Thursday, January 20, 2011

DVH parameters for Cervical HDR brachytherapy

In the Red Journal this week:

A very interesting article from the Vienna group, exploring thresholds for late toxicity with cervical brachytherapy. They review 141 patients, and arrive at a threshold for significant (G2-4) late effects for the rectal D2cc of 75Gy. Their data for bladder is a little less well established, but they arrive at a threshold of 100Gy for D2cc. They could determine no thresholds for sigmoid toxicity as it was a very rare occurrence in their cohort.

One thing to note when interpreting this data is that the Vienna group gives 7Gy x 4 over the course of 1 weeks application, which is different that most US practice with brachy (5-6Gy in 5 fractions, with a frequency of ~2/week). While the doses reported are in EQD2 terms, one must realize that these conversions are based on theory and assumptions about alpha beta ratios which may not entirely apply to each brachy schedule. Nonetheless, this remains the best data around for modern 3D dosimetry in cervical brachytherapy.

Link and abstract

Dose–Volume Histogram Parameters and Late Side Effects in Magnetic Resonance Image–Guided Adaptive Cervical Cancer Brachytherapy: "Purpose: To evaluate the predictive value of dose–volume histogram (DVH) parameters for late side effects of the rectum, sigmoid colon, and bladder in image-guided brachytherapy for cervix cancer patients.Methods and Materials: A total of 141 patients received external-beam radiotherapy and image-guided brachytherapy with or without chemotherapy. The DVH parameters for the most exposed 2, 1, and 0.1 cm3 (D2cc, D1cc, and D0.1cc) of the rectum, sigmoid, and bladder, as well as International Commission on Radiation Units and Measurements point doses (DICRU) were computed. Total doses were converted to equivalent doses in 2 Gy by applying the linear-quadratic model (α/β = 3 Gy). Late side effects were prospectively assessed using the Late Effects in Normal Tissues–Subjective, Objective, Management and Analytic score. The following patient groups were defined: Group 1: no side effects (Grade 0); Group 2: side effects (Grade 1–4); Group 3: minor side effects (Grade 0–1); and Group 4: major side effects (Grade 2–4).Results: The median follow-up was 51 months. The overall 5-year actuarial side effect rates were 12% for rectum, 3% for sigmoid, and 23% for bladder. The mean total D2cc were 65 ± 12 Gy for rectum, 62 ± 12 Gy for sigmoid, and 95 ± 22 Gy for bladder. For rectum, statistically significant differences were observed between Groups 1 and 2 in all DVH parameters and DICRU. Between Groups 3 and 4, no difference was observed for D0.1cc. For sigmoid, significant differences were observed for D2cc and D1cc, but not for D0.1cc in all groups. For bladder, significant differences were observed for all DVH parameters only comparing Groups 3 and 4. No differences were observed for DICRU.Conclusions: The parameters D2cc and D1cc have a good predictive value for rectal toxicity. For sigmoid, no prediction could be postulated because of limited data. In bladder, DVH parameters were predictive only for major toxicity."

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