Principles of Radiation Oncology

Respiratory gating in patients with lung carcinoma undergoing radiotherapy

Aim:

This study aims to compare the gating signals of patients with lung cancer recorded during the planning computed tomography scan with the ones recorded during treatment fractions. The results provide insights into how representative the respiratory signals from the planning scan are for radiation dose partitioning.

Materials and methods:

The amplitude and frequency of the respiratory signals of 29 patients with lung carcinoma were analysed and compared with the amplitude and frequency of those recorded during their planning scans. Moreover, a cross-correlation analysis was performed between the difference between the planning scan and fractions and features from the planning scan.

Results:

Two patients showed significantly different amplitude and frequency during treatment fractions compared to those from the planning scan. These patients showed low variances in frequency and amplitude during the different fractions. The difference between planning scan and fractions is correlated with the variances within the planning scan.

Findings:

Respiratory signals can differ between the planning scan and the fractions. In this case, a new planning scan may be beneficial. The respiratory signals from the planning scan may be predictive of whether the planning scan will be representative and usable as a control measure during radiotherapy fractions.

Methoxyamine potentiates iododeoxyuridine-induced radiosensitization by altering cell cycle kinetics and enhancing senescence

We previously reported that methoxyamine (an inhibitor of base excision repair) potentiates iododeoxyuridine (IUdR)-induced radiosensitization in human tumor cells. In this study, we investigated the potential mechanisms of this enhanced cell death. Human colorectal carcinoma RKO cells were exposed to IUdR (3 micromol/L) and/or methoxyamine (3 mmol/L) for 48 hours before ionizing radiation (5 Gy). We found that IUdR/methoxyamine altered cell cycle kinetics and led to an increased G1 population but a decreased S population before ionizing radiation. Immediately following ionizing radiation (up to 6 hours), IUdR/methoxyamine-pretreated cells showed a stringent G1-S checkpoint but an insufficient G2-M checkpoint, whereas a prolonged G1 arrest, containing 2CG1 and 4CG1 cells, was found at later times up to 72 hours. Levels of cell cycle-specific markers [p21, p27, cyclin A, cyclin B1, and pcdc2(Y15)] and DNA damage signaling proteins [gammaH2AX, pChk1(S317), and pChk2(T68)] supported these altered cell cycle kinetics. Interestingly, we found that IUdR/methoxyamine pretreatment reduced ionizing radiation-induced apoptosis. Additionally, the extent of cell death through necrosis or autophagy seemed similar in all (IUdR +/- methoxyamine + ionizing radiation) treatment groups. However, a larger population of senescence-activated beta-galactosidase-positive cells was seen in IUdR/methoxyamine/ionizing radiation-treated cells, which was correlated with the increased activation of the senescence factors p53 and pRb. These data indicate that IUdR/methoxyamine pretreatment enhanced the effects of ionizing radiation by causing a prolonged G1 cell cycle arrest and by promoting stress-induced premature senescence. Thus, senescence, a novel ionizing radiation-induced tumor suppression pathway, may be effectively targeted by IUdR/methoxyamine pretreatment, resulting in an improved therapeutic gain for ionizing radiation.