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Evaluation of volumetric modulated arc therapy for postmastectomy treatment.

ABSTRACT: PURPOSE: To examine the feasibility of volumetric modulated arc therapy (VMAT) for post mastectomy radiotherapy (PMRT). METHODS AND MATERIALS: Fifteen PMRT patients previously treated at our clinic with helical tomotherapy (HT) were identified for the study. Planning target volumes (PTV) included the chest wall and regional lymph nodes. A systematic approach to constructing VMAT that met the clinical goals was devised. VMAT plans were then constructed for each patient and compared with HT plans with which they had been treated. The resulting plans were compared on the basis of PTV coverage; dose homogeneity index (DHI) and conformity index (CI); dose to organs at risk (OAR); tumor control probability (TCP), normal tissue complication probability (NTCP) and secondary cancer complication probability (SCCP); and treatment delivery time. Differences were tested for significance using the paired Student's t-test. RESULTS: Both modalities produced clinically acceptable PMRT plans. VMAT plans showed better CI (p<0.01) and better OAR sparing at low doses than HT plans, particularly at doses less than 5 Gy. On the other hand, HT plans showed better DHI (p<0.01) and showed better OAR sparing at higher doses. Both modalities achieved nearly 100% tumor control probability and approximately 1% NTCP in the lungs and heart. VMAT showed lower SCCP than HT (p<0.01), though both plans showed higher SCCP values than conventional mixed beam (electron-photon) plans reported by our group previously. VMAT plans required 66.2% less time to deliver than HT. CONCLUSIONS: Both VMAT and HT provide acceptable treatment plans for PMRT. Both techniques are currently utilized at our institution.

SUBMITTER: Nichols GP

PROVIDER: S-EPMC3984750 | biostudies-other | 2014

REPOSITORIES: biostudies-other

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Evaluation of volumetric modulated arc therapy for postmastectomy treatment.

Nichols Geoffrey P GP Fontenot Jonas D JD Gibbons John P JP Sanders Mary Ella ME

Radiation oncology (London, England) 20140226

<h4>Purpose</h4>To examine the feasibility of volumetric modulated arc therapy (VMAT) for post mastectomy radiotherapy (PMRT).<h4>Methods and materials</h4>Fifteen PMRT patients previously treated at our clinic with helical tomotherapy (HT) were identified for the study. Planning target volumes (PTV) included the chest wall and regional lymph nodes. A systematic approach to constructing VMAT that met the clinical goals was devised. VMAT plans were then constructed for each patient and compared w ...[more]

PMID: 24571913

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Project description:It is crucial to spare lung when treating early stage lung carcinoma with stereotactic body radiotherapy (SBRT) for minimizing the radiation induced toxicities, such as radiation pneumonitis and late fibrosis. A retrospective study was performed with a combination of approaches to determine the optimal range of prescription isodose line (P-IDL) within which lung tissue was best spared in SBRT plans with Volumetric-Modulated Arc Therapy (VMAT) and Monte-Carlo-like dose calculation algorithm. Twenty clinically-delivered SBRT lung plans were optimized using traditional LINAC MLC based approaches: an average P-IDL of (88.8 ± 0.5)% (the error bar of all the data is the 95% confidence interval (CI)). The plans were then re-optimized using a new combination of approaches with variation of P-IDL from 60% to 90% for each case. The combination of approaches included finding and utilizing an optimal P-IDL, implementing tuning ring structures internal and external to the target, as well as normal tissue objective and equivalent. The plans were evaluated with the following indexes: 1. R50%, the ratio of 50% prescription isodose volume to the plan target volume (PTV); 2. V20 and V5, the volume of lung within 20Gy and 5Gy, respectively; 3. PCI, the Paddick comformity index; 4. D2cm, the maximum dose at 2 cm from PTV in any direction; 5. MLD, the mean dose in total lung volume; 6. Focal Index (FI), an indicator of dose in the core of the target. The optimal P-IDL was found to be in the range of 75-80%. The average optimal P-IDL for the 20 cases was (77.9 ± 0.9)%. With the optimization strategies the average PCI was increased by (10.3 ± 2.1)%; the average R50%, V20, V5, D2cm and MLD were decreased by (29.1 ± 4.1)%, (26.9 ± 5.4)%, (13.9 ± 3.5)%, (13.4 ± 4.3)% and (16.7 ± 2.3)%, respectively. The FI was increased by (23.7 ± 1.3)%. The optimal P-IDL range was 75-80% for SBRT VMAT lung treatment plans. The application of the set of optimization approaches can significantly improve the lung sparing in SBRT VMAT plans with AXB dose calculation algorithm and makes treatment plans more conformal in high, intermediate and low dose regions, while higher dose is delivered to the target.

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Evaluation of volumetric modulated arc therapy for postmastectomy treatment.

Publications

Evaluation of volumetric modulated arc therapy for postmastectomy treatment.

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