Prophylactic Replacement of Voice Prosthesis | 181 7 VPG1 (regular VP-users) was subdivided into two groups. PG1: primary laryngectomy with or without additional treatments and PG2: salvage laryngectomy for recurrence, second primary tumor or a laryngectomy for a functional reason (see figure 1). The median device lifetime in PG1 was 81 days and in PG2 65 days. The Mann-Whitney-U test showed a significant difference in device lifetime (P<0.01). Device lifetime cut-off points For all groups the 70% cut-off point (DL70) was calculated, which was used for the calculations in the prophylactic replacement model and are shown in table 2. Table 2. DL70 cut-off points for the PVPR model. Patient groups DL70 All patients 40 days VPG1 41 days VPG2 90 days PG1 45 days PG2 39 days Variability in device lifetime Device lifetimes showed great variability, both within and between patients. The median within patient SD of device lifetime in all patients was 64.5 days (range 1.4 - 909.3). For VPG1, the median within patient SD was 85.3 days (range 11.2 - 909.3), whereas, for VPG2, the median within patient SD was 53.6 days (range 1.4-667.4). This difference in SD of the device lifetime was significant (Mann-Whitney U, p<0.05). Note that all three cases the median within patient SDs are of the same order of magnitude as the (overall) median device lifetime, indicating a high Coefficient of Variation (see figure 2). Prophylactic Voice Prosthesis Replacement When applying PVPR to all patients, using the DL70 of 40 days, the calculated median number of used VPs per year was 9.7 VPs (range 9.1 - 48.1), implying more than six (6.2) additional VPs per patient per year (range 0.0 - 9.0) to prevent 70% of the leakage events. PVPR after 40 days in case of no leakage would lead to a net mean in situ time of 38 days in the set of all patients.
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