Abstract
To compare the dosimetric coverage of target volumes and organs at risk in the radical treatment of nasopharyngeal carcinoma (NPC) between intensity-modulated radiotherapy (IMRT) and three- dimensional conformal radiotherapy (3DCRT). Data from 10 consecutive patients treated with IMRT from June-October 2011 in Penang General Hospital were collected retrospectively for analysis. For each patient, dose volume histograms were generated for both the IMRT and 3DCRT plans using a total dose of 70Gy. Comparison of the plans was accomplished by comparing the target volume coverage (5 measures) and sparing of organs at risk (17 organs) for each patient using both IMRT and 3DCRT. The means of each comparison target volume coverage measures and organs at risk measures were obtained and tested for statistical significance using the paired Student t-test. All 5 measures for target volume coverage showed marked dosimetric superiority of IMRT over 3DCRT. V70 and V66.5 for PTV70 showed an absolute improvement of 39.3% and 24.1% respectively. V59.4 and V56.4 for PTV59.4 showed advantages of 18.4% and 16.4%. Moreover, the mean PTV70 dose revealed a 5.1 Gy higher dose with IMRT. Only 4 out of 17 organs at risk showed statistically significant difference in their means which were clinically meaningful between the IMRT and 3DCRT techniques. IMRT was superior in sparing the spinal cord (less 5.8Gy), V30 of right parotid (less 14.3%) and V30 of the left parotid (less 13.1%). The V55 of the left cochlea was lower with 3DCRT (less 44.3%). IMRT is superior to 3DCRT due to its dosimetric advantage in target volume coverage while delivering acceptable doses to organs at risk. A total dose of 70Gy with IMRT should be considered as a standard of care for radical treatment of NPC.
Highlights
Nasopharyngeal carcinoma (NPC) is prevalent in China and the South-east Asian region with a peak incidence rate of 20 per 100,000 person-years in HongKong (Law et al, 2007)
Dose volume histograms were generated for both the intensity-modulated radiotherapy (IMRT) and 3DCRT plans using a total dose of 70Gy
V70 and V66.5 for PTV70 showed an absolute improvement of 39.3% and 24.1% respectively
Summary
Nasopharyngeal carcinoma (NPC) is prevalent in China and the South-east Asian region with a peak incidence rate of 20 per 100,000 person-years in HongKong (Law et al, 2007). Two meta-analyses involving more than 2500 patients and ten randomized trials reported an absolute survival benefit of 4-6% at 5 years and this benefit was most pronounced with concurrent chemoirradiation (Langendijk et al, 2004; Baujat et al, 2006) As such the key to improving survival for NPC lies in advancement of RT technique and this area has seen remarkable progress over the last decade. 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) These studies were done with different protocols from that of our institution and included different total doses to different target volumes. With this study we set out to demonstrate the superiority of IMRT compared to 3DCRT regarding the target volume coverage while maintaining acceptable dosage to the OARs
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