International journal of radiation oncology, biology, physics 2014-07-01
Predictors of rectal tolerance observed in a dose-escalated phase 1-2 trial of stereotactic body radiation therapy for prostate cancer.
Abstract
Purpose
To convey the occurrence of isolated cases of severe rectal toxicity at the highest dose level tested in 5-fraction stereotactic body radiation therapy (SBRT) for localized prostate cancer; and to rationally test potential causal mechanisms to guide future studies and experiments to aid in mitigating or altogether avoiding such severe bowel injury.
Methods and materials
Clinical and treatment planning data were analyzed from 91 patients enrolled from 2006 to 2011 on a dose-escalation (45, 47.5, and 50 Gy in 5 fractions) phase 1/2 clinical study of SBRT for localized prostate cancer.
Results
At the highest dose level, 6.6% of patients treated (6 of 91) developed high-grade rectal toxicity, 5 of whom required colostomy. Grade 3+ delayed rectal toxicity was strongly correlated with volume of rectal wall receiving 50 Gy >3 cm(3) (P<.0001), and treatment of >35% circumference of rectal wall to 39 Gy (P=.003). Grade 2+ acute rectal toxicity was significantly correlated with treatment of >50% circumference of rectal wall to 24 Gy (P=.010).
Conclusion
Caution is advised when considering high-dose SBRT for treatment of tumors near bowel structures, including prostate cancer. Threshold dose constraints developed from physiologic principles are defined, and if respected can minimize risk of severe rectal toxicity.
Related Questions
How do you determine dose for prostate SBRT?
The Stanford experience published by King et al was an important one describing a prospective experience of SBRT at dose levels of 35-36.25 Gy, and these dose levels were used based upon prior single institution retrospective reports from community practice settings where a good deal of experience ...
Is there really substantial evidence to avoid central lesions for SBRT?
Much has been learned since the cautionary data from Indiana University was published showing increased toxicity when using SBRT for centrally-located lung cancers. One should be aware that there is an increased risk when treating tumors in this location with SBRT fractionation schemes. I am aware o...