HJAR Nov/Dec 2020

HEALTHCARE JOURNAL OF ARKANSAS I  NOV / DEC 2020 57 Scott Yakoubian Director of Medical Physics, Dosimetry and RSO CARTI, Inc. specific information from the patient’s CT scan to generate a unique model of the patient and construct a custom bolus that more precisely matches their specific anat- omy. A3-D-printed bolus can be used when it is necessary to compensate for missing tissue in a patient who has had surgery, to make an irregular surface more uniform or to increase the dose to the skin when treat- ing skin cancer. The use of 3-D bolus im- proves the sparing of healthy tissue, reduces air gaps (which can cause issues with dose conformity), accommodates and corrects for anatomical irregularities and reduces hot spots (which may result in unnecessary breaks or gaps in treatment). And, most im- portantly, it improves treatment accuracy and dose distribution. Data derived from treatment-planning systems can optimize the 3-D-printed bolus in ways that were never possible before with hand-sculpted bolus. Flexible, patient-spe- cific bolus provide superior fit and adhere to the surface of complex anatomies, such as a breast, significantly better. These fac- tors make a 3-D-printed bolus far superior for the precision delivery of the intended dose of radiation. Plus, delivering the radia- tionmore accurately should give us the best chance of controlling cancer and preventing a recurrence. Early use of this technology, hardware and software has resulted in the accuracy of fit of the 3-D bolus being improved rela- tive to standard sheet bolus, with the fre- quency of air gaps larger than or equal to 5 mm reduced from 30 percent to 13 percent. Also, setup times were reduced with 3-D- printed bolus by 27 percent when compared to standard sheet bolus. Finally, the use of patient-specific, custom, 3-D-printed bolus improved reproducibility of placement of the bolus device for additional planning CT’s and daily treatments and improved patient experience and comfort. In the future, the integration of 3-D print- ing technology with imaging and planning systems are likely to continue to grow. 3-D printing technology allows the precise con- struction of custombolus and other types of tissue compensators. By taking advantage of the modulated electron bolus (MEB) plans created in 3-D printing software, radiation oncology teams can demonstrate superior sparing of healthy tissues and distal OARs (organs at risk) while significantly reducing hotspots compared to photon IMRT (inten- sity modulated radiotherapy) delivery, i.e., VMAT (volumetric modulated arc therapy) (see Figures 1A, 1B and 1C above). For some patients, 3-D printing technology will re- sult in a more accurate, specific targeting of their cancer. The benefits to the patients include im- proved quality of life, reduced setup times, improved patient comfort and enhanced reproducibility and reliability of the bolus throughout the entire treatment course. The ability to print the precise, patient-specific bolus required for some electron and/or photon treatments is a powerful tool for radiation therapy departments. And, thanks to ongoing improvements in cost and reliability, 3-D printing is becoming more common in cancer centers, allowing even the most difficult cases to be planned and treated swiftly. n Radiation oncologist Christopher Pope, MD, treats patients at the CARTI Cancer Center in Conway. He completed residency in radiation oncology at University of Louisville in Louisville, Kentucky, and received a medical degree from Louisiana State University School of Medicine in New Orleans, Louisiana. Scott Yakoubian, Director of Medical Physics, Dosimetry and RSO, leads the department that covers all of CARTI’s treatment locations that offer radiation oncology.Yakoubian serves on the State of Arkansas’ Ionizing Radiation Licensure Committee and serves on an American Association of Medical Physicists Leadership subcommittee.He received a degree fromGeorgia Institute ofTechnology and has been in the field for 27 years. Figure 1A. Treatment plan using VMAT was rejected due to splay of intermediate dose. Figure 1B. Standard electron field with uniform thickness bolus delivers a high dose to underlying healthy tissue and has a high presence of hotspots. Figure 1C. Same electron field as center image - however, using Adaptiiv’s MEB spares underlying healthy tissue and significantly reduces hotspots.