Retrospective feasibility study of simultaneous integrated boost in cervical cancer using tomotherapy: the impact of organ motion and tumor regression

Abstract

BackgroundWhole pelvis intensity modulated radiotherapy (IMRT) is increasingly being used to treat cervical cancer aiming to reduce side effects. Encouraged by this, some groups have proposed the use of simultaneous integrated boost (SIB) to target the tumor, either to get a higher tumoricidal effect or to replace brachytherapy. Nevertheless, physiological organ movement and rapid tumor regression throughout treatment might substantially reduce any benefit of this approach.PurposeTo evaluate the clinical target volume - simultaneous integrated boost (CTV-SIB) regression and motion during chemo-radiotherapy (CRT) for cervical cancer, and to monitor treatment progress dosimetrically and volumetrically to ensure treatment goals are met.Methods and materialsTen patients treated with standard doses of CRT and brachytherapy were retrospectively re-planned using a helical Tomotherapy - SIB technique for the hypothetical scenario of this feasibility study. Target and organs at risk (OAR) were contoured on deformable fused planning-computed tomography and megavoltage computed tomography images. The CTV-SIB volume regression was determined. The center of mass (CM) was used to evaluate the degree of motion. The Dice’s similarity coefficient (DSC) was used to assess the spatial overlap of CTV-SIBs between scans. A cumulative dose-volume histogram modeled estimated delivered doses.ResultsThe CTV-SIB relative reduction was between 31 and 70%. The mean maximum CM change was 12.5, 9, and 3 mm in the superior-inferior, antero-posterior, and right-left dimensions, respectively. The CTV-SIB-DSC approached 1 in the first week of treatment, indicating almost perfect overlap. CTV-SIB-DSC regressed linearly during therapy, and by the end of treatment was 0.5, indicating 50% discordance. Two patients received less than 95% of the prescribed dose. Much higher doses to the OAR were observed. A multiple regression analysis showed a significant interaction between CTV-SIB reduction and OAR dose increase.ConclusionsThe CTV-SIB had important regression and motion during CRT, receiving lower therapeutic doses than expected. The OAR had unpredictable shifts and received higher doses. The use of SIB without frequent adaptation of the treatment plan exposes cervical cancer patients to an unpredictable risk of under-dosing the target and/or overdosing adjacent critical structures. In that scenario, brachytherapy continues to be the gold standard approach.

Simultaneously integrated boost (SIB) spares OAR and reduces treatment time in locally advanced cervical cancer

“…The reduction in treatment time is of particular clinical significance as previous work from our institution (12) and others (13‐15) has demonstrated that protracted treatment duration compromises local control in this patient population. Because nodal targets are not expected to be greatly affected by organ motion (26) and because modest doses are indicated for nodal targets by NCCN guidelines, this is an ideal scenario in which to harness the power of SIB planning. To our knowledge, this is the first study to demonstrate the advantages of SIB over sIMRT for boosting PET‐avid nodal targets in locally advanced cervical cancer in a systematic manner.…”

“…Organ motion and CTV regression during treatment are also important factors to consider when prescribing higher doses to a boost volume. Herrera et al (26) used weekly on‐board megavoltage CT to track target volume motion and regression during six weeks of treatment. The pelvic CTV volume decreased over six weeks for all patients, but did not result in underdosing except in the two patients whose uteri became retroverted during the course of treatment.…”

Short-course PET based simultaneous integrated boost for locally advanced cervical cancer

“…The dosimetric effects of anatomical changes will be greater for IMPT than VMAT as proton stopping power is more sensitive to tissue changes than the corresponding photon interaction coefficients. These effects have previously been investigated for standard and dose escalated intensity modulated radiotherapy (IMRT) of cervix cancer [ 25 , 26 ] and for IMPT with a SIB for prostate cancer [ 27 ]. Herrera et al [ 26 ] analyzed dose escalation of a central target volume including the uterus over 28 fractions using deformable registration of weekly CBCT images.…”

“…These effects have previously been investigated for standard and dose escalated intensity modulated radiotherapy (IMRT) of cervix cancer [ 25 , 26 ] and for IMPT with a SIB for prostate cancer [ 27 ]. Herrera et al [ 26 ] analyzed dose escalation of a central target volume including the uterus over 28 fractions using deformable registration of weekly CBCT images. They found, compared to planned values, overdosage of adjacent OARs correlating with tumour shrinkage and recommended frequent plan adaptation.…”

Intensified intensity-modulated radiotherapy in anal cancer with prevalent HPV p16 positivity

“…This approach has its advantages compared to sequential dosage increment, namely: the possibility to deliver different fraction doses to different volumes, shorten overall treatment time (OTT), and guarantee better coverage of Gross Tumor Volume (GTV) with non-target tissue sparing. SIB use has also been investigated in diseases other than anal canal cancer, such as head and neck cancer and cervical cancer, and where it has been demonstrated to be feasible and act to reduce acute toxicity [6][7][8] . Here we present the results of a study carried out with an intensified radiotherapy regimen associated with chemotherapy that was applied in order to improve oncologic efficacy and reduce overall acute toxicity in patients with squamous cell carcinoma of the anal canal treated at our center.…”