Dosimetric variations of target volumes and organs at risk in nasopharyngeal carcinoma intensity-modulated radiotherapy

Zhang, X; M, Li; Cao, Jianzhong; Jw, Luo; Gz, Xu; Gao, Lina; Jiang, Y.; Huang, Xiaodong; Xiao, Jianping; S, Li; Dai, Jianrong

doi:10.1259/bjr/20695672

Cited by 20 publications

(17 citation statements)

References 12 publications

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“…This was consistent with the study of Zhang et al, in which a planning CT and weekly repeat CT were scanned to study the actual dose variability of targets and OARs for 11 NPC patients during IMRT [21]. The average maximum doses represented by D1 for the brainstem and spinal cord were not significant different between planned and delivered doses.…”

Section: Discussionsupporting

confidence: 88%

CBCT-based volumetric and dosimetric variation evaluation of volumetric modulated arc radiotherapy in the treatment of nasopharyngeal cancer patients

Jin

Shang³

et al. 2013

Radiat Oncol

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ObjectiveTo investigate the anatomic and dosimetric variations of volumetric modulated arc therapy (VMAT) in the treatment of nasopharyngeal cancer (NPC) patients based on weekly cone beam CT (CBCT).Materials and methodsTen NPC patients treated by VMAT with weekly CBCT for setup corrections were reviewed retrospectively. Deformed volumes of targets and organs at risk (OARs) in the CBCT were compared with those in the planning CT. Delivered doses were recalculated based on weekly CBCT and compared with the planned doses.ResultsNo significant volumetric changes on targets, brainstem, and spinal cord were observed. The average volumes of right and left parotid measured from the fifth CBCT were about 4.4 and 4.5 cm3 less than those from the first CBCT, respectively. There were no significant dose differences between average planned and delivered doses for targets, brainstem and spinal cord. For right parotid, the delivered mean dose was 10.5 cGy higher (p = 0.004) than the planned value per fraction, and the V26 and V32 increased by 7.5% (p = 0.002) and 7.4% (p = 0.01), respectively. For the left parotid, the D50 (dose to the 50% volume) was 8.8 cGy higher (p = 0.03) than the planned values per fraction, and the V26 increased by 8.8% (p = 0.002).ConclusionWeekly CBCTs were applied directly to study the continuous volume changes and resulting dosimetric variations of targets and OARs for NPC patients undergoing VMAT. Significant volumetric and dosimetric variations were observed for parotids. Replanning after 30 Gy will benefit the protection on parotids.

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Section: Discussionsupporting

confidence: 88%

CBCT-based volumetric and dosimetric variation evaluation of volumetric modulated arc radiotherapy in the treatment of nasopharyngeal cancer patients

Jin

Shang³

et al. 2013

Radiat Oncol

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“…This was consistent with the results of the studies by Wang et al [6] and Zhang et al [11], but was contradictory to the results of a study by Hansen et al [10]. Although the dose coverage of the target volumes remained unchanged in the current study, the D max and D mean delivered to the spinal cord had increased significantly in the hybrid IMRT plan, if without adaptive replanning.…”

Section: Discussionsupporting

confidence: 78%

Volume and Dosimetric Variations During Two-Phase Adaptive Intensity-Modulated Radiotherapy for Locally Advanced Nasopharyngeal Carcinoma

Wang

Zhang

Zhou

et al. 2014

Bio-Medical Materials and Engineering

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The aims of this study were to evaluate the volume and dosimetric variations during IMRT for locally advanced NPC and to identify the benefits of a two-phase adaptive IMRT method. Twenty patients with locally advanced NPC having received IMRT treatment were included. Each patient had both an initial planning CT (CT-1) and a repeated CT scan (CT-2) after treatment at a dose of 40 Gy. Three IMRT planning scenarios were compared: (1) the initial plan on the CT-1 (plan-1);(2) the hybrid plan recalculated the initial plan on the CT-2 (plan-2); (3) the replan generated on the CT-2 being used to complete the course of IMRT (plan-3). The mean gross target volume and mean volumes of the positive neck lymph nodes, high-risk clinical target volume, and the left and right parotid glands significantly decreased by 30.2%, 45.1%, 21.1%, 14.7% and 18.2%, respectively on the CT-2. Comparing plan-2 with plan-1, the dose coverage of the targets remained unchanged, whereas the dose delivered to the parotid glands and spinal cord increased significantly. These patients with locally advanced NPC might benefit from replanning because of the sparing of the parotid glands and spinal cord.

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“…For head and neck cancer including NPCs, however, considerable geometric changes can occur due to tumor shrinkage and weight loss, water and fat re-distribution, etc., throughout the course of IMRT (3)(4)(5). Therefore, additional efforts are needed to optimize the radiation dose delivered to the target volumes (TV) and organs at risk (5)(6)(7)(8)(9)(10)(11)(12). In addition, a gradual volumetric loss and the shift of the center of mass of the gross tumor volume (GTV) and clinical target volume (CTV) at several timepoints have been quantified with repeated imaging in previous studies (4,5,12).…”

Section: Introductionmentioning

confidence: 99%

The tumor shape changes of nasopharyngeal cancer during chemoradiotherapy: the estimated margin to cover the geometrical variation

Tan

Xu³

et al. 2016

Quant. Imaging Med. Surg.

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Background: Considerable geometrical change occurs during chemoradiotherapy (CRT) course of nasopharyngeal carcinoma (NPC). This aim of this study was to quantify the volumetric and surface variability of the target volumes (TV) and to estimate the expanded margin to maintain acceptable geometrical coverage.Methods: Twenty patients with locally advanced nasopharyngeal cancer underwent one planning CT (pCT) and six weekly repeated CT (rCT) scans during the treatment course of definitive CRT. The TV included the gross tumor volume (GTV) of the primary tumor, large (shortest diameter >3.0 cm) and small (diameter >1 cm and ≤3 cm) positive neck lymph nodes, and low-risk clinical target volume (CTV _Lr ) that were delineated manually on the pCT and each rCT. When comparing TV in pCT (V _pCT ) and TV in rCT (V _rCT ), the overlapping index (OI), Dice similarity coefficient (DSC), shortest perpendicular distance (SPD), and overall standard deviation (overall SD) were calculated to present the geometric changes. An isotropical margin was expanded outward around CTV _Lr in pCT to establish the mimic planning target volume (PTV).An OI ≥0.95 was defined as acceptable geometrical coverage.Results: For all TV, DSCs decreased, and the SPDs and overall SD increased with the increasing number of fractions delivered. The DSCs of all gross TV were <70% after the third week. The mean SPDs were 1.5-2.5 mm in the first week and 5.2-6.2 mm in the last week. The OI and DSC in concurrent CRT were smaller than those in the sequential therapy; and similarly the SPD and overall SD in the concurrent therapy were larger than those in the sequential one. To maintain >95% geometrical coverage, a 2-mm additional margin could maintain the coverage throughout the treatment course and a 1-mm margin could maintain the desired coverage if there is an adaptive re-planning no later than the third week of the treatment course.Conclusions: Both volumetric coverage and surface of the tumour underwent the progressive changes during the treatment course of CRT. One to two mm as the expanded margin to establish the PTV is required to maintain >95% geometrical coverage.

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Dosimetric variations of target volumes and organs at risk in nasopharyngeal carcinoma intensity-modulated radiotherapy

Cited by 20 publications

References 12 publications

CBCT-based volumetric and dosimetric variation evaluation of volumetric modulated arc radiotherapy in the treatment of nasopharyngeal cancer patients

CBCT-based volumetric and dosimetric variation evaluation of volumetric modulated arc radiotherapy in the treatment of nasopharyngeal cancer patients

Volume and Dosimetric Variations During Two-Phase Adaptive Intensity-Modulated Radiotherapy for Locally Advanced Nasopharyngeal Carcinoma

The tumor shape changes of nasopharyngeal cancer during chemoradiotherapy: the estimated margin to cover the geometrical variation

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