Room: Exhibit Hall
Purpose: To compare the dosimetric characteristics and delivery efficiency between non-coplanar VMAT plans and Cyberknife plans for larynx SBRT patients.
Methods: An in-house Alderson Rando Phantom with vocal cord features was used to evaluate the dose discrepancy in larynx air cavity between EclipseTM AAA and AcurosXB dose calculation engines. AcurosXB was subsequently adopted for offering better dose accuracy inside the air cavity. Ten patients diagnosed of cTis-T2N0M0 glottic larynx carcinoma were selected, and retrospectively planned in Eclipse using the non-coplanar VMAT technique to benchmark against the original plans designed by a Cyberknife SBRT larynx protocol (42.5Gy/5Fx). For the original Cyberknife plans, Monte-Carlo(Multiplan) calculation was used to achieve accurate dose calculation for PTVs with air cavity. The dosimetric and clinical efficiency comparisons were performed with metrics including PTV coverage, maximum doses to various OARs, R50, homogeneity index, conformity index and treatment time estimation.
Results: The phantom study suggested AcurosXB engine has better agreement with film measurement even for the small air cavity inside larynx. The non-coplanar VMAT achieved comparable dosimetric endpoints to Cyberknife. The average PTV coverages are 95% and 96% for VMAT and Cyberknife respectively. The average maximum doses (VMAT/Cyberknife) to OARs are 12.58Gy/13.94Gy (p>0.4) to carotid arteries, 8.64Gy/5.79Gy (p<0.001) to spinal cord, 41.87Gy/41.47Gy (p>0.7) to skin and 16.16Gy/18.13Gy (p<0.01) to contralateral arytenoid. Corresponding average R50 and homogeneity index are 5.91/5.04 (p<0.004), and 1.08/1.15 (p<0.01). Cyberknife has better dose sparing on spinal cord; however, both are well below the tolerance of 28Gy. VMAT plan has better dose sparing on contralateral arytenoid. VMAT also achieved similar conformity index as Cyberknife (1.17 and 1.19, p>0.35), using less than 1/3 of the total MUs which halves the treatment time.
Conclusion: Larynx SBRT can be conducted on either Cyberknife or conventional LINAC with dosimetrically equivalent target coverage and similar OAR sparing.
Not Applicable / None Entered.