Quantifying daily variation in volume and dose to the prostate, rectum and bladder using cone-beam computerised tomography

Abstract

Introduction: In the era of dose escalation for localised prostate cancer, the dose-volume histogram (DVH) is integral to the assessment of rectum and bladder dose constraints. However, reliance on a single planning computerised tomography-based (P-CT) dose distribution may not account for variations in delivered dose that results from deformation of the prostate, bladder and rectum. This study uses conebeam CT (CBCT) datasets from five patients to investigate the concordance between the dose prediction from the initial treatment plan and the dose delivered during treatment.Methods: The intensity-modulated radiation therapy distribution used for treatment was superimposed on alternate day CBCT images for each patient. Dose metrics and absolute volumes for the prostate, rectum and bladder were extracted from the CBCT-based DVH. Differences in dose and volumes were compared with the P-CT values, and significance was tested using the Wilcoxon signed-rank test.Results: For all five case studies, the prostate dose coverage on CBCT plans was lower than predicted with an average reduction of 3% in mean dose. Significant differences in rectal volumes and dose were observed in two out of five and four out of five patients, respectively. Reductions in bladder volume and subsequent increases in dose were observed for three out of five patients. Conclusion:The DVH from P-CT was unable to consistently predict the dose delivered to the bladder and rectum. The current bowel and bladder preparation protocols used at our institution did not eliminate variation in bladder and rectum volumes for the five patients included in this study.

Determination of optimal PTV margin for patients receiving CBCT‐guided prostate IMRT: comparative analysis based on CBCT dose calculation with four different margins

“…However, variations in the daily setup and physiological changes in the volumes of the bladder and rectum can result in displacement and deformation of the prostate during treatment, consequently changing the dose distribution to the target and adjacent organs (3) . Dosimetric studies have indicated that the DVH produced at the time of planning may not be an exact representation of the actual dose received during treatment (4) . Translational shifts in the prostate during the course of radiotherapy have been reported.…”

Trajectory log analysis and cone‐beam CT‐based daily dose calculation to investigate the dosimetric accuracy of intensity‐modulated radiotherapy for gynecologic cancer

“…Specifically, the magnitude of dose differences to a target strongly depends on the patient. Another study by McParland et al 29 that evaluated fractional doses to prostate cancers showed that the dose differences to the prostate CTV D 98% decreased by 3% for the mean and 4.6% for the maximum. This inconsistency is attributed to the differences in the total treatment period, beam energy, and image quality of CBCT.…”

Dosimetric impact of organ at risk daily variation during prostate stereotactic ablative radiotherapy

“…Our findings are difficult to compare to the literature, where studies in conventional prostate radiotherapy describe varying methods to assess delivered dose with only two studies identified in the SABR setting. 15,18,[24][25][26][27][28][29][30][31][32] Evidence of volume changes is lacking in SABR with inter fraction rectal variation well documented in conventional radiotherapy. 17,25,26,33,34 We found no systematic change for rectal volume, although Maund et al (2014) report rectal volume decreases on treatment.…”

“…Dose-volume histogram (DVH) data are derived from CT, which forecasts treatment dose, meaning effects of daily organ changes may be ignored. [14][15][16][17] For this reason, DVH being representative of the delivered plan is central to the success of an advanced planning technique. 18 Organ motion can result in setup error and geometric uncertainty, which may negatively impact target coverage and normal tissue dose.…”