Does lemon juice increase radioiodine reaccumulation within the parotid glands more than if lemon juice is not administered?
OBJECTIVE
The protective effect of sialagogues following I therapy became controversial after a study proposed that sialagogues increase the reaccumulation of I in the parotid glands (PGs) to a level higher than when sialagogues are not administered ('rebound effect'). The present study examined PG radiopharmacokinetics within 2-4 h after radioiodine administration to evaluate whether sialagogues cause a 'rebound effect'.


PATIENTS AND METHODS
This prospective study was conducted at the Medstar Washington Hospital Center. The study patients had (i) differentiated thyroid cancer, (ii) no history of salivary gland disease or medications affecting the salivary glands, (iii) a clinical salivary scan (SS) with lemon juice (LJ) (SSwLJ) that was performed before I therapy, and (iv) a second SS performed without LJ (SSwoLJ) performed prior to I therapy after giving informed consent. Each PG was assessed for I uptake using time-activity curves (TACs) that were (i) corrected for background and decay, (ii) smoothed using a seven-point unweighted moving average, and (iii) normalized to the administered I activity. TACs of the SSwLJ and SSwoLJ were compared with activity at each time point over 120 min. Areas under the TACs for the PGs were calculated for each gland's SSwLJ and SSwoLJ, and the relative percentage change in potential radiation absorbed dose (PRAD) was calculated.


RESULTS
A total of 2100 time points were analyzed in nine patients (18 PGs). I activity in the PGs on SSwLJ exceeded activity seen on the SSwoLJ at 134 time points (6.3%), and 98 (73%) of these were on the basis of spontaneous salivation during SSwoLJ. Mean percentage decrease in relative PRAD was 34.2±17.4% (range, 3.1-66.1%).


CONCLUSION
During the time period studied, LJ administration did not result in a 'rebound effect' but resulted in mean relative decrease of 34.2% in PRAD to the PGs.