Anteriorly Oriented Beam Arrangements with Daily in Vivo Range Verification for Proton Therapy of Prostate Cancer: Rectal Toxicity Rates.
Article
Polf, Jerimy C, Chuong, Michael, Zhang, Bin et al. (2016). Anteriorly Oriented Beam Arrangements with Daily in Vivo Range Verification for Proton Therapy of Prostate Cancer: Rectal Toxicity Rates.
. 2(4), 509-517. 10.14338/ijpt-15-00015.1
Polf, Jerimy C, Chuong, Michael, Zhang, Bin et al. (2016). Anteriorly Oriented Beam Arrangements with Daily in Vivo Range Verification for Proton Therapy of Prostate Cancer: Rectal Toxicity Rates.
. 2(4), 509-517. 10.14338/ijpt-15-00015.1
To model whether in vivo range verification could reduce high-grade rectal toxicity for patients with prostate cancer treated with pencil beam scanning proton therapy by allowing novel proton beam arrangements compared to standard lateral opposed beams.
Materials and methods
Proton plans were generated for 8 patients with prostate cancer previously treated with photons by volumetric-modulated arc therapy (VMAT). The VMAT plans were generated by using a uniform 6-mm planning target volume (PTV) expansion. For the proton plans an additional distal margin (3.5% of beam range) was added to the uniform 6-mm PTV to account for range uncertainty, using 3 beam arrangements: (1) lateral opposed beams (LAT), (2) left and right anterior oblique beams (LAO/RAO), and (3) a single anterior-posterior beam (AP). Assuming use of in vivo range verification, plans were generated by using a reduced distal PTV and distal range uncertainty expansion (2 mm each) with AP (AP-2 mm) and LAO/RAO (LAO/RAO-2 mm) beam arrangements. Estimates of normal tissue complication probability (NTCP) for ≥grade 2 rectal bleeding were generated by using the Lyman-Kutcher-Burman model.
Results
Each proton and photon plan was able to achieve all prespecified rectal and bladder constraints. For the VMAT, LAT, AP, and LAO/RAO plans, estimated NTCP values for ≥grade 2 rectal bleeding were 0.19, 0.21, 0.24, and 0.2, respectively. For the AP-2 mm and LAO/RAO-2 mm plans, NTCP values were reduced to 0.11 and 0.1 with respect to ≥grade 2 rectal bleeding.
Conclusion
Presuming that in vivo range verification for pencil beam scanning proton therapy could localize the distal falloff of the Bragg peak to within 2 mm, novel beam arrangements (AP and LAO/RAO) may reduce the risk of serious rectal bleeding, compared to VMAT and LAT proton treatment techniques. These are achieved without an increase in modeled bladder complication rates.
