Critical appraisal of volumetric-modulated arc therapy compared with electrons for the radiotherapy of cutaneous Kaposi's sarcoma of lower extremities with bone sparing.

The British journal of radiology

PubMedID: 23392192

Nicolini G, Abraham S, Fogliata A, Jordaan A, Clivio A, Vanetti E, Cozzi L. Critical appraisal of volumetric-modulated arc therapy compared with electrons for the radiotherapy of cutaneous Kaposi's sarcoma of lower extremities with bone sparing. Br J Radiol. 2013;86(1023):20120543.
OBJECTIVE
To evaluate the use of volumetric-modulated arc therapy [VMAT, RapidArc® (RA); Varian Medical Systems, Palo Alto, CA] for the treatment of cutaneous Kaposi's sarcoma (KS) of lower extremities with adequate target coverage and high bone sparing, and to compare VMAT with electron beam therapy.

METHODS
10 patients were planned with either RA or electron beams. The dose was prescribed to 30 Gy, 10 fractions, to mean the planning target volume (PTV), and significant maximum dose to bone was limited to 30 Gy. Plans were designed for 6-MV photon beams for RA and 6 MeV for electrons. Dose distributions were computed with AcurosXB® (Varian Medical Systems) for photons and with a Monte Carlo algorithm for electrons.

RESULTS
V(90%) was 97.3±1.2 for RA plans and 78.2±2.6 for electrons; similarly, V(107%) was 2.5±2.2 and 37.7±3.4, respectively. RA met coverage criteria. Concerning bone sparing, D(2%) was 29.6±1.1 for RA and 31.0±2.4 for electrons. Although acceptable for bone involvement, pronounced target coverage violations were obtained for electron plans. Monitor units were similar for electrons and RA, although for the latter they increased when superior bone sparing was imposed. Delivery times were 12.1±4.0 min for electrons and 4.8±1.3 min for the most modulated RA plans.

CONCLUSION
High plan quality was shown for KS in the lower extremities using VMAT, and this might simplify their management in comparison with the more conventional usage of electrons, particularly in institutes with limited staff resources and heavy workloads.

ADVANCES IN KNOWLEDGE
VMAT is also dosimetrically extremely advantageous in a typology of treatments where electron beam therapy is mainly considered to be effective owing to the limited penetration of the beams.