Radiation Physics

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TU_1_3120 - A Dosimetric Study to Assess the Feasibility of Prototype Treatment Planning Software for a New Biology-guided Radiation Therapy System

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

A Dosimetric Study to Assess the Feasibility of Prototype Treatment Planning Software for a New Biology-guided Radiation Therapy System
J. Liang1, A. Liu1, C. Han1, A. Da Silva2, S. Zhang1, and J. Y. C. Wong1; 1City of Hope National Medical Center, Duarte, CA, 2RefleXion Medical, Inc., Hayward, CA

Purpose/Objective(s): Biology-guided radiotherapy (BgRT) is a new modality under development that combines a 6 MV linac with PET, CT and MV imaging systems on a ring gantry that rotates at 60 rpm. The system provides digital dose modulation using 64 binary MLC with a nominal leaf width of 6.25 mm at isocenter. Axial delivery mode is used to sequentially translate the couch in small steps then fire intensity modulated beamlets over many gantry rotations while the couch is stationary. This study is to evaluate the prototype BgRT treatment planning system (TPS) for IMRT cases without PET-guidance.

Materials/Methods: 5 post-prostatectomy patients (45 Gy in 25 fxs to the prostate bed and pelvic lymph nodes) and 5 esophageal adenocarcinoma patients (45 Gy in 25 fxs to the primary tumor and grossly involved regional lymph nodes) previously treated with helical tomotherapy (HT) were selected for the retrospective planning study. OAR constraints followed RTOG 0534 (prostate) and RTOG 1010 (esophagus) recommendations. Three plans were generated for each case: prototype TPS, VMAT and HT. Typical plan parameters were: 2 coplanar full arcs in VMAT; 2.5 cm fixed jaw, pitch 0.287, modulation factor 2.5 in HT; 2 cm fan beam width with 51 firing positions in prototype TPS.

Results: Clinically acceptable plans were achieved in all techniques with comparable plan quality in terms of target dose coverage and OAR sparing. Table 1 summarizes the averaged results of OAR doses for all cases. HT and VMAT plans had significantly better PTV dose homogeneity over prototype TPS plans (two-tailed paired t-test, p<0.05). The standard deviation of prostate PTV dose was 1.4±0.2 Gy for prototype TPS, 0.8±0.2 Gy for VMAT and 0.6±0.1 Gy for HT. The standard deviation of esophagus PTV dose was 2.0±0.3 Gy for prototype TPS, 0.9±0.2 Gy for VMAT, and 0.7±0.1 Gy for HT. Prototype TPS and VMAT provided improved superior/inferior dose penumbra compared to HT with 2.5 cm fixed jaw. Lower mean dose to penile bulb (inferior to the prostate PTV) was found in prototype TPS (12.9±4.1 Gy) and VMAT (10.1±5.0 Gy) as compared to HT plans (26.1±3.9 Gy), p<0.05. Reduced V20 in kidney (inferior to the esophagus PTV) was achieved in prototype TPS (8.2±3.1%) and VMAT (8.5±2.8%) as compared to HT plans (15.7±4.7%), p<0.05.

Conclusion: A prototype BgRT TPS was investigated for prostate and esophagus cases. The system provided comparable plan quality to that obtained using VMAT or HT.

Table 1. Average Dosimetric Results

Prostate Cases (n=5)

Esophagus Cases (n=5)

OARs Parameter

HT

VMAT

Prototype TPS

OARs Parameter

HT

VMAT

Prototype TPS

Bladder Mean Dose (Gy)

30.4

28.6

30.9

Heart Mean Dose (Gy)

21.9

24.4

23.2

Rectum Mean Dose (Gy)

22.7

20.1

24.0

Lung V20 (%)

8.7%

8.4%

9.4%

Penile Bulb Mean Dose (Gy)

26.1

10.1

12.9

V5 (%)

56.1%

61.4%

59.4%

Bowel Dmax (Gy)

45.3

45.0

46.7

Kidney V20 (%)

15.7%

8.5%

8.2%

V30 (%)

9.2%

9.0%

10.3%

Spinal Cord Max Dose D0.03cc (Gy)

35.2

31.2

33.0

Author Disclosure: J. Liang: Research Grant; RefleXion Medical, Inc. A. Liu: Research Grant; RefleXion Medical, Inc. A. Da Silva: Stock Options; RefleXion Medical, Inc. S. Zhang: Employee; University of Southern California. Research Grant; RefleXion Medical, Inc. J.Y. Wong: Research Grant; RefleXion Medical, Inc. Board Member; City of Hope Medical Group Medical Foundation.

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  • Rostem Bassalow
    Medical Physicist
    RefleXion Medical

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