RESUMEN
The aim of this study is to prospectively evaluate and model surrogate explanatory variables (SEVs) of target coverage and rectal dose pertaining to soft tissue anatomy visualised on cone beam computed tomography (CBCT) for incorporation into post-prostatectomy treatment coverage verification protocols. Twenty post-prostatectomy patients treated with conformal prostate bed radiotherapy (64-74 Gy) underwent CBCT daily at fractions 1 to 5, and then weekly. Treatment coverage was defined on each CBCT using 'PTV95', percentage of the CBCT PTV covered by original treatment fields, and 'RECTD50', dose delivered to 50% of CBCT rectal volume by original treatment fields. Three candidate SEVs for treatment coverage were defined for each scan: anterior rectal wall movement, change in bladder length and bladder base movement. Both anterior rectal wall movement and increase in bladder length predicted for the decreased PTV95 (P < 0.001 for each). Anterior movement of the anterior rectal wall predicted for increased RECTD50 (P < 0.001). Predictive models for the PTV95 and RECTD50 that accept the significant SEVs as inputs were developed. We developed simple CBCT-acquired soft tissue anatomic surrogate measures that signal changes in target coverage and rectal dose during post-prostatectomy radiotherapy. Conventional bony anatomy patient position verification protocols were inadequate in accounting for soft tissue target and organ variation seen with CBCT.
Asunto(s)
Tomografía Computarizada de Haz Cónico/métodos , Técnicas de Apoyo para la Decisión , Evaluación de Resultado en la Atención de Salud/métodos , Prostatectomía/métodos , Neoplasias de la Próstata/diagnóstico por imagen , Neoplasias de la Próstata/terapia , Humanos , Masculino , Cuidados Posoperatorios/métodos , Pronóstico , Radioterapia Adyuvante/estadística & datos numéricos , Resultado del TratamientoRESUMEN
We present the results of a pilot study designed to investigate methods that may be applied to develop a patient position correction protocol for the post-prostatectomy patient receiving radiotherapy. Imaging was carried out with cone beam CT (CBCT) to investigate its suitability for detecting changes in rectal and bladder volumes and movements of these organs relative to the treatment planning CT. Eligible patients were imaged daily during the first week of treatment and weekly thereafter. Surrogate explanatory variables, including distance from the isocentre to the anterior rectum and bladder length, were tested for their potential to substitute for contouring entire organs and predict for changes in coverage of the planning treatment volume (PTV) by the 95% isodose (PTV95) and the maximum dose delivered to 50% of the rectal volume (RECTD50). The PTV defined on the CBCT images was larger than that defined on the planning CT and resulted in a decrease in the PTV95. Bladder length correlated with bladder volume and changes in bladder volume were associated with a decrease in PTV95. Rectal volumes changed randomly during treatment. There was a trend for the rectum to move anteriorly as treatment progressed. CBCT may be used to define the PTV, rectum and bladder though the reason for an apparent increase in PTV on CBCT requires further investigation. The bladder length and distance to the anterior rectal wall are potential surrogate explanatory variables. Further studies will be designed to test values of these surrogates that predict the need for a change in isocentre position.
Asunto(s)
Tomografía Computarizada de Haz Cónico/métodos , Recurrencia Local de Neoplasia/diagnóstico por imagen , Recurrencia Local de Neoplasia/radioterapia , Prostatectomía , Neoplasias de la Próstata/diagnóstico por imagen , Neoplasias de la Próstata/terapia , Humanos , Masculino , Proyectos Piloto , Cuidados Posoperatorios/métodos , Resultado del TratamientoRESUMEN
Using implanted gold seeds as fiducial markers to verify the position of the prostate in radiation therapy is well accepted and is becoming the standard of practice and requirement for international multicentre trials. In 2006 the decision was made at the Peter MacCallum Caner Centre (Peter Mac) to plan for and implement this process as standard clinical practice for radical dose prostate treatments (74-78 Gy). Before this, programme verification of field placement for prostate cancer radiation treatment was routinely carried out using regular off-line electronic portal imaging with matching of bony anatomy. A small multidisciplinary team investigated and assisted in the implementation of this new practice across the Peter Mac sites at East Melbourne and our three satellite centres. Issues considered included seed size, number and position in the prostate, implant equipment, imaging equipment and procedure and consent and information forms. The use of a custom made fiducial pack, comprehensive patient information and a daily on-line imaging process was implemented. The experience of the first 28 patients at Peter Mac from January 2007 to May 2007 inclusive is reported on.