Biomedical subjects

Yu-Ming Liu

Publications and source records attributed to Yu-Ming Liu.

5 recordsLinked to original sources

PubMed2006

The role and strategy of IMRT in radiotherapy of pelvic tumors: Dose escalation and critical organ sparing in prostate cancer.

PURPOSE: To investigate the intensity-modulated radiotherapy (IMRT) strategy in dose escalation of prostate and pelvic lymph nodes. METHODS AND MATERIALS: Plan dosimetric data of 10 prostate cancer patients were compared with two-dimensional (2D) or IMRT techniques for pelvis (two-dimensional whole pelvic radiation therapy [2D-WPRT] or IM-WPRT) to receive 50 Gy or 54 Gy and additional prostate boost by three-dimensional conformal radiation therapy or IMRT (3D-PBRT or IM-PBRT) techniques up to 72 Gy or 78 Gy. Dose-volume histograms (DVHs), normal tissue complication probabilities (NTCP) of critical organ, and conformity of target volume in various combinations were calculated. RESULTS: In DVH analysis, the plans with IM-WPRT (54 Gy) and additional boost up to 78 Gy had lower rectal and bladder volume percentage at 50 Gy and 60 Gy, compared with those with 2D-WPRT (50 Gy) and additional boost up to 72 Gy or 78 Gy. Those with IM-WPRT (54 Gy) also had better small bowel sparing at 30 Gy and 50 Gy, compared with those with 2D-WPRT (50 Gy). In NTCP, those with IM-WPRT and total dose of 78 Gy achieved lower complication rates in rectum and small bowel, compared with those of 2D-WPRT with total dose of 72 Gy. In conformity, those with IM-WPRT had better conformity compared with those with 2D-WPRT with significance (p < 0.005). No significant difference in DVHs, NTCP, or conformity was found between IM-PBRT and 3D-PBRT after IM-WPRT. CONCLUSIONS: Initial pelvic IMRT is the most important strategy in dose escalation and critical organ sparing. IM-WPRT is recommended for patients requiring WPRT. There is not much benefit for critical organ sparing by IMRT after 2D-WPRT.

Humans↗

PubMed2004

Prostate movement during simulation resulting from retrograde urethrogram compared with "natural" prostate movement.

PURPOSE: Retrograde urethrography (UG) is commonly used at the time of simulation to assist in defining the prostate apex. Some investigators have reported that performing the UG introduces error by causing prostate displacement. We investigate the movement of the prostate caused by the retrograde UG. METHODS AND MATERIALS: Twenty-four patients treated with three-dimensional conformal radiotherapy for prostate cancer who had gold marker seeds placed into their prostates were studied. Marker seed locations at the time of simulation and on the portal images acquired just before the treatment were compared with the locations on digitally reconstructed radiographs (DRR). Movement in the superior-inferior and anteroposterior directions as seen on lateral images was measured from 402 portal images by offline customized imaging software and evaluated using analysis of variance methods for continuous variables and chi-square statistics for categoric variables. RESULTS: "Natural" nonrandom movement of the prostate around an "origin" as defined by markers on DRR was observed. This movement tends to be in a superior and anterior direction, with the average shift being 1 mm and 0.82 mm, respectively. The magnitude of movement in the superior direction averaged 2.88 mm compared with 1.64 mm in the inferior direction (p = 0.04). There was slightly greater movement after the UG compared with mean "natural" movement but the difference was less than 3 mm in either direction on average (difference: superior-inferior = 2.64 mm, p = 0.004; anteroposterior = 2.24, p = 0.035). CONCLUSIONS: Use of the UG induces a small but clinically insignificant displacement of the prostate when "natural" movement is taken into account.

Humans↗

PubMed2004

A study of planning dose constraints for treatment of nasopharyngeal carcinoma using a commercial inverse treatment planning system.

PURPOSE: The purpose of this study was to develop and test planning dose constraint templates for tumor and normal structures in the treatment of nasopharyngeal carcinoma (NPC) using a specific commercial inverse treatment planning system. METHODS AND MATERIALS: Planning dose constraint templates were developed based on the analyses of dose-volume histograms (DVHs) of tumor targets and adjacent sensitive structures by clinically approved treatment plans of 9 T1-2 and 16 T3-4 NPC patients treated with inverse planned intensity-modulated radiation therapy (IP-IMRT). DVHs of sensitive structures were analyzed by examining multiple defined endpoints, based on the characteristics of each sensitive structure. For each subgroup of patients with T1-2 and T3-4 NPC, the resulting mean values of these defined endpoint doses were considered as templates for planning dose constraints and subsequently applied to a second group of patients, 5 with T1-2 NPC and 5 with T3-4 NPC. The 10 regenerated plans (called new plans) were compared to the original clinical plans that were used to treat the second group of patients, based on plan conformity index and DVHs. RESULTS: The conformity indices of the new plans were comparable to the original plans with no statistical difference (p = 0.85). Among the serial sensitive structures evaluated, there was a significant decrease with the new plans in the dose to the spinal cord when analyzed by the maximum dose (p = 0.001), doses encompassing 1 cc of the spinal cord volume (p = 0.001) and 3 cc of the spinal cord volume (p = 0.001). There was no significant difference in the mean maximum dose to the brainstem between the new plans and the original plans (p = 0.36). However, a significant difference in the mean maximum dose to the brainstem was seen among the different T-stages (p = 0.04). A decrease with the new plan to the brainstem in the doses encompassing 5% and 10% of the volume was of borderline statistical significance (p = 0.08 and p = 0.06, respectively). There were no statistical differences between the new plans and the original plans in the mean doses to the chiasm, optic nerve, or eye for each of the endpoints considered. For parallel sensitive structures in the new plans, there was a significant increase in the average mean dose to the parotid glands (p = 0.01), a decrease that was of borderline significance in the average mean dose to the temporomandibular joint (p = 0.07), but no difference in the average mean dose to the ear. CONCLUSIONS: The statistical analysis showed that new plans are comparable to the original plans for most of the sensitive structures except for a trade-off between a dose reduction to the spinal cord in the new plans and an increase in the mean dose to the parotid glands. These tested planning dose constraint templates can serve as good "starting points" for an inverse plan of NPC using a specific commercial inverse treatment planning system.

Brain Stem↗

PubMed2004

A new alkaloid and its artificial derivative with an indazole ring from Nigella glandulifera.

A new compound, nigeglanine (1), and its new artificial derivative (1a), were isolated from the seeds of Nigella glandulifera, together with a known aporphine alkaloid, fuzitine (2). Their structures were established by spectral analysis, including two-dimensional (2D)-NMR spectroscopy. Nigeglanine (1) is the third natural product determined to contain an indazole nucleus.

Alkaloids↗

PubMed2003

(Non)-migration of radiopaque markers used for on-line localization of the prostate with an electronic portal imaging device.

PURPOSE: Radiopaque gold markers can be implanted in the prostate to visualize its position on portal images during radiation therapy. This procedure assumes that the markers do not move within the prostate. In this work we test this assumptiom. METHODS AND MATERIALS: Three markers were implanted transrectally in the prostate of patients undergoing external radiation therapy. An orthogonal pair of portal images was acquired periodically throughout the course of radiation therapy with an a-Si electronic portal imaging device (EPID). The marker coordinates were determined, and the distances between the implanted markers were recorded. The distance time trend is used to evaluate the magnitude of marker migration. RESULTS: The average standard deviation (SD) of the distances between markers was 1.3 mm (range 0.44 to 3.04 mm). Three of the 11 patients show a SD larger than 2 mm. For these patients, all three distances show a simultaneous reduction with time, compatible with a shrinking of the prostate. All had been treated with neoadjuvant hormone therapy. For 1 of the 3 patients, this reduction in volume was confirmed with a repeat computed tomographic scan. CONCLUSION: None of the 33 markers studied migrated significantly. The implantation of three radiopaque gold markers enables accurate and precise on-line verification of the prostate position during external beam radiation therapy. The use of three markers provides a tool to monitor prostate position and volume changes that can occur over time due to hormone or radiation therapy.

Gold↗