RBE of π - Beams in the Bragg Peak Region Determined with Polyploidy Induction in Mammalian Cells Irradiated in Vivo

Radiobiological Considerations for Pions in Radiotherapy

“…The estimated RBE values, obtained in both plant and animal cell systems by observation of both cell-lethal and nonlethal effects, range from about 2 to about 5. The RBE estimates of L o u g h -m a n et al [46] for a pure pion beam suggest that removal of contaminating particles by special devices (e.g., electrostatic separators) may increase peakregion pion RBE. Additionally, narrowing the beam's momentum spectrum should result in a sharper Bragg peak region, further increasing peak-region pion RBE.…”

“…The estimation of RBE based on polyploid induction gives Beam RBE Star 4-7t_ + jjL" + e -2.5 Star + jt~2. 8 Star only 4.6 We have introduced corrections made after publication of the L o u g h m a n et al [46] paper.…”

“…All the mice were injected with 106 L-2 lymphoma cells 3 and 5 days prior to the beginning of the irradiation. Animals bearing 3-day-old tumors at the beginning of the experiment were used for cytological studies [23,45,46], and the mice starting irradiation with 5-day-old tumors were used to test tumor-forming ability [24]. Control experiments under identical conditions were carried out using " Co y-rays and were done at a comparable dose rate as a low LET control.…”

“…[45,46] used LAF, mice carrying L-2 lymphoma ascites tumor cells to study cytological effects of the negative pions at plateau and at peak. Lymphoma cells aspirated from mice at various times following pion irradiation were examined cytologically, and four characteristics were scored: mitotic index, frequency of polyploid metaphase cells, frequency of anaphase cells displaying 'bridges', and chromosome counts of metaphase cells.…”

“…With still larger particles, RBE begins to fall although the OER remains about 1.0. Interest in pions arises from the high peak-to-plateau ratio of their Bragg peak, the broadness of the peak, RBE factors of about 3 to 5 [23,24,26,46,59,70], the reduction of the oxygen effect [60], and the ability to produce by scanning techniques, sharply defined therapeutic volumes of large size, e.g., 10 x 10 x 10 cm [59,73],…”