Impact of Geometric Uncertainties on Dose Distribution During Intensity Modulated Radiotherapy of Head-and-neck Cancer: The Need for a Planning Target Volume and A Planning Organ-at-Risk Volume

We assessed the effect of geometric uncertainties on target coverage and on dose to the organs at risk (OARS) during intensity-modulated radiotherapy (IMRT) for head-and-neck cancer, and we estimated the required margins for the planning target volume (PTV) and the planning organ-at-risk volume (PRV). For eight headand- neck cancer patients, we generated IMRT plans with localization uncertainty margins of 0 mm, 2.5 mm, and 5.0 mm. The beam intensities were then applied on repeat computed tomography (CT) scans obtained weekly during treatment, and dose distributions were recalculated. The dose–volume histogram analysis for the repeat CT scans showed that target coverage was adequate (V100 ≥ 95%) for only 12.5% of the gross tumour volumes, 54.3% of the upper-neck clinical target volumes (CTVS), and 27.4% of the lower-neck CTVS when no margins were added for PTV. The use of 2.5-mm and 5.0-mm margins significantly improved target coverage, but the mean dose to the contralateral parotid increased from 25.9 Gy to 29.2 Gy. Maximum dose to the spinal cord was above limit in 57.7%, 34.6%, and 15.4% of cases when 0-mm, 2.5-mm, and 5.0-mm margins (respectively) were used for PRV. Significant deviations from the prescribed dose can occur during IMRT treatment delivery for headand- neck cancer. The use of 2.5-mm to 5.0-mm margins for PTV and PRV greatly reduces the risk of underdosing targets and of overdosing the spinal cord.

Download Full-text

Relationship Between Pelvic Organ-at-Risk Dose and Clinical Target Volume in Postprostatectomy Patients Receiving Intensity-Modulated Radiotherapy

International Journal of Radiation Oncology*Biology*Physics ◽

10.1016/j.ijrobp.2010.10.033 ◽

2012 ◽

Vol 82 (5) ◽

pp. 1897-1902 ◽

Cited By ~ 1

Author(s):

Sinisa Stanic ◽

Mathew Mathai ◽

Jing Cui ◽

James A. Purdy ◽

Richard K. Valicenti

Keyword(s):

At Risk ◽

Clinical Target Volume ◽

Intensity Modulated Radiotherapy ◽

Target Volume ◽

Pelvic Organ ◽

Intensity Modulated ◽

Organ At Risk

Download Full-text

A comparative dosimetric study comparing dose to the carotid artery using 3D conformal radiotherapy and intensity-modulated radiotherapy for T1-T2 glottic cancer at Gharbia Cancer Society, Egypt

Journal of Radiotherapy in Practice ◽

10.1017/s1460396917000048 ◽

2017 ◽

Vol 16 (2) ◽

pp. 177-182

Author(s):

Mohamed Mahmoud ◽

Safa Elfaramawy ◽

Maha H. Mokhtar

Keyword(s):

Spinal Cord ◽

Carotid Artery ◽

Intensity Modulated Radiotherapy ◽

Conformal Radiotherapy ◽

Target Volume ◽

Target Coverage ◽

Imrt Plan ◽

Intensity Modulated ◽

3D Conformal Radiotherapy ◽

Dosimetric Study

AbstractPurposeThis is a dosimetric study to compare the feasibility of carotid artery sparing as a primary objective, as well as planning target volume coverage and dose to spinal cord as a secondary objective, by using 3D conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT) for patients with early glottis cancer.Patients and methodsSix patients who had been treated for early stage glottic carcinoma (stage T1-2 N0M0) were included in this study. All patients were immobilised in the supine position with a thermoplastic mask and treatment planning computed tomography scans were obtained from the top of the skull to the top of aortic arch with a 3-mm slice thickness. Two plans were created for every patient, one using 3DCRT and the second using IMRT. Comparison between the two plans was undertaken and analysis was made regarding the dose to the carotids arteries, target coverage and doses to the organs at risk.ResultsFor target coverage, theV95%for both plans was the same with no significant difference, hot spots were the highest in 3DCRT withp=0·002, the homogeneity index for IMRT plan was better than 3DCRT (p=0·0001). Regarding the dose to the carotids, it was significantly lower in the IMRT plan compared with the 3DCRT plan (p=0·01). The spinal cord dose was significantly higher in the IMRT plan.ConclusionIMRT significantly reduces the radiation dose to the carotid arteries compared with 3DCRT while maintaining clinical target volume coverage. Such a results assists in decreasing the incidence of radiation-induced carotid stenosis, thus improving the quality of life for patients.

Download Full-text