Comparison of rectal dose reduction by a hydrogel spacer among 3D conformal radiotherapy, volumetric-modulated arc therapy, helical tomotherapy, CyberKnife and proton therapy

Abstract

This study aimed to evaluate the rectal dose reduction with hydrogel spacer in 3D conformal radiotherapy (3DCRT), volumetric modulated arc therapy (VMAT), helical tomotherapy (HT), CyberKnife (CK) and proton therapy. Twenty patients who had hydrogel spacer for prostate radiotherapy were retrospectively enrolled. Computed tomography (CT) images with or without hydrogel spacer were used to evaluate rectal dose reduction. In total, 200 plans (20 patients × 2 CT images × 5 techniques) were created using the following criteria: 3DCRT, VMAT and HT [76 Gy/38 fractions (Fr), planning target volume (PTV) D50%], CK (36.25 Gy/5 Fr, PTV D95%) and proton therapy (63 GyE/21 Fr, PTV D50%). Rectal dose reduction was evaluated using low-/middle-dose (D20%, D50% and D80%) and high-dose (D2%) ranges. Rectal dose reduction of each dose index was compared for each technique. Significant rectal dose reduction (P < 0.001) between the treatment plans on pre- and post-CT images were achieved for all modalities for D50%, D20% and D2%. In particular, the dose reduction of high-dose (D2%) ranges were −40.61 ± 11.19, −32.44 ± 5.51, −25.90 ± 9.89, −13.63 ± 8.27 and −8.06 ± 4.19%, for proton therapy, CK, HT, VMAT and 3DCRT, respectively. The area under the rectum dose–volume histogram curves were 34.15 ± 3.67 and 34.36 ± 5.24% (P = 0.7841) for 3DCRT with hydrogel spacer and VMAT without hydrogel spacer, respectively. Our results indicated that 3DCRT with hydrogel spacer would reduce the medical cost by replacing the conventional VMAT without spacer for prostate cancer treatment, from the point of view of the rectal dose. For the high-dose gradient region, proton therapy and SBRT with CK showed larger rectal dose reduction than other techniques.

Plan comparison of prostate stereotactic radiotherapy in spacer implant patients

“…Saito et al compared the CK plans with and without hydrogel spacer. Interestingly, they reported that the D 2% values of the rectum were 36.10 ± 1.52 and 24.33 ± 1.81 Gy without and with the spacer, respectively, when using more than 150 beams 16 . In our study, the average number of beams was 77 (range, 51–96).…”

“…Nowadays, we can use the SBRT technique more safely because of the advent of rectal hydrogel spacers 14‐16 17 .…”

“…Nowadays, we can use the SBRT technique more safely because of the advent of rectal hydrogel spacers. 14 , 15 , 16 With the advent of these spacers, there is an increasing interest in prostate SBRT using a conventional linear accelerator (Linac), which cannot use the tumor tracking method of the CK. 17 Some studies have compared the dose distribution between CK and other techniques in cases without hydrogel spacers.…”

Effect of a hydrogel spacer on the intrafractional prostate motion during CyberKnife treatment for prostate cancer

“…Recently, a hydrogel spacer (SpaceOAR TM System, Augmenix Inc., Waltham, MA) was introduced, and it helped reducing rectal toxicities via the insertion of an absorbable hydrogel between the prostate and rectum 11,12 . The use of a hydrogel spacer stably reduced the rectal dose in all EBRT modalities 13 . Moreover, for high‐precision EBRT, it is important to control inter‐ and intrafractional prostate motion.…”

“…stably reduced the rectal dose in all EBRT modalities. 13 Moreover, for high-precision EBRT, it is important to control inter-and intrafractional prostate motion. Among the several radiotherapy modalities, CyberKnife (Accuray, Sunnyvale, CA) can be used to acquire 2D images per 5-150 s by using 2-kV x-ray devices (target locating system [TLS]), resulting in high-precision image-guided radiotherapy.…”