Extended distance non-isocentric treatment in stereotactic body radiation therapy (SBRT) for lung cancer
Purpose: To obtain the maximum differential non-coplanar beams angle for a faster dose dropping outside Plan Target Volume (PTV) for lung cancer treated by Stereotactic body radiation therapy (SBRT), an extended distance non-isocentric (EDNI) treatment method was explored and developed.
Methods: The EDNI requires delivering of the treatment beam at 120 cm or farther for sauce axial distance (SAD) instead of standard 100 cm. This change provides a more compact dose distribution around PTV and the lower toxicity to organs at risk (OAR) due to benefit of 120 cm SAD and more choice of beam and couch angle. A hand calculation formula for the translation between 100 SAD and EDNI was used to verify the treatment plan results. A phantom for end to end study based on this EDNI technique was used to compare with standard 100 SAD deliveries for SBRT. Three patients who underwent SBRT treatment were randomly chosen to demonstrate the benefits of EDNI technique. These treatment re-plans were applied to EDNI and evaluated for conformal index (CI) of PTV, R50% of PTV, 2 cm distance (D2cm) of PTV and Maximum dose (Dmax)of OARs to compare with original clinical plans.
Results: All of the cases delivered by the EDNI technique satisfied dose requirements of RTOG 0263 and showed a faster dose dropping outside of PTV than standard SAD deliveries. The distance from PTV after 1.5 cm for the EDNI technique had a smaller maximum dose and much lower standard deviation for dose distribution. The EDNI applied plans for patients showed less R50% and D2cm of PTV (P≤ 0.05), also similar results for Dmax of esophagus, trachea and spinal cord.
Conclusion: The EDNI method enhances the capabilities of linear accelerators as far as the increased gradient of dose drop-off outside of PTV is concerned. More angular separation between beams leads to more compact dose distributions, which allow decreasing volume of high dose exposure in SBRT treatments and better dose distribution on sensitive organs to minimize the treatment toxicity.
Zimmermann FB, Geinitz H, Schill S, et al. Stereotactic hypofractionated radiation therapy for stage I non-small cell lung cancer. Lung Cancer 2005; 48:107-14.
Fakiris AJ, McGarry RC, Yiannoutsos CT, et al. Stereotactic body radiation therapy for early-stage non-small-cell lung carcinoma: four-year results of a prospective phase II study. Int J Radiat Oncol Biol Phys 2009; 75:677-82.
McGarry RC, Papiez L, Williams M, et al. Stereotactic body radiation therapy of early-stage non-small-cell lung carcinoma: phase I study. Int J Radiat Oncol Biol Phys 2005; 63:1010-5.
Timmerman RD, Park C, Kavanagh BD. The North American experience with stereotactic body radiation therapy in non-small cell lung cancer. J Thorac Oncol 2007; 2:S101-12.
Timmerman RD, Kavanagh BD, Cho LC, et al. Stereotactic body radiation therapy in multiple organ sites. Journal of clinical oncology. J Clin Oncol 2007; 25:947-52.
Timmerman R, McGarry R, Yiannoutsos C, et al. Excessive toxicity when treating central tumors in a phase II study of stereotactic body radiation therapy for medically inoperable early-stage lung cancer. J Clin Oncol 2006; 24:4833-9.
Xiao Y, Papiez L, Paulus R, et al. Dosimetric evaluation of heterogeneity corrections for RTOG 0236: stereotactic body radiotherapy of inoperable stage I-II non-small-cell lung cancer. Int J Radiat Oncol Biol Phys 2009; 73:1235-42.
Lo SS, Fakiris AJ, Chang EL, et al. Stereotactic body radiation therapy: a novel treatment modality. Nat Rev Clin Oncol 2010; 7:44-54.
Hua C, Chang J, Yenice K, Chan M, Amols H. A practical approach to prevent gantry-couch collision for linac-based radiosurgery. Med Phys 2004; 31:2128-34.
Humm JL. Collision avoidance in computer optimized treatment planning. Med Phys 1994; 21:1053-64.
Webb S. The problem of isotropically orienting N converging vectors in space with application to radiotherapy planning. Phys Med Biol 1995; 40:945-54.
Papiez L, Lu M, Langer M. On the Isotropic Distribution of Beam Directions. Math Mod Meth Appl Sci 2000; 10:991-1000.
Huang L, Park K, Boike T, et al. A study on the dosimetric accuracy of treatment planning for stereotactic body radiation therapy of lung cancer using average and maximum intensity projection images. Radiother Oncol 2010; 96:48-54.
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