Ove R, Wallner K, Badiozamani K, Korjsseon T, Sutlief S
Department of Radiation Oncology, University of Alabama Medical Center, Birmingham, AL, USA.
Int J Radiat Oncol Biol Phys. 2001 May 1;50(1):257-63. doi: 10.1016/s0360-3016(01)01471-7.
Whereas custom-designed plans are the norm for prostate brachytherapy, the relationship between linear prostate dimensions and volume calls into question the routine need for customized treatment planning. With the goal of streamlining the treatment-planning process, we have compared the treatment margins (TMs) achieved with one standard plan applied to patients with a wide range of prostate volumes.
Preimplant transrectal ultrasound (TRUS) images of 50 unselected University of Washington patients with T1-T2 cancer and a prostate volume between 20 cc and 50 cc were studied. Patients were arbitrarily grouped into categories of 20-30 cc, 30-40 cc, and 40-50 cc. A standard 19-needle plan was devised for patients in the 30- to 40-cc range, using an arbitrary minimum margin of 5 mm around the gross tumor volume (GTV), making use of inverse planning technology to achieve 100% coverage of the target volume with accentuation of dose at the periphery and sparing of the central region. The idealized plan was applied to each patient's TRUS study. The distances (TMs) between the prostatic edge (GTV) and treated volume (TV) were determined perpendicular to the prostatic margin.
Averaged over the entire patient group, the ratio of thickness to width was 1.4, whereas the ratio of length to width was 1.3. These values were fairly constant over the range of volumes, emphasizing that the prostate retains its general shape as volume increases. The idealized standard plan was overlaid on the ultrasound images of the 17 patients in the 30- to 40-cc group and the V100, the percentage of target volume receiving 100% or more of the prescription dose, was 98% or greater for 15 of the 17 patients. The lateral and posterior TMs fell within a narrow range, most being within 2 mm of the idealized 5-mm TM. To estimate whether a 10-cc volume-interval stratification was reasonable, the standard plan generated from the 30- to 40-cc prostate model was applied to 5 patients each from the 20- to 30-cc group and the 40- to 50-cc group. Using the standard plan designed for the 30- to 40-cc group, the TMs were closer to 10 mm than to 5 mm for the smaller volume glands and too small for the larger volume ones, assuming an ideal margin of 5 mm.
The application of standardized plans to prostate brachytherapy is feasible. Stratifying the volume in 10-cc intervals appears to be adequate, suggesting that the majority of cases appropriate for treatment with brachytherapy might be treated with three standard plans. While the authors believe that the use of a limited number of standard treatment plans is feasible, practical, and medically acceptable, it should be emphasized that the use of a standard plan should always be previewed by computer-aided application to the particular patient's planning images.
鉴于定制设计的方案是前列腺近距离放射治疗的标准做法，前列腺线性尺寸与体积之间的关系对常规定制治疗计划的必要性提出了质疑。为了简化治疗计划流程，我们比较了将一个标准方案应用于前列腺体积范围广泛的患者时所获得的治疗边界（TM）。
研究了华盛顿大学50例未经挑选的T1 - T2期癌症患者的植入前经直肠超声（TRUS）图像，前列腺体积在20立方厘米至50立方厘米之间。患者被任意分为20 - 30立方厘米、30 - 40立方厘米和40 - 50立方厘米三组。为30至40立方厘米范围内的患者设计了一个标准的19针方案，在大体肿瘤体积（GTV）周围使用任意最小边界5毫米，利用逆向计划技术实现靶体积100%的覆盖，同时在外围增强剂量并保护中心区域。将理想化方案应用于每位患者的TRUS研究。确定前列腺边缘（GTV）与治疗体积（TV）之间垂直于前列腺边缘的距离（TM）。
在整个患者组中平均来看，厚度与宽度之比为1.4，而长度与宽度之比为1.3。这些值在体积范围内相当恒定，强调随着体积增加前列腺保持其大致形状。将理想化的标准方案叠加在30至40立方厘米组的17例患者的超声图像上，对于17例患者中的15例，接受100%或更多处方剂量的靶体积百分比（V100）为98%或更高。外侧和后侧的TM落在一个狭窄范围内，大多数在理想化的5毫米TM的2毫米范围内。为了评估10立方厘米体积间隔分层是否合理，将从30至40立方厘米前列腺模型生成的标准方案应用于20至30立方厘米组和40至50立方厘米组各5例患者。使用为30至40立方厘米组设计的标准方案，对于较小体积的腺体，TM更接近10毫米而非5毫米，而对于较大体积的腺体则太小，假设理想边界为5毫米。
将标准化方案应用于前列腺近距离放射治疗是可行的。以10立方厘米间隔对体积进行分层似乎是足够的，这表明大多数适合近距离放射治疗的病例可能用三个标准方案进行治疗。虽然作者认为使用有限数量的标准治疗方案是可行的、实用的且在医学上是可接受的，但应强调在对特定患者的计划图像进行计算机辅助应用之前，应始终预先查看标准方案的使用情况。
