A Dosimetric Comparison of Lattice, Brass, and Proton Grid Therapy Treatment Plans.

Our purpose was to dosimetrically compare volumetric modulated arc therapy (VMAT) lattice radiation therapy (LRT), brass, and proton grid therapy planning techniques and suggest potential clinical applications for each. Four plans delivering 20 Gy in 1 fraction were created for each of 22 patients. Brass and proton grid plans used a single static field and the same beam angle. Proton grid plans used the same beam size and spacing as the brass block. Two VMAT LRT plans were generated for each patient: one with 1-cm diameter lattice points spaced 2-cm center-to-center (2-cm VMAT) and another with 1.5-cm diameter lattice points spaced 3-cm center-to-center (3- cm VMAT). Maximum, minimum, mean, and equivalent uniform dose and the dose to 90%, 50%, 20%, 10%, and 5% (D90%[%], D50%[%], etc) of gross tumor volume (GTV) were reported. D10%/D90% characterized dose heterogeneity. Normal tissue dose was generalized by the maximum dose and volume in cubic centimeters of tissue outside the GTV receiving 30% and 50% of prescription (body-GTV V30%[cm3]; body-GTV V50%[cm3]). VMAT LRT plans delivered the highest maximum GTV doses while brass and proton plans delivered higher D5%(%), D10%(%), and D20%(%) values. D50%(%), D90%(%), and minimum dose varied little between plan types. Proton and brass plans had the highest dose heterogeneity. Two-centimeter VMAT and brass grid plans had the highest mean GTV doses. Two-centimeter VMAT plans had the highest equivalent uniform dose, followed by 3-cm VMAT, brass, and proton plans. VMAT LRT plans exhibited the lowest normal tissue maximum and body GTV V30%(cm3) and body GTV V50%(cm3) values. An in-depth comparison of target and normal tissue dosimetric parameters for common photon and proton grid therapy planning techniques was made. Strengths of each plan type were noted leading to general recommendations on usage.

Grams MP ，Tseung HSWC ，Ito S ，Zhang Y ，Owen D ，Park SS ，Ahmed SK ，Petersen IA ，Haddock MG ，Harmsen WS ，Ma DJ ... -  《-》

Feasibility Study of 3D-VMAT-Based GRID Therapy.

Zhang X ，Griffin RJ ，Galhardo EP ，Penagaricano J ... -  《-》

Dosimetric study of uniform scanning proton therapy planning for prostate cancer patients with a metal hip prosthesis, and comparison with volumetric-modulated arc therapy.

Rana S ，Cheng C ，Zheng Y ，Hsi W ，Zeidan O ，Schreuder N ，Vargas C ，Larson G ... -  《Journal of Applied Clinical Medical Physics》

Comparison of treatment planning approaches for spatially fractionated irradiation of deep tumors.

The purpose of this work was to compare the dosimetry and delivery times of 3D-conformal (3DCRT)-, volumetric modulated arc therapy (VMAT)-, and tomotherapy-based approaches for spatially fractionated radiation therapy for deep tumor targets. Two virtual GRID phantoms were created consisting of 7 "target" cylinders (1-cm diameter) aligned longitudinally along the tumor in a honey-comb pattern, mimicking a conventional GRID block, with 2-cm center-to-center spacing (GRID2 cm ) and 3-cm center-to-center spacing (GRID3 cm ), all contained within a larger cylinder (8 and 10 cm in diameter for the GRID2 cm and GRID3 cm , respectively). In a single patient, a GRID3 cm structure was created within the gross tumor volume (GTV). Tomotherapy, VMAT (6 MV + 6 MV-flattening-filter-free) and multi-leaf collimator segment 3DCRT (6 MV) plans were created using commercially available software. Two tomotherapy plans were created with field widths (TOMO2.5 cm ) 2.5 cm and (TOMO5 cm ) 5 cm. Prescriptions for all plans were set to deliver a mean dose of 15 Gy to the GRID targets in one fraction. The mean dose to the GRID target and the heterogeneity of the dose distribution (peak-to-valley and peak-to-edge dose ratios) inside the GRID target were obtained. The volume of normal tissue receiving 7.5 Gy was determined. The peak-to-valley ratios for GRID2 cm /GRID3 cm /Patient were 2.1/2.3/2.8, 1.7/1.5/2.8, 1.7/1.9/2.4, and 1.8/2.0/2.8 for the 3DCRT, VMAT, TOMO5 cm , and TOMO2.5 cm plans, respectively. The peak-to-edge ratios for GRID2 cm /GRID3 cm /Patient were 2.8/3.2/5.4, 2.1/1.8/5.4, 2.0/2.2/3.9, 2.1/2.7/5.2 and for the 3DCRT, VMAT, TOMO5 cm , and TOMO2.5 cm plans, respectively. The volume of normal tissue receiving 7.5 Gy was lowest in the TOMO2.5 cm plan (GRID2 cm /GRID3 cm /Patient = 54 cm3 /19 cm3 /10 cm3 ). The VMAT plans had the lowest delivery times (GRID2 cm /GRID3 cm /Patient = 17 min/8 min/9 min). Our results present, for the first time, preliminary evidence comparing IMRT-GRID approaches which result in high-dose "islands" within a target, mimicking what is achieved with a conventional GRID block but without high-dose "tail" regions outside of the target. These approaches differ modestly in their ability to achieve high peak-to-edge ratios and also differ in delivery times.

Sheikh K ，Hrinivich WT ，Bell LA ，Moore JA ，Laub W ，Viswanathan AN ，Yan Y ，McNutt TR ，Meyer J ... -  《Journal of Applied Clinical Medical Physics》

An Analysis of Plan Robustness for Esophageal Tumors: Comparing Volumetric Modulated Arc Therapy Plans and Spot Scanning Proton Planning.

Planning studies to compare x-ray and proton techniques and to select the most suitable technique for each patient have been hampered by the nonequivalence of several aspects of treatment planning and delivery. A fair comparison should compare similarly advanced delivery techniques from current clinical practice and also assess the robustness of each technique. The present study therefore compared volumetric modulated arc therapy (VMAT) and single-field optimization (SFO) spot scanning proton therapy plans created using a simultaneous integrated boost (SIB) for dose escalation in midesophageal cancer and analyzed the effect of setup and range uncertainties on these plans. For 21 patients, SIB plans with a physical dose prescription of 2 Gy or 2.5 Gy/fraction in 25 fractions to planning target volume (PTV)50Gy or PTV62.5Gy (primary tumor with 0.5 cm margins) were created and evaluated for robustness to random setup errors and proton range errors. Dose-volume metrics were compared for the optimal and uncertainty plans, with P<.05 (Wilcoxon) considered significant. SFO reduced the mean lung dose by 51.4% (range 35.1%-76.1%) and the mean heart dose by 40.9% (range 15.0%-57.4%) compared with VMAT. Proton plan robustness to a 3.5% range error was acceptable. For all patients, the clinical target volume D98 was 95.0% to 100.4% of the prescribed dose and gross tumor volume (GTV) D98 was 98.8% to 101%. Setup error robustness was patient anatomy dependent, and the potential minimum dose per fraction was always lower with SFO than with VMAT. The clinical target volume D98 was lower by 0.6% to 7.8% of the prescribed dose, and the GTV D98 was lower by 0.3% to 2.2% of the prescribed GTV dose. The SFO plans achieved significant sparing of normal tissue compared with the VMAT plans for midesophageal cancer. The target dose coverage in the SIB proton plans was less robust to random setup errors and might be unacceptable for certain patients. Robust optimization to ensure adequate target coverage of SIB proton plans might be beneficial.

Warren S ，Partridge M ，Bolsi A ，Lomax AJ ，Hurt C ，Crosby T ，Hawkins MA ... -  《-》