The treatment for head and neck cancer (HNC) is based on three therapeutic modalities: radiotherapy (RT), chemotherapy, and surgery.1 The aim of RT is to control tumours with the least possible damage to adjacent normal tissues.2 For most initial cases, RT as a sole modality is considered the standard treatment; however, advanced cases must receive RT in association with chemotherapy and/or surgery.3

Despite efforts on RT planning to preserve non-neoplastic tissues in tumour region, these are inevitably included into the irradiation fields and suffer consequences as well.4,5 Intensity and extent of the radiation-induced effects depends mainly on factors related to treatment such as total radiation dose, radiation dose per fraction, irradiated volume, dose distribution in tissue volume, association with chemotherapy,2,6 and its duration.7

Regarding HNC treatment, the major salivary glands often receive significant radiation doses.8 Although the cytotoxic mechanisms of the radiation in salivary tissue are still not elucidated,7,9 atrophy and acinar degeneration are histological findings often encountered.10,11 As consequences, the subjective perception of dry mouth (or xerostomia) and the objective reduction in salivary flow rate (SFR) (or hyposalivation) are common,7,12 dose-dependent, irreversible complications.9,13 Additionally, they are almost always accompanied by changes in the salivary characteristics such as pH values, immunoglobulin levels, electrolyte balance, protein concentrations, viscosity, and colour.8,10,12

It is known that there is no direct relationship between xerostomia and low SFR, so efforts are needed to measure each one independently.14 In order to assess xerostomia in irradiated patients, some specific scales have been developed.9,13 Likewise, quality of life questionnaires have the goal of evaluating xerostomia in conjunction with other well-described side effects of the HNC treatment.13,15 Thus, even subjectively, an overview of the patient's state is achieved.

The procedure used to assess objectively SFR (sialometry) is performed using several techniques, each one having its own advantages, disadvantages, and challenges.16,17 A poor reproducibility16 and a number of methods present in the literature,4,6,10,11,13 however, may lead to inconsistent results and inappropriate direct comparisons. Furthermore, there is no reliable, validated method to evaluate SFRs of HNC patients submitted to RT.

Based on the widespread 97-09 protocol of the Radiation Therapy Oncology Group (RTOG),18 sialometry tests were developed and applied in order to carry out easy, rapid, accurate assessments in HNC patients post-RT.

Sialometries are performed by drainage, expectoration, or weighing cotton wool balls soaked with saliva. Some of these techniques aim to selectively collect the secretion of each salivary gland, but with little clinical applicability (e.g. catheterization of salivary ducts). On the other hand, techniques which take into account the whole saliva volume collected over a period of time are the most used since they are faster, easier, and cheaper.16

The well-known RTOG's protocol has been developed to evaluate the mitigating effect of pilocarpine on hyposalivation and mucositis in patients undergoing RT.18 So, from our experience in using this protocol for irradiated patients with no method of prevention and treatment for hyposalivation,19,20 we considered necessary adapting it to post-RT patients. The unstimulated sialometry, in particular, could be substantially improved by our methods, since it is based on the collection of extremely small amount of saliva.

During the procedures, the glass funnel facilitated the saliva collection and also prevented a possible volume loss due to the larger area for expectoration. The highly viscous saliva that adhered to the funnel surface could be easily removed with the aid of the metal spatula and distilled water. Another important point was the addition of simethicone to the solution to decrease the surface tension of gas bubbles and to disperse foam. Thus, we could measure the total saliva volume immediately, avoiding further losses related to the need of leaving the saliva samples to rest.

Concerning the presence of stimulation in sialometries, gustatory (citric acid) and mechanical agents (paraffin, silicone, unflavoured chewing gum) are used to simulate patients’ conditions throughout the day (e.g. eating and chewing). It is believed that the absence of stimulation reflects the physiological status of the sublingual and submandibular glands, as these are responsible for baseline salivary secretion. On the other hand, mechanical stimulants promote marked response of the parotid glands and gustatory stimulants activate the three pairs of major salivary gland simultaneously.17

From our standpoint, clinicians should carry out both sialometries for a thorough evaluation of irradiated patients. For the stimulated sialometry, the use of 2% citrate solution seems to be more advantageous because the three pairs of major salivary glands (responsible for 90% of saliva output) are evaluated at the same time.7,12 Also, edentulous patients cannot be assessed using mechanical stimulations.

Our data showed the marked, persistent, well-recognised radiation-induced reduction in SFR.7,9,12,13,19,20 The lack of statistically significant difference between both groups and the quite similar results obtained suggest that our modifications in RTOG's protocol were satisfactory and applicable. In general, the results from the novel sialometries could be obtained more quickly than those of RTOG. Moreover, our method was easier than the others and did not require costly materials, factors really important for the routine clinical use.

This paper encourages further researches with bigger samples to apply these novel sialometries in post-irradiated patients. Likewise, it would be interesting to investigate whether this method is suitable for other diseases and pathological conditions which also result in low SFR (e.g. Sjögren's Syndrome).

The authors declare no conflicts of interest.