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British Journal of Radiology (2004) 77, 143-145
© 2004 British Institute of Radiology
doi: 10.1259/bjr/71128393
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Short communication

Barium paste: useful for primary tumour localization in oral cancer

B K Yap, MBChB, MRCP, FRCR1, N J Slevin, MBChB, FRCP, FRCR1 and A Ahamad, MBBS, FRCR2

1 Department of Clinical Oncology, Christie Hospital NHS Trust, Wilmslow Road, Withington, Manchester M20 4BX, UK and 2 Department of Radiation Oncology, MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA

The role of external beam radiotherapy (RT) in the management of squamous cell carcinoma (SCC) of the oral cavity is well established. The local control for early tumours (T1 and T2 lesions), when managed with RT is comparable with surgery although a direct comparison in a randomized setting is lacking. Multimodality treatment using surgical resection, RT and chemotherapy are usually required for more advanced lesions. However, with recent refinement and advancement in reconstructive techniques, surgery has gained popularity in many centres, as functional impairment from modern free flap techniques is considerably less than older surgical techniques. Nevertheless, for small volume oral cavity tumours, radiotherapy still offers excellent local control and functional results. Some patients are often too frail or unwilling to undergo radical surgery. Therefore, radiotherapy remains an effective alternative to surgery.

One of the potential disadvantages of RT for oral cavity cancer is osteoradionecrosis (ORN) of the mandible. This late effect of RT may contribute to continuing morbidity in patients that are otherwise cured of their cancers and should be prevented where possible. Numerous clinical and physical factors have been reported [1] to be associated with ORN; these factors are summarized in Table 1Go. However, the underlying cause of ORN is often speculative as most studies are retrospective and heterogeneous.


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  		Table 1. Factors associated with the risk of osteoradionecrosis

 
The effect of radiotherapy field size or irradiated volume, as a treatment-related factor for ORN is not comprehensively established in the literature. We previously reported the relationship between normal tissue late effects and RT treatment volume in a cohort of 333 patients with SCC of the oral cavity treated with radical radiotherapy [2]. There was no grade 3 or 4 late morbidity seen at radiation doses of 50 Gy and 52.5 Gy in 3 weeks for volumes less than 700 cm3 and 300 cm3, respectively. This clearly shows a dose–response relationship between volume and late morbidity for the dose range 50–52.5 Gy. Withers et al [3] in a retrospective analysis of 676 head and neck patients reported a significant influence of radiotherapy portal field size for mandibular necrosis. They estimated a relative hazard of 1.15 (p=0.02) for ORN for every unit 10 cm2 increase in field size. This is further supported from analyses by Glanzmann et al [4] of the volume of mandible receiving the dose prescribed to the target. In that study, the irradiated mandible volume was scored from 1 (radiotherapy field including only the ramus ascendens) to 7 (ramus horizontalis, including chin region and angle included in radiotherapy field). Univariate analysis performed on the basis of this score showed a score of 4 or higher (more than half of the horizontal ramus was irradiated) significantly increased the risk of ORN. This is consistent with the consideration of bone to be composed of serially arranged functional subunits described by Withers et al [5], where failure in any one subunit leads to cortical bone fracture. Thus, increasing the length of mandible included in the radiotherapy treatment volume will increase the risk of ORN.

Local control of head and neck SCC depends on the delivery of a high biologically effective dose (BED) of radiotherapy to the primary site. However, the relationship between radiation dose and the risk of ORN is also well established [1]. All the 20 events of ORN observed by Glanzmann et al [4] among 189 patients treated for oral cavity and pharyngeal cancer were seen in patients treated with a target dose higher than 66 Gy using conventional fractionation.

The key to the success of definitive radiotherapy for oral cavity cancer is to deliver a high BED of radiation to a small planning target volume to minimize late toxicity. Therefore, tumour localization is a critical step in field placement for either the primary or boost fields. The oral cavity affords easy direct visualization and palpation of tumours. In two-dimensional radiotherapy planning, the position of the tumour related to bony landmarks is noted for field placement on simulator images. This is traditionally aided by placement of radio-opaque gold seed markers. There are several disadvantages with the use of gold seed markers. Firstly, this is an invasive procedure where oral mucosa has to be anaesthetized prior to the introduction of the applicator gun containing the gold seed markers. Secondly, the procedure is highly operator dependent as the ejected marker seed may be placed at an inappropriate distance from the tumour margin. Thirdly, there is potential for seed migration, which may result in under or over-estimation of clinical target volume. For these reasons, we have abandoned using gold seed markers at our institution and barium paste (a radio-opaque marker paste) is used instead. Moreover, barium paste offers the advantage over gold seeds of providing a two-dimensional view of the primary tumour on a lateral and anterior radiograph at the same time. Barium paste adheres to the oral mucosa when it comes into contact with the saliva. It is prepared by mixing barium sulphate powder with an adhesive carmellose gelatin paste (ORABASE®; ConvaTec Ltd, Uxbridge, UK). The approximate ratio of barium sulphate powder to paste is 1:2 by volume (3:5 by weight), which produces a sticky dough texture. Too little barium sulphate powder would result in poor radio-opacity and too little ORABASE® paste would reduce the adhesive property of the barium paste. Prior to application of the barium paste, excess saliva and food debris over the tumour are removed with absorbent gauze to prevent displacement of the paste. The barium paste is then applied onto the surface of the tumour. The volume of the paste should be sufficient to cover the gross tumour. Simulator images are then taken as shown in Figure 1Go (lateral view) and Figure 2Go (anterior view). The patient removes the barium paste from his/her mouth after the simulator images have been taken. This method of localization allows accurate delineation of the primary tumour for radiotherapy planning.



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  		Figure 1. Lateral simulator view of oral cancer localized by barium paste.

 


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  		Figure 2. Anterior simulator view centred on radio-opaque paste.

 
CT scan-based, three-dimensional conformal radiotherapy and intensity modulated radiotherapy are increasingly used in radiotherapy planning for head and neck cancers. However, identifying small oral cavity lesions using CT scan may be difficult due to the opposition of adjacent mucous surfaces and the artefact produced by amalgam dental fillings. Hence, barium paste remains a useful tool to aid target localization in conventional radiotherapy planning. Furthermore, it can also be used in conjunction with verification films for CT scan-based radiotherapy plans prior to starting radiation treatment.

In conclusion, this simple technique using barium paste helps the accurate delivery of high BED of radiotherapy to the primary tumour in oral cavity cancer. Accurate localization of the gross tumour enables the planning target volume to be reduced in order to minimize the late morbidity of radiotherapy.


   Footnotes
 
The abstract version of this paper will be presented at the 89th Scientific Meeting of the Radiological Society of North America, 30 November–5 December 2004. Back

Received for publication June 26, 2003. Revision received September 8, 2003. Accepted for publication September 24, 2003.


   References
Top
 References
 

  1. Jereczek-Fossa BA, Orecchia R. Radiotherapy-induced mandibular bone complications. Cancer Treat Rev 2002;28:65–74.[CrossRef][Medline]
  2. Turner SL, Slevin NJ, Gupta NK, Swindell R. Radical external beam radiotherapy for 333 squamous carcinomas of the oral cavity — evaluation of late morbidity and a watch policy for clinically negative neck. Radiother Oncol 1996;41:21–9.[Medline]
  3. Withers HR, Peters LJ, et al. Late normal tissue sequelae from radiation therapy for carcinoma of the tonsil: patterns of fractionation study of radiobiology. Int J Radiat Oncol Biol Phys 1995;33:563–8.[Medline]
  4. Glanzmann CH, Gratz KW. Radionecrosis of the mandibula: a retrospective analysis of the incidence and risk factors. Radiother Oncol 1995;36:94–100.[Medline]
  5. Withers HR, Taylor JMG, Maciejewski B. Treatment volume and tissue tolerance. Int J Radiat Oncol Biol Phys 1988;14:791–5.



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