RESUMEN
PURPOSE: Intrafraction prostate displacement (IFPD) through the course of conventionally fractionated radiotherapy was observed by real-time tracking. MATERIALS AND METHODS: IFPD was observed by using a CyberKnife real-time tracking system over 39 serial fractions in two patients. Stereoscopic X-ray images tracking the implanted fiducial markers were obtained with mean intervals of 58 s. In preparation for treatment, urination was performed routinely 1 h before treatment and rectal gas was evacuated if necessary. Patients were immobilized by a thermoplastic body shell. RESULTS: The maximal absolute values of IFPD in all 78 fractions were 7.9, 2.1, and 11.5 mm in cranio-caudal (CC), left-right (LR), and antero-posterior (AP) direction, respectively. Only in 5 % of fractions (4/78 fractions), the maximal absolute values of IFPD were 5.0 mm or larger. In these fractions, large IFPD was temporary or persistent. IFPD of ≥3 mm was detected in only ~2-3 % of all obtained tracking images. CONCLUSIONS: Daily maximal IFPD changed day by day. Although maximal IFPD was more than 10 mm, IFPD of ≥3 mm was observed in a comparatively small proportion of treatment time. Through the course of conventionally fractionated radiotherapy, fractions with IFPD of ≥5 mm were infrequent.
Asunto(s)
Neoplasias de la Próstata/diagnóstico por imagen , Neoplasias de la Próstata/radioterapia , Anciano , Fraccionamiento de la Dosis de Radiación , Marcadores Fiduciales , Humanos , Inmovilización , Masculino , Estadificación de Neoplasias , Neoplasias de la Próstata/patología , Planificación de la Radioterapia Asistida por Computador , Procedimientos Quirúrgicos Robotizados , Tomografía Computarizada por Rayos X , Resultado del TratamientoRESUMEN
PURPOSE: In stereotactic conformal radiotherapy of the CyberKnife, multiple narrow beams from a cylindrical collimator are delivered to a planning target volume (PTV) without an isocenter by inverse planning. The influence of collimator size on stereotactic conformal radiotherapy was examined. MATERIALS AND METHODS: Five targets including two spherical targets (2.1 ml, 16.4 ml), an ellipsoidal target (2.9 ml), and two irregularly shaped targets (1.6 ml, 6.6 ml) were evaluated. Conformity and homogeneity of dose distribution, doses covering 95% volume of PTVs (D95), dose volume histograms (DVHs), and patterns of dose distribution were investigated in relation to collimator size for each target. We evaluated conformity and homogeneity using VD95/PTV (VD95 = volume covered by a D95 isodose surface) and Dmax/Dmin (Dmax, Dmin = maximum and minimum dose within the PTV, respectively), respectively. RESULTS: Conformity and homogeneity were not significantly influenced by collimator size. By using a considerably smaller collimator compared with the minor axis of the target the central dose of the target fell by less than 10% and D95 often decreased slightly. CONCLUSION: In stereotactic conformal radiotherapy of the CyberKnife, a smaller collimator tended to reduce the central dose and D95. These characteristics of the CyberKnife system should be considered.