Intensity-Modulated Radiation Therapy Versus 3D Conformal Radiotherapy for Postoperative Gynecologic Cancer: Are They Covering the Same Planning Target Volume?

A Dosimetric Analysis of Modified Volumetric Modulated Arc Therapy for Bone Marrow Sparing Radiotherapy in Cervical Cancer-An alternative Approach to Conventional VMAT

BACKGROUND

External beam radiotherapy remains the primary treatment modality in cervical cancer. Nowadays Intensity Modulated Radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) are increasingly being used to reduce normal tissue toxicity. The drawback of conventional  VMAT is that a considerable volume of pelvic bone marrow receives a low dose.

AIM

We analyzed whether there was a way to reduce the volume of the low dose regions of bone marrow, and assessed the potential benefit of conventional-4Arc (C-4Arc VMAT), and Modified-4Arc (M-4Arc VMAT) over the conventional 2 ARC VMAT.

MATERIALS AND METHODS

Twelve clinically proven locally advanced cervical cancer patients treated with concurrent chemo-radiotherapy by Conventional VMAT (RapidArc) in dual rotation mode (C-2Arc VMAT) were selected for this study.C-4Arc VMAT and M-4Arc VMAT dose plans were generated for these twelve patients and these three different types of plans were evaluated for the quality and compared dosimetrically.

RESULTS

M-4Arc VMAT designs exhibited a greater bone marrow sparing when compared with conventional VMATs with respect to volume receiving 5Gy to 35Gy without compromising PTV dose coverage. M-4Arc VMAT plans, the bone marrow volume receiving 30 Gy (V30Gy),40Gy (V40Gy), and mean doses were lower than the C- 4 Arc plan and a similar result was observed for V50(Gy) also when comparing with the standard 2 Arc plan. In modified VMAT plans, the rectum and bladder dose volumes were lower than standard VMAT. Similarly, the bowel bag V35(Gy), V40(Gy), V50(Gy), mean doses. The right and left femoral head doses were reduced significantly when compared to conventional VMAT plans.

CONCLUSION

The M-4Arc VMAT plans are better than the C-2Arc and C-4Arc VMAT plans for reducing the dose to bone marrow by limiting the MLC field width travel.

A Prospective Randomized Study of Intensity-Modulated Radiation Therapy Versus Three-Dimensional Conformal Radiation Therapy With Concurrent Chemotherapy in Locally Advanced Carcinoma Cervix

Background: External Beam Radiotherapy is the treatment of choice of locally advanced carcinoma cervix (LACC). The two techniques, three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT), have been compared previously in terms of outcomes and toxicities. IMRT has still not shown any benefit over 3DCRT in terms of local control and survival. Hence, the present study was conducted to compare local control and toxicities among both techniques.

Material & Methods: Fifty-four patients of LACC (FIGO IB2-IVA) were randomized to receive 50 Gray in 25 fractions by either 3DCRT or IMRT with concurrent cisplatin-based chemotherapy followed by brachytherapy. Plans were compared for planning target volume (PTV) coverage, dose to organs at risk (OAR), homogeneity index (HI), and conformity index (CI). Patients were assessed for acute toxicity and local control for three months.

Results: Out of 54 patients, 27 received treatment by 3DCRT and 27 by IMRT technique. Dosimetric evaluation for PTV coverage was similar in both arms. D15, D35, and D50 (dose to 15%, 35%, and 50% volume, respectively) for bladder were significantly reduced in the IMRT arm. Dosimetry for rectum and bowel bag was similar in both. There was a significantly decreased dose to femoral heads in the IMRT arm. Patients in the 3DCRT arm had significant grade 1 and 2 anemia and neutropenia compared to the IMRT arm. Local control for three months was similar in both the arms.

Conclusion: IMRT is associated with decreased acute hematological toxicity compared to 3DCRT with similar local control. Long-term follow-up is needed to assess any difference in long-term toxicity and survival between the two arms.

Pharmacological Interventions for the Prevention and Treatment of Kidney Injury Induced by Radiotherapy: Molecular Mechanisms and Clinical Perspectives

More than half of cancer patients need radiotherapy during the course of their treatment. Despite the beneficial aspects, the destructive effects of radiation beams on normal tissues lead to oxidative stress, inflammation, and cell injury. Kidneys are affected during radiotherapy of abdominal malignancies. Radiation nephropathy eventually leads to the release of factors triggering systemic inflammation. Currently, there is no proven prophylactic or therapeutic intervention for the management of radiation-induced nephropathy. This article reviews the biomarkers involved in the pathophysiology of radiation-induced nephropathy and its underlying molecular mechanisms. The efficacy of compounds with potential radio-protective properties on amelioration of inflammation and oxidative stress is also discussed. By outlining the approaches for preventing and treating this critical side effect, we evaluate the potential treatment of radiation-induced nephropathy. Available preclinical and clinical studies on these compounds are also scrutinized.

Robustness of elective lymph node target coverage with shrinking Planning Target Volume margins in external beam radiotherapy of locally advanced cervical cancer

BACKGROUND AND PURPOSE

Image-Guidance decreases set-up uncertainties, which may allow for Planning Target Volume (PTV) margins reduction. This study evaluates the robustness of the elective lymph node target coverage to translational and rotational set-up errors in combination with shrinking PTV margins and determines the gain for the Organs At Risk (OARs).

MATERIAL AND METHODS

Ten cervix cancer patients who underwent external beam radiotherapy with 45 Gy/25Fx were analysed. Daily Image-Guidance was based on bony registration of Cone Beam CT (CBCT) to planning CT (pCT) and daily couch correction (translation and yaw). On each pCT, four Volumetric Modulated Arc Therapy dose-plans were generated with PTV margins of 0, 3, 5 and 8 mm. The elective clinical target volume (CTV-E) was propagated from daily CBCTs to the pCT to evaluate daily CTV-E dose. Additional systematic translational isocenter shifts of 2 mm were simulated. D98% (dose received by 98% of the volume of interest) and D99.9% were extracted from each CTV-E for all dose-plans and scenarios. Total dose was accumulated by Dose-Volume Histogram addition. The dosimetric impact of PTV margin reduction on the OARs was evaluated through V30Gy (volume included within the 30 Gy isodose), V40Gy and body V43Gy.

RESULTS

When decreasing the PTV margin from 5 to 0 mm, bowel V30Gy was decreased by 13% (from 247 cm3 to 214 cm3), body V43Gy by 19% (from 1462 cm3 to 1188 cm3) and PTV by 39% (from 1416 to 870 cm3). The dosimetric impact of combined systematic shifts and residual rotations on the elective target with a 0 mm PTV margin was a decrease of D98% (mean ± SD) from 44.1 Gy ± 0.4 Gy to 43.7 Gy ± 0.8 Gy and a minimum of 42.4 Gy.

CONCLUSION

PTV margin reduction from 5 to 0 mm induced significant OARs dosimetric gains while elective target coverage remained robust to positioning uncertainties.

The role of volumetric modulated arc therapy (VMAT) in gynaecological radiation therapy: A dosimetric comparison of intensity modulated radiation therapy versus VMAT

INTRODUCTION

For gynaecological cancers, volumetric modulated arc therapy (VMAT) offers comparable plan quality with shorter treatment delivery times when compared to intensity modulated radiation therapy (IMRT).

METHODS

The clinical IMRT plans of twenty gynaecological cancer patients were compared with a retrospectively generated VMAT plan. Planning target volume (PTV) metrics compared were D95 > 99%, homogeneity index, and conformity index. Organs at risk (OAR) doses compared were bladder V45 < 35%, bowel V40 < 30%, femoral head and neck (FHN) V30 < 50%, V44 < 35% and V44 < 5%. Plan quality was also assessed by comparing the monitor units (MU), treatment time and the patient-specific quality assurance results.

RESULTS

VMAT and IMRT resulted in comparable PTV coverage with D95 values of 98.92% ± 0.69% and 98.91% ± 1.43% respectively, and homogeneity index values of 0.08 ± 0.02 (VMAT) and 0.08 ± 0.03 (IMRT). The conformity index for VMAT was 0.93 ± 0.04 and IMRT 0.85 ± 0.06 (P < 0.001). For the bowel tolerance (40 Gy < 30%) VMAT resulted in 22.39% ± 12.5% compared to 28.8% ± 16.78% for IMRT, with bladder and FHN VMAT doses also lower. VMAT MU were 694.35 ± 126.56 compared to 606.8 ± 96.16 for IMRT (P < 0.01). Treatment times of 6.6 ± 0.82 min and 2.47 ± 0.35 min were achieved for IMRT and VMAT respectively.

CONCLUSION

VMAT showed improvements in sparing OAR compared to IMRT. Target volume coverage with VMAT was equivalent or better than that of IMRT. These results in conjunction with the confirmed shorter treatment delivery time, have led to the development and implementation of a clinical protocol.