Department of Radiotherapy and Radiation Medicine, Institute of Medical Sciences, BHU, Varanasi, India.
Cancer Radiother. 2021 Feb;25(1):8-12. doi: 10.1016/j.canrad.2020.05.015. Epub 2020 Dec 5.
To explore the possibility of revising the spinal cord tolerance dose in Simultaneously Integrated Boost (SIB) intensity modulated treatment plan of locally advanced head and neck (H&N) cancer and assessment of achieved planning gain due to the revision. In SIB regimen, the Organ at Risk (OARs) tolerance dose is equally distributed throughout the treatment. Clinicians have usually considered the spinal cord tolerance to be the same as in conventional technique. However, in SIB fractionation regimen with intensity modulation treatment, the spinal cord may receive a physical dose of 45Gy, with much lesser dose per fraction than 2Gy per fraction. So when the dose of spinal cord is distributed throughout the treatment, the tolerance dose limit of physical dose can be considered higher than the usual conventional dose limits. In this study, an attempt has been made to explore the possibilities of dose escalation and treatment planning benefits while exploiting this "Window of Opportunity (WoO)" of increase in spinal cord and Planning Risk Volume (PRV) spinal cord tolerance dose.
A total of 12 patients CT data set along with approved structure set of H&N cancer used for treatment planning in. Three independent SIB VMAT plans named as SPC, SPR and SPDE were generated for the 12 patients. First plan (SPC) was generated by considering standard spinal cord tissue constraint of maximum dose of 45Gy and PRV spinal cord maximum dose 50Gy as per QUANTEC summary and second plan (SPR) was generated considering spinal cord tissue constraint of maximum dose 52.50Gy and PRV spinal cord maximum dose 56.35Gy while optimization and dose calculation. The objectives for rest of the Organ at Risk (OAR) were kept same in both the plans during optimization and dose calculation. The SPC plan was copied for creation of third plan (SPDE) in which dose was escalated by increasing dose per fraction for target volumes such that dose to spinal cord reached a maximum dose of 52.50Gy and PRV spinal cord maximum dose of 56.35Gy. In this plan there have been changes to only dose per fraction, however dose optimization and dose calculation have not been performed. Radiobiological parameters TCP and NTCP were also calculated by using indigenously developed software.
Considering the increase of spinal cord tolerance dose as "window of opportunity", a sufficient escalation in physical dose, Biological Effective Dose (BED) and Tumor Control Probability (TCP) was observed for all target volumes with acceptable level of NTCP values.
Sufficient dose escalation and increased in TCP for target volumes or effective planning benefits can be achieved by revising the spinal cord tolerance dose in intensity modulated SIB treatment of locally advanced H&N cancers.
探索修订局部晚期头颈部（H&N）癌症同时整合增强（SIB）强度调制治疗计划中脊髓耐受剂量的可能性，并评估修订后获得的规划增益。在 SIB 方案中，危及器官（OAR）的耐受剂量在整个治疗过程中平均分配。临床医生通常认为脊髓耐受与常规技术相同。然而，在 SIB 分割方案中，脊髓可能会接收到 45Gy 的物理剂量，每个剂量比常规的 2Gy 每个剂量小得多。因此，当脊髓剂量分布在整个治疗过程中时，可以考虑脊髓耐受剂量限制的物理剂量高于常规剂量限制。在这项研究中，我们试图探索在利用脊髓和计划风险体积（PRV）脊髓耐受剂量增加的“机会之窗（WoO）”的同时，提高剂量和治疗计划获益的可能性。
共纳入 12 例患者的 CT 数据集和用于治疗计划的 H&N 癌症的批准结构集。为 12 例患者生成了三个独立的 SIB VMAT 计划，分别命名为 SPC、SPR 和 SPDE。第一个计划（SPC）是通过考虑脊髓组织最大剂量为 45Gy 的标准脊髓组织约束和 QUANTEC 摘要中的 PRV 脊髓最大剂量 50Gy 来生成的，第二个计划（SPR）是通过考虑脊髓组织最大剂量为 52.50Gy 和 PRV 脊髓最大剂量为 56.35Gy 来生成的，同时进行优化和剂量计算。在优化和剂量计算过程中，其他 OAR 的目标保持不变。SPC 计划被复制用于创建第三个计划（SPDE），其中通过增加靶区的每个剂量来提高剂量，使得脊髓剂量达到最大剂量 52.50Gy 和 PRV 脊髓最大剂量 56.35Gy。在这个计划中，只有每个剂量的剂量发生了变化，但是没有进行剂量优化和剂量计算。也使用自主开发的软件计算了放射生物学参数 TCP 和 NTCP。
考虑到脊髓耐受剂量的增加作为“机会之窗”，所有靶区的物理剂量、生物有效剂量（BED）和肿瘤控制概率（TCP）都有足够的提高，同时保持可接受的 NTCP 值水平。
通过修订局部晚期 H&N 癌症的强度调制 SIB 治疗中的脊髓耐受剂量，可以实现靶区的足够剂量提高和 TCP 的增加，从而获得有效的规划获益。
