Shang, Charles

Simulated Annealing algorithm is utilized for Intensity Modulated Radiation Therapy IMRT optimization.
The goal in IMRT is to give the prescribed radiation dose to the tumor while minimizing the dose given
to normal organs.

Purpose: To explore offset values in dose optimization with pencil beam (PB) algorithm
to minimize dosimetric differences with plans calculated with Monte Carlo (MC) for lung cancer
treatment with Stereotactic Body Radiotherapy (SBRT). Methods: 20 cases of Non-Small Cell
Lung Cancer, treated with gated full motion range SBRT were selected. According to the
proximity of the Gross Tumor Volume (GTV) to the chest wall, two groups are defined.
Treatment plans were created on 4D average intensity projection (AIP) CT set with Brainlab
iPlanDose® 4.1.2 planning system. The D97 of PTV was normalized to 50Gy using the fast PB
and compared with MC. The optimized plan was then recomputed over each 4D respiratory
phase, and compared with MC. Results: The mean difference in the PB and MC D97 of the ITV
was 10.5% (±0.8%) of the prescription dose (50Gy). PB algorithm showed 2.3-2.4% less
overestimation to the D97 of the ITV, when comparing to MC, in the maximum exhalation phase
than in the maximal inhalation phase. Significantly smaller dose difference between PB and MC
is also shown in plans for peripheral lesions (7.7 ± 0.7%) versus for central lesions (12.7±0.8%)
(p< 0.01). Conclusions: The dosimetric differences between PB and MC can be reasonably
predicted depending on the location of lesion in the lung, and may be used as offset value in dose
optimization with PB. Caution is suggested when using the maximum inhalation phase for
treatment planning.

The purpose of this study is to investigate the changes of the pericardial dose at different respiratory phases and statuses in accelerated partial breast irradiation (APBI) using Cyberknife M6™ multileaf collimators (CK-MLC). Anonymous 6 female patient files with respiration gated four-dimensional computed tomography (4DCT) sets, and 6 left breast cancer cases with CT images in free-breathing (FB) and deep inhalation breath-hold (BH) were selected. One CT image set from each patient was planned for APBI in Accuray Multiplan™ 5.2, and respectively compared its pericardial dose with those from CT sets of other respiratory phases. All the comparable CT images were fused in the planning system according to the left chest wall, among which the lung gap anterior to the pericardium varies by the lung expansion. For the purpose of this study, the tumor volume was outlined in the media-lower quadrant of the left breast where this lung gap is relatively small. All the plans in this study met the requirements set by the National Surgical Adjuvant Breast and Bowel Project/Radiation Therapy Oncology Group (NSABP/RTOG), specifically protocol B-39/RTOG 0413. From the comparisons in this investigation, the mean relative pericardial dose of the BH CT group showed significant or 45% (p < 0.01) lower value than that of FB CT group. However, in FB 4DCT group, 3 of 6 cases indicated a meaningful reduction (p < 0.05) in 100% inhalation phase when compared with the mean dose over other phases. The inconsistent pericardial doses were displayed in FB 4DCT group due to minimal changes in the anterior lung gap of the pericardium, when the diaphragmatic breathing was dominant in those patients.

Evaluation of dose optimization using the Pencil Beam (PB) and Monte Carlo (MC) algorithms may allow physicists to apply dosimetric offsets to account for inaccuracies of the PB algorithm for lung cancer treatment with Stereotactic Body Radiotherapy (SBRT). 20 cases of Non-Small Cell Lung Cancer (NSCLC) were selected. Treatment plans were created with Brainlab iPlanDose® 4.1.2. The D97 of the Planning Target Volume (PTV) was normalized to 50 Gy on the Average Intensity Projection (AIP) using the fast PB and compared with MC. This exact plan with the same beam Monitor Units (MUs) was recalculated over each respiratory phase. The results show that the PB algorithm has a 2.3-2.4% less overestimation at the maximum exhalation phase than the maximum inhalation phase when compared to MC. Significantly smaller dose difference between PB and MC is also shown in plans for peripheral lesions (7.7 ± 0.7%) versus central lesions (12.7±0.8%)(p< 0.01).

An improved method is introduced for prediction of local tumor control following lung
stereotactic body radiation therapy (SBRT) for early stage non-small cell lung cancer
(NSCLC) patients using 18F-fluorodeoxyglucose positron emission tomography (18F-FDG
PET). A normalized background-corrected tumor maximum Standard Uptake Value
(SUVcmax) is introduced using the mean uptake of adjacent aorta (SUVref), instead of
the maximum uptake of lung tumor (SUVmax). This method minimizes the variations
associated with SUVmax and objectively demonstrates a strong correlation between the
low SUVcmax (< 2.5-3.0) and local control of post lung SBRT. The false positive rates
of both SUVmax and SUVcmax increase with inclusion of early (<6 months) PET scans,
therefore such inclusion is not recommended for assessing local tumor control of post
lung SBRT.