Volumetric arc therapy for stereotactic body radiotherapy in early lung cancer

Hegi-Johnson, F.; Unicomb, K.; West, K.; Small, K.; White, S.; Barber, J.; Van Tilburg, K.; Yeghiaian-Alvandi, R.
March 2013
Journal of Radiosurgery & SBRT;2013 Supplement 2.1, Vol. 2, p120
Academic Journal
Introduction: Stereotactic body radiotherapy(SBRT) for early lung cancer results in excellent local control and potentially improved survival, but demands high levels of dose conformality. To achieve this with 3D-conformal radiotherapy(3D-CRT) and intensity modulated radiotherapy (IMRT) large numbers of beams, and non-coplanar techniques are often required. Hence treatment times are long, increasing the risk of patient motion. Volumetric arc therapy(VMAT) may result in improved dosimetric outcomes, and reduce treatment time. We report on a planning study comparing VMAT to coplanar (CP) and non-coplanar (NCP) 3D-CRT and IMRT, and our initial clinical results. Methods: Pinnacle VMAT, and CP and NCP 3D-CRT and IMRT plans for delivery on Elekta Linacs of 5 patients were compared. All plans were single arc, with 4 degree spacing and 1 cm MLC. The following dosimetric characteristics were assessed: target coverage (coverage with the prescribed dose), dose conformality (100% conformity indices, D2cm and volume of tissue outside PTV receiving high dose, defined as >105% of prescription dose) and V20 (volume of lung receiving 20 Gy). Results: Dosimetric Outcomes VMAT achieved equivalent radiotherapy target coverage to 3D-CRT and IMRT (>98.2%). However, 3D-CRT plans had a large volume of surrounding normal tissue receiving a high dose (24.0% and 21.3% of the PTV volume for CP and NCP respectively) when compared to VMAT and IMRT plans (3.9% and 4-5% respectively). 100% conformity indices were lowest for VMAT and NCP IMRT (1.1 for both) and highest for 3D-CRT (1.5 and 1.4 for CP and NCP respectively). D2cm was also lowest for VMAT and NCP IMRT (26.1 Gyand 25.3 Gy) and highestfor3D-CRT plans (29.4 Gy and 28.7 Gy for CP and NCP respectively). V20 was between 4.4 and 6.1% for all plans. Clinical outcomes VMAT treatment time takes 35 minutes, and beam-on time is 8 minutes. With short follow-up (range 4 weeks to 6 months), 1 patient has developed worsening dyspnoea and grade 3 pneumonitis. No other Grade 2 or greater toxicity was seen in the other 4 patients. Conclusions: Clinical implementation of VMAT was successfully demonstrated, and has resulted in fast treatment times for our SBRT lung patients. VMAT plans are similar in quality to NCP IMRT, but are much faster to deliver due to reduced gantry and couch movements. 3D-CRT plans were unable to deliver equivalent dose conformality, and a much larger region of normal tissue was exposed to a high dose when equivalent PTV coverage was achieved. Disclosure: No significant relationships.


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