Two-dimensional in vivo rectal dosimetry using an endorectal balloon with unfoldable radiochromic film during prostate cancer radiotherapy

Online daily adaptive proton therapy

It is recognized that the use of a single plan calculated on an image acquired some time before the treatment is generally insufficient to accurately represent the daily dose to the target and to the organs at risk. This is particularly true for protons, due to the physical finite range. Although this characteristic enables the generation of steep dose gradients, which is essential for highly conformal radiotherapy, it also tightens the dependency of the delivered dose to the range accuracy. In particular, the use of an outdated patient anatomy is one of the most significant sources of range inaccuracy, thus affecting the quality of the planned dose distribution. A plan should be ideally adapted as soon as anatomical variations occur, ideally online. In this review, we describe in detail the different steps of the adaptive workflow and discuss the challenges and corresponding state-of-the art developments in particular for an online adaptive strategy.

Rectal retractor application during image-guided dose-escalated prostate radiotherapy

PURPOSE

To investigate efficacy of a rectal retractor (RR) on rectal dose during image-guided dose-escalated prostate three-dimensional conformal radiotherapy (3DCRT).

PATIENTS AND METHODS

In all, 21 patients with localized prostate cancer were treated with a RR for 3DCRT in 40 × 2 Gy. Patient underwent two scans for radiotherapy planning, without and with RR. RR was used for the first half of the treatment sessions. Two plans were created for each patient to compare the effect of RR on rectal doses. PTW-31014 Pinpoint chamber embedded within RR was used for in vivo dosimetry in 6 of 21 patients. The patient tolerance and acute rectal toxicity were surveyed during radiotherapy using Common Terminology Criteria for Adverse Events (CTCAE) v.4.0.

RESULTS

Patients tolerated the RR well during 20 fractions with mild degree of anal irritation. Using a RR significantly reduced the rectal wall (RW), anterior RW and posterior RW dose-volume parameters. The average RW D_mean was 29.4 and 43.0 Gy for plans with and without RR, respectively. The mean discrepancy between the measured dose and planned dose was -3.8% (±4.9%). Grade 1 diarrhea, rectal urgency and proctitis occurred in 4, 2 and 3 cases, respectively. There were no grade ≥2 acute rectal toxicities during the treatment.

CONCLUSION

Rectal retraction resulted in a significant reduction of rectal doses with a safe toxicity profile, which may reduce rectal toxicity. Dosimeter inserted into the RR providing a practical method for in vivo dosimetric verification. Further prospective clinical studies will be necessary to demonstrate the clinical advantage of RR.

Two-dimensional in vivo rectal dosimetry during high-dose-rate brachytherapy for cervical cancer: a phantom study

BACKGROUND

The aim of the present study was to verify the dosimetric accuracy of two-dimensional (2D) in vivo rectal dosimetry using an endorectal balloon (ERB) with unfoldable EBT3 films for high-dose-rate (HDR) brachytherapy for cervical cancer. The clinical applicability of the technique was discussed.

MATERIAL AND METHODS

ERB inflation makes the EBT3 films unrolled, whereas its deflation makes them rolled. Patient-specific quality assurance (pQA) tests were performed in 20 patient plans using an Ir-192 remote afterloading system and a water-filled cervical phantom with the ERB. The dose distributions measured in ERBs were compared with those of the treatment plans.

RESULTS

The absolute dose profiles measured by the ERBs were in good agreement with those of treatment plans. The global gamma passing rates were 96-100% and 91-100% over 20 pQAs under the criteria of 3%/3 mm and 3%/2 mm, respectively, with a 30% low-dose threshold. Dose-volume histograms of the rectal wall were obtained from the measured dose distributions and showed small volume differences less than 2% on average from the patients' plans over the entire dose interval. The positioning error of the applicator set was detectable with high sensitivity of 12% dose area variation per mm. Additionally, the clinical applicability of the ERB was evaluated in volunteers, and none of them felt any pain when the ERB was inserted or removed.

CONCLUSIONS

The 2D in vivo rectal dosimetry using the ERB with EBT3 films was effective and might be clinically applicable for HDR brachytherapy for cervical and prostate cancers to monitor treatment accuracy and consistency as well as to predict rectal toxicity.