Adequacy of Target Volume Drawn Based On "Slow" CT Scan for SBRT Lung Treatment in Helical TomoTherapy

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Medical Physics





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Purpose: In this project, we investigated adequacy of “slow” CT for Stereotactic Body Radiation Therapy (SBRT) utilizing helical TomoTherapy treatment technique and confirmation of dose delivered to the moving target volume. Methods: Presently various CT simulation techniques such as slow CT, fast CT, four-dimensional CT(4DCT) and breath-hold(BH) are employed for treatment planning and delivery of radiation therapy treatment to account for tumor motion in chest and abdominal area.Due to limitations of Hi Art TomoTherapy systems, only slow scan CT scan technique can be employed to account for tumor motion. Hi Art TomoTherapy systems are equipped with MVCT that not only provide means to localize tumor volume, but can also be used for adaptive planning to confirm dose delivered to the target volume. Four patients with lung lesions were prescribed SBRT treatment and were gone through CT simulations employing “Slow CT Scan” technique in conjunction with planning CT on Siemens Biograph PET/CT. CT images were imported in Pinnacle treatment planning system. CT/Slow CT images were used to draw GTV/PTV and other critical structures volumes. All patients have gone through MVCT imaging prior to each treatment delivery. Shifts were employed based on MVCT/Planning CT fusion prior to the treatment delivery. Latter MVCT acquired for localization prior to each treatment delivery was utilized to compute dose utilizing the TomoTherapy Planned Adaptive application. Results: TomoTherapy Planned Adaptive application enabled calculation of actual dose delivered to the patient during each treatment fraction utilizing the pretreatment megavoltage computed tomography (MVCT). Dose coverage to PTV, GTV, and D2cm computed for each fraction were compared to the values obtained per approved treatment plan. Conclusion: Results of our investigations show that tumor volumes drawn based on slow CT scan appropriately account for tumor motion and enables to provide adequate coverage to the target volumes during high dose treatment.


Analytical, Diagnostic and Therapeutic Techniques and Equipment



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