Stereotactic Radiosurgery for Prostate Cancer by Michael J. Zelefsky

Author:Michael J. Zelefsky
Language: eng
Format: epub, pdf
ISBN: 9783319924533
Publisher: Springer International Publishing

8.3.2 Profile and Etiology of Late Gastrointestinal Morbidity

Late gastrointestinal toxicity is a concern for patients treated with SBRT; however, due to tight treatment margins [65], image-guided therapy, and the favorable therapeutic ratio associated with hypofractionation, the incidence of high grade toxicity is quite modest. Although most follow-up remains relatively short in comparison to data from conventionally fractionated series, rates of late grade 2+ toxicity are reportedly less than 15% [23, 24, 66, 67], while grade 3+ toxicity is quite rare. Urgency and frequency, which can be pronounced acutely, are generally not present and do not reappear once the initial symptoms have resolved.

The most common late rectal toxicity following SBRT is hematochezia. The incidence of this adverse effect is not clear, as rates reported in the literature vary widely, which may be secondary to differences in toxicity reporting. Nonetheless, the rate of hematochezia requiring aggressive intervention, such as argon plasma coagulation (APC), is likely quite low, with one large series reporting an actuarial 2-year rate of 1.5% [37], which compares favorably to the EBRT and IMRT literature. However, another study, in which patients were treated using a strategy that prioritized target coverage over risk of toxicity, reported a high-grade hematochezia rate of 19.4%, although the investigators used a non-standard grading schema [68]. The rate of rectal bleeding requiring more than two sessions of APC in this study was 3.1%.

A more concerning adverse effect of SBRT, particularly in the setting of dose escalation, is loss of integrity of the rectal wall, including rectal ulcers or rectourethral fistulae. While these toxicities are typically not observed in patients treated with standard SBRT doses (35–40 Gy in five fractions), there are reports in the literature of high grade rectal toxicity requiring emergent cauterization or diverting colostomy [69]. In this study, 6.6% of patients treated to a total prostate dose of 50 Gy in five fractions experienced grade 3+ rectal toxicity. While retrospective analyses of the data suggest that high-grade toxicity may be limited by limiting the volume of rectal wall receiving 50 Gy below 3 cm3 and keeping <35% of the rectal wall circumference to 39 Gy [70], given the limited toxicity and excellent oncologic outcomes associated with lower dose-per-fraction regimens, extreme dose escalation is not recommended outside the context of a clinical trial.

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