Purpose: The largest in vivo dosimetry study for interstitial brachytherapy yet examined was performed using new radiophotoluminescence glass dosimeters (RPLGDs). Based on the results, a dose prescription technique achieving high reproducibility and eliminating large hyperdose sleeves was studied.
Methods and materials: For 61 head-and-neck cancer patients who underwent high-dose-rate interstitial brachytherapy, new RPLGDs were used for an in vivo study. The Paris System was used for implant. An arbitrary isodose surface was selected for dose prescription. Locations of 83 dosimeters were categorized as on target (n = 52) or on nontarget organ (n = 31) and were also scaled according to % basal dose isodose surface (% BDIS). Compatibility (measured dose/calculated dose) was analyzed according to location. The hyperdose sleeve was assessed in terms of prescription surface expressed in % BDIS.
Results: The spread of compatibilities was larger for on nontarget organ (1.06 +/- 0.32) than for on target (0.87 +/- 0.17, p = 0.01). Within on target RPLGDs, compatibility on <95% BDIS (0.95 +/- 0.10) was better than on > or =95% BDIS (0.84 +/- 0.18, p = 0.02). The number of patients with diameter of hyperdose sleeve > or =10 mm was increased with a dose prescription to <77% BDIS (p = 0.046). For nontarget organs, the maximal positive deviation was 84% of the calculated dose.
Conclusions: Dose prescription is recommended to >77% and <95% BDIS for reproducibility and elimination of excessive hyperdose sleeve. For organs at risk, radioprotection should be considered even when calculated dose seems sufficiently low. Further development of planning software is necessary to prevent overestimation.