital, SW3 6JJ, London, UK.|The Institute of Cancer Research, SW3 6JB, London, UK.|The Institute of Cancer Research, SM2 5NG, Sutton, UK.
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Harrington
Head and Neck Unit, Royal Marsden Hospital, Downs road, SM2 5PT, Sutton, Surrey, UK.|Head and Neck Unit, Royal Marsden Hospital, SW3 6JJ, London, UK.|The Institute of Cancer Research, SW3 6JB, London, UK.|The Institute of Cancer Research, SM2 5NG, Sutton, UK.
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Newbold
Head and Neck Unit, Royal Marsden Hospital, Downs road, SM2 5PT, Sutton, Surrey, UK. sabhide@yahoo.com.|Head and Neck Unit, Royal Marsden Hospital, SW3 6JJ, London, UK. sabhide@yahoo.com.|The Institute of Cancer Research, SW3 6JB, London, UK. sabhide@yahoo.com.|The Institute of Cancer Research, SM2 5NG, Sutton, UK. sabhide@yahoo.com.
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Bhide
D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000209:etiology* / Q000473:pathology; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects* / Q000379:methods*; D018570:Risk Assessment; D014067:Tonsillar Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D016896:Treatment Outcome; D047368:Tumor Burden / Q000528:radiation effects
Conformal radiotherapy; Intensity-modulated radiotherapy; Ipsilateral oropharynx radiotherapy; Organs at risk; Radiation induced cancer; Volumetric-modulated arc therapy