Rectal dose constraints for salvage iodine-125 prostate brachytherapy

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• 作者：Max Peters¹ ; ^{M.Peters-10@umcutrecht.nl" class="auth_mail" title="E-mail the corresponding author} ; Carel J. Hoekstra² ; Jochem R.N. van der Voort van Zyp¹ ; Hendrik Westendorp² ; Sandrine M.G. van de Pol² ; Marinus A. Moerland¹ ; Metha Maenhout¹ ; Rob Kattevilder² ; Marco van Vulpen¹
• 关键词：Focal salvage ; Total salvage ; Prostate cancer ; I-125 brachytherapy ; Dose constraints ; Rectum ; Toxicity
• 刊名：Brachytherapy
• 出版年：2016
• 出版时间：January-February 2016
• 年：2016
• 卷：15
• 期：1
• 页码：85-93
• 全文大小：728 K

文摘

Organ-confined prostate cancer recurrences after primary radiotherapy can be treated with salvage iodine-125 brachytherapy. Options include total salvage (TS) or focal salvage (FS). TS often leads to severe late gastrointestinal (GI) toxicity. Differences in rectal dosimetry between TS and FS are presented and dose constraints proposed to reduce late severe GI toxicity (>90 days).

Methods and Materials

Intraoperative dosimetry and 30-day CT-dosimetry of 20 FS and 28 TS patients were evaluated. GI toxicity was evaluated using the common terminology criteria for adverse events-4. With receiver operating characteristic analysis, dosimetry cutoff values to prevent severe late GI toxicity were assessed.

Results

FS reduces rectal dose significantly. Median D_0.1cc, D_1cc, D_2cc, and V₁₀₀ reductions were 38 Gy (p = 0.002), 46 Gy (p < 0.0001), 46 Gy (p < 0.0001), and 0.41 cc (p = 0.0001), respectively, compared with TS. FS patients had no late severe GI toxicity. TS patients with severe GI toxicity (41%, n = 11) showed significantly higher rectal doses than TS patients without GI toxicity (59%, n = 16). Median D_0.1cc, D_1cc, D_2cc, and V₁₀₀ differences were 29 Gy (p < 0.001), 17 Gy (p = 0.001), 28 Gy (p < 0.001), and 0.45 cc (p = 0.001). With receiver operating characteristic analysis, restrictions for the D_0.1cc, D_1cc, D_2cc, and V₁₀₀ are <160 Gy (area under the curve [AUC], 0.88; 95% confidence interval [CI] 0.76–1.00), <119 Gy (AUC, 0.87; 95% CI, 0.74–1.00), <102 Gy (AUC, 0.89; 95% CI, 0.77–1.00), and <0.38 cc (AUC, 0.88; 95% CI, 0.75–1.00), respectively. Thirty-day CT dosimetry showed minor overestimation of intraoperative D_2cc (median, 10 Gy [p = 0.02]).

Conclusions

FS reduces rectal dose compared with TS. D_0.1cc, D_1cc, D_2cc, and V₁₀₀ restrictions were 160 Gy, 120 Gy, 100 Gy, and 0.35 cc. Taking correlation into account, the D_2cc <100 Gy might be sufficient for clinical practice. Larger series and multivariable models are necessary to further assess the found restrictions.