Neck Node Bolus Technique in the Treatment of Nasopharyngeal Carcinoma with Intensity-modulated Radiotherapy

Purpose: To study the effect of bolus versus no bolus in the coverage of the nodal tumour volume withintensity-modulated radiotherapy (IMRT) for the treatment of nasopharyngeal carcinoma (NPC). Methods andMaterials: This retrospective study used data from 5 consecutive patients with NPC who were treated with bolusfor large neck nodes using IMRT from November 2011-January 2012 in our institute. All these patients weretreated radically with IMRT according to our institution’s protocol. Re-planning with IMRT without bolus forthese patients with exactly the same target volumes were done for comparison. Comparison of the plans was doneby comparing the V70 of PTV70-N, V66.5 of PTV70-N, V65.1 of PTV70-N and the surface dose of the PTV70-N.
Results: The mean size of the largest diameter of the enlarged lymph nodes for the 5 patients was 3.9 cm. Themean distance of the GTV-N to the skin surface was 0.6 cm. The mean V70 of PTV70-N for the 5 patients showedan absolute advantage of 10.8% (92.4% vs. 81.6%) for the plan with bolus while the V66.5 of PTV70-N had anadvantage of 8.1% (97.0% vs. 88.9%). The mean V65.1 also had an advantage of 7.1% (97.6% vs. 90.5%). Themean surface dose for the PTV70-N was also much higher at 61.1 Gy for the plans with bolus compared to only23.5 Gy for the plans without bolus.
Conclusion: Neck node bolus technique should be strongly considered inthe treatment of NPC with enlarged lymph nodes treated with IMRT. It yields a superior dosimetry comparedt o non-bolus plans with acceptable skin toxicity.