Room: Exhibit Hall
Purpose: Multiple disease site treatments can be optimized by comprehensive planning of all volumes to be treated simultaneously. We compared the dosimetric quality of VMAT and TomoTherapy based treatment plans for a patient treated concurrently for laryngeal and lung cancer.
Methods: A patient with squamous carcinoma of the larynx and non-small cell lung cancer received definitive treatment using VMAT. The primary laryngeal cancer had three PTVs treated to 70 Gy, 59.4 Gy and 54 Gy in 30 fractions, and the primary lung cancer was treated to 60 Gy in 30 fractions. The 54 Gy Laryngeal PTV and Lung PTV were composed of two separate upper and lower volumes. Thus a total of six PTVs were treated in a composite plan. Relevant RTOG protocols were used to assess dose coverage and Organs at Risk (OAR) constraints. The patient was retrospectively re-planned using TomoTherapy to compare results with the VMAT plan. Dose in Remaining Volume at Risk (RVR) as defined by ICRU 83 was compared.
Results: Dose coverage in the upper lung PTV was better in the TomoTherapy plan compared to VMAT plan (V95 = 100% Vs V95 = 80.5%). Both plans met the dose coverage requirements for the remaining 5 PTVs. Of the 10 OARs evaluated, TomoTherapy met constraints for 7 of them while VMAT met constraints for 5 OARs. Normal lung (Lung- CTV) received more dose in VMAT (V20 = 34.5%, mean = 18.2 Gy) compared to TomoTherapy (V20 = 26.9%, mean = 17.8 Gy). Mean and maximum dose for RVR was higher for TomoTherapy (mean: 11.3 Gy, max: 78.8 Gy) compared to VMAT (mean = 10.3 Gy, max = 76.9 Gy).
Conclusion: Our results indicate that for this complex PTV configuration, TomoTherapy provides better PTV dose coverage, lower dose to OARs and similar RVR dose compared to VMAT plan.