1.The consistency of BV before radiotherapy
Radiotherapy is the main method of postoperative prevention and local recurrence treatment in the pelvic cancer. Day-to-day anatomical variations complicate bladder cancer radiotherapy treatment [16]. Treating with a full bladder leads to unpredictability in bladder filling, and some authors suggest that this becomes more pronounced as treatment progresses, which could be due to poor patient compliance, disease-related anatomical changes that interfere with bladder innervation, or treatment-associated toxicity [24-28].
First of all, there were differences in BV between gender and age. U1 of patients over 60 years was 277.6±134.3mL, which was much different from the target volume. Thus, it is suggested that patients above 60 years drank more 180mL water after self-controlled maintenance for 30 minutes, so that the BV is closer to the target volume. It can be seen that the capacity of bladder to self-controlled maintenance varies from person to person. Chang Jee Suk et al reported that patients were asked to drink unspecified volume of water because we thought there were wide variations of abilities in drinking water and suppressing urination [32]. Besides, retaining urine was anticipated to become more difficult over the course of treatment because of radiation cystitis [33].
Secondly, the comparison of BV in three steps showed that there was no significant difference between U1 and UT. It was indicated that when patients drank 540mL water after emptying bladder and then waiting for 1 hour, the bladder volume before and during radiotherapy was consistent. We consider that using the BVI 9400 to measure the BV can better ensure that the bladder reached the filling state during radiotherapy. There was significant difference in bladder volume between U0 and U0.5. Thus, Bladder scan was a strategy that has been considered for increasing consistency with bladder volume. Similar to Cramp et al resulted [11]. Most patients will go to Simulation CT scan on the same day after Immobilization. By this time, patient's BV has reached the target volume, then go to CT room to report. While waiting for the Simulation CT scan, the BV continued to increase, resulting in a larger amount of BV in the Simulation CT scan than the other two steps. Therefore, it was recommended that the radiation therapist can allow patients to empty their bladder before Simulation CT scan, and then drank water to self-controlled maintenance.
Thirdly, there was a statistical difference between Ut and UT in the "Immobilization" and "Simulation CT scan" steps. However, there was no statistical difference between the Ut and the UT in the X-ray Simulation. It was previously reported that biofeedback could improve the consistency of BV despite a lack of statistical significance [18]. The method (drinking 540mL water after emptying bladder and then waiting for 1 hour) can improve and obtain the reliable feeling about self-controlled maintenance. Because the patient was subjected to the Simulation CT scan after the Immobilization was completed.
Moreover, most patients can achieve the target volume on the first chief complaint of urgency. Some patients still needed the second or the third complaint of urgency. In addition to the patient's physical factors, it was possible that the patient’s chief complaint of urgency was not true. Waiting for (75.2±49.9) min after emptying the bladder, patients complained of urgency. Because patients’ waiting for a long time leads to tension, impatience and urgent completion of the treatment, they tell the radiation therapist “urgency”. But their volume doesn’t reach expected standards. In order that the patient can get the better cooperation with treatment, the radiotherapy can be more accurate and the burden of work can be reduced, the radiation therapist should tell each patient the importance of filling bladder and how long it will take to wait. While patients are waiting, the radiation therapist need to appease the patient’s mood.
2.The consistency of BV during radiotherapy
There are many uncertain factors in the treatment of pelvic cancer, and the most concerned is the filling state of the bladder. The BV changes during the course of radiotherapy [17-22]. Bladder and rectal volumes tend to decrease as a function of time during treatment [23]. A research reported that during the first week of radiotherapy treatment, 50% of patients had more than 50% change in BV. And on the fifth week of treatment 64% of patients had more than 50% change in BV compared to the planned BV [2]. Hynds et al found that 76% (828/1090), 53% (579/1090), 36% (393/1090) BV during radiotherapy were >50mL, >100mL, >150mL difference [1]. Compared with the planned volume, all men had at least one BV reduction of more than 50% during treatment. The reduction in BV was probably correlated with incidence and severity of acute diarrhea [2].
In the result of BV measurement process during radiotherapy, first of all, it showed that there were statistically significant differences between UP and UT of 18 patients with pelvic cancer (P <0.05), with a difference of 17.81%. The RBV was negatively correlated with the number of radiotherapy (r=-0.5726, p=0.0028). With the inter-fraction radiotherapy, the overall RBV of 18 patients gradually decreased and the overall decrease was 5.53%. The larger the standard deviation was, the greater the degree of dispersion would be. Stam et al believed that SD = 47.2% can be considered that the daily variation of BV was large [18], while the overall SD = 2% of 18 patients was much less than 47.2% during radiotherapy. The change in the RBV between the inter-fractions was small.
Secondly, it showed that 18 patients obtained a total of 450 BV (18*25), and the consistency rate was about 82.89% (373/450). 15 patients (15/18) passed, and the consistency rate was 96% (360/375). The consistency rate has no linear relationship with age (P = 0.2741), similar to Mullaney [13]. It showed that although the reduction of bladder capacity caused by radiotherapy was unavoidable, but patients drank 540mL of water before radiotherapy and urination suppressing training; therefore, most patient’s BV can be consistent with the planned BV.
Thirdly, it showed that 3 patients (3/18) failed, and the consistency rate was 17.33% (13/75), but their BV remained relatively consistent between inter-fractions. The reason for the failure may be that ultrasound assessment of BV was less satisfactory in real patients than in normal volunteers. It was noted that there was considerable variability in the shapes of different bladders and at varying volumes. These methods were not applicable to all patients, either because the bladder outline was too indistinct or the bladder was too large to demonstrate on a single scan [34]. Although BS provides an effective means of assessing BV prior to treatment, studies showed that improvements in BV consistency are more difficult to attain [1,18,35,36]. Nevertheless, there are some articles which have supported the use of the BS in a radiation therapy setting [17,35,36]. The plausible explanation is that if the BV for the first time of radiotherapy cannot reach the planned BV (UP) due to the poor condition of the patient or the measurement error of the radiation therapist. But during clinical treatment, the patient's actual BV is used as the treatment BV and the first radiotherapy is used as the reference standard, so the patient's BV fails during the entire radiotherapy process. Therefore, for a small number of special patients, attention should be paid to rational determination of BV before treatment.
Shogo Hatanaka et al reported that the decrease of BV will lead to the increase of bladder dose, for both the small and large bowel, and they found a significant association between the Dmax values and BV variation (the dose of small and large bowel less than 60Gy and 65Gy) [29]. Yaparpalvi R et al found that the small intestine area with 45 Gy was greater in the bladder emptying condition compared to the bladder filling state (The average was 328.0±174.8 vs 176.0±87.5 cm) [25]. Frizzell B et al made a definitive treatment for prostate cancer, according to the influence of BV on rectal radiotherapy dose. The filling of bladder was compared with emptied bladder, the average exposure dose of rectum decreased by 27.6 Gy, and there was significant difference (P=0.031) [30]. Buchali et al found that when the BV increased, the exposure dose decreased. A full bladder led to a mean reduction in organ dose in median from 94-87% calculated for 50% of the BV. For 66% of the BV the dose could be reduced in median from 78-61% and for the whole bladder from 42-39% [31]. Fujioka C et al reported optimal BVs at treatment planning must be investigated to both maintain reproducibility of the BV and dose constraints for the bladder [8].
At present, the standard of "pass" bladder volume before radiotherapy for patients with pelvic cancer is not clear. In actual clinical practice, the radiation therapist usually judges whether the measured BV meets the planned BV (UP) based on experience. Patients who fail to reach the planned BV need to suppress urination for many times, which virtually increases the patient's mental tension and physical discomfort, and reduces the efficiency of radiotherapy. However, urination suppressing training before radiotherapy and the maintenance intervention during radiotherapy showed that 82.89% (373/450) of the 18 patients in the range of (50%, 155%) were able to keep consistency with UP and UT. This indicates that the consistency range is reasonable. (50%,155%) can determine whether the bladder filling of patients with pelvic cancer is consistent with the planned BV before radiotherapy, reducing the patient's mental pressure and physical discomfort, improving the efficiency of radiation therapy. However, urination suppressing training used in the present study was frequently used in clinical practice in the setting of dose escalation to the pelvic cancer patients. Despite these limitations, there are very few data in the literature on the optimal BV at treatment planning and during radiotherapy in pelvic cancer; therefore, we hope that the present results will serve as reference values for other institutions.