Radiation treatment planning and delivery strategies for a pregnant brain tumor patient

Abstract

The management of a pregnant patient in radiation oncology is an infrequent event requiring careful consideration by both the physician and physicist. The aim of this manuscript was to highlight treatment planning techniques and detail measurements of fetal dose for a pregnant patient recently requiring treatment for a brain cancer. A 27‐year‐old woman was treated during gestational weeks 19–25 for a resected grade 3 astrocytoma to 50.4 Gy in 28 fractions, followed by an additional 9 Gy boost in five fractions. Four potential plans were developed for the patient: a 6 MV 3D‐conformal treatment plan with enhanced dynamic wedges, a 6 MV step‐and‐shoot (SnS) intensity‐modulated radiation therapy (IMRT) plan, an unflattened 6 MV SnS IMRT plan, and an Accuray TomoTherapy HDA helical IMRT treatment plan. All treatment plans used strategies to reduce peripheral dose. Fetal dose was estimated for each treatment plan using available literature references, and measurements were made using thermoluminescent dosimeters (TLDs) and an ionization chamber with an anthropomorphic phantom. TLD measurements from a full‐course radiation delivery ranged from 1.0 to 1.6 cGy for the 3D‐conformal treatment plan, from 1.0 to 1.5 cGy for the 6 MV SnS IMRT plan, from 0.6 to 1.0 cGy for the unflattened 6 MV SnS IMRT plan, and from 1.9 to 2.6 cGy for the TomoTherapy treatment plan. The unflattened 6 MV SnS IMRT treatment plan was selected for treatment for this particular patient, though the fetal doses from all treatment plans were deemed acceptable. The cumulative dose to the patient's unshielded fetus is estimated to be 1.0 cGy at most. The planning technique and distance between the treatment target and fetus both contributed to this relatively low fetal dose. Relevant treatment planning strategies and treatment delivery considerations are discussed to aid radiation oncologists and medical physicists in the management of pregnant patients.

Assessment of Fetal Dose and Health Effect to the Fetus from Breast Cancer Radiotherapy during Pregnancy

“…Moreover, in-vivo measurements are invasive for patients and are only possible for patients in the first trimester of pregnancy [3]. Second, although phantom measurements of fetal dose are usually performed [4], these measurements only give the point dose and the measured fetal dose could be unrealistic because phantoms are made of tissue-equivalent materials. Furthermore, if detectors are not specifically calibrated for the out-of-field dose, uncertainties in dose measurement are likely to occur [1,4].…”

Challenges with Adjuvant Radiation for Intracranial Chondrosarcoma in Pregnancy

“…For situations where RT contributes significantly to disease control and QOL, RT may be planned in later pregnancy with necessary precautions, such as pretreatment phantom-based dose simulations, abdominal lead shielding to reduce fetal exposure, treatment plan modifications (linear accelerator with beam energy <10 MV preferred over cobalt-60, 3DCRT with minimal beam modifying devices preferred over intensity modulated RT, flattening filter-free beams). 11 During cranial RT in the second trimester, the fetal position is at a distance of 40 to 50 cm from the cranial field edge. At this distance, the contribution from external scatter exceeds that from internal scatter.…”

Evaluation of a new foetal shielding device for pregnant brain tumour patients

“…However, it is important to thoroughly review the effects of high-modulation techniques such as VMAT or IMRT on foetal dose, since such therapies can increase scattered and leakage doses. The previous shielding structures were mostly designed to shield the upper part of the patient; few shielding structures were proposed to shield the scattered and leakage doses that occur when gantry is located at around 180° and for the internal scattered radiation [ 1 , 3 , 4 , 8 ]. Thus, the previously designed structures would not be sufficient for VMAT or IMRT using gantry angles of approximately 180°.…”

“…On the other hand, the smallest foetal dose was delivered in 6 MV FFF VMAT, and the beam delivery time was 83 s, similar to the 6 MV VMAT. This is due to the reduction in head leakage caused by the flattening filter, and approximately 20% reduction in foetal dose in VMAT using 6 MV FFF compared to 6 MV was observed [ 3 ]. The average beam delivery time in IMRTs was approximately 230 s, which was increased by approximately 35% compared to the 6 MV FFF VMAT, and a higher foetal dose was measured.…”

“…Although radiation therapy is rarely performed for pregnant patients, it has been used for pregnant patients with breast, head and neck cancer, Hodgkin’s disease, leukaemia, and brain tumour [ 1 – 3 ]. For such patients, it is important to consider target control and saving of the surrounding organs at risk (OARs) as well as foetal dose reduction.…”