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Dosimetric Evaluation of 3 Dimensional Conformal Radiotherapy (3DCRT), Dynamic Conformal Arc Therapy (DCAT) & Volumetric Arc Therapy (VMAT) in the Management of Non-Small Cell Lung Cancer (NSCLC) Using Stereotactic Body Radiotherapy (SBRT)

H Malhotra

B Rauschenbach, L Mackowiak, H Malhotra*, Roswell Park Cancer Institute, Buffalo, NY

SU-E-T-479 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Initial clinical results of NSCLC usually delivered using 3DCRT & using extreme hypo-fractionated radiotherapy (SBRT) have been very encouraging. Dynamic-conformal-arc therapy or volumetric-arc therapy could also be potentially used to deliver the tumorcidal dosage. This study aims to evaluate 3D conformal radiation therapy techniques (3DCRT) vs DCAT & VMAT planning methods using dosimetric indices and doses to critical structures as per various Radiation Therapy Oncology Group (RTOG) protocols 0236, 0813, and 0915 for treating Non-Small Cell Lung Cancer (NSCLC) patients using SBRT for tumors based on their geographical location within thorax.

Methods: 25 patients (5 in each lobe) previously treated with 3DCRT were retrospectively re-planned with DCAT & VMAT methods. All treatment plans were designed to ensure 95% of the PTV volume gets 100% of the prescription dose. Same dosimetric indices & dose to critical structures were used to evaluate respective plan qualities.

Results: The conformity index of 3DCRT, DCAT & VMAT was 1.2 ±0.1, 1.2±.1, 1.0±.0, respectively. The respective volume (cc) of PTV exceeding 105% of the prescription were 3.3 ±2.5, 3.1±.2.8, 0.2±.0.3. The ratio of 50% isodose volume over PTV volume was found to be 4.1 ±0.9, 1±0.5, 3.6±.0.3, respectively for 3DCRT, DCAT & VMAT. The respective V20 values for 3DCRT, DCAT & VMAT were found to 4.0 ±2.6, 4.2±3.1, 3.8±.2.9.

Conclusion: Our analysis show that almost all DCAT & VMAT plans provided better conformity with the PTV and generally better sparing of tumor critical structures & satisfied respective RTOG constraints. DCAT & VMAT are possible alternative to 3DCRT for the treatment of NSCLC with SBRT regardless of the location of the tumor within in the thorax. The use of VMAT for NSCLC cases has the potential to shorten treatment planning times as well as treatment times experienced by the patient while satisfying planning constraints.

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