A clinical evaluation of setup errors for a prostate immobilization system

A comparison of interfraction setup error, patient comfort, and therapist acceptance for 2 different prostate radiation therapy immobilization devices

PURPOSE

Our purpose was to investigate interfraction setup error of the immobilization device required to implement transperineal ultrasound compared with the current, standard immobilization device. Patient comfort and radiation therapist (RT) satisfaction were also assessed.

METHODS AND MATERIALS

Cone beam computed tomography images were acquired before 4069 fractions from 111 patients (control group, n = 56; intervention group, n = 55) were analyzed. The intervention group was immobilized using the Clarity Immobilization System (CIS), comprising a knee rest with autoscan probe kit and transperineal ultrasound probe (n = 55), and control group using a leg immobilizer (LI) (n = 56). Interfraction setup errors were compared for both groups. Weekly questionnaires using a 10-point visual analog scale were administered to both patient groups to measure and compare patient comfort. RT acceptance for both devices was also compared using a survey.

RESULTS

There was no significant difference in the magnitude of interfraction cone beam computed tomography-derived setup shifts in the lateral and anteroposterior direction between the LI and CIS (P = .878 and .690, respectively). However, a significant difference (P = .003) was observed in the superoinferior direction between the 2 groups of patients. Patient-reported level of comfort and stability demonstrated no significant difference between groups (P = .994 and .132). RT user acceptance measures for the LI and CIS were ease of handling (100% vs 53.7%), storage (100% vs 61.1%), and cleaning of the devices (100% vs 64.8%), respectively.

CONCLUSIONS

The CIS demonstrated stability and reproducibility in prostate treatment setup comparable to LI. The CIS device had no impact on patient comfort; however, RTs indicated a preference for LI over the CIS mainly because of its weight and bulkiness.

Acurácia na reprodutibilidade do posicionamento diário de pacientes submetidos a radioterapia conformada (RT3D) para câncer de próstata

OBJETIVO: Avaliar a reprodutibilidade do posicionamento de pacientes com diagnóstico de câncer de próstata submetidos a radioterapia conformada. MATERIAIS E MÉTODOS: Foram avaliados 960 (posições anterior e lateral) filmes radiológicos, de um total de 120 pacientes que receberam radioterapia conformada na próstata com técnica isocêntrica. As imagens foram obtidas em acelerador linear de partículas 6 MV. Aplicou-se protocolo específico para planejamento e tratamento da próstata, com o paciente em posição supina, mãos colocadas sobre o tórax, pés apoiados em suporte apropriado. Diariamente, os pacientes foram posicionados conforme demarcações na pele, coincidentes com os lasers da sala. Os filmes radiológicos foram comparados com as radiografias reconstruídas digitalmente (digitally reconstructed radiography - DRR) em sistema de planejamento computadorizado Eclipse, a partir das tomografias. As radiografias de posicionamento foram realizadas no primeiro dia e após, semanalmente, até o término do tratamento. RESULTADOS: As médias dos deslocamentos observados foram de 1,99 ± 1,25 mm no sentido crânio-caudal, 1,37 ± 0,84 mm no látero-lateral e 1,94 ± 1,10 mm no ântero-posterior. CONCLUSÃO: O uso de protocolos específicos para posicionamento dos pacientes é possível na prática clínica, possibilita reprodutibilidade adequada e rápida correção dos possíveis erros.

Theoretical foundation for real-time prostate localization using an inductively coupled transmitter and a superconducting quantum interference device (SQUID) magnetometer system

Real‐time, 3D localization of the prostate for intensity‐modulated radiotherapy can be accomplished with passively charged radio frequency transmitters and superconducting quantum interference device (SQUID) magnetometers. The overall system design consists of an external dipole antenna as a power source for charging a microchip implant transmitter and SQUID magnetometers for signal detection. An external dipole antenna charges an on‐chip capacitor through inductive coupling in the near field region through a small implant inductor. The charge and discharge sequence between the external antenna and the implant circuit can be defined by half duplex, full duplex, or sequential operations. The resulting implant discharge current creates an alternating magnetic field through the inductor. The field is detected by the surrounding magnetometers, and the location of the implant transmitter can be calculated. Problems associated with this system design are interrelated with the signal strength at the detectors, detector sensitivity, and charge time of the implant capacitor. The physical parameters required for optimizing the system for real‐time applications are the operating frequency, implant inductance and capacitance, the external dipole current and loop radius, the detector distance, and mutual inductance. Consequently, the sequential operating mode is the best choice for real‐time localization for constraints requiring positioning within 1 s due to the mutual inductance and detector sensitivity. We present the theoretical foundation for designing a real‐time, 3D prostate localization system including the associated physical parameters and demonstrate the feasibility and physical limitations for such a system.

PACS number: 87.53.‐j

Prostate immobilization using a rectal balloon

We use a rectal balloon for prostate immobilization during intensity modulated radiotherapy (IMRT) prostate treatment. To improve the accuracy of our prostate planning target volume, we have measured prostate displacements using computed tomography (CT)-CT fusion on patients that previously received gold seed implants. The study consists of ten patients that were scanned twice per week during the course of IMRT treatment. In addition to biweekly scans, breathing studies were performed on each patient to estimate organ motion during treatment. The prostate displacement in the anterior-posterior and the lateral direction is minimal, on the order of measurement uncertainty (~1 mm). The standard deviation of the superior-inferior (SI) displacements is 1.78 mm. The breathing studies show that no organ displacement was detected during normal breathing conditions with a rectal balloon.