Investigation of Effect of Air Gap between Surface and Bolus on Dose Distribution for 6 MV Photon Beam

Year 2023, Volume: 19 Issue: 4, 389 - 393, 29.12.2023

Osman Vefa Gül

https://doi.org/10.18466/cbayarfbe.1391876

Abstract

In radiotherapy, tissue equivalent boluses are frequently used in the treatment of superficially located tumors. The air gap between the patient's skin and the bolus may cause dosimetric uncertainties. This study aims to dosimetrically investigate the effect of the air gap between the surface and the bolus on dose distribution. Computed tomography (CT) images of the phantom were obtained and transferred to the treatment planning system (TPS). In the TPS, a bolus was placed on the phantom surface and then air gaps were created between the bolus and the surface. The effect of the air gaps between the surface and the 5 mm thick bolus on the dose distribution was analyzed with the point doses obtained from the TPS. For the 6 MV X-ray, it was observed that the air gap negatively affected the surface doses calculated by TPS. Accordingly, an inverse correlation was found between air gap and surface dose. It is recommended that bolus use, especially in curved anatomical regions, should be applied before CT scanning as much as possible. When using bolus material in radiotherapy, it is recommended to be careful not to leave an air gap between the surface and the bolus.

Keywords

Air-gap effect, bolus, radiotherapy, skin dose

References

• [1]. Burnet, N. G. (2004). Defining the tumour and target volumes for radiotherapy. Cancer Imaging, 4(2), 153-161.
• [2]. Mukherji, A. (2018). Basics of planning and management of patients during radiation therapy : a guide for students and practitioners. New York, NY: Springer Berlin Heidelberg.
• [3]. Park, J. M., Kim, J.-i., Heon Choi, C., Chie, E. K., Kim, I. H., & Ye, S.-J. (2012). Photon energy-modulated radiotherapy: Monte Carlo simulation and treatment planning study. Medical Physics, 39(3), 1265-1277.
• [4]. Fadzil, M. S. A., Noor, N. M., Tamchek, N., Ung, N. M., Abdullah, N., Dolah, M. T., & Bradley, D. A. (2022). A cross-validation study of Ge-doped silica optical fibres and TLD-100 systems for high energy photon dosimetry audit under non-reference conditions. Radiation Physics and Chemistry, 200.
• [5]. Dogan, N., & Glasgow, G. P. (2003). Surface and build‐up region dosimetry for obliquely incident intensity modulated radiotherapy 6 MV x rays. Medical Physics, 30(12), 3091-3096.
• [6]. Zhang, C., Lewin, W., Cullen, A., Thommen, D., & Hill, R. (2023). Evaluation of 3D-printed bolus for radiotherapy using megavoltage X-ray beams. Radiological Physics and Technology, 16(3), 414-421.
• [7]. Wang, X., Wang, X., Xiang, Z., Zeng, Y., Liu, F., Shao, B., . . . Liu, L. (2021). The Clinical Application of 3D-Printed Boluses in Superficial Tumor Radiotherapy. Frontiers in Oncology, 11.
• [8]. Wang, K. M., Rickards, A. J., Bingham, T., Tward, J. D., & Price, R. G. (2022). Technical note: Evaluation of a silicone‐based custom bolus for radiation therapy of a superficial pelvic tumor. Journal of Applied Clinical Medical Physics, 23(4).
• [9]. Endarko, E. (2021). Evaluation of Dosimetric Properties of Handmade Bolus for Megavoltage Electron and Photon Radiation Therapy. Journal of Biomedical Physics and Engineering, 11(06).
• [10]. Lu, Y., Song, J., Yao, X., An, M., Shi, Q., & Huang, X. (2021). 3D Printing Polymer-based Bolus Used for Radiotherapy. Int J Bioprint, 7(4), 414.
• [11]. Dyer, B. A., Campos, D. D., Hernandez, D. D., Wright, C. L., Perks, J. R., Lucero, S. A., . . . Rao, S. S. (2020). Characterization and clinical validation of patient-specific three-dimensional printed tissue-equivalent bolus for radiotherapy of head and neck malignancies involving skin. Physica Medica, 77, 138-145.
• [12]. Aras, S., Tanzer, I. O., & Ikizceli, T. (2020). Dosimetric Comparison of Superflab and Specially Prepared Bolus Materials Used in Radiotherapy Practice. European Journal of Breast Health, 16(3), 167-170
• [13]. Khan, Y., Villarreal-Barajas, J. E., Udowicz, M., Sinha, R., Muhammad, W., Abbasi, A. N., & Hussain, A. (2013). Clinical and Dosimetric Implications of Air Gaps between Bolus and Skin Surface during Radiation Therapy. Journal of Cancer Therapy, 04(07), 1251-1255.
• [14]. Srinivas, C., Lobo, D., Banerjee, S., Ravichandran, R., Putha, S., Prakash Saxena, P. U., Sunny, J. (2020). Influence of air gap under bolus in the dosimetry of a clinical 6 MV photon beam. Journal of Medical Physics, 45(3).
• [15]. Butson, M. J., Cheung, T., Yu, P., & Metcalfe, P. (2000). Effects on skin dose from unwanted air gaps under bolus in photon beam radiotherapy. Radiation Measurements, 32(3), 201-204.