Personalized Radiotherapy Shields May Effectively Protect Healthy Tissue During RT for Prostate, Oral Cancer

Three-dimensionally (3D) printed radioprotective shields based on volumetric CT imaging was protective of healthy GI mucosal tissues in a proof-of-concept study using rats and pigs, a team of researchers at Harvard, Brigham and Women’s Hospital, Dana-Farber Cancer Institute, and MIT, in Boston, recently reported in Advanced Science.¹

“[O]ur radiation-attenuating devices reduced oral mucositis and proctitis in animals and modeling showed dose sparing in human simulations,” reported lead author James Byrne, MD, PhD, of the Giovanni Traverso lab at Brigham and Women’s Hospital, and coauthors.¹

“Our results support the feasibility of personalized devices for reducing the side effects of radiation therapy,” Dr Byrne said in a press release about the study.

More than 50% of cancer patients undergo radiation therapy but damage to radiosensitive healthy, nontarget tissues near tumors is a common toxicity. Most will experience radiation-induced toxicities and tissue injury, the authors noted.¹ Those toxicities are commonly dose-limiting, reducing the efficacy of treatment. Important advances have been made in 3-dimensionally conforming and intensity-modulated external beam radiotherapy techniques to spare nontarget tissues. But particularly for head and neck, esophageal, gastrointestinal, and rectal malignancies, painful radiation mucositis force many patients to curtail treatment.^1,2

Anatomy-Tailored Radiation Shields

Three-dimensional printing allows production of patient anatomy-tailored shields and more comfortable positional immobilization aides less expensively than can other methods.³ These fabrication techniques are being used to produce radiation dosimetry phantoms and surgical planning models and to address other gaps in radiation oncology’s patient-protection toolkit.^3-6

Three-dimensional technologies can use alloys and chemical composites as printing material. The team studied the use of high atomic number (Z) elements and compounds that can block radiation backscatter as 3D printing materials, including bismuth, lead, and mercury.¹ The elemental lead and bismuth were 3 times more effective at attenuating radiation than an acrylic resin mixture that included lead and bismuth, they noted. Mercury outperformed other liquid materials, proving twice as attenuating as Galinstan.¹

Positive Results With Animal Models, Human Simulations

Using CT scans, the researchers 3D printed tailored shields with these materials, and then tested how effectively they shielded oral and prostate tissue against radiation in rats.¹

“The attenuating devices were designed to protect approximately half of the area that is at risk for normal tissue injury,” reported the researchers.¹ “Seven out of 7 control animals treated with radiation to the oral cavity had gross ulcerations on their tongue compared to 0 of 7 animals with the radioprotective device in place.”

Using CT images, the team then designed, printed, and placed intra-oral, esophageal, and rectal shields in pigs, as evidence that the techniques can be successfully scaled up from rats to larger animals.

In subsequent dosimetry modeling simulations, the team found that irradiation of oral mucosa in human patients might be reduced by 30% in those undergoing head and neck cancer radiotherapy and by 15% in patients with prostate cancer without affecting radiation dose to target tumor tissue.¹ Radiation shields were more cost-effective than hydrogel rectal spacers, they reported.¹

Oral anatomy varies “tremendously” among patients, the authors noted.¹ Tailoring oral radiation shields to patients’ palate anatomy will likely improve patient comfort during treatment, improving adherence.

Conclusions

“Verified in both small and large animal models as well as human simulations, our results support the feasibility of personalized devices for reduction of radiation dose and associated side effects through displacement and attenuation of the radiation dose,” they concluded.¹

It is still early days, the authors cautioned; larger validation studies are needed before clinical trials with human patients.

The concept of 3D printed personalized radiotherapy shields is not new and other proposed applications are proliferating, but most of the research published to date has been, like this new report, small and preclinical.²

“Cancer staging scans are routinely used for radiation treatment planning and can be easily integrated into device development” with 3D technologies, Dr Byrne said. “This personalized approach could be applicable to a variety of cancers and holds the potential to reduce the burden of radiation injury and toxicity for our patients.”

Disclosure: This research was supported by the National Institutes of Health and the Prostate Cancer Foundation.

References

1. Byrne JD, Young CC, Chu JN, et al. Personalized radiation attenuating materials for gastrointestinal mucosal protection. Adv Sci. 2021;8(12):2100510. doi:10.1002/advs.202100510
2. Rooney MK, Rosenberg DM, Braunstein S, et al. Three-dimensional printing in radiation oncology: a systematic review of the literature. J App Clin Med Phys. 2020;21(8):15-26. doi:10.1002/acm2.12907
3. Ehler ED. Utilization of 3D printing in clinical medical physics. AIP Conf Proceedings. Published online April 30, 2021. doi:10.1063/5.0051637
4. Tino R, Yeo A, Leary M, Brandt M, Kron T. A systematic review on 3D-printed imaging and dosimetry phantoms in radiation therapy. Technol Cancer Res Treat. First published on September 12, 2019. doi:10.1177/1533033819870208
5. Rahimy E, Skinner L, Kim YH, Hoppe RT. Technical report: 3D-printed patient-specific scalp shield for hair preservation in total skin electron therapy. Tech Innov Pat Supp Radiat Oncol. 2021;18:12-15. doi:10.1016/j.tipsro.2021.03.002
6. Craft DF, Lentz J, Armstrong M, et al. Three-dimensionally printed on-skin radiation shields using high-density filament. Practical Radiat Oncol. 2020;10(6):E543-E550. doi:10.1016/j.prro.2020.03.012