Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
Phys Med Biol. 2010 Dec 21;55(24):7425-38. doi: 10.1088/0031-9155/55/24/003. Epub 2010 Nov 19.
A detailed Monte Carlo model of a proton therapy treatment head was commissioned to simulate the delivery of small field proton treatments. Small fields are challenging in the planning and quality assurance process because of aperture scattering and dosimetric disequilibrium. Four patients with small fields used in all or parts of their treatment course were studied, including two stereotactic patients and two fractionated patients. For the two stereotactic patients the overall difference of the dose covering at least 95% of the gross tumor volume between the Monte Carlo calculations and the delivery was -0.2% and -1.6%, respectively. For the two fractionated patients the overall difference of the dose covering at least 95% of the clinical target volume was -3.0% and 1.0%, respectively. We have thus confirmed that our current planning and delivery process for small proton fields is accurate enough to treat small lesions in the patient. Furthermore, we studied the impact of field size corrections and identified limitations of the pencil beam algorithm for predicting hot and cold spots and range degradation in the target due scattering in heterogeneities. For the four cases studied in this paper, these limitations appear to impact individual field calculations, but do not have a significant impact on the prescribed dose over multiple fields.
委托制作了一个质子治疗头的详细蒙特卡罗模型，以模拟小射野质子治疗的实施。由于孔径散射和剂量失衡，小射野在规划和质量保证过程中极具挑战性。研究了 4 名患者的小射野治疗，他们全部或部分采用了小射野治疗，包括 2 名立体定向患者和 2 名分次治疗患者。对于 2 名立体定向患者，蒙特卡罗计算和实施的至少 95%肿瘤体积覆盖的剂量总体差异分别为-0.2%和-1.6%。对于 2 名分次治疗患者，至少 95%临床靶体积覆盖的剂量总体差异分别为-3.0%和 1.0%。因此，我们确认目前用于小质子野的计划和实施过程足以治疗患者的小病变。此外，我们研究了射野大小校正的影响，并确定了铅笔束算法在预测由于散射引起的热点和冷点以及目标内射程退化方面的局限性。对于本文研究的 4 个病例，这些局限性似乎会影响单个射野的计算，但不会对多个射野的规定剂量产生显著影响。
