Spatial and Dosimetric Variability of Organs at Risk in Head-and-Neck Intensity-Modulated Radiotherapy

Robar, James L.; Day, A. C.; Clancey, James; Kelly, R; Yewondwossen, Mammo; Hollenhorst, Helmut; Rajaraman, Murali; Wilke, Derek

doi:10.1016/j.ijrobp.2007.01.030

Cited by 143 publications

(132 citation statements)

References 20 publications

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“…Despite the limited number of patients entered in our study (16), an important part of our results were nevertheless statistically significant. Furthermore, our sample size is also larger than most used in published works related to this topic — for example, studies carried out by Barker et al, (8) Hansen et al, (16) Robar et al, (13) Lee et al, 11 , 15 and Castadot et al (9) included 14, 13, 15, 10, and 10 patients, respectively. Taking into account all of the above factors, the average data shown in Tables 3and 4 could therefore help to identify dosimetric variables at risk of suffering changes during patient radiation treatment.…”

Section: Discussionmentioning

confidence: 99%

Dose variations in tumor volumes and organs at risk during IMRT for head‐and‐neck cancer

Beltran

Ramos

Rovira

et al. 2012

J Applied Clin Med Phys

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Many head‐and‐neck cancer (HNC) patients treated with radiotherapy suffer significant anatomical changes due to tumor shrinkage or weight loss. The purpose of this study was to assess dose changes over target volumes and organs at risk during intensity‐modulated radiotherapy for HNC patients. Sixteen HNC IMRT patients, all requiring bilateral neck irradiation, were enrolled in the study. A CTplan was performed and the initial dose distribution was calculated. During the treatment, two subsequent CTs at the 15th (CT15) and 25th (CT25) fractions were acquired. The initial plan was calculated on the CT15 and CT25, and dose‐volume differences related to the CTplan were assessed. For target volumes, mean values of nearmaximun absorbed dose (normalD2%) increased at the 25th fraction, and doses covering 95% and 98% of volume decreased significantly at the 15th fraction. Contralateral and ipsilateral parotid gland mean doses increased by 6.1% (range: ‐5.4, 23.5%) and 4.7% (range: ‐9.1, 22.3%), respectively, at CT25. The normalD2% in the spinal cord increased by 1.8 Gy at CT15. Mean absorbed dose increases at CT15 and CT25 were observed in: the lips, 3.8% and 5.3%; the oral cavity, 3.5% and 2.5%; and lower middle neck structure, 1.9% and 1.6%. Anatomical changes during treatment of HNC patients affect dose distribution and induce a loss of dose coverage to target volumes and an overdosage to critical structures. Appropriate organs at risk have to be contoured and monitored in order to know if the initial plan remains suitable during the course of the treatment. Reported dosimetric data can help to identify patients who could benefit from adaptive radiotherapy.PACS numbers: 87.53.Kn, 87.55.Dk

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Section: Discussionmentioning

confidence: 99%

Dose variations in tumor volumes and organs at risk during IMRT for head‐and‐neck cancer

Beltran

Ramos

Rovira

et al. 2012

J Applied Clin Med Phys

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“…Whether or not these results are relevant to the human salivary glands requires further research. Also, our results relate to the mean SMG doses calculated from the planning CT. A medial shift of the parotid glands during therapy in some patients may increase their mean doses compared with the treatment plans (47)(48). No comparable data exists for the SMGs.…”

Section: Discussionmentioning

confidence: 99%

Dose-Effect Relationships for the Submandibular Salivary Glands and Implications for Their Sparing by Intensity Modulated Radiotherapy

Murdoch‐Kinch

Kim

Vineberg

et al. 2008

International Journal of Radiation Oncology*Biology*Physics

212

143

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Purpose-Submandibular salivary glands (SMGs) dysfunction contributes to xerostomia after radiotherapy (RT) of head and neck (HN) cancer. We assessed SMG dose-response relationships and their implications for sparing these glands by intensity modulated radiotherapy (IMRT).Patients and Methods-148 HN cancer patients underwent unstimulated and stimulated SMG salivary flow rate measurements selectively from Wharton's duct orifices, before RT and periodically through 24 months after RT. Correlations of flow rates and mean SMG doses were modeled throughout all time points. IMRT re-planning in eight patients whose contralateral level I was not a target incorporated the results in a new cost function aiming to spare contralateral SMGs.Results-Stimulated SMG flow rates decreased exponentially by (1.2%) Gy as mean doses increased up to 39 Gy threshold, and then plateaued near zero. At mean doses ≤39 Gy, but not higher, flow rates recovered over time at 2.2%/month. Similarly, the unstimulated salivary flow rates decreased exponentially by (3%) Gy as mean dose increased and recovered over time if mean dose was <39 Gy. IMRT re-planning reduced mean contralateral SMG dose by average 12 Gy, achieving ≤39 Gy in 5/8 patients, without target under-dosing, increasing the mean doses to the parotid glands and swallowing structures by average 2-3 Gy.Conclusions-SMG salivary flow rates depended on mean dose with recovery over time up to a threshold of 39 Gy. Substantial SMG dose reduction to below this threshold and without target under-dosing is feasible in some patients, at the expense of modestly higher doses to some other organs.

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“…The results demonstrated that IMRT replanning could significantly increase doses to target volumes and decrease doses to OARs. In a study [4] of head and neck cancer patients with different primary sites, as well as different treatment modalities, at least three repeated CT scans were acquired for each patient 1 week into treatment, and weekly thereafter. After the initial plan was recalculated on all the CT sets, a significant dose variability was described in the left parotid and inferior spinal cord but not in the right parotid, brain stem and superior spinal cord.…”

Section: Correlation Between Dosimetric Variability Of Organs At Riskmentioning

confidence: 99%

“…Gross tumour volumes decreased at a median rate of 0.2 cm 3 per treatment day, while parotid glands decreased at a median rate of 0.19 cm 3 per day and shifted medially because of weight loss due to treatment. Robar et al [4] documented that both parotid glands showed a median translation of 0.85 mm per week, and glands shrank by 4.9% per week. In the study by Kuo et al [5], the lymph nodes in head and neck cancer underwent a volume reduction of more than 50% after 45 Gy of treatment, which may increase actual radiation doses to the parotid glands.…”

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confidence: 99%

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

Zhang

M²,

Cao³

et al. 2012

The British Journal of Radiology

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Objective: The aim of this study was to evaluate the actual dose variability to the targets and organs at risk (OARs) during nasopharyngeal carcinoma (NPC) intensitymodulated radiotherapy (IMRT) and to investigate the significance of replanning. Methods: 11 NPC patients were included in this study. Each patient had both a planning CT and weekly repeated CT. Simulated plans that were generated by using the same beam configurations mapped to the repeated CT represented the actual delivered doses to the target volumes and OARs. An IMRT replanning was performed with the fifth week CT scan. Doses among the initial plan, the simulated plans and replanning were compared. Results: There were no significant dosimetric differences in the gross tumour volume, clinical target volume (CTV) 1 or CTV2 for either the simulated plans or the replanning compared with the initial plan. Dosimetric variability of both parotid glands and the brain stem were unique to each individual, and doses to the spinal cord were always maintained within the limit. Replanning in the fifth week had significantly decreased the doses delivered to both parotids (p-values of the mean dose were 0.015 and 0.026 for the left and right parotid, respectively), whereas it did not reduce the doses to the brain stem and spinal cord. There was no relationship between dose variability and weight loss. Conclusions: There are no significant dose changes for target volumes and spinal cord, and doses to the brain stem and both parotid glands changed individually during NPC IMRT. Replanning helps to spare bilateral parotids.

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Spatial and Dosimetric Variability of Organs at Risk in Head-and-Neck Intensity-Modulated Radiotherapy

Cited by 143 publications

References 20 publications

Dose variations in tumor volumes and organs at risk during IMRT for head‐and‐neck cancer

Dose variations in tumor volumes and organs at risk during IMRT for head‐and‐neck cancer

Dose-Effect Relationships for the Submandibular Salivary Glands and Implications for Their Sparing by Intensity Modulated Radiotherapy

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

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