About this Research Topic
It has been widely accepted that prostate cancer has a great sensitivity to dose per fraction. HDR brachytherapy has had great success for twenty years in treating early prostate cancer by capitalizing on this and delivering a few large fractions of radiation. Over the last decade, many researchers have begun exploring using these large dose fractions with stereotactic techniques(SBRT) to deliver external radiation in a focused and highly accurate manner. The data that has emerged, with up to six year followup, shows high rates of biochemical control with mild late toxicity, emulating the success of HDR brachytherapy in a non invasive outpatient setting.
Although the overall concept shows great early success, specific questions regarding delivery techniques still remain.
It is not yet clear exactly what dose and what number of fractions is optimal for maximizing control and minimizing toxicity. A dose of 35 Gy in 5 days seems to be sufficient for lower risk cases but it is unclear if that is true for the more aggressive lesions.
Although most early reports used daily treatments, some have used every other day or even weekly scheduling. Also, the majority of early papers reported on use of Cyberknife, but many researchers are now using other devices such as Rapid Arc Linacs or Tomotherapy. Whether there is an advantage to any of the different dose schedules or treatment devices remains an open question. Distribution of dose throughout the prostate can be done in a homogeneous manner versus a heterogeneous HDR type of plan. Thus far, no difference in control rates can be seen between the two planning methods, but more followup is needed to be further clarify this.
Finally, most researchers have reported results with low risk and intermediate risk patients, with high control rates. Less is known whether this technique is appropriate for high risk patients, and if so, whether combining external pelvic radiotherapy with SBRT is the optimal method to deal with this subset of patients.
Exploring these questions will be important as this technique becomes more mainstream. Thus far, excellent control rates and low toxicity combined with faster treatment times and lower cost have the potential of making radiation therapy for prostate cancer more widely available to patients around the world, especially in nations with limited machine capacity.
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