Aim: The aim of this study is to compare the dosimetric difference for radiotherapy of nasopharyngeal carcinoma (NPC) between volumetric-modulated arc therapy (VMAT) and dynamic intensity-modulated radiation therapy (IMRT) using Varian Eclipse TPS following simultaneously integrated boost (SIB) protocol.

Patients and Method: Fifteen patients with NPC underwent SIB protocol were retrospectively selected for this study. The Gross tumour volume (GTV) of NPC contained nasopharynx gross target volume and the positive neck lymph nodes, PTV1 contained the clinical target volume (CTV) of high-risk sites and the whole nasopharynx and PTV2 contained the CTV of low-risk sites. The prescription dose of PTV1 was 69.96 Gy/33 fractions, and for PTV2 59.4 Gy/33 fractions. VMAT (two full arcs) and IMRT (9 equally spaced fields) plans were designed for each patient using SIB strategies. The dose constraints were set for a high conformal and homogenous dose distribution to the PTV with minimal dose to the organ at risks (OAR).The plan was first done for IMRT, using the same dose constraints VMAT plans were generated. The monitor unit (MU) and other dosimetric difference between IMRT and VMAT were compared.

Results: The fraction of prescribed dose received by 95%of PTV volume showed a better result for IMRT, resulting in a significant difference with p < 0.05, while no significant differences were found for Homogeneity Index and Conformity Index (p > 0.05). Similarly for OARs and remaining volume at risk no significant differences were found between IMRT and VMAT. The total MU for IMRT (1837.67 ± 141.54) is more than VMAT (625.33 ± 49.02) with p <0.05.

Conclusion: This study shows that VMAT can achieve similar target coverage and homogeneity as IMRT except with fewer MUs and less delivery time compared to IMRT in cases of nasopharyngeal carcinomas.

Keywords: Nasopharynx, carcinoma, IMRT, VMAT, Monitor Unit, Dosimetry.

1. com.2021. Update.[online] Available at: <https://www.uptodate.com/contents/epidemiology-etiology-and-diagnosis-of-nasopharyngeal-carcinoma? search=nasopharyngeal%20carcinoma&source=search_search&selectedTitle=1-83&usage_t..... [Accessed 22 November 2021]
2. Lee, T.-F. et al. (2011) “Comparative analysis of SmartArc-based dual arc volumetric-modulated arc radiotherapy (VMAT) versus intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma,” Journal of Applied Clinical Medical Physics, 12(4), pp. 158–174. Available at: https://doi.org/10.1120/jacmp.v12i4.3587.
3. Li, S. et al. (2018) “Dosimetric comparisons of volumetric modulated arc therapy and tomotherapy for early T-stage nasopharyngeal carcinoma,” BioMed Research International, 2018, pp. 1–8. Available at: https://doi.org/10.1155/2018/2653497.
4. Verbakel, WFAR et al. (2009) "Volumetric intensity-modulated arc therapy vs conventional IMRT in head-and-neck cancer: A comparative planning and dosimetric study," International Journal of Radiation Oncology*Biology*Physics, 74(1), pp. 252–259. Available at: https://doi.org/10.1016/j.ijrobp.2008.12.033.
5. Kim, J.W. et al. (2012) “IMRT with simultaneous integrated boost and concurrent chemotherapy for nasopharyngeal cancer: Plan evaluation and treatment outcome,” Japanese Journal of Clinical Oncology, 42(12), pp. 1152–1160. Available at: https://doi.org/10.1093/jjco/hys169.
6. Hall, E.J. (2006) “Intensity-modulated radiation therapy, protons, and the risk of second cancers,” International Journal of Radiation Oncology*Biology*Physics, 65(1), pp. 1–7. Available at: https://doi.org/10.1016/j.ijrobp.2006.01.027.
7. Otto, K. (2007) “Volumetric modulated arc therapy: IMRT in a single gantry arc,” Medical Physics, 35(1), pp. 310–317. Available at: https://doi.org/10.1118/1.2818738.
8. Vanetti, E. et al. (2009) “Volumetric modulated arc radiotherapy for carcinomas of the oro-pharynx, hypo-pharynx and larynx: A treatment planning comparison with fixed field imrt,” Radiotherapy and Oncology, 92(1), pp. 111–117. Available at: https://doi.org/10.1016/j.radonc.2008.12.008. .
9. Jin, X. et al. (2013) “Comparison of whole-field simultaneous integrated boost VMAT and IMRT in the treatment of Nasopharyngeal Cancer,” Medical Dosimetry, 38(4), pp. 418–423. Available at: https://doi.org/10.1016/j.meddos.2013.05.004.
10. MSC Centre, Intensity-modulated Radiotherapy — A New Standard for Treating Nasopharyngeal Carcinoma ?, (2002) 211–212.
11. Xia, K.K. Fu, G.W. Wong, C. Akazawa, L.J. Verhey, Comparison of treatment plans involving intensity-modulated radiotherapy for nasopharyngeal carcinoma, Int. J. Radiat. Oncol. Biol. Phys. 48 (2000) 329–337. https://doi.org/10.1016/S0360-3016(00)00585-X.
12. Ning, Z.-H. et al. (2013) “Single arc volumetric-modulated arc therapy is sufficient for nasopharyngeal carcinoma: A dosimetric comparison with dual arc vmat and dynamic MLC and step-and-shoot intensity-modulated radiotherapy,” Radiation Oncology, 8(1). Available at: https://doi.org/10.1186/1748-717x-8-237.
13. Wolden, S.L. et al. (2001) “Failure of a 3D conformal boost to improve radiotherapy for nasopharyngeal carcinoma,” International Journal of Radiation Oncology*Biology*Physics, 49(5), pp. 1229–1234. Available at: https://doi.org/10.1016/s0360-3016(00)01588-1.
14. Lee, T.-F. et al. (2012) “Dual arc volumetric-modulated arc radiotherapy (VMAT) of nasopharyngeal carcinomas: A simultaneous integrated boost treatment plan comparison with intensity-modulated Radiotherapies and single ARC VMAT,” Clinical Oncology, 24(3), pp. 196–207. Available at: https://doi.org/10.1016/j.clon.2011.06.006.
15. Zhao, N. et al. (2015) “A hybrid IMRT/VMAT technique for the treatment of Nasopharyngeal Cancer,” BioMed Research International, 2015, pp. 1–8. Available at: https://doi.org/10.1155/2015/940102.
16. Mellon, E.A. et al. (2015) “A dosimetric comparison of volumetric modulated arc therapy with step-and-shoot intensity modulated radiation therapy for prostate cancer,” Practical Radiation Oncology, 5(1), pp. 11–15. Available at: https://doi.org/10.1016/j.prro.2014.03.003.
17. Mahantshetty, U. et al. (2010) “Whole abdomen radiation therapy in ovarian cancers: A comparison between fixed beam and volumetric arc based intensity modulation,” Radiation Oncology, 5(1). Available at: https://doi.org/10.1186/1748-717x-5-106.
18. Stieler, F. et al. (2011) “A comparison of several modulated radiotherapy techniques for head and neck cancer and dosimetric validation of VMAT,” Radiotherapy and Oncology, 101(3), pp. 388–393. Available at: https://doi.org/10.1016/j.radonc.2011.08.023.
19. Kim, K. et al. (2009) “Intensity-modulated radiation therapy with simultaneous integrated boost technique following neoadjuvant chemotherapy for locoregionally advanced nasopharyngeal carcinoma,” Head & Neck, 31(9), pp. 1121–1128. Available at: https://doi.org/10.1002/hed.21076.
20. Grégoire, V. et al. (2006) “Proposal for the delineation of the nodal CTV in the node-positive and the post-operative neck,” Radiotherapy and Oncology, 79(1), pp. 15–20. Available at: https://doi.org/10.1016/j.radonc.2006.03.009.
21. Wong, F.C.S. et al. (2010) “Whole-field simultaneous integrated-boost intensity-modulated radiotherapy for patients with nasopharyngeal carcinoma,” International Journal of Radiation Oncology*Biology*Physics, 76(1), pp. 138–145. Available at: https://doi.org/10.1016/j.ijrobp.2009.01.084.

Lisha Warlaitthma

Medical Physicist, Eden Medical Center, Dimapur, Nagaland 797112, India