Metwaly Mohamed, Awaad Awaad Mousa, El-Sayed El-Sayed Mahmoud, Sallam Abdel Sattar Mohamed
Radiation Physics Department, Faculty of Science, Ain Shams University, Cairo.
Radiotherapy Department, Faculty of Science, Ain Shams University, Cairo, Egypt.
J Appl Clin Med Phys. 2007 Nov 5;8(4):114-128. doi: 10.1120/jacmp.v8i4.2488.
In this study, we present an intensity-modulated radiotherapy technique based on forward planning dose calculations to provide a concave dose distribution to the prostate and seminal vesicles by means of modified dynamic arc therapy (M-DAT). Dynamic arcs (350 degrees) conforming to the beam's eye view of the prostate and seminal vesicles while shielding the rectum, combined with two lateral oblique conformal fields (15 degrees with respect to laterals) fitting the prostate only,were applied to deliver doses of 78 Gy and 61.23 Gy in 39 fractions to the prostate and seminal vesicles respectively. Dynamic wedges (45 degrees of thick end, anteriorly oriented) were used with conformal beams to adjust the dose homogeneity to the prostate, although in some cases, hard wedges (30 degrees of thick part,inferiorly oriented) were used with arcs to adjust the dose coverage to the seminal vesicles. The M-DAT was applied to 10 patients in supine and 10 patients in prone positioning to determine the proper patient positioning for optimum protection of the rectum. The M-DAT was compared with the simplified intensity-modulated arc therapy (SIMAT) technique, composed of three phases of bilateral dynamic arcs. The mean rectal dose in M-DAT for prone patients was 22.5 +/- 5.1 Gy; in M-DAT and SIMAT for supine patients, it was 30.2 +/- 5.1 Gy and 39.4 +/- 6.0 Gy respectively. The doses to 15%, 25%, 35%, and 50% of the rectum volume in M-DAT for prone patients were 44.5 +/- 10.2 Gy, 33.0 +/- 8.2 Gy, 25.3 +/- 6.4 Gy, and 16.3 +/- 5.6 Gy respectively. These values were lower than those in M-DAT and in SIMAT for supine patients by 7.7%, 18.2%, 22.4%, and 28.5% and by 25.0%, 32.1%, 34.9%, and 41.9% of the prescribed dose (78 Gy) respectively. Ion chamber measurements showed good agreement of the calculated and measured isocentric dose (maximum deviation of 3.5%). Accuracy of the dose distribution calculation was evaluated by film dosimetry using a gamma index, allowing 3% dose variation and 4 mm distance to agreement as the individual acceptance criteria in prostate and seminal vesicle levels alike for all supine and prone patients. We found that fewer than 10% of the pixels in the dose distribution of the calculated area of10 x 10-cm failed the acceptance criteria. These pixels were observed mainly in the low-dose regions, particularly at the level of the seminal vesicles. In conclusion, the single-phase M-DAT technique with patients in the prone position was found to provide the intended coverage of the prescribed doses to the prostate and seminal vesicles with improved protection for the rectum. Accordingly, M-DAT has replaced non-modulated conformal radiotherapy or SIMAT as the standard treatment for prostate cancer in our department.
在本研究中，我们提出了一种基于正向计划剂量计算的调强放射治疗技术，通过改良动态弧形治疗（M-DAT）为前列腺和精囊提供凹形剂量分布。动态弧形（350度）与前列腺和精囊的射野方向一致，同时遮挡直肠，再结合两个仅适用于前列腺的侧向斜野（相对于侧方为15度），分别以39次分割给予前列腺78 Gy、精囊61.23 Gy的剂量。适形射野使用动态楔形板（厚端45度，向前定向）来调整前列腺的剂量均匀性，不过在某些情况下，弧形野使用硬楔形板（厚部30度，向下定向）来调整精囊的剂量覆盖范围。M-DAT应用于10例仰卧位患者和10例俯卧位患者，以确定最佳保护直肠的合适患者体位。将M-DAT与简化调强弧形治疗（SIMAT）技术进行比较，SIMAT技术由双侧动态弧形的三个阶段组成。俯卧位患者M-DAT中的平均直肠剂量为22.5±5.1 Gy；仰卧位患者M-DAT和SIMAT中的平均直肠剂量分别为30.2±5.1 Gy和39.4±6.0 Gy。俯卧位患者M-DAT中直肠体积的15%、25%、35%和50%所接受的剂量分别为44.5±10.2 Gy、33.0±8.2 Gy、25.3±6.4 Gy和16.3±5.6 Gy。这些值分别比仰卧位患者M-DAT和SIMAT中的值低7.7%、18.2%、22.4%和28.5%，以及分别低规定剂量（78 Gy）的25.0%、32.1%、34.9%和41.9%。电离室测量显示计算的等中心剂量与测量值吻合良好（最大偏差为3.5%）。通过使用γ指数的胶片剂量测定法评估剂量分布计算的准确性，对于所有仰卧位和俯卧位患者，在前列腺和精囊层面均将3%的剂量变化和4 mm的距离一致性作为个体接受标准。我们发现，在计算区域10×10-cm的剂量分布中，不到10%的像素未达到接受标准。这些像素主要出现在低剂量区域，尤其是在精囊层面。总之，发现患者处于俯卧位的单相M-DAT技术能够为前列腺和精囊提供规定剂量的预期覆盖范围，同时对直肠有更好的保护。因此，M-DAT已取代非调强适形放疗或SIMAT，成为我们科室前列腺癌的标准治疗方法。
