Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Ontario, Canada; Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada.
Radiation Medicine Program, Princess Margaret Cancer Centre, Toronto, Ontario, Canada.
Int J Radiat Oncol Biol Phys. 2014 Aug 1;89(5):1121-1128. doi: 10.1016/j.ijrobp.2014.04.051. Epub 2014 Jul 8.
The dosimetric impact of dose probability based planning target volume (PTV) margins for liver cancer patients receiving stereotactic body radiation therapy (SBRT) was compared with standard PTV based on the internal target volume (ITV). Plan robustness was evaluated by accumulating the treatment dose to ensure delivery of the intended plan.
Twenty patients planned on exhale CT for 27 to 50 Gy in 6 fractions using an ITV-based PTV and treated free-breathing were retrospectively evaluated. Isotoxic, dose escalated plans were created on midposition computed tomography (CT), representing the mean breathing position, using a dose probability PTV. The delivered doses were accumulated using biomechanical deformable registration of the daily cone beam CT based on liver targeting at the exhale or mean breathing position, for the exhale and midposition CT plans, respectively.
The dose probability PTVs were on average 38% smaller than the ITV-based PTV, enabling an average ± standard deviation increase in the planned dose to 95% of the PTV of 4.0 ± 2.8 Gy (9 ± 5%) on the midposition CT (P<.01). For both plans, the delivered minimum gross tumor volume (GTV) doses were greater than the planned nominal prescribed dose in all 20 patients and greater than the planned dose to 95% of the PTV in 18 (90%) patients. Nine patients (45%) had 1 or more GTVs with a delivered minimum dose more than 5 Gy higher with the midposition CT plan using dose probability PTV, compared with the delivered dose with the exhale CT plan using ITV-based PTV.
For isotoxic liver SBRT planned and delivered at the mean respiratory, reduced dose probability PTV enables a mean escalation of 4 Gy (9%) in 6 fractions over ITV-based PTV. This may potentially improve local control without increasing the risk of tumor underdosing.
比较基于剂量概率的肝癌患者立体定向体部放射治疗（SBRT）计划靶区（PTV）边界与基于内部靶区（ITV）的标准 PTV 的剂量学影响。通过累积治疗剂量来评估计划稳健性，以确保计划的实施。
回顾性分析了 20 例在呼气 CT 上接受 27 至 50 Gy 分 6 次治疗的患者，采用 ITV 基础 PTV 进行计划。创建了基于中位置 CT（midposition CT）的等毒性、剂量递增计划，代表了呼吸时的平均位置，采用剂量概率 PTV。使用基于肝脏靶区的生物力学可变形注册，将每日锥形束 CT 与呼气或平均呼吸位置进行配准，将呼气和中位置 CT 计划的剂量进行累积。
剂量概率 PTV 平均比 ITV 基础 PTV 小 38%，这使得在中位置 CT 上，计划剂量到 PTV 的 95%的平均±标准偏差增加了 4.0±2.8 Gy（9±5%）（P<.01）。对于两种计划，所有 20 例患者的 GTV 最低受量均大于计划的名义规定剂量，18 例（90%）患者的 GTV 最低受量大于计划剂量到 PTV 的 95%。与 ITV 基础 PTV 相比，使用剂量概率 PTV 的中位置 CT 计划时，有 9 例（45%）患者的 1 个或多个 GTV 的最低受量高出 5 Gy 以上，而使用 ITV 基础 PTV 的呼气 CT 计划时，GTV 的最低受量没有超过 5 Gy。
对于等毒性肝 SBRT，在平均呼吸时，采用基于剂量概率的减小 PTV 可使 6 次分割的剂量平均增加 4 Gy（9%），超过 ITV 基础 PTV。这可能会在不增加肿瘤剂量不足风险的情况下提高局部控制率。
