Hydrogel spacers in prostate radiotherapy: a promising approach to decrease rectal toxicity

SpaceOAR© hydrogel rectal dose reduction prediction model: a decision support tool

Prostate cancer external beam radiation therapy can result in toxicity due to organ at risk (OAR) dose, potentially impairing quality of life. A polyethylene glycol-based spacer, SpaceOAR© hydrogel (SOH), implanted between prostate gland and rectum may significantly reduce dose received by the rectum and hence risk of rectal toxicity. SOH implant is not equally effective in all patients. Determining patients in which the implant will offer most benefit, in terms of rectal dose reduction, allows for effective management of SOH resources. Several factors have been shown to be correlated with reduction in rectal dose including distance between rectum and planning treatment volume (PTV), volume of rectum in the PTV, and change in rectum volume pre- to post-SOH. Several of these factors along with other pre-SOH CT metrics were able to predict reduction in rectal dose associated with SOH implant. Rectal V55Gy metric, was selected as the dose level of interest in the context of 60 Gy in 20 fraction treatment plans. Models were produced to predict change in RV55Gy and pre-SOH hydrogel RV55Gy. These models offered R-squared between 0.81 and 0.88 with statistical significance in each model. Applying an ω 1  = 3% lower limit of pre-SOH RV55 Gy and an ω 2  = 3.5% lower limit on change in RV55 Gy, retained 60% of patients experiencing the largest rectal dose reduction from the hydrogel. This may offer a clinically useful tool in deciding which patients should receive SOH implant given limited resources. Predictive models, nomograms, and a workflow diagram were produced for clinical management of SOH implant.

Derivation of Dose/Volume Constraints for the Anorectum from Clinician- and Patient-Reported Outcomes in the CHHiP Trial of Radiation Therapy Fractionation

PURPOSE

The CHHiP trial randomized 3216 men with localized prostate cancer (1:1:1) to 3 radiation therapy fractionation schedules: 74 Gy in 37 fractions over 7.4 weeks; 60 Gy in 20 fractions over 4 weeks; and 57 Gy in 19 fractions over 3.8 weeks. Literature-based dose constraints were applied with arithmetic adjustment for the hypofractionated arms. This study aimed to derive anorectal dose constraints using prospectively collected clinician-reported outcomes (CROs) and patient-reported outcomes (PROs) and to assess the added predictive value of spatial dose metrics.

METHODS AND MATERIALS

A case-control study design was used; 7 CRO and 5 PRO bowel symptoms were evaluated. Cases experienced a moderate or worse symptom 1 to 5 years after-radiation therapy and did not have the symptom before radiation therapy. Controls did not experience the symptom at baseline or between 1 to 5 years after radiation therapy. The anorectum was recontoured from the anal verge to the rectosigmoid junction; dose/volume parameters were extracted. Univariate logistic regression, atlases of complication indices, and bootstrapped receiver-operating-characteristic analysis (1000 replicates, balanced outcomes) were used to derive dose constraints for the whole cohort (hypofractionated schedules were converted to 2-Gy equivalent schedules using α/β = 3 Gy) and separate hypofractionated/conventional fractionation cohorts. Only areas under the curve with 95% confidence interval lower limits >0.5 were considered statistically significant. Any constraint derived in <95% to 99% of bootstraps was excluded.

RESULTS

Statistically significant dose constraints were derived for CROs but not PROs. Intermediate to high doses were important for rectal bleeding, whereas intermediate doses were important for increased bowel frequency, fecal incontinence, and rectal pain. Spatial dose metrics did not improve prediction of CROs or PROs. A new panel of dose constraints for hypofractionated schedules to 60 Gy or 57 Gy are V20Gy <85%, V30Gy <57%, V40Gy <38%, V50Gy <22%, and V60Gy <0.01%.

CONCLUSIONS

Dose constraints differed among symptoms, indicating potentially different pathogenesis of radiation-induced side effects. Derived dose constraints were stricter than those used in CHHiP and may reduce bowel symptoms after radiation therapy.

Assessing localized dosimetric effects due to unplanned gas cavities during pelvic MR-guided radiotherapy using Monte Carlo simulations

PURPOSE

It has been proposed that beam modulation and opposing beam configurations can cancel effects of the Electron Return Effect (ERE) during MR-guided radiotherapy (MRgRT). However, this may not always be the case for unplanned gas cavities outside of the target in the pelvic region. We evaluate dosimetric effects, including effects in the rectal wall, due to unplanned spherical air cavities during MRgRT.

METHODS

Nine virtual cuboid water phantoms containing spherical air cavities (0.5-7.5 cm diameter) and a reference phantom without air were created. Monte Carlo dose calculations of 7 MV photons under the influence of a 1.5 T transverse magnetic field were produced using Monaco 5.19.02 Treatment Planning System (TPS) (Elekta AB, Stockholm, Sweden). Cavities in the path of a single and multiple beam plans were considered. Dose distributions of phantoms with and without air cavities were compared (ΔD% ) using a spherical coordinate system originating in the center of the cavity. Effects in the rectal wall were quantified by comparing dose volume histogram (DVH) parameters for solid and gaseous filling from simulated rectal wall structures.

RESULTS

Max(ΔD% ) of ~70% and 20% were observed around large cavities in the path of a single and multiple beam plans, respectively. Approximately 45 cm3 of phantom surrounding the largest cavity in a single beam received dose changes of >10%. Dmean in the rectal wall was unchanged when comparing gaseous and solid filling in the path of a single beam; however, D1cc and Dmax increased by up to ~45% and ~63%, respectively.

CONCLUSIONS

Unplanned gas cavities in the path of a single beam during pelvic MRgRT with a 1.5 T transverse magnetic field cause dose changes which may impact toxicity in the rectal wall, depending on local dose and fractionation. Effects are reduced but not eliminated with a five-beam plan.

Biodegradable implantable balloons: Mechanical stability under physiological conditions

Rotator cuff tendons injuries occurs as a result of trauma, e.g. due to falling, mechanical injuries and frequent overhead activity and as natural degenerative tears in elderly people. Biodegradable balloon shaped spacer of Poly-(L-lactide-co-ε-caprolactone) (PLCL) are applied in the treatment of these injuries. This type of treatment involves insertion of inflated biodegradable implant into the tissues of the damaged region in the shoulder to avoid shoulder impingement and reduce friction between the acromion and the humeral head and propagation of inflammation. The implant must maintain integrity under significant mechanical loading in order to remain effective. However, with time, the implant is exposed to the risk of failure due to the high pressure caused by the muscular motion and the friction with the bones. We report in this study the limits of the mechanical stability of the PLCL balloon shape spacer (implant) under prolonged cyclic loading, so as to be able to predict their physical stability in vivo. We have demonstrated in an in vitro settings that the implant withstands fatigue cycles for significantly longer than 8 weeks, which provides sufficient time window for patients to perform substantial rehabilitation and recover from an injury. The data presented herein is expected to assist medical practitioners in safety and efficacy measurements and assessment following spacer implantation.

Rectal wall dose-volume effect of pre- or post KUSHEN Ningjiaos relationship with 3D brachytherapy in cervical cancer patients

BACKGROUND

The present prospective study evaluated the safety and efficacy of the rectum following KUSHEN Ningjiaos in cervical cancer. We compared rectal wall changes during brachytherapy with or without KUSHEN Ningjiaos in cervical cancer patients and analyzed the difference in spatial dose distribution, including whole rectum-wall (R-w), anterior rectum-wall (R-a) and posterior rectum-wall (R-p).

METHODS AND MATERIALS

One hundred cervical cancer patients with and without KUSHEN Ningjiaos were treated with brachytherapy (600 cGy). The whole R-w was divided into two areas of R-a and R-p, and R-w dose surface map were constructed. The volume of each R-w was compared in patients pre- and post-KUSHEN Ningjiaos.

RESULTS

When the pre- vs. post-KUSHEN groups were compared the volume of R-w increased. In the post-KUSHEN group, a significantly higher proportion of the D2cc of V_R-w and V_R-a compared with the pre-KUSHEN group showed that the D2cc_mean increased from 532.45 cGy to 564.7 cGy and 533.51 cGy to 565.26 cGy, respectively; however, results demonstrated a decrease in the D2cc_mean of R-p from 260.5 cGy to 240.0868 cGy (P < 0.05). The insertion of KUSHEN Ningjiaos resulted in a reduction of the relative volume of R-p exposed to high doses, and regressive analysis showed that the D_R-p-max correlated most strongly with V_R-w and D2cc_R-p (P < 0.01 and P < 0.05, respectively).

CONCLUSION

The insertion of KUSHEN Ningjiaos can protect the rectum. KUSHEN Ningjiaos appears to be safe and well tolerated; therefore, we believe that there will be fewer adverse events after brachytherapy for patients.

TRIAL REGISTRATION

A multi-center, prospective clinical trial for KUSHEN Ningjiaos was inserted into rectum to reduce the rate of radiation proctitis in three-dimensional brachytherapy of cervical cancer. ChiCTR1900021631 . 2 Mar 2019-Retrospectively registered.

Maximizing rectal dose sparing with hydrogel: A retrospective planning study

External beam radiation therapy for prostate cancer can result in urinary, sexual, and rectal side effects, often impairing quality of life. A polyethylene glycol‐based product, SpaceOAR© hydrogel (SOH), implanted into the connective tissue between the prostate gland and rectum can significantly reduce the dose received by the rectum and hence risk of rectal toxicity. The optimal way to manage the hydrogel and rectal structures for plan optimization is therefore of interest. In 13 patients, computerized tomography (CT) scans were taken pre‐ and post‐SpaceOAR© implant. A prescription of 60 Gy in 20 fractions was planned on both scans. Six treatment plans were produced per anonymized dataset using either a structure of rectum plus the hydrogel, termed composite rectum wall (CRW), or rectal wall (RW) as an inverse optimization structure and intensity modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT) as a treatment technique. Dose‐volume histogram metrics were compared between plans to determine which optimization structure and treatment technique offered the maximum rectal dose sparing. RW structures offered a statistically significant decrease in rectal dose over CRW structures, whereas the treatment technique (IMRT vs VMAT) did not significantly affect the rectal dose. There was improvement seen in bladder and penile bulb dose when VMAT was used as a treatment technique. Overall, treatment plans using the RW optimization structure offered the lowest rectal dose while VMAT treatment technique offered the lowest bladder and penile bulb dose.