Dosimetric comparison of intensity-modulated, conformal, and four-field pelvic radiotherapy boost plans for gynecologic cancer: a retrospective planning study

Philip Chan,Anthony Fyles,Gregory Perkins,Inhwan Yeo,Michael Milosevic

doi:10.1186/1748-717x-1-13

Abstract

PurposeTo evaluate intensity-modulated radiation therapy (IMRT) as an alternative to conformal radiotherapy (CRT) or 4-field box boost (4FB) in women with gynecologic malignancies who are unsuitable for brachytherapy for technical or medical reasons.MethodsDosimetric and toxicity information was analyzed for 12 patients with cervical (8), endometrial (2) or vaginal (2) cancer previously treated with external beam pelvic radiotherapy and a CRT boost. Optimized IMRT boost treatment plans were then developed for each of the 12 patients and compared to CRT and 4FB plans. The plans were compared in terms of dose conformality and critical normal tissue avoidance.ResultsThe median planning target volume (PTV) was 151 cm3 (range 58–512 cm3). The median overlap of the contoured rectum with the PTV was 15 (1–56) %, and 11 (4–35) % for the bladder. Two of the 12 patients, both with large PTVs and large overlap of the contoured rectum and PTV, developed grade 3 rectal bleeding. The dose conformity was significantly improved with IMRT over CRT and 4FB (p ≤ 0.001 for both). IMRT also yielded an overall improvement in the rectal and bladder dose-volume distributions relative to CRT and 4FB. The volume of rectum that received the highest doses (>66% of the prescription) was reduced by 22% (p < 0.001) with IMRT relative to 4FB, and the bladder volume was reduced by 19% (p < 0.001). This was at the expense of an increase in the volume of these organs receiving doses in the lowest range (<33%).ConclusionThese results indicate that IMRT can improve target coverage and reduce dose to critical structures in gynecologic patients receiving an external beam radiotherapy boost. This dosimetric advantage will be integrated with other patient and treatment-specific factors, particularly internal tumor movement during fractionated radiotherapy, in the context of a future image-guided radiation therapy study.

Highlights

Intra-uterine brachytherapy following external beam radiotherapy is an integral component of the treatment of locally advanced cervix cancer
Patients who are unable to proceed with brachytherapy because of insufficient tumor regression during external beam radiotherapy, irregular pelvic anatomy or concurrent medical problems are at substantially higher risk of pelvic tumor recurrence [1,2]
Patients who could not undergo brachytherapy received additional external beam radiotherapy delivered to the gross tumor alone in most radiation centres around the world, usually using a 4-field box technique (4FB)

Summary

Introduction

Intra-uterine brachytherapy following external beam radiotherapy is an integral component of the treatment of locally advanced cervix cancer. It may reflect the lower total dose of radiotherapy that can safely be delivered to the tumor in the absence of brachytherapy In support of the latter, several studies have suggested a dose-response relationship for cervix cancer [3,4,5]. Modern techniques of precision radiation delivery like intensity-modulated radiation therapy (IMRT) allow the dose to be "sculpted" to the tumor volume while at the same time minimizing the dose to adjacent dose-limiting normal tissues [6,7]. This theoretically offers the opportunity to escalate the tumor dose with the expectation of improved local control. To achieve this goal, the IMRT boost needs to be delivered in an optimal manner with close attention to normal tissue dose-volume constraints and daily target localization

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