ABSTRACT
Objective:To evaluate the effects of the changes in respiratory status on gated stereotactic radiotherapy under free breathing guided by real-time position management (RPM).Methods:This study simulated the baseline shift, change in respiratory rate, end-expiratory delay, end-inspiratory delay, and irregular breathing using an in-house developed motion phantom. Moreover, this study analyzed the correlation between the changes in the above states of three plans, three-dimensional conformal radiotherapy(3D-CRT), intensity modulated radiotherapy(IMRT), and volumetric modulated arc therapy(VMAT) and the position of the ball at the center of the motion phantom (L) and the exposed dose of the phantom in the ionization chamber (the dose).Results:The in-house developed phantom presented high setup repeatability and measurement stability. There was a positive correlation between L and the baseline shift ( r = 0.99, P < 0.01). The change in the dose was less than 4% when the baseline shift was less than the setup error, while the dose declined rapidly and was negatively correlated with the baseline shift otherwise ( r= -0.95, P < 0.01). Moreover, there was statistically significant difference in dose when the baseline shift exceeded the setup error or not ( Z = -3.06, P < 0.01). There was no significant difference in the rate of the dose affected by baseline shift in the three plans ( P > 0.05). The changes in respiratory rate had little effect on L and the dose. Both end-inspiratory delay and end-expiratory delay reduced the planned dose of the three plans, with a maximum decrease of up to -1.74%. Furthermore, the end-inspiratory delay has greater effects on the planned dose than the end-expiratory delay( Z = -2.67, P< 0.01). However, there was no significant correlation between the dose and the delay duration ( P > 0.05), and no significant difference in the rate of the planned dose of the three plans affected by respiratory waveform change ( P > 0.05). Irregular breathing had greater effects on the dose. Specifically, the dose from six repeated measurements of 3D-CR, IMRT, VMAT was (709.68±180.00), (751.40±127.16), and (750.00±185.60) cGy, respectively, all less than the prescribed dose with a poor consistency. Conclusions:The changes in the patients′ respiratory status will reduce the dose, especially when the baseline shift exceeds the setup error threshold or large respiratory waveform variation corresponding to irregular breathing occurs. Moreover, there is no correlation between the decrease in the dose and the radiotherapy technology.
ABSTRACT
Objective To explore the effect of respiratory movement on the dose distribution in the TOMO therapy target area. Methods The motion phantom was used to simulate human respiratory movement. The SNC patient analysis software was used to compare the films of the study group with those of the control group, and the effect of respiratory movement on the dose distribution in the TOMO target area was evaluated by the “pass rate” index. Results Visual observation showed that the distribution of film gray in the head-foot direction (i.e., direction of movement) was significantly different with or without respiratory movement. Film analysis showed that the maximum deviation between the width of the target wrapping curve and the treatment plan value was about 2.4 mm at no respiratory movement and about 27.2 mm at respiratory movement; the penumbra width of the target area was 31 mm (head direction) and 28.5 mm (foot direction) at no respiratory movement and 39.7 mm (head direction) and 37 mm (foot direction) at respiratory movement; the “pass rate” of target dose distribution was only 12.3%. Conclusion Respiratory movement has a great impact on the dose distribution in the TOMO target area in the direction of movement. When making clinical treatment plan, the impact of respiratory movement on the dose distribution in the TOMO target area can not be ignored.
ABSTRACT
Respiration gating radiotherapy technique developed in consideration of the movement of body surface and internal organs during respiration, is categorized into the method of analyzing the respiratory volume for data processing and that of keeping track of fiducial landmark or dermatologic markers based on radiography. However, since these methods require high-priced equipments for treatment and are used for the specific radiotherapy. Therefore, we should develop new essential method whilst ruling out the possible problems. This study aims to obtain body surface motion by using the couch based computer-controlled motion phantom (CBMP) and US sensor, and to develop respiration gating techniques that can adjust patients' beds by using opposite values of the data obtained. The CBMP made to measure body surface motion is composed of a BS II microprocessor, sensor, host computer and stepping motor etc. And the program to control and operate it was developed. After the CBMP was adjusted by entering random movement data, and the phantom movements were acquired using the sensors, the two data were compared and analyzed. And then, after the movements by respiration were acquired by using a rabbit, the real-time respiration gating techniques were drawn by operating the phantom with the opposite values of the data. The result of analyzing the acquisition-correction delay time for the data value shows that the data value coincided within 1% and that the acquisition-correction delay time was obtained real-time (2.34 x 10(-4) sec). And the movement was the maximum movement was 6 mm in Z direction, in which the respiratory cycle was 2.9 seconds. This study successfully confirms the clinical application possibility of respiration gating techniques by using a CBMP and sensor.