A total of 170 HDR fractions were delivered to 34 patients with tandem and ovoid (17 patients), tandem and ring (5 patients), tandem and cylinder (2 patients), or a combination (10 patients). Twenty-four LDR fractions were delivered to 16 patients with tandem and ovoid (5 patients), tandem and interstitial (8 patients), or both (3 patients). lists patient and tumor characteristics. Proportionally more Stage III and IVA patients received LDR radiation than HDR. There was no difference in the median tandem length inserted: 6 cm for both HDR (range [rg], 4–7 cm) and LDR (rg, 5–7 cm).
Patient and tumor characteristics.
The median EB dose for both HDR and LDR patients was 45 Gy (rg, 40–50.4 Gy). The median cumulative BT dose was 27.5 Gy (rg, 25-27.5Gy) in 4–5 fractions prescribed to Point A for the HDR patients, and 42.5 Gy (rg, 36–50 Gy) over 1–2 fractions prescribed at 0.4–0.8 Gy/hr for the LDR patients. The median activity at the tip of the LDR tandem was 13.5 mgRaeq (rg, 6.2–14.3 mgRaeq).
The median distance between the sigmoid and the tandem was 1.7 cm (rg, 0.1–6.16 cm) for HDR plans and 2.7 cm (rg, 1.17–4.52 cm) for LDR. One or more dwell positions at the tip of the tandem were turned off in 20% (30/146) of HDR fractions as part of the dose optimization process. The median distance from the sigmoid to the 100% isodose line in the HDR plans was -0.1 cm (rg, -1.4–2.5 cm), with the sigmoid falling within the high-dose region; for LDR the corresponding median distance was 0.44 cm (rg, -0.73–5.2 cm). Among HDR fractions, the coefficient of variation (CV) of the within-patient (among-fraction) sigmoid-to-tandem distance was 40%. The variation among patients as evaluated by ANOVA was significant, given the estimated within-patient variation (p<0.01).
Only the proximity of the sigmoid to the tandem was significantly related to sigmoid dose (p<0.01). Tandem length, type of applicator (categorical T/O vs. T/R vs. T/I vs. T/C), dose rate (HDR vs LDR), and bladder and rectal dose were not significantly related to sigmoid dose using linear regression. Therefore, multivariate analysis was not performed.
lists the D0.1cc and D2cc total doses EQD2 (EB+BT) delivered to the OAR. The cumulative LDR EB + BT dose was significantly higher for the bladder and rectal D2cc (p=0.02, p=<0.01). depicts the ratio of prescribed sigmoid dose (D0.1cc and D2cc) to point A prescription dose for HDR and LDR patients. The BT dose to the sigmoid, rectum, and bladder and the ratio of delivered BT dose to the OAR as compared with the prescribed BT dose to point A are reported in .
Sigmoid, bladder and rectum EQD2 with an α/β = 3.
Figure 1 The ratio of sigmoid DVH dose to prescribed point A dose as DO.1cc or D2cc for HDR and LDR brachytherapy. The diamond shape reflects the 95% Confidence Interval of the mean. The bar represents two standard deviations above and below the mean. The box (more ...)
The ratio of sigmoid D0.1 cc to prescribed point A dose in T/O patients showed no significant difference between HDR and LDR, although the significance was limited by the small number of subjects (median D0.1cc and D2cc for HDR, 0.78 and 0.51; median D0.1cc and D2cc for LDR, 0.69 and 0.57; for comparison of HDR versus LDR, D0.1cc p=0.52 and D2cc p=0.65).
With a median follow-up of 31.2 months (rg, 10.8 – 50.4 months), there were no grade 3–4 sigmoid toxicities in either the HDR or LDR group. Two patients in the HDR group and one in the LDR group required rehydration for diarrhea, which had not resolved from the EB portion of treatment. In the LDR group, one patient with extensive Stage IVA disease at diagnosis developed a recto-vaginal fistula requiring surgical correction.