Hunt Margie A, Jackson Andrew, Narayana Ashwatha, Lee Nancy
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Int J Radiat Oncol Biol Phys. 2006 Sep 1;66(1):296-304. doi: 10.1016/j.ijrobp.2006.05.028.
PURPOSE/OBJECTIVE: To determine the relationship between the parotid volume, parotid-planning target volume (PTV) overlap, and dosimetric sparing of the parotid with intensity-modulated radiation therapy (IMRT).
Parotid data were collected retrospectively for 51 patients treated with simultaneous boost IMRT. Unresectable patients received 54 or 59.4 Gy to subclinical disease, 70 Gy to gross disease. Patients treated postoperatively received 54, 60, and 66 Gy to low-risk, high-risk, and tumor bed regions. Volume and mean dose of each gland and gland segments outside of and overlapping the PTV were collected. Proximity of each gland to each PTV was recorded.
Dosimetric sparing (mean dose <or =26.5 Gy) was achieved in 66 of 71 glands with < or =21% parotid-PTV overlap and 8 of 23 glands with >21% overlap (p = <0.0001). Among spared glands, the median mean dose in the overlap region was 55.0 Gy in glands with < or =21% overlap, but only 45.4 Gy when overlap >21%. Median mean dose was 25.9 Gy to glands overlapping PTV(54) or PTV(59) alone and 30.0 Gy to those abutting PTV(70) (p < 0.001). Although proximity to PTV(70) was associated with higher parotid dose, satisfactory sparing was achieved in 24 of 43 ipsilateral glands.
Dosimetric sparing of the parotid is feasible when the parotid-PTV overlap is less than approximately 20%. With more overlap, sparing may result in low doses within the overlap region, possibly leading to inadequate PTV coverage. Gland proximity to the high-dose PTV is associated with higher mean dose but does not always preclude dosimetric sparing.
确定腮腺体积、腮腺计划靶区（PTV）重叠以及调强放射治疗（IMRT）对腮腺的剂量学保护之间的关系。
回顾性收集51例接受同步推量IMRT治疗患者的腮腺数据。不可切除患者亚临床病灶接受54或59.4 Gy照射，大体病灶接受70 Gy照射。术后治疗患者低危、高危和瘤床区域分别接受54、60和66 Gy照射。收集每个腺体及PTV外和与PTV重叠部分的腺体节段的体积和平均剂量。记录每个腺体与每个PTV的接近程度。
71个腺体中，腮腺-PTV重叠≤21%的66个腺体实现了剂量学保护（平均剂量≤26.5 Gy），而重叠>21%的23个腺体中有8个实现了剂量学保护（p<0.0001）。在实现剂量学保护的腺体中，重叠≤21%的腺体重叠区域平均剂量中位数为55.0 Gy，而重叠>21%时仅为45.4 Gy。单独与PTV(54)或PTV(59)重叠的腺体平均剂量中位数为25.9 Gy，与PTV(70)相邻的腺体平均剂量中位数为30.0 Gy（p<0.001）。尽管与PTV(70)接近与腮腺剂量较高有关，但43个同侧腺体中有24个实现了满意的剂量学保护。
当腮腺-PTV重叠小于约20%时，对腮腺进行剂量学保护是可行的。重叠越多，保护可能导致重叠区域内剂量较低，可能导致PTV覆盖不足。腺体与高剂量PTV的接近程度与较高的平均剂量有关，但并不总是排除剂量学保护。
