Interstitial injection of 32P-chromic phosphate during lung cancer resection to treat occult lymphatic metastasis

Monte Carlo-based dose calculation for (32)P patch source for superficial brachytherapy applications

Skin cancer treatment involving ³²P source is an easy, less expensive method of treatment limited to small and superficial lesions of approximately 1 mm deep. Bhabha Atomic Research Centre (BARC) has indigenously developed ³²P nafion-based patch source (1 cm × 1 cm) for treating skin cancer. For this source, the values of dose per unit activity at different depths including dose profiles in water are calculated using the EGSnrc-based Monte Carlo code system. For an initial activity of 1 Bq distributed in 1 cm² surface area of the source, the calculated central axis depth dose values are 3.62 × 10^-10 GyBq^-1 and 8.41 × 10^-11 GyBq^-1at 0.0125 and 1 mm depths in water, respectively. Hence, the treatment time calculated for delivering therapeutic dose of 30 Gy at 1 mm depth along the central axis of the source involving 37 MBq activity is about 2.7 hrs.

Phosphorus-32, a clinically available drug, inhibits cancer growth by inducing DNA double-strand breakage

Radioisotopes that emit electrons (beta particles), such as radioiodine, can effectively kill target cells, including cancer cells. Aqueous ³²P[PO₄] is a pure beta-emitter that has been used for several decades to treat non-malignant human myeloproliferative diseases. ³²P[PO₄] was directly compared to a more powerful pure beta-emitter, the clinically important ⁹⁰Y isotope. In vitro, ³²P[PO₄] was more effective at killing cells than was the more powerful isotope ⁹⁰Y (P ≤ 0.001) and also caused substantially more double-stranded DNA breaks than did ⁹⁰Y. In vivo, a single low-dose intravenous dose of aqueous elemental ³²P significantly inhibited tumor growth in the syngeneic murine cancer model (P ≤ 0.001). This effect is exerted by direct incorporation into nascent DNA chains, resulting in double-stranded breakage, a unique mechanism not duplicatable by other, more powerful electron-emitting radioisotopes. ³²P[PO₄] should be considered for human clinical trials as a potential novel anti-cancer drug.

Bioevaluation study of 32P-CP-PLLA particle brachytherapy in a rabbit VX2 lung tumor model

OBJECTIVE

The purpose of this study was to investigate the therapy effects of intratumoral administration of (32)P-CP-PLLA particles in a rabbit VX2 lung tumor model.

METHODS

16 rabbits with tumors were randomly divided into 4 groups. 4 rabbits served as untreated controls, and others received intratumoral administration of (32)P-CP-PLLA particles with CT guidance. The total radioactivities in treated groups were as follows: a low activity was 93 MBq (n=4) (group 1), a medium activity was 185 MBq (n=4) (group 2) and a high activity was 370 MBq (n=4) (group 3). Brachytherapy treated VX2 tumors underwent (18)F-FDG PET/CT at 0 day, 3 day, 7 day and 14 day postinjection. In control group, (18)F-FDG PET/CT images were acquired at the same time points but without any treatment. Bremsstrahlung SPECT images were performed at 14 days after intratumoral brachytherapy in treated groups. After Bremsstrahlung SPECT and last (18)F-FDG PET/CT imagings, the rabbits were euthanized and the tumors were removed for histological examination.

RESULTS

Bremsstrahlung SPECT images study indicated that there was no leakage of (32)P out of the injection site at 14 days after treatment. Compared with the control, the tumor volumes in treated groups significantly decreased, and (32)P-CP-PLLA particle produced a reduction in maximum or mean SUV of VX2 tumor (p<0.05). The percentage changes in maximum and mean SUV gradually decreased in group 1 and group 2 from day 3 to day 14 (p<0.05). A transient increase in (18)F-FDG accumulation at group 3 occurred due to the inflammatory reaction elements. Activity dependence was seen in HE and PCNA staining after 14 days treatment among three treated groups (p<0.05).

CONCLUSIONS

Our data suggested that (32)P-CP-PLLA particle localized on the injecting sites. This novel brachytherapy device efficiently suppressed the growth of the VX2 tumors implanted in the rabbit.

[Experimental study of CT guided ³²P-CP-PLLA microparticle implantation in the treatment of rabbit VX2 lung tumor]

背景与目的

新型放射性植入剂³²P-磷酸铬-聚-L-乳酸（³²P-CP-PLLA）粒子具有良好的生物相容性和降解性，适用于实体肿瘤的近距离放射治疗。本研究旨在探讨兔VX2肺肿瘤经³²P-CP-PLLA粒子瘤体间植入近距离治疗前后PET/CT显像及病理学的变化，分析³²P-CP-PLLA粒子植入对荷VX2肺癌兔肿瘤生长及凋亡相关蛋白的影响。

方法

24只荷瘤兔随机分成4组。每组6只。1组-3组为治疗组；4组为对照组。在CT导引下经皮穿刺将总放射性活度为93 MBq、185 MBq和370 MBq的³²P-CP-PLLA粒子分别植入1组、2组和3组肿瘤组织内。对照组不做任何干预。分别在治疗后第0天、第3天、第7天和第14天进行¹⁸F-FDG PET/CT显像，观察标准摄取值（standardized uptake value, SUV）的变化。最后1次PET/CT显像后处死荷瘤兔，取出肿瘤组织，进行病理学检查和免疫组织化学分析，比较肿瘤细胞形态和凋亡基因（bcl-2, bax）表达的变化。

结果

第0天时，治疗组和对照组之间SUVmax无明显差异。治疗后第14天，1组、2组和3组SUVmax值分别为1.1±0.19、0.80±0.10和2.85±0.15，均较对照组（5.61±0.50）明显下降。第7天-第14天时，1组和2组SUVmax较第3天呈现持续下降趋势，且呈剂量效应关系（P < 0.05）。治疗后第3天-第14天，3组SUVmax较第0天显著上升，并在第7天达到峰值，后明显下降。同期3组SUVmax明显低于对照组SUVmax。HE染色显示近粒子处的肿瘤细胞变性坏死，坏死程度随剂量的增加而严重。3组可见坏死组织周围有大量炎性细胞浸润，而1组-2组炎性细胞浸润不明显。免疫组化显示治疗组bcl-2表达强度低于对照组，bax表达强度高于对照组（P < 0.05）。治疗组bcl-2/bax比值明显下调（P < 0.05）。凋亡基因的表达呈剂量效应关系。

结论

³²P-CP-PLLA粒子持续照射可直接杀伤VX2肿瘤细胞从而抑制其葡萄糖代谢功能。远离粒子处虽可见存活肿瘤细胞，但凋亡基因表达明显异于对照组。³²P-CP-PLLA粒子可通过电离辐射诱导bcl-2和bax基因参与VX2移植瘤细胞凋亡过程的调控，从而抑制肿瘤生长。