Total marrow lymphoid irradiation IMRT treatment using a novel CT-linac
Dazhen JiangDi DengYu XiongDajiang WangJian Ping GongHongli ZhaoZhirong BaoYongchang WeiConghua XieLecheng JiaCan LiaoShuo LiuHui LiuXiaoyong Wang
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Abstract Background A novel CT-linac (kilovolt fan-beam CT-linac) has been introduced into total marrow and lymphoid irradiation (TMLI) treatment. Its integrated kilovolt fan-beam CT (kV FBCT) can be used not only for image guidance (IGRT) but also to re-calculate the dose. Purpose This study reported our clinical routine on performing TMIL treatment on the CT-linac, as well as dose distribution comparison between planned and re-calculated based on IGRT FBCT image sets. Methods 11 sets of data from 5 male and 6 female patients who had underwent the TMLI treatment with uRT-linac 506c were selected for this study. The planning target volumes consist of all skeletal bones exclusion of the mandible and lymphatic sanctuary sites. A planned dose of 10 Gy was prescribed to all skeletal bones exclusion of the mandible in two fractions and 12 Gy in two fractions was prescribed to lymphatic sanctuary sites. Each TMLI plan contained two sub-plans, one dynamic IMRT for the upper body and the other VMAT for the lower extremity. Two attempts were made to obtain homogeneous dose in the overlapping region, i.e., applying two plans with different isocenters for the treatment of two fractions, and using a dose gradient matching scheme. The CT scans, including planning CT and IGRT FBCT, were stitched to a whole body CT scan for dose distribution evaluation. Results The average beam-on time of Planupper is 30.6 min, ranging from 24.9 to 37.5 min, and the average beam-on time of Planlower is 6.3 min, ranging from 5.7 to 8.2 min. For the planned dose distribution, the 94.79% of the PTVbone is covered by the prescription dose of 10 Gy (V10), and the 94.68% of the PTVlymph is covered by the prescription dose of 12 Gy (V12). For the re-calculated dose distribution, the 92.17% of the PTVbone is covered by the prescription dose of 10 Gy (V10), and the 90.07% of the PTVlymph is covered by the prescription dose of 12 Gy (V12). The results showed that there is a significant difference ( p < 0.05) between planning V10, V12 and delivery V10, V12. There is no significant difference ( p > 0.05) between planned dose and re-calculated dose on selected organs, except for right lens ( p < 0.05, Dmax). The actual delivered maximum dose of right lens is apparently larger than the planned dose of it. Conclusion TMLI treatment can be performed on the CT-linac with clinical acceptable quality and high efficiency. Evaluation of the recalculated dose on IGRT FBCT suggests the treatment was delivered with adequate target coverage.Keywords:
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Our image‐guided radiation therapy (IGRT) protocol for post‐prostatectomy patients involves acquiring a kV cone beam computed tomography (CBCT) dataset at each fraction and shifting the treatment couch to align the surgical clips. This IGRT strategy requires significant resources, and delivers non‐negligible dose to normal tissues. The objective of this work is to evaluate this IGRT protocol against two alternative strategies in terms of the dose‐volume statistics for target and organ at risk regions. Our method involves deforming the planning CT to the CBCT dataset acquired at each fraction, computing dose on the deformed dataset, and inversely transforming the dose back onto the original planning CT dataset. The treatments of six patients were evaluated assuming three IGRT scenarios: no IGRT, daily IGRT using the clinically employed couch shifts, and alternating day IGRT. The doses delivered to the clinical target volumes are within approximately 3.2, 1.3, and 2.1% of the plan for the non‐IGRT, daily, and alternating day IGRT protocols, respectively. Doses to relevant portions of the organs at risk deviate from the plan by up to 10.5, 13.1 and 10.7% for non‐IGRT, daily IGRT, and alternating day IGRT protocols, respectively. Some cases do not differ significantly between IGRT and non‐IGRT protocols in terms of cumulative DVHs, highlighting the difficult task of correcting prostate bed deformations via the treatment couch translations. In general, the alternating day IGRT protocol was found to result in a clinically insignificant deviation in delivered dose while providing a significant reduction in resource use and patient imaging dose.
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