Image‐guided, intensity modulated radiation therapy (IG‐IMRT) reduces dose to pelvic organs at risk without losing dose coverage to the planning target volume (PTV) and might permit margin reductions potentially resulting in lower toxicity. Appropriate PTV margins have not been established for IG‐IMRT in abdominopelvic tumours in dogs, and herein we explore if our usual PTV 5 mm margin can be reduced further. Datasets from dogs that underwent IG‐IMRT for non‐genitourinary abdominopelvic neoplasia with 5 mm‐PTV expansion were included in this retrospective virtual study. The clinical target volumes and organs at risk (OAR) colon, rectum, spinal cord were adapted to each co‐registered cone‐beam computed tomography (CBCT) used for positioning. New treatment plans were generated and smaller PTV margins of 3 mm and 4 mm evaluated with respect to adequate dose coverage and normal tissue complication probability (NTCP) of OAR. Ten dogs with a total of 70 CBCTs were included. Doses to the OAR of each CBCT deviated mildly from the originally planned doses. In some plans, insufficient build‐up of the high dose‐area at the body surface was found due to inadequate or missing bolus placement. Overall, the margin reduction to 4 mm or 3 mm did not impair dose coverage and led to significantly lower NTCP in all OAR except for spinal cord delayed myelopathy. However, overall NTCP for spinal cord was very low (<4%). PTV‐margins depend on patient immobilization and treatment technique and accuracy. IG‐IMRT allows treatment with very small margins in the abdominopelvic region, ensuring appropriate target dose coverage, while minimizing NTCP.

中文翻译：

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减少犬腹盆腔肿瘤的边缘：对剂量覆盖和正常组织并发症概率的影响

图像引导的调强放射治疗 (IG-IMRT) 减少了对处于危险中的盆腔器官的剂量，而不会失去对计划靶区 (PTV) 的剂量覆盖，并且可能允许减少边缘，从而可能导致较低的毒性。尚未为犬腹盆腔肿瘤的 IG-IMRT 建立适当的 PTV 切缘，在此我们探讨是否可以进一步减小我们通常的 PTV 5 mm 切缘。这项回顾性虚拟研究包括来自接受 IG-IMRT 治疗非泌尿生殖系统腹盆腔肿瘤且 PTV 扩大 5 mm 的狗的数据集。临床目标体积和危险器官 (OAR) 结肠、直肠、脊髓适用于每个用于定位的联合配准锥形束计算机断层扫描 (CBCT)。制定了新的治疗计划，并就 OAR 的足够剂量覆盖和正常组织并发症概率 (NTCP) 评估了 3 mm 和 4 mm 的较小 PTV 边缘。包括 10 只狗，总共 70 次 CBCT。每个 CBCT 的 OAR 剂量与最初计划的剂量略有不同。在一些计划中，由于推注位置不充分或缺失，发现体表的高剂量区域积聚不足。总体而言，边缘减少至 4 mm 或 3 mm 并未影响剂量覆盖，并导致除脊髓延迟性脊髓病外的所有 OAR 中的 NTCP 显着降低。然而，脊髓的整体 NTCP 非常低（<4%）。PTV 边缘取决于患者的固定和治疗技术和准确性。IG-IMRT 允许在腹盆腔区域进行非常小的边缘治疗，