Relations between dose cumulated in organs at risk and treatment based on different image-guidance strategies of cervical cancer

Study on Appropriate Rectal Volume for External Irradiation in Patients With Cervical Cancer

Objective

To investigate the appropriate rectal volume for external irradiation of cervical cancer.

Methods

A retrospective study of 143 patients with cervical cancer who underwent external radiotherapy from January 2017 to September 2020 was conducted. Average rectum volumes and the cumulative dose (V30, V40, V50, D2cc) to organs at risk (bladder, rectum, and small bowel) during radiotherapy were evaluated using the treatment planning system. Rates of radiation cystitis and radiation proctitis were assessed.

Results

The median follow-up was 48 months, and the included patients had a median age of 53 years. Patients were divided into 3 groups based on their average rectum volume: Group A: <40 ml; Group B: 40–70 ml; and Group C: ≥70 ml. V30 and V40 in the rectum bladder and small bowel were highest in Group A (mean ± SD standard deviation), but V50 and D2cc in the rectum and bladder were highest in Group C (mean ± SD). Patients in Group B had the lower incidence of both radiation cystitis and radiation proctitis. (p<0.05).

Conclusions

For external irradiation in patients with cervical cancer, a rectum volume of 40–70 ml seems most appropriate, whereas >70 ml increases the risk of severe radiation cystitis and radiation proctitis, and <40 ml increases the risk of mild radiation cystitis and mild radiation proctitis.

Dosimetric impact of Acuros XB on cervix radiotherapy using RapidArc technique: a dosimetric study

Background

Acuros XB (AXB) may predict better rectal toxicities and treatment outcomes in cervix carcinoma. The aim of the study was to quantify the potential impact of AXB computations on the cervix radiotherapy using the RapidArc (RA ) technique as compared to anisotropic analytical algorithm (AA) computations.

Materials and methods

A cohort of 30 patients previously cared for cervix carcinoma (stages II-IIIB) was selected for the present analysis. The RA plans were computed using AA and AXB dose computation engines under identical beam setup and MLC pattern.

Results

There was no significant (p > 0.05) difference in D_95% and D_98% to the planning target volume (PTV); moreover, a significant (p < 0.05) rise was noticed for mean dose to the PTV (0.26%), D_50% (0.26%), D_2% (0.80%) and V_110% (44.24%) for AXB computation as compared to AA computations. Further, AXB estimated a significantly (p < 0.05) lower value for maximum and minimum dose to the PTV. Additionally, there was a significant (p < 0.05) reduction observed in mean dose to organs at risk (OARs) for AXB computation as compared to AA, though the reduction in mean dose was non-significant (p > 0.05) for the rectum. The maximum difference observed was 4.78% for the rectum V_50Gy, 1.72%, 1.15% in mean dose and 2.22%, 1.48% in D_2% of the left femur and right femur, respectively, between AA and AXB dose estimations.

Conclusion

For similar target coverage, there were significant differences observed between the AAA and AXB computations. AA underestimates the V_50Gy of the rectum and overestimates the mean dose and D_2% for femoral heads as compared to AXB. Therefore, the use of AXB in the case of cervix carcinoma may predict better rectal toxicities and treatment outcomes in cervix carcinoma using the RA technique.

Forecasting of the composite dose for organs at risk and solid targets with random movements during different image-guided scenarios of the photon radiation therapy. Solution for the Varian therapeutic line

Background

This study aims to develop a useful tool for robust plan analysis which includes the effects of soft tissue deformations on simulated dose distributions. The solution was benchmarked in the light of the commercial method implemented in Eclipse^TM treatment planning system (TPS).

Materials and methods

Study was carried out on data of one patient with prostate-restricted cancer. The workflow of the procedure developed focused on three executive elements: in-house script to create a set of artificial CT images and for movement simulation of the CT V; the Velocity^TM software for the calculations of the deformation matrixes and, then, to generate deformed CT sets; the Eclipse^TM TPS for dose re-calculations and analysis. Two scenarios were examined — first when the recalculation was done for the original geometry and second, when the isocentre from the original plan geometry was moved according to the movement of the CT V. The dose distributions were analysed on dose volume histograms (DVHs) in the light of the results obtained from the method implemented in the Eclipse^TM TPS.

Results

The DVHs from our methods are more informative than the DVH from commercially implemented tools. For the first scenario, the highest impact on dose uncertainty has boundary positions of the CT V to the CT V-PTV margin. Using the second scenario, it is the relation of the CT V position to the whole body that has the highest effect on dose uncertainty.

Conclusion

Our method enables a more accurate analysis of the treatment plan robustness than the method currently implemented in Eclipse^TM TPS.

Comparison of three different phantoms used for Winston-Lutz test with Artiscan software

BACKGROUND

One of the most important test in every quality assurances process of medical linear accelerators is the Winston-Lutz test, allowing an evaluation of the treatment isocentre in the light of uncertainty of the position of the collimator, the gantry and the couch.

AIM

The purpose of this work was analysis of the results of the Winston-Lutz test performed with three different phantoms for two different accelerators.

MATERIALS AND METHODS

Measurements were performed on two Varian machines: TrueBeam equipped with aS1200 EPID and TrueBeam equipped with aS1000 EPID. During the study three different phantoms dedicated for verification of the radiation isocentre were used: PTW Isoball, AQUILAB Isocentre Phantom and Varian Isocentre Cube. Analysis of the DICOM images was performed in Artiscan software.

RESULTS

For TrueBeam with as1200 EPID, gantry MV isocentre was about 0.18 mm larger for Varian Isocentre Cube than for two other phantoms used in this study. The largest variability of this parameter was observed for the couch. The results differed to 1.16 mm. For TrueBeam with as1000 EPID, results for collimator isocentre with PTW Isoball phantom were about 0.10 mm larger than for two other phantoms. For the gantry, results obtained with Varian Isocentre Cube were 0.21 mm larger.

CONCLUSION

The obtained results for all three phantoms are within the accepted tolerance range. The largest differences were observed for treatment couch, which may be related to the phantom mobility during couch movement.

Impact of different optimization strategies on the compatibility between planned and delivered doses during radiation therapy of cervical cancer

PURPOSE

To analyse the impact of different optimization strategies on the compatibility between planned and delivered doses during radiotherapy of cervical cancer.

MATERIAL/METHODS

Four treatment plans differing in optimisation strategies were prepared for ten cervical cancer cases. These were: volumetric modulated arc therapy with (_OPT) and without optimization of the doses in the bone marrow and for two sets of margins applied to the clinical target volume that arose from image guidance based on the bones (IG(B)) and soft tissues (IG(ST)). The plans were subjected to dosimetric verification by using the ArcCHECK system and 3DVH software. The planned dose distributions were compared with the corresponding measured dose distributions in the light of complexity of the plans and its deliverability.

RESULTS

The clinically significant impact of the plans complexity on their deliverability is visible only for the gamma passing rates analysis performed in a local mode and directly in the organs. While more general analyses show statistically significant differences, the clinical relevance of them has not been confirmed. The analysis showed that IG(ST)_OPT and IG(B)_OPT significantly differ from IG(ST) and IG(B). The clinical acceptance of IG(ST)_OPT obtained for hard combinations of gamma acceptance criteria (2%/2 mm) confirm its satisfactory deliverability. In turn, for IG(B)_OPT in the case of the rectum, the combination of 2%/2 mm did not meet the criteria of acceptance.

CONCLUSION

Despite the complexity of the IG(ST)_OPT, the results of analysis confirm the acceptance of its deliverability when 2%/2 mm gamma acceptance criteria are used during the analysis.

Extended-field bone marrow sparing radiotherapy for primary chemoradiotherapy in cervical cancer patients with para-aortic lymphadenopathy: Volumetric-modulated arc therapy versus helical tomotherapy

BACKGROUND

Extended-field (EF) bone marrow-sparing (BMS) radiotherapy is attracting interest for cervical cancer patients with para-aortic lymphadenopathy.

OBJECTIVE

To compare dosimetric quality of volumetric-modulated arc therapy (VMAT) vs. helical tomotherapy (HT) during EF BMS radiotherapy.

METHODS

HT dose-volume histogram parameters including (1) coverage, homogeneity, and conformity of target volumes, (2) sparing of organs-at-risk, (3) monitor units, and (4) estimated treatment time were compared with those of VMAT in 20 cervical cancer patients who underwent EF BMS radiotherapy. The pelvic and para-aortic regions received 45-Gy dose (25 fractions), with simultaneous integrated boost of 55 Gy (25 fractions) for pelvic and para-aortic lymphadenopathy, followed by a parametrial boost of 9 Gy (5 fractions).

RESULTS

The HT-based and VMAT techniques achieved adequate and similar target volume coverage with good dose homogeneity and conformity, while sparing all organs-at-risk, including the rectum, bladder, bowel, bone marrow, femoral head, kidney, and spinal cord. The HT treatment plan had significantly higher monitor units (p < 0.001) and longer estimated treatment times (p < 0.001).

CONCLUSIONS

VMAT and HT plans are suitable for EF BMS radiotherapy, which can achieve adequate target volume coverage while sufficiently sparing normal tissue. In addition, VMAT, compared to HT planning, yielded shorter estimated treatment times.

Impact of bladder volume on treatment planning and clinical outcomes of radiotherapy for patients with cervical cancer

Objective

This study aimed to investigate the impact of bladder volume on treatment planning and clinical outcomes of radiotherapy for patients with cervical cancer.

Materials and methods

One hundred and sixty-six patients with locally advanced cervical cancer were selected in this retrospective study. The patients were divided into four groups according to their average bladder volume during radiotherapy (external beam radiation therapy and intracavitary brachytherapy): group A: V<100 mL, group B: 100 mL≤V≤150 mL, group C: 150 mL<V≤200 mL, group D: V>200 mL. The bladder volume and the cumulative dose to planning target (D90), bladder (D2cc), rectum (D2cc), and sigmoid (D2cc) were calculated using the treatment planning system. Treatment outcomes including late adverse events (the maximum grade of radiation-induced proctitis and cystitis), the objective response rate of tumor and lymph node, overall survival (OS), and progression-free survival (PFS) were collected. Additionally, the correlation between bladder volume and the irradiated dose of organs at risk and treatment outcomes was analyzed.

Results

The median follow-up time was 28 months. The D90 and D2cc of the rectum in group A were the highest (P<0.05). The D2cc of the bladder in group D was the highest (P<0.05). There was no significant difference in the tumor and lymph node regression rate, OS, and PFS among the groups. The difference in the late radiation-induced proctitis and cystitis maximum grade among the four groups was statistically significant (P<0.001, P=0.022, respectively), with group A the most serious and group B the mildest.

Conclusion

For patients with cervical cancer, the bladder volume significantly affected the delivered dose to target, rectum, and bladder. When the bladder volume range was 100–150 mL, the rate of late radiation-induced proctitis and cystitis was low and the degree of reaction was mild. This is thought to be the optimum bladder volume for patients with cervical cancer during radiotherapy.